WO2020035203A1

WO2020035203A1 - Apparatus and method for clearing and detecting marks

Info

Publication number: WO2020035203A1
Application number: PCT/EP2019/067113
Authority: WO
Inventors: Bastiaan Lambertus Wilhelmus Marinus VAN DE VEN; Chanpreet KAUR; Jeroen Johan Maarten VAN DE WIJDEVEN; Yang-Shan Huang; Andre Bernardus Jeunink; Tamara DRUZHININA; Victoria VORONINA
Original assignee: ASML Netherlands BV
Current assignee: ASML Netherlands BV
Priority date: 2018-08-16
Filing date: 2019-06-27
Publication date: 2020-02-20
Anticipated expiration: 2021-02-16
Also published as: NL2023593A

Abstract

Disclosed is an apparatus for processing at least a first substrate in a lithographic process, which first substrate comprises a mask layer and one or more marks arranged below said mask layer, the apparatus comprising a first substrate support configured to hold the first substrate, a clearing tool configured to clear at least one of the marks by clearing an area of the mask layer above said mark while the first substrate is arranged on the first substrate support, and a measurement tool configured to determine a position of at least one of the cleared marks while the first substrate is arranged on the first substrate support.

Description

Apparatus and method for clearing and detecting marks

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP application no. 18189315.7, which was filed on 16 August 2018 and which is incorporated herein in its entirety by reference.

FIELD

[0002] The present invention relates to the clearing and detecting of marks, in particular marks as present on a semiconductor substrate.

BACKGROUND

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern (also often referred to as“design layout’’ or “design’’) of a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate (e.g., a wafer).

[0004] As semiconductor manufacturing processes continue to advance, the dimensions of circuit elements have continually been reduced while the amount of functional elements, such as transistors, per device has been steadily increasing over decades, following a trend commonly referred to as‘Moore’s law’. To keep up with Moore’s law the semiconductor industry is chasing technologies that enable to create increasingly smaller features. To project a pattern on a substrate a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which are patterned on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm and 13.5 nm. A lithographic apparatus, which uses extreme ultraviolet (EUV) radiation, having a wavelength within a range of 4 nm to 20 nm, for example 6.7 nm or 13.5 nm, may be used to form smaller features on a substrate than a lithographic apparatus which uses, for example, radiation with a wavelength of 193 nm.

[0005] In the manufacture of complex devices, typically many lithographic patterning steps are performed, thereby forming functional features in successive layers on the substrate. A critical aspect of performance of the lithographic apparatus is therefore the ability to place the applied pattern correctly and accurately in relation to features laid down in previous layers (by the same apparatus or a different lithographic apparatus). For this purpose, the substrate is provided with one or more sets of marks. Each mark is a structure whose position can be measured at a later time using a position sensor, typically an optical position sensor. The position sensor may be referred to as“alignment sensor’’ and marks may be referred to as“alignment marks’’.

[0006] A lithographic apparatus may include one or more (e.g. a plurality of) alignment sensors by which positions of alignment marks provided on a substrate can be measured accurately. Alignment (or position) sensors may use optical phenomena such as diffraction and interference to obtain position information from alignment marks formed on the substrate. An example of an alignment sensor used in current lithographic apparatus is based on a self-referencing interferometer as described in US6961116. Various enhancements and modifications of the position sensor have been developed, for example as disclosed in US2015261097A1. The contents of all of these publications are incorporated herein by reference.

[0007] A mark, or alignment mark, may comprise a series of bars formed on or in a layer provided on the substrate or formed (directly) in the substrate. The bars may be regularly spaced and act as grating lines so that the mark can be regarded as a diffraction grating with a well-known spatial period (pitch). Depending on the orientation of these grating lines, a mark may be designed to allow measurement of a position along the X axis, or along the Y axis (which is oriented substantially perpendicular to the X axis). A mark comprising bars that are arranged at +45 degrees and/or -45 degrees with respect to both the X- and Y-axes allows for a combined X- and Y- measurement using techniques as described in

US2009/195768A, which is incorporated by reference.

[0008] An alignment sensor may scan each mark optically with a spot of radiation to obtain a periodically varying signal, such as a sine wave. The phase of this signal is analyzed, to determine the position of the mark and, hence, of the substrate relative to the alignment sensor, which, in turn, is fixated relative to a reference frame of a lithographic apparatus. So-called coarse and fine marks may be provided, related to different (coarse and fine) mark dimensions, so that the alignment sensor can distinguish between different cycles of the periodic signal, as well as the exact position (phase) within a cycle. Marks of different pitches may also be used for this purpose. In another example an alignment sensor comprises an image sensor in which images of the marks are analyzed and translated into position information.

[0009] Measuring the position of the marks may also provide information on a deformation of the substrate on which the marks are provided, for example in the form of a wafer grid. Deformation of the substrate may occur by, for example, electrostatic clamping of the substrate to the substrate table and/or heating of the substrate when the substrate is exposed to radiation.

[00010] One or more layers of the substrate may be arranged above the marks, including a mask layer which may e.g. be a top layer. Recent technological developments, such as 3D-NAND processes, require said mask layer to be of a material which is opaque for the optical radiation emitted by the alignment sensor, resulting in the alignment sensor being unable to detect the mark.

[00011] In addition, there is a continuous demand of the semiconductor industry to create increasingly smaller features. This requires an increasing level of accuracy as well as a reduced overlay. This increased level of accuracy can partly be obtained by measuring the positions of more marks.

[00012] It has been proposed to remove a part of a layer above the mark using an additional etching or laser ablation process.

SUMMARY

[00013] It is an object of the invention to mitigate one or more of the disadvantages mentioned above or at least provide an alternative for the clearing and detecting of marks.

[00014] This object is achieved with an apparatus for processing at least a first substrate in a lithographic process, which first substrate comprises a mask layer and one or more marks arranged below said mask layer. The apparatus comprises a first substrate support configured to hold the first substrate, a clearing tool configured to clear at least one of the marks by clearing an area of the mask layer above said mark while the first substrate is arranged on the first substrate support, and a measurement tool configured to determine a position of at least one of the cleared marks while the first substrate is arranged on the first substrate support.

[00015] The apparatus according to the invention integrates the clearing tool and the measurement tool in a single apparatus, thereby enabling the processing of the first substrate by both tools while the first substrate is on the first substrate support. There is thus no need to transfer the substrate from one support to another, or from one apparatus to another apparatus, in between the clearing performed by the clearing tool and the position measurement as performed by the measurement tool. The time required for processing the first substrate may thus be reduced, allowing to clear and detect more marks in a given time period..

[00016] In an embodiment the apparatus comprises a clearing station which comprises the clearing tool and a measurement station which comprises the measurement tool, wherein the apparatus further comprises a positioner configured to move the first substrate support from the clearing station to the measurement station. In this embodiment the apparatus comprises multiple stations and the position of the first substrate support can be controlled by the positioner.

[00017] In a further embodiment the apparatus further comprises a second substrate support configured to hold a second substrate which comprises a mask layer and one or more marks arranged below said mask layer. The second substrate holder is configured to be arranged in the clearing station while the first substrate holder is arranged in the measurement station, and the clearing tool is configured to clear at least one of the marks of the second substrate by clearing an area of the mask layer above said marks while the measurement tool is determining the position of the at least one of the cleared marks of the first substrate. In this embodiment advantageously two substrates can be processed at the same time in the apparatus, increasing the efficiency of the apparatus and allowing to clear and detect more marks of each substrate in a given time period.

[00018] In an embodiment the measurement station further comprises a supplementary clearing tool configured to clear an area of the mask layer above said mark while the first substrate is arranged on the first substrate support. In case the clearing of the marks takes more time than the measuring of their position, this embodiment advantageously shifts a part of said clearing to the measurement station such that the time period the substrate is in the clearing station and the measurement station can remain approximately equal, thereby increasing the efficiency of the apparatus.

[00019] In an embodiment the apparatus further comprises a third substrate support configured to hold a third substrate which comprises a mask layer and one or more marks arranged below said mask layer, and at least one further clearing station comprising a further clearing tool configured to, while the clearing tool is clearing the marks of the first substrate, clear at least one of the marks of the third substrate by clearing an area of the mask layer above said mark while the third substrate is arranged on the third substrate support. In this embodiment the apparatus comprises multiple clearing stations which can each clear marks on another substrate at the same time. The efficiency of the apparatus is increased, e.g. if the clearing of the marks requires a different time period than the measuring of their positions.

[00020] In an embodiment the apparatus comprises a fourth substrate support configured to hold a fourth substrate which comprises a mask layer and one or more marks arranged below said mask layer, and at least one further measurement station comprising a further measurement tool configured to, while the measurement tool is determining a position the cleared marks of the first substrate, determine a position of at least one of the cleared marks of the fourth substrate while the fourth substrate is arranged on the fourth substrate support. In this embodiment the apparatus comprises multiple measurement stations which can each determine positions of marks on another substrate at the same time. The efficiency of the apparatus is increased, e.g. if the measuring of the positions of the marks requires a different time period than the clearing of the marks.

[00021] In an embodiment the apparatus further comprises a first position measurement module configured to measure a position of the first substrate support when the first substrate support is in the clearing station, and a second position measurement module configured to measure a position of the first substrate support when the first substrate support is in the measurement station. The second position measurement module is configured to measure the position of the first substrate support with a higher precision than the first position measurement module. This embodiment advantageously applies lower precision requirements for the clearing of the marks, such that simpler and/or more cost-effective components can be used in the clearing station.

[00022] In an embodiment of the apparatus according to the invention, the apparatus comprises a first station which comprises the clearing tool and the measurement tool. In this embodiment the apparatus further comprises a second station comprising a second substrate support configured to hold a second substrate comprising a mask layer and one or more marks arranged below said mask layer, while the first substrate support is holding the first substrate, a second clearing tool configured to clear at least one of the marks of the second substrate by clearing an area of the mask layer above said mark while the second substrate is arranged on the second substrate support, a second measurement tool configured to determine a position of at least one of the cleared marks of the second substrate while the second substrate is arranged on the second substrate support. In this embodiment advantageously a substrate can be processed in each of the first and the second station at the same time, both said first and second station being configured to clear the marks and measure their position.

[00023] In an embodiment of the apparatus the clearing tool further comprises an image sensor configured to capture an image of at least a part of the first substrate, and a processing unit configured to determine a position of at least one of the one or more marks below the mask layer based on said image, and to determine the area of the mask layer to be cleared based on the position of said mark.

Advantageously the position where the clearing is required can be determined and the clearing can be controlled accordingly.

[00024] In an embodiment the clearing tool comprises a laser ablation tool configured to clear the area of the mask layer by emitting laser pulses on the mask layer. Laser ablation has shown to be an efficient and cost-effective method for clearing marks.

[00025] In a further embodiment the laser ablation tool comprises an ultra-short pulsed laser module configured to emit Gaussian laser pulses and a top-hat shaper configured to transform the Gaussian laser pulses into laser pulses having a top-hat shaped energy density. Advantageously the mask layer is subjected to short laser pulses with a high but near-uniform energy density, which remove material from the mask layer.

[00026] In an embodiment the laser pulses emitted on the mask layer have a size which is substantially equal to the area of the mask layer which is to be cleared. Advantageously the area cleared with the apparatus according to this embodiment is of high quality.

[00027] In an embodiment the laser ablation tool further comprises at least one mirror arranged in an optical path of the emitted laser pulses, which mirror is configured to be adjustable to control the direction of the laser pulses emitted on the mask layer; and/or the laser ablation tool further comprises at least one size shaper configured to control the size of the laser pulses emitted on the mask layer. Advantageously this embodiment allows to control which part of the mask layer is subjected to the laser pulses.

[00028] In an embodiment the clearing tool further comprises a feedback camera configured to capture an image during the clearing of at least a part of the first substrate comprising at least the area of the mask layer which is being cleared, and a processing unit configured to determine at least one clearing process parameter based on said image, wherein said processing unit is further configured to, based on said clearing process parameter, control or stop the clearing. Advantageously the feedback camera monitors the actual clearing and the image taking by said feedback camera is used to provide feedback for the clearing.

[00029] In a further embodiment wherein the clearing tool comprises the laser ablation tool, the clearing comprises sequentially emitting multiple laser pulses on the area of the mask layer with the laser ablation tool. In this embodiment the feedback camera is configured to capture the image after at least a first laser pulse has been emitted on the mask layer, and the processing unit is configured to control the clearing by controlling for a subsequently emitted laser pulse a position of the first substrate, and/or a location on the mask layer on which the laser pulse is emitted, and/or a size of the laser pulse.

Advantageously for subsequent laser pulses the clearing is controlled based on the provided feedback.

[00030] In an embodiment the processing unit is configured to compare the image with a reference image and/or to compare the clearing process parameter with a reference parameter. Advantageously a reference for the present clearing is provided.

[00031] In an embodiment the clearing tool is configured to clear multiple areas of the mask layer at the same time. Advantageously the time required for clearing a given number of marks can be reduced.

[00032] In an embodiment the apparatus further comprises a substrate loader configured to arrange the first substrate on the first substrate support and/or to unload the first substrate from the first substrate support. Advantageously the first substrate can be loaded and unloaded from the apparatus.

[00033] The invention further relates to a system comprising the apparatus according to the invention, e.g. according to one or more of the embodiments mentioned above, and a lithographic apparatus.

[00034] In an embodiment of the system according to the invention, the lithographic apparatus comprises: an apparatus substrate support configured to hold the first substrate, a mask support constructed to support a patterning device and connected to a first apparatus positioner configured to position the patterning device, a projection system configured to project a pattern imparted to a radiation beam by the patterning device onto the first substrate while the first substrate is arranged on the apparatus substrate support, and a second apparatus positioner configured to position the apparatus substrate support. At least one of the first apparatus positioner and the second apparatus positioner is configured to position the patterning device or the apparatus substrate support, respectively, based on measurements obtained by the measurement tool of the apparatus. In this embodiment advantageously the measurements obtained by the measurement tool of the apparatus according to the invention are used in the lithographic apparatus, thereby reducing the measurements that need to be done when the first substrate is in arranged on the apparatus substrate support. As a result, the first substrate needs to be in the lithographic apparatus for a shorter period of time, increasing the throughput of the lithographic apparatus.

[00035] In an embodiment of the system according to the invention, the lithographic apparatus comprises an apparatus substrate support configured to hold the first substrate, a projection system configured to project a pattern onto the first substrate while the first substrate is arranged on the apparatus substrate support, and a position measurement system configured to determine a position of the first substrate by detecting at least one of the cleared marks while the first substrate is arranged on the apparatus substrate support. In this embodiment advantageously the position of the first substrate is determined using marks that have been cleared in the apparatus according to the invention.

[00036] In an embodiment the system according to the invention comprises a plurality of apparatuses according to the invention, wherein the system is configured to process at least one substrate in each of multiple of the plurality of apparatuses while projecting the pattern onto another substrate in the lithographic apparatus. Advantageously multiple substrates are being processed at the same time, while the lithographic apparatus is projecting a pattern on another substrate. The lithographic apparatus can be used at almost constantly, increasing the efficiency, and/or the substrates can be in one of the apparatuses according to the invention for a longer time, allowing to clear and detect more marks, thereby increasing the accuracy of the lithographic process and/or decreasing overlay.

[00037] The invention further relates to a method for processing at least a first substrate, which first substrate comprises a mask layer and one or more marks arranged below said mask layer. The method comprises the following steps: arranging the first substrate on a first substrate support, clearing at least one of the marks with a clearing tool by clearing an area of the mask layer above said mark while the first substrate is arranged on the first substrate support, determining a position of at least one of the cleared marks with a measurement tool while the first substrate is arranged on the first substrate support.

[00038] The method according to the invention performs the clearing of the marks and the determining of their position tool while the first substrate is on the first substrate support. The time required for processing the first substrate is reduced, allowing to clear and detect more marks in a given time period.

[00039] It is noted that the method according to invention can optionally be performed using an apparatus and/or system according to the invention.

[00040] In an embodiment the method further comprising the following steps: arranging a second substrate on a second substrate holder, which second substrate comprises a mask layer and one or more marks arranged below said mask layer; clearing at least one of the marks of the second substrate with the clearing tool by clearing an area of the mask layer of above said marks, said second substrate being arranged on the second substrate support, while determining a position of the at least one of the cleared marks of the first substrate with the measurement tool, said first substrate being arranged on the first substrate support. In this embodiment advantageously two substrates can be processed at the same time, increasing the efficiency of the apparatus and allowing to clear and detect more marks of each substrate within a given time period

[00041] In an embodiment the method further comprises the following steps: arranging a third substrate on a third substrate holder, which third substrate comprises a mask layer and one or more marks arranged below said mask layer; clearing, while clearing the marks of the first substrate with the clearing tool, at least one of the marks of the third substrate with a further clearing tool by clearing an area of the mask layer above said mark while the third substrate is arranged on the third substrate support. In this embodiment the apparatus comprises multiple marker clearing tools which can each clear marks on another substrate at the same time. The efficiency of the apparatus is increased, e.g. if the clearing of the marks requires a different time period than the measuring of their positions.

[00042] In an embodiment the method further comprises the steps of: arranging a fourth substrate on a fourth substrate holder, which fourth substrate comprises a mask layer and one or more marks arranged below said mask layer; determining, while determining the position of the cleared marks of the first substrate with the measurement tool, a position of at least one of the cleared marks of the fourth substrate with a further measurement tool, while the fourth substrate is arranged on the fourth substrate support. In this embodiment the apparatus comprises multiple measurement tools which can each determine positions of marks on another substrate at the same time. The efficiency of the apparatus is increased, e.g. if the measuring of the positions of the marks requires a different time period than the clearing of the marks.

[00043] In an embodiment the method comprises the steps of: arranging a second substrate on a second substrate holder, which second substrate also comprises a mask layer and one or more marks arranged below said mask layer; clearing at least one of the marks of the second substrate with a second clearing tool by clearing an area of the mask layer above said mark while the second substrate is arranged on the second substrate support; determining a position of at least one of the cleared marks of the second substrate with a second measurement tool while the second substrate is arranged on the second substrate support. In this embodiment advantageously a substrate can be processed on the first substrate holder and the second substrate holder at the same time, wherein for both said first and second substrate holder an individual clearing tool and measurement tool is provided.

[00044] In an embodiment the method further comprises the steps of: capturing an image of at least a part of the first substrate determining a position of at least one of the one or more marks below the mask layer based on said image; and determining the area of the mask layer to be cleared based on the position of said mark. Advantageously the position where the clearing is required can be determined and the clearing can be controlled accordingly.

[00045] In an embodiment the method further comprises the following steps: capturing an image with a feedback camera during the clearing of at least of part of the first substrate comprising at least the area of the mask layer which is being cleared; determining at least one clearing process parameter based on said image; controlling or stopping the clearing based on said clearing process parameter. Advantageously the feedback camera monitors the actual clearing and the image taking by said feedback camera is used to provide feedback for the clearing.

[00046] The invention according to a second aspect further relates to an apparatus for processing at least a first substrate in a lithographic process, which first substrate comprises a mask layer and one or more marks arranged below said mask layer. The apparatus comprises a first substrate support and a second substrate support configured to hold the first substrate, a clearing tool configured to clear at least one of the marks by clearing an area of the mask layer above said mark while the first substrate is arranged on the first substrate support, and a measurement tool configured to determine a position of at least one of the cleared marks while the first substrate is arranged on the second substrate support.

[00047] It is noted that the apparatus according to the second aspect may comprises any one or more of the features described herein with respect to the apparatus according to the invention.

[00048] For example, in an embodiment the clearing tool further comprises a feedback camera configured to capture an image during the clearing of at least a part of the first substrate comprising at least the area of the mask layer which is being cleared, and a processing unit configured to determine at least one clearing process parameter based on said image, wherein said processing unit is further configured to, based on said clearing process parameter, control or stop the clearing. Advantageously the feedback camera monitors the actual clearing and the image taking by said feedback camera is used to provide feedback for the clearing

[00049] In a further embodiment wherein the clearing tool comprises a laser ablation tool, the clearing comprises sequentially emitting multiple laser pulses on the area of the mask layer with the laser ablation tool. In this embodiment the feedback camera is configured to capture the image after at least a first laser pulse has been emitted on the mask layer, and the processing unit is configured to control the clearing by controlling for a subsequently emitted laser pulse a position of the first substrate, and/or a location on the mask layer on which the laser pulse is emitted, and/or a size of the laser pulse. Advantageously for subsequent laser pulses the clearing is controlled based on the provided feedback. [00050] In an embodiment the processing unit is configured to compare the image with a reference image and/or to compare the clearing process parameter with a reference parameter. Advantageously a reference for the present clearing is provided.

[00051] Other features which may be added in any combination include but are not limited to:

processing multiple substrates at the same time; the clearing station and measurement station; the positioner; additional substrate supports, measurement tools and/or clearing tools; the first and second position measurement module; the second station; the image sensor; the laser ablation tool in any of the described embodiments; the substrate loader; the apparatus being used in a system comprising a lithographic apparatus according to any of the embodiments described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[00052] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings wherein like reference numerals indicate like features, in which:

Figure 1 depicts a schematic overview of a lithographic apparatus;

Figure 2 is a schematic block diagram of an embodiment of an alignment sensor;

Figure 3a shows an example of a mark with a mask layer arranged on a substrate;

Figure 3b shows the mark of figure 3a wherein the mask layer is cleared;

Figure 4 shows a top view of an apparatus according to the invention;

Figure 5 shows a further embodiment of the invention comprising a clearing station and a measurement station;

Figure 6 shows an embodiment of a laser ablation tool;

Figure 7 shows an embodiment of the apparatus wherein the measurement station comprises an optional supplementary clearing tool;

Figure 8 illustrates an embodiment of the apparatus comprising a further clearing station;

Figure 9 illustrates an embodiment of the apparatus according to the invention comprising a further measurement station;

Figure 10 shows an embodiment of the invention comprising a first station and a second station; Figure 11 illustrates an embodiment of the apparatus according to the second aspect of the invention.

DETAIFED DESCRIPTION

[00053] In the present document, the terms“radiation” and“beam” are used to encompass ah types of electromagnetic radiation, including ultraviolet radiation (e.g. with a wavelength of 365, 248, 193, 157 or 126 nm) and EUV (extreme ultra-violet radiation, e.g. having a wavelength in the range of about 5-100 nm).

[00054] The term“reticle”,“mask” or“patterning device” as employed in this text may be broadly interpreted as referring to a generic patterning device that can be used to endow an incoming radiation beam with a patterned cross-section, corresponding to a pattern that is to be created in a target portion of the substrate. The term“light valve” can also be used in this context. Besides the classic mask

(transmissive or reflective, binary, phase-shifting, hybrid, etc.), examples of other such patterning devices include a programmable mirror array and a programmable LCD array.

[00055] Figure 1 schematically depicts a lithographic apparatus LA. The lithographic apparatus LA includes an illumination system (also referred to as illuminator) IL configured to condition a radiation beam B (e.g., UV radiation, DUV radiation or EUV radiation), a mask support (e.g., a mask table) MT constructed to support a patterning device (e.g., a mask) MA and connected to a first apparatus positioner PM configured to accurately position the patterning device MA in accordance with certain parameters, an apparatus substrate support (e.g., a wafer table) WT constructed to hold a substrate (e.g., a resist coated wafer) W and connected to a second apparatus positioner PW configured to accurately position the apparatus substrate support in accordance with certain parameters, and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[00056] In operation, the illumination system IL receives a radiation beam from a radiation source SO, e.g. via a beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, and/or other types of optical components, or any combination thereof, for directing, shaping, and/or controlling radiation. The illuminator IL may be used to condition the radiation beam B to have a desired spatial and angular intensity distribution in its cross section at a plane of the patterning device MA.

[00057] The term“projection system” PS used herein should be broadly interpreted as encompassing various types of projection system, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and/or electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, and/or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the more general term“projection system” PS.

[00058] The lithographic apparatus LA may be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g., water, so as to fill a space between the projection system PS and the substrate W - which is also referred to as immersion lithography. More information on immersion techniques is given in US6952253, which is incorporated herein by reference.

[00059] The lithographic apparatus LA may also be of a type having two or more apparatus substrate supports WT (also named“dual stage’’). In such“multiple stage’’ machine, the apparatus substrate supports WT may be used in parallel, and/or steps in preparation of a subsequent exposure of the substrate W may be carried out on the substrate W located on one of the apparatus substrate support WT while another substrate W on the other apparatus substrate support WT is being used for exposing a pattern on the other substrate W.

[00060] In addition to the apparatus substrate support WT, the lithographic apparatus LA may comprise a measurement stage. The measurement stage is arranged to hold a sensor and/or a cleaning device. The sensor may be arranged to measure a property of the projection system PS or a property of the radiation beam B. The measurement stage may hold multiple sensors. The cleaning device may be arranged to clean part of the lithographic apparatus, for example a part of the projection system PS or a part of a system that provides the immersion liquid. The measurement stage may move beneath the projection system PS when the apparatus substrate support WT is away from the projection system PS.

[00061] In operation, the radiation beam B is incident on the patterning device, e.g. mask, MA which is held on the mask support MT, and is patterned by the pattern (design layout) present on patterning device MA. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second apparatus positioner PW and a position measurement system IF, the apparatus substrate support WT can be moved accurately, e.g., so as to position different target portions C in the path of the radiation beam B at a focused and aligned position. Similarly, the first apparatus positioner PM and possibly another position sensor (which is not explicitly depicted in Figure 1) may be used to accurately position the patterning device MA with respect to the path of the radiation beam B. Patterning device MA and substrate W may be aligned using mask alignment marks Ml, M2 and substrate alignment marks Pl, P2. Although the substrate alignment marks Pl, P2 as illustrated occupy dedicated target portions, they may be located in spaces between target portions. Substrate alignment marks Pl, P2 are known as scribe-lane alignment marks when these are located between the target portions C.

[00062] To clarify the invention, a Cartesian coordinate system is used. The Cartesian coordinate system has three axis, i.e., an x-axis, a y-axis and a z-axis. Each of the three axis is orthogonal to the other two axis. A rotation around the x-axis is referred to as an Rx-rotation. A rotation around the y-axis is referred to as an Ry-rotation. A rotation around about the z-axis is referred to as an Rz -rotation. The x- axis and the y-axis define a horizontal plane, whereas the z-axis is in a vertical direction. The Cartesian coordinate system is not limiting the invention and is used for clarification only. Instead, another coordinate system, such as a cylindrical coordinate system, may be used to clarify the invention. The orientation of the Cartesian coordinate system may be different, for example, such that the z-axis has a component along the horizontal plane.

[00063] Figure 2 is a schematic block diagram of an embodiment of a known alignment sensor AS, such as is described, for example, in US6961116, and which is incorporated by reference. However, other embodiments of known alignment sensors are envisioned, for example alignment sensors using image sensors and image processing to determine an alignment position of at least one mark on a substrate. Radiation source RSO provides a beam RB of radiation of one or more wavelengths, which is diverted by diverting optics onto a mark, such as mark AM located on substrate W, as an illumination spot SP. In this example the diverting optics comprises a spot mirror SM and an objective lens OL. The illumination spot SP, by which the mark AM is illuminated, may be slightly smaller in diameter than the width of the mark itself.

[00064] Radiation diffracted by the mark AM is collimated (in this example via the objective lens OL) into an information-carrying beam IB. The term“diffracted” is intended to include zero-order diffraction from the mark (which may be referred to as reflection). A self-referencing interferometer SRI, e.g. of the type disclosed in US6961116 mentioned above, interferes the beam IB with itself after which the beam is received by a photodetector PD. Additional optics (not shown) may be included to provide separate beams in case more than one wavelength is created by the radiation source RSO. The photodetector may be a single element, or it may comprise a number of pixels, if desired. The photodetector may comprise a sensor array.

[00065] The diverting optics, which in this example comprises the spot mirror SM, may also serve to block zero order radiation reflected from the mark, so that the information-carrying beam IB comprises only higher order diffracted radiation from the mark AM (this is not essential to the measurement, but improves signal to noise ratios).

[00066] Intensity signals SI are supplied to a processing unit PU. By a combination of optical processing in the block SRI and computational processing in the unit PU, values for X- and Y-position on the substrate relative to a reference frame are output.

[00067] A single measurement of the type illustrated only fixes the position of the mark within a certain range corresponding to one pitch of the mark. Coarser measurement techniques are used in conjunction with this to identify which period of a sine wave is the one containing the marked position. The same process at coarser and/or finer levels may be repeated at different wavelengths for increased accuracy and/or for robust detection of the mark irrespective of the materials from which the mark is made, and materials on and/or below which the mark is provided. The wavelengths may be multiplexed and de- multiplexed optically so as to be processed simultaneously, and/or they may be multiplexed by time division or frequency division.

[00068] In this example, the alignment sensor and spot SP remain stationary, while it is the substrate W that moves. The alignment sensor can thus be mounted rigidly and accurately to a reference frame, while effectively scanning the mark AM in a direction opposite to the direction of movement of substrate W. The substrate W is controlled in this movement by its mounting on a substrate support and a substrate positioning system controlling the movement of the substrate support. A substrate support position sensor (e.g. an interferometer) measures the position of the substrate support (not shown). In an embodiment, one or more (alignment) marks are provided on the substrate support. A measurement of the position of the marks provided on the substrate support allows the position of the substrate support as determined by the position sensor to be calibrated (e.g. relative to a frame to which the alignment system is connected).

A measurement of the position of the alignment marks provided on the substrate allows the position of the substrate relative to the substrate support to be determined.

[00069] Fig. 3a shows an example of a mark 100 arranged on a substrate 10. It is noted however that numerous embodiments are possible for the marks, which may e.g. be an alignment mark AM as shown in fig. 2. In the example in fig. 3a the mark 100 comprises an opaque material 103 and a first transparent material 104. The mark 100 further comprises a second transparent material 106. Reflective interfaces l02a are further provided on a top surface of the mark 100, while another reflective interface l02b defines a bottom reflective interface. The reflective interfaces l02a, l02b are e.g. formed by a large refractive index difference between material above it and the material below it.

[00070] Above the mark 100 multiple layers 10.1, 10.2, 10.3, 10.4 of the substrate 10 are arranged. It is noted that in the context of this invention terms like“above” and“higher” with respect to“below” and “lower” are to be interpreted as seen in the direction the substrate 10 is traditionally formed, i.e. the first layer of the substrate being lower than any subsequently arranged layers. Traditionally the substrate 10 will be arranged horizontally on a substrate support with the lower layers actually being below the higher layers.

[00071] It is noted that although four layers 10.1, 10.2, 10.3, 10.4 are shown in this example, in practice any number of layers may occur. The three bottom layers 10.1, 10.2, 10.3 are made of transparent material. In the context of this invention transparent refers the capability of radiation used in a measurement beam 105 of the alignment sensor to go through these layers. Layer 10.4 however, is a mask layer which is made of hard material, which may e.g. comprise amorphous carbon and/or high density metals, e.g. tungsten, and is opaque for optical wavelengths, e.g. including visible and infrared light. The mask layer 10.4 is thus opaque for the measurement beam 105, resulting in the measurement beam 105 being reflected without being able to detect the mark 100. The mask layer 10.4 may e.g. be 1-2 micrometers thick.

[00072] It therefore desired to clear an area l0.4a of the mask layer 10.4 above the alignment mark 100, as is shown in fig. 3b. In the context of this invention clearing means adapting the mask layer 10.4 such that the mark 100 below the mask layer 10.4 becomes detectable for a measurement tool, which e.g. emits the measurement beam 105. In this example material of the mask layer 10.4 is at least partly removed in the area l0.4a, allowing the measurement beam 105 to propagate through the substrate 10 and reach the mark 100. In other embodiments one or more properties of the mask layer 10.4 are changed, for example making a part of the mask layer not opaque, such that a part of the measurement beam 105 propagates through the substrate 10 and reach the mark 100.

[00073] The measurement beam 105 which is emitted onto the mark 100 will partly be reflected by the reflective interfaces l02a on the top surface and partly by the reflective interfaces l02b on the bottom reflective interface, resulting in different reflected beams each comprising components of the

measurement beam 105 reflected on the mark 100. In this example the mark 100 functions as a phase grating, causing a phase change in the reflected beams by which the position of the mark 100 can be determined. An optical path difference between the different reflected beams of the measurement beam 105 allows a detector to generate an mark detection signal, e.g. based on a phase difference between said reflections when they reach a sensor of the detector arranged to detect said reflected beams, e.g. the photodetector PD in fig. 2. Based on this the position of the mark can be determined. Other type of alignment marks are also envisioned.

[00074] It is noted that in practice reflection may occur from all materials, the reflective interfaces l02a, l02b however cause the dominating reflected beams. It is further noted that in the context of the present invention reflection is intended to include diffraction and the reflective beams are intended to include diffracted beams. Optionally the measurement beam 105 is emitted by a radiation source such as laser, and may e.g. comprise radiation in a narrow wavelength bandwidth, e.g. with a width of 5 nm or less.

[00075] The substrate 10 is typically provided with a plurality of marks 100, e.g. 40 or more. When more of these marks 100 are detected and measured, the position of the substrate 10, in particular the position of the target portions of the substrate 10, can be determined with higher precision, allowing for a reduced overlay error between the layers of the substrate 10 and/or to project the desired pattern onto the target portions of the substrate 10 with higher precision. However, as for each of these marks 100 the area l0.4a of the mask layer 10.4 needs to be cleared in addition to the detecting of the marks 100 themselves, this part of the lithographic process becomes time consuming and may be a bottleneck, slowing down the overall lithographic process and reducing the throughput. [00076] The invention therefore provides an apparatus for processing at least a first substrate in a lithographic process of which an embodiment is schematically shown in top view in fig. 4. The apparatus comprises a first substrate support 1001 which is configured to hold a first substrate 1010, said first substrate 1010 comprising a mask layer and one or more marks arranged below said mask layer. The apparatus furthermore comprises a clearing tool 201, schematically depicted in fig. 4. The clearing tool 201 is configured to clear at least one of the marks by clearing an area l0l0.4a of the mask layer above said mark while the first substrate 1010 is arranged on the first substrate support 1001. The apparatus further comprises a measurement tool 301, also schematically depicted in fig. 4. The measurement tool 301 is configured to determine a position of at least one of the cleared marks while the first substrate is arranged on the first substrate support.

[00077] Fig. 4 further schematically shows an optional substrate loader 202 which is configured to arrange, and optionally pre-align, the first substrate 1010 on the first substrate support 1001 and/or to unload the first substrate 1010 from the first substrate support 1001. The substrate loader 202 may e.g. comprise a robot for transporting the first substrate 1010 from an interface of the apparatus with the outside world to the substrate support 1001 and back. Such an interface may e.g. comprise a load lock.

[00078] In the shown embodiment the apparatus further comprises a memory 381 connected to the measurement tool 301 for storing measurements obtained by the measurement tool 301. Alternatively, or in addition, the measurement tool 301 may comprise a communication link, e.g. a wired or wireless communication link, to transmit the measurement data as obtained by the measurement tool 301. Said communication link may e.g. be in communication with a lithographic apparatus or a control unit thereof.

[00079] The invention thus provides in an apparatus with which the marks can be cleared and their position can be determined, while the first substrate 1010 remains on the same first substrate support 1001. Advantageously the time required for clearing the marks and determining their position is reduced. This allows for a higher throughput, and/or to clear and detect more marks in a given time period. By determining the position of more marks, in particular alignment marks, the accuracy of the exposure process, in particular the positioning of the target portions relative to the patterned beam of radiation can be improved. As a consequence, an overlay error between consecutive layers may be decreased as well. In accordance with the present invention, the marks that are cleared may e.g. be alignment marks and/or overlay marks. Clearing overlay marks may in particular be advantageous to determine the overlay before etching. As such undesirable overlay can be earlier detected, e.g. before the etching. A layer, e.g. the mask layer, may then be stripped and a new layer can be arranged on the first substrate 1010. On said new layer alignment and exposure can be repeated with better overlay. This saves cost and time in the lithographic process. [00080] Fig. 5 shows a further embodiment of the invention. In the shown embodiment the apparatus comprises a clearing station 200 which comprises the clearing tool 201 and a measurement station 300 which comprises the measurement tool 301. In the shown situation the first substrate support 1001, which is holding the first substrate 1010, is arranged in the measurement station 300. In the clearing station 200 a second substrate support 1101 is provided which is configured to hold a second substrate 1110, said second substrate 1110 comprising a mask layer and one or more marks arranged below said mask layer. It is noted that the second substrate support 1101 may be embodied similarly as described with respect to the first substrate support 1001 and the second substrate 1110 similarly as the first substrate 1010.

[00081] In the shown embodiment the apparatus further comprises a positioner (not shown) which is configured to move the first substrate support 1010 from the clearing station 200 to the measurement station 300, as is indicated by arrow 1050, and back to the clearing station, as is indicated by arrow 1051. A second positioner (not shown) is configured to move the second substrate support 1110 according to the same route.

[00082] In the embodiment shown in fig. 5, the clearing tool 201 is configured to clear at least one of the marks of the second substrate 1110 by clearing an area of the mask layer above the marks, said second substrate 1110 being arranged on the second substrate support 1101, while the measurement tool 301 is determining the position of at least one of the cleared marks of the first substrate 1010, said first substrate 1010 being arranged on the first substrate support 1001.

[00083] In this embodiment, the invention allows to process multiple substrates 1010, 1110 at the same time, thereby reducing the time required for the clearing of the marks and the detecting of their positions even further. Preferably the time that any substrate 1010, 1110 is in the clearing station 200 is approximately equal to the time it is in the measurement station 300, e.g. in the range of 10-15 seconds.

[00084] It is noted that although in fig. 5 the substrate loader 202 of the clearing station 200 is configured to both load and unload the substrates 1010, 1110, it is also possible to provide a substrate unloader (not shown) in the measurement station 300 such that the substrates 1010, 1110 are loaded in the clearing station and unloaded in the measurement station 300.

[00085] In the shown embodiment the clearing station 200 comprises a first position measurement module 221 which is schematically depicted. The first position measurement module 221 is configured to measure a position of the first substrate support 1001 when the first substrate support 1001 is in the clearing station 200.

[00086] For example, the first position measurement module 221 may comprise an interferometer system. An interferometer system is known from, for example, United States patent US6,020,964, filed on July 13, 1998, hereby incorporated by reference. The interferometer system may comprise a beam splitter, a mirror, a reference mirror and a sensor. A beam of radiation is split by the beam splitter into a reference beam and a measurement beam 221.1. The measurement beam 221.1 propagates to the mirror and is reflected by the mirror back to the beam splitter. The reference beam propagates to the reference mirror and is reflected by the reference mirror back to the beam splitter. At the beam splitter, the measurement beam 221.1 and the reference beam are combined into a combined radiation beam. The combined radiation beam is incident on the sensor. The sensor determines a phase or a frequency of the combined radiation beam. The sensor generates a signal based on the phase or the frequency. The signal is representative of a displacement of the mirror. In the shown embodiment, the mirror is connected to the substrate supports 1101, 1001. The reference mirror may be connected to a metrology frame. In an embodiment, the measurement beam 221.1 and the reference beam are combined into a combined radiation beam by an additional optical component instead of the beam splitter.

[00087] In the shown embodiment the measurement station 300 comprises a second position measurement module 321 which is schematically depicted. The second position measurement module 321 configured to measure a position of the first substrate support 1001 when the first substrate support 1001 is in the measurement station 300.

[00088] For example, the second position measurement module 321 may comprise an encoder system. An encoder system is known from for example, United States patent application US2007/0058173A1, filed on September 7, 2006, hereby incorporated by reference. The encoder system comprises an encoder head, a grating and a sensor. The encoder system may receive a primary radiation beam and a secondary radiation beam. Both the primary radiation beam as well as the secondary radiation beam originate from the same radiation beam 321.1, i.e., the original radiation beam 321.1. At least one of the primary radiation beam and the secondary radiation beam is created by diffracting the original radiation beam 321.1 with the grating. If both the primary radiation beam and the secondary radiation beam are created by diffracting the original radiation beam 321.1 with the grating, the primary radiation beam needs to have a different diffraction order than the secondary radiation beam. Different diffraction orders are, for example,+lst order, -lst order, +2nd order and -2nd order. The encoder system optically combines the primary radiation beam and the secondary radiation beam into a combined radiation beam. A sensor in the encoder head determines a phase or phase difference of the combined radiation beam. The sensor generates a signal based on the phase or phase difference. The signal is representative of a position of the encoder head relative to the grating. One of the encoder head and the grating may be arranged on the substrate supports 1101, 1001. The other of the encoder head and the grating may be arranged on a metrology frame or a base frame. Although schematically depicted as being arranged next to the substrate supports 1101, 1001, in an example, a plurality of encoder heads are arranged on a metrology frame above the substrate supports 1101, 1001, whereas a grating is arranged on a top surface of the substrate supports 1101, 1001. In another example, a grating is arranged on a bottom surface of the substrate supports 1101, 1001, and an encoder head is arranged below the substrate supports 1101, 1001

[00089] It is noted that it is also possible for second position measurement module 321 to comprise an interferometer system and/or for the first position measurement module 221 to comprise an encoder system.

[00090] In an embodiment the second position measurement module 321 is configured to measure the position of the first substrate support 1001 with a higher precision than the first position measurement module 221. For clearing the marks the precision may be less crucial since the cleared area should be larger than the mark. However, the position of the marks is normally measured with a relatively high precision. As such, simpler and/or cheaper components can be used for the first position measurement module 221. For example, the precision of the first position measurement module 221 may be in the order of micrometers while the precision of the second position measurement module 321 is in the order of nanometers.

[00091] The measurement tool 301 may be embodied as the alignment sensor shown in fig. 2.

[00092] In an embodiment the clearing tool 201 comprises a laser ablation tool, of which an example is shown in fig. 6. The laser ablation tool is configured to clear the area of the mask layer by emitting laser pulses 262 on the mask layer.

[00093] The energy of the laser pulses 262 affects the hard mask material and provides a hole in the hard mask, e.g. the material is heated by the absorbed laser energy and evaporates or sublimates or the material is converted into a plasma. The laser ablation tool may comprise a debris removal module (not shown) for removing material of the hard mask that is left behind by the laser ablation process. The debris removal module may e.g. be embodied as disclosed in PCT/EP2018/069601, which is incorporated herein by reference.

[00094] In an embodiment the laser ablation tool comprises an ultra-short pulsed laser module 250 configured to emit a laser beam comprising Gaussian laser pulses 260.1. The ultra-short pulsed laser module 250 emits ultrashort pulses of radiation, e.g. including electromagnetic radiation, e.g. visible or non-visible light, preferably of the order of several hundreds of femtoseconds to ten picoseconds. High output peak power allows to remove material of the mask layer. The laser ablation tool further comprises a top-hat shaper 251 configured to transform the Gaussian laser pulses 260.1 into the laser pulses 260.2 having a top-hat shaped energy density. A top-hat energy density means that the laser pulses 260.2 have a near-uniform energy density over a cross-section of the laser beam, such that the material of the mask layer of the first substrate 1010 is subjected to near-uniform energy density where the laser pulses 262 are emitted onto the first substrate 1010. For example, the laser pulse 262 may comprise an energy density in the order of 0.135 J/cm². [00095] In an embodiment the laser ablation tool further comprises a size shaper 257 configured to dynamically control the size of the laser pulses 262 emitted on the mask layer. In this case the laser ablation tool may be part of a stand-alone clearing tool without a measurement tool.

[00096] For example, the size shaper 257 may comprise a spatial light modulator. A spatial light modulator is a known device that can manipulate light by modulating the amplitude, phase or polarization of the light waves in the two dimensions of space and time. It comprises one or more programmable liquid crystal based pixel mirrors with which beam 260.2 can be converted into beam 260.2 with the desired shape and size.

[00097] Preferably the laser ablation tool further comprises at least one mirror arranged in an optical path of the laser pulses, which mirror is configured to be adjustable to control the direction of the laser pulses 262 emitted on the mask layer. In the shown example the laser ablation tool comprises two optional Galvanomirrors 252, 253 for this, which are configured to direct the laser pulses 262. The term Galvanomirror is used herein to indicate a Galvano scanner mirror which comprises a motor for rotating said mirror in at least one direction. Galvanomirror 252 reflects beam 261.1, comprising laser pulses, into beam 261.2 and allows adjusting the laser pulse 262 in the Y-direction by rotating the Galvanomirror 252 around its axis. Galvanomirror 253 reflects beam 261.2 into 261.3 and allows adjusting the laser pulse 262 in the X-direction by rotating the Galvanomirror 253 around its axis.

[00098] Mirror 254 further directs the beam into objective lens 255 which focusses the laser pulse 262 on the mask layer of the first substrate 1010. It is noted that in an embodiment one or more of the Galvanomirrors 252, 254, mirror 254, size shaper 257 and top-hat shaper 251 may be arranged in a scanhead. In an embodiment the laser ablation tool may further comprise a beam expander, e.g. arranged between the ultra-short pulsed laser module 250 and the top-hat shaper 251.

[00099] Optionally the laser pulses 262 emitted on the mask layer have a size which is substantially equal to the area of the mask layer which is to be cleared. As such the mark can be cleared by subjecting the area substantially equally to energy of the laser pulses 262, leaving a smooth hole. For example, the laser pulse 262 may cover an area in the order of 100 x 40 micrometer. A clearing method whereby the applied laser pulses cover an area having substantially the same size as the area to be cleared may be referred to as percussion drilling or a percussion drilling method. As an alternative to this so-called percussion drilling method, it is also possible to apply a so-called meandering method, wherein the size of the laser pulses 262 is considerably smaller than the area to be cleared. This allows to clear an area with any size and/or shape as long as it is larger than said size of the laser pulses 262. For example, the laser pulse 262 may cover an area with a diameter in the order of 10 micrometer. Combinations of the percussion drilling method and the meandering method are also possible, e.g. wherein the percussion drilling method is applied first to clear the majority of the area and the meandering method is applied thereafter to clear small additional parts to better clear the mark.

[000100] In an embodiment the laser ablation tool further comprises a spot monitor sensor 290 arranged on the first substrate support 1001. With said spot monitor sensor 290 the intensity and energy density of the laser pulse 260 can be measured, e.g. by arranging the spot monitor sensor 290 under the objective lens 255. As such the laser pulse 262 can be monitored, as some properties may e.g. drift over time due to ageing of components.

[000101] In the embodiments of the laser ablation tool as described above and below, such as a laser ablation tool comprising at least one mirror arranged in an optical path of the laser pulses and/or a size shaper, and/or a spot monitor sensor, the laser ablation tool may alternatively be comprised in a stand alone clearing tool without a measurement tool.

[000102] In an embodiment the clearing tool further comprises an optional image sensor 256 which is configured to capture an image of at least a part of the first substrate 1010, and a processing unit 280 configured to determine a position of at least one of the one or more marks below the mask layer based on said image, and to determine the area of the mask layer to be cleared based on the position of said mark.

[000103] The image sensor 256 may e.g. be a charge-coupled device (CCD). The image sensor 256 may be configured to take the image before the clearing tool clears or starts clearing the mask layer. Although the mask layer is opaque for the measurement beam of the measurement tool, the image taken with the image sensor 256 may show the position of the mark below the mask layer. The image is delivered, via output terminal 256.1, communication signal 256a and input terminal 280.1, to the processing unit 280. The processing unit 280 determines from said image the position of the mark below the mask layer, from which the area to be cleared can be determined. Based on this, a position of the first substrate 1010 can be adapted, e.g. using the positioner to position the first substrate holder 1001, and/or a location on the mask layer on which the laser pulse 262 is emitted can be adapted, e.g. using Galvanomirrors 252, 253, and/or a size of the laser pulse 262 can be adapted, e.g. using the size shaper 257. The processing unit 280 may be configured to control one or more of these parameters with control signal 280a which is outputted via output terminal 280.3, and which may be connected (not shown) to one or more of the positioners, size shaper 257 and/or Galvanomirrors 252, 253 or control units of these components. The motors of the Galvanomirrors 252, 253 are preferably configured to react and position the Galvanomirrors 252, 253 at a frequency which is at least equal to the frequency the laser pulses 262 are emitted, such that it is possible to correct the position of the Galvanomirrors 252, 253 for a subsequent laser pulse 262 when required.

[000104] In an embodiment the clearing tool further comprises an optional feedback camera 270 which is configured to capture an image during the clearing of at least of part of the first substrate 1010 comprising at least the area of the mask layer which is being cleared, and the processing unit 280 is configured to determine at least one clearing process parameter based on said image, wherein said processing unit is further configured to, based on said clearing process parameter, control or stop the clearing.

[000105] In a further embodiment wherein the clearing comprises sequentially emitting multiple laser pulses 262 on the area of the mask layer with the laser ablation tool, the feedback camera 270 is configured to capture the image after at least a first laser pulse 262 has been emitted on the mask layer. In this embodiment processing unit 280 is configured to control the clearing by controlling, for a subsequently emitted laser pulse 262, a position of the first substrate 1010, and/or a location on the mask layer on which the laser pulse 262 is emitted, and/or a size of the laser pulse 262.

[000106] The feedback camera 270 thus provides a feedback-loop with real-time information on the clearing by taking images during the clearing. Said images are via output terminal 270.1, communication signal 270a and input terminal 280.2 delivered to processing unit 280, which is configured to derive information from these images, and determine at least one clearing process parameter from this information. Said clearing process parameter may e.g. relate to the accuracy and/or progress of the clearing. Based on the clearing process parameter the processing unit 280 may determine to stop the clearing, e.g. if sufficient material of the hard mask has been removed such that the mark is detectable by the measurement tool. Usually other layers of the first substrate 1010 are arranged between the hard mask and the mark, and those layers are preferably not or as little as possible exposed to the laser pulses 262.

[000107] Advantageously the feedback camera 270 uses the actual real-time situation to derive the information, providing a feedback loop which enables detecting errors of various causes. This allows to compensate for each of these errors, including errors due to positioning of the substrate table 1001 or due to aiming of the laser pulses 262, or any random errors. Regardless of how the error is caused, the clearing can be adjusted, e.g. by adjusting the location or size of the laser pulse 262, or by positioning the substrate support 1001. By improving the location of the hard mask on which the laser pulse 262 is emitted, the resulting hole can have better defined edges and be more reproducible among the holes in a single substrate 1010.

[000108] The feedback-loop provided by the feedback camera 270 allows to control the clearing better and clear the area by making a high quality hole. Such high quality hole includes smooth edges, which allows to position a resist over the hole with less roughness than what would be caused by non-smooth edges. Alignment accuracy and accuracy of resist-patterns are improved with this embodiment. In an embodiment the edge of the hole can also be controlled by controlling the size of the laser pulse 262 with the size shaper 257. For example, by increasing or narrowing the size of the laser pulse 262 a smoother edge may be achieved. In addition when increasing the size of laser pulse 262, debris which is e.g.

disposed around the edge, may be removed by the increased laser pulse 262. [000109] Controlling the clearing includes that, based on a clearing process parameter, a position of the first substrate 1010 can be adapted, e.g. using the positioner to position the first substrate holder 1001, and/or a location on the mask layer on which the laser pulse 262 is emitted can be adapted, e.g. using Galvanomirrors 252, 253, and/or a size of the laser pulse 262 can be adapted, e.g. using the size shaper 257. The processing unit 280 may be configured to control one or more of these parameters with control signal 280a which is outputted via output terminal 280.3, and which may be connected (not shown) to one or more of the positioners, size shaper 257, and/or Galvanomirrors 252, 253, or control units of these features.

[000110] In a further embodiment the processing unit is configured to compare the image with a reference image and/or to compare the clearing process parameter with a reference parameter. Based on the reference image and/or reference parameter the processing unit can determine whether the clearing needs to be adjusted. The reference image and/or reference parameter may e.g. be taken from a reference clearing at the same relative point in time, e.g. after approximately the same number of laser pulses have been emitted on the mask layer. The reference image and/or or reference parameter may e.g. be obtained from performing the clearing on a test substrate.

[000111] The feedback camera 270 is preferably a high-speed camera such that images can be taken in between of laser pulses 262 and/or when the laser pulse 262 hits the area. By taking an image when the laser pulse 262 hits the area the precision of the laser pulse 262 can easily be derived from the image.

[000112] It is noted that it is possible to embody the image sensor 256 and the feedback camera 270 in a single device or even a single camera. It is noted that it is possible to have two separate processing units for the image sensor 256 and the feedback camera 270, respectively.

[000113] It is noted that although the clearing tool is depicted as clearing one area of the mask layer at a time, the clearing tool may also be configured to clear multiple, e.g. two, three or four, areas at the same time. For example, the clearing tool may be configured, e.g. by comprising multiple laser ablation tools, to emit multiple laser pulses 262 at the same time on different areas of the hard mask. In such embodiment the clearing tool may also comprise multiple feedback cameras 270, each configured to take images of one of the areas that are being cleared.

[000114] Fig. 7 shows an embodiment of the apparatus according to the invention, wherein the measurement station 300 comprises an optional supplementary clearing tool 311. Said supplementary clearing tool 311 is configured to clear an area l0l0.4a of the mask layer above a mark while the first substrate 1010 is arranged on the first substrate support 1001.

[000115] For example, the supplementary clearing tool 311 may be configured to finish the clearing of the areas l0l0.4a of the mask layer which has been started by the clearing tool 201. For example, the clearing tool 201 may be configured to clear a relatively big area !0l0.4a using a percussion drilling method, and the supplementary clearing tool 311 may be configured to use a meandering method to finish clearing the area l0l0.4a. It is noted that the supplementary clearing tool 311 may be embodied similarly to any of the embodiments described with respect to the clearing tool 201.

[000116] The supplementary clearing tool 311 is in particular advantageous if the clearing takes longer than the measuring of the positions of the cleared marks. By performing a part of the clearing in the measurement station 300, the time period that the substrate 1010, 1110 is processed in the clearing station 200 can be arranged to be approximately equal to the time period that the substrate 1010, 1110 is processed in the measurement station 300. By doing so, the use of the apparatus is optimized and more substrates 1010, 1110 can be processed in a given time period.

[000117] Fig. 8 illustrates an embodiment of the apparatus comprising a further clearing station 400. In this embodiment the apparatus comprises a third substrate support 1201 configured to hold a third substrate 1210 which comprises a mask layer and one or more marks arranged below said mask layer. The apparatus further comprises at least one further clearing station 400 comprising a further clearing tool 401 configured to, while the clearing tool 201 is clearing the marks of the first substrate 1010, clear at least one of the marks of the third substrate 1210 by clearing an area of the mask layer above said mark while the third substrate 1210 is arranged on the third substrate support 1201.

[000118] This embodiment allows to clear the mask layer of two substrates 1010, 1210 at the same time, which is in particular advantageous if the clearing takes longer than the measuring of the positions of the cleared marks. It is noted that the third substrate support 1201 may be embodied similarly as described with respect to the first substrate support 1001 and the third substrate 1210 similarly as the first substrate 1010. The further clearing station 400 may be embodied similarly as described with respect to the clearing station 200 and the further clearing tool 401 similarly as described with respect to the clearing tool 201.

[000119] In the situation shown in fig. 8 the first substrate 1010 and the third substrate 1210 are arranged in the clearing station 200 and the further clearing station 400, respectively, while the second substrate 1110 is arranged in the measurement station 300. It should be noted that any of the substrate holders 1001, 1101, 1201 can be arranged in any of the clearing station 200, the further clearing station 400 and the measurement station 300 by using positioners (not shown) to move them according to arrows 2001, 2002, 2003, 2004.

[000120] Fig. 9 illustrates an embodiment of the apparatus according to the invention comprising a further measurement station 500. In this embodiment the apparatus comprises a fourth substrate support 1301 configured to hold a fourth substrate 1310 which comprises a mask layer and one or more marks arranged below said mask layer. The apparatus further comprises at least one further measurement station 500 comprising a further measurement tool 501 configured to, while the measurement tool 301 is determining a position the cleared marks of the first substrate 1010, determine a position of at least one of the cleared marks of the fourth substrate 1310 while the fourth substrate 1310 is arranged on the fourth substrate support 1301.

[000121] This embodiment allows to measure the position of the marks on two substrates 1010, 1310 at the same time, which is in particular advantageous if the measuring of the positions of the cleared marks takes longer than the clearing process. The further measurement station also comprises a further memory 581 connected to the further measurement tool 501 for storing measurements obtained by the further measurement tool 501. It is noted that the fourth substrate support 1301 may be embodied similarly as described with respect to the first substrate support 1001 and the fourth substrate 1310 similarly as the first substrate 1010. The further measurement station 500 may be embodied similarly as described with respect to the measurement station 200 and the further measurement tool 501 similarly as described with respect to the measurement tool 301.

[000122] In the embodiment shown in fig. 9 the first substrate 1010 and the fourth substrate 1310 are arranged in the measurement station 300 and the further measurement station 500, respectively, while the second substrate 1110 is arranged in the clearing station 300. It should be noted that any of the substrate holders 1001, 1101, 1301 can be arranged in any of the clearing station 200, the measurement station 300 and the further measurement station 500 by using positioners (not shown) to move them according to arrows 3001, 3002, 3003, 3004.

[000123] It is noted that although in fig. 8 and fig. 9 the further clearing station 400 and the further measurement station 500 are shown separately, they may also be used in combination in a single embodiment. Furthermore, additional further clearing stations and/or additional further measurement stations may be applied for further optimization.

[000124] Fig. 10 shows an embodiment of the invention comprising a first station 800 and a second station 900. The first station 800 comprises the clearing tool 201 and the measurement tool 301. The second station 900 comprises a second substrate support 1901 configured to hold a second substrate 1910 comprising a mask layer and one or more marks arranged below said mask layer, while the first substrate support 1001 is holding the first substrate 1010. The second station 900 further comprises a second clearing tool 901 configured to clear at least one of the marks of the second substrate 1910 by clearing an area of the mask layer above said mark while the second substrate 1910 is arranged on the second substrate support 1901, and a second measurement tool 911 configured to determine a position of at least one of the cleared marks of the second substrate 1910 while the second substrate 1910 is arranged on the second substrate support 1901.

[000125] In the shown example the second station further comprises a second memory 981 connected to the second measurement tool 911 for storing measurements obtained by the second measurement tool 911. It is also possible however to connect the second measurement tool 911 with the memory 381 for storing the measurements of both measurement tools 301, 911 in the same memory 381. It is noted that all features and components of the second station 900 may be embodied similarly as their counterparts in the first station 800.

[000126] In this embodiment the first station 800 and second station 900 are embodied similarly such that each of them a substrate 1010, 1910 can be processed at the same time, allowing to process more substrates 1010, 1910 in a given time period.

[000127] The invention further relates to a system comprising the apparatus according to one or more of the embodiments illustrated herein, and a lithographic apparatus, which may e.g. be embodied according to the lithographic apparatus LA shown in fig. 1.

[000128] In an embodiment the lithographic apparatus LA may comprise an apparatus substrate support WT configured to hold the first substrate, a mask support MT constructed to support a patterning device and connected to a first apparatus positioner PM configured to accurately position the patterning device MA, a projection system PS configured to project a pattern imparted to a radiation beam B by the patterning device MA onto the first substrate while the first substrate is arranged on the apparatus substrate support WT, and a second apparatus positioner PW configured to accurately position the apparatus substrate support WT. In this embodiment at least one of the first apparatus positioner PM and the second apparatus positioner PW is configured to position the patterning device MA or the apparatus substrate support WT, respectively, based on measurements obtained by the measurement tool of the apparatus according to the invention.

[000129] For example, the measurement tool of the apparatus according to the invention may be configured to measure a position of a plurality of cleared marks and store them in a memory. Based on these measurements the relative positions of these marks to each other can be determined, providing information on the arrangement of the first substrate. When the first substrate is thereafter arranged on the apparatus substrate support WT it may be sufficient to determine to position of only a few marks. From the measurements done in the measurement tool of the apparatus according to the invention the position of the other marks can be derived and the first apparatus positioner PM and/or the second apparatus positioner PW can be controlled based thereon. The time required for the first substrate to be processed in the lithographic apparatus LA is thereby reduced.

[000130] In an embodiment the lithographic apparatus LA may comprise an apparatus substrate support WT configured to hold the first substrate, a projection system PS configured to project a pattern onto the first substrate while the first substrate is arranged on the apparatus substrate support WT, and a position measurement system PMS configured to determine a position of the first substrate by detecting at least one of the cleared marks while the first substrate is arranged on the apparatus substrate support WT. In this embodiment the marks cleared by the apparatus according to the invention can be used to determine the position of the first substrate when it is processed in the lithographic apparatus.

[000131] In an embodiment the system may comprise, next to the lithographic apparatus LA, a plurality of apparatuses according to the invention. In this embodiment the system is configured to process at least one substrate in each of the plurality of apparatuses while projecting the pattern onto another substrate in the lithographic apparatus LA. This is in particular advantageous if the clearing and detecting of the marks takes more time than the projecting of the pattern, e.g. because increasing requirements of precision demand more marks to be detected.

[000132] It is noted that it is envisaged that the clearing station may also be applied and claimed without the measurement station, in particular when including advantageous features such as the feedback camera and/or the image sensor.

[000133] Figure 11 illustrates an embodiment of the apparatus according to the second aspect of the invention, which is an apparatus for processing at least a first substrate 1010 in a lithographic process, which first substrate 1010 comprises a mask layer and one or more marks arranged below said mask layer. The apparatus comprises a first substrate support 1001 and a second substrate support 1101 configured to hold the first substrate 1010, a clearing tool 201 configured to clear at least one of the marks by clearing an area l0l0.4a of the mask layer above said marks while the first substrate 1010 is arranged on the first substrate support 1001, e.g. on the location indicated by dashed lines 1010’ in fig. 11, and a measurement tool 301 configured to determine a position of at least one of the cleared marks while the first substrate 1010 is arranged on the second substrate support 1101.

[000134] In the shown embodiment the clearing tool 201 is arranged in a clearing station 200 and the measurement tool is arranged in a measurement station 300. The apparatus in the shown embodiment further comprises an optional transfer tool 1 which is configured to transfer the first substrate 1010 from the first substrate support 1001 to the second substrate support 1101.

[000135] It is noted that any of the components and features of the apparatus shown in fig. 11 may be embodied according to one or more of the embodiments of similar components and features described with respect to any of figs. 1-10. Furthermore any of the features or components described with respect to said figs. 1-10 may also be added to the apparatus shown in fig. 11.

[000136] Although specific reference may be made in this text to the use of a lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc. [000137] Although specific reference may be made in this text to embodiments of the invention in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatus.

Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrate) or mask (or other patterning device). These apparatus may be generally referred to as lithographic tools. Such a lithographic tool may use vacuum conditions or ambient (non-vacuum) conditions.

[000138] Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention, where the context allows, is not limited to optical lithography and may be used in other applications, for example imprint lithography.

[000139] Where the context allows, embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may also be implemented as instructions stored on a machine -readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read only memory (ROM); random access memory (RAM); magnetic storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g. carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions.

However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. and in doing that may cause actuators or other devices to interact with the physical world.

[000140] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

1. Apparatus for processing at least a first substrate in a lithographic process, which first substrate comprises a mask layer and one or more marks arranged below said mask layer, the apparatus comprising:

a. a first substrate support configured to hold the first substrate,

b. a clearing tool configured to clear at least one of the marks by clearing an area of the mask layer above said mark while the first substrate is arranged on the first substrate support,

c. a measurement tool configured to determine a position of at least one of the cleared

marks while the first substrate is arranged on the first substrate support.

2. Apparatus according to claim 1 , comprising a clearing station which comprises the clearing tool and a measurement station which comprises the measurement tool, wherein the apparatus further comprises a positioner configured to move the first substrate support from the clearing station to the measurement station.

3. Apparatus according to claim 2, further comprising a second substrate support configured to hold a second substrate which comprises a mask layer and one or more marks arranged below said mask layer,

wherein the second substrate holder is configured to be arranged in the clearing station while the first substrate holder is arranged in the measurement station, and

wherein the clearing tool is configured to clear at least one of the marks of the second substrate by clearing an area of the mask layer above said marks while the measurement tool is determining the position of the at least one of the cleared marks of the first substrate.

4. Apparatus according to claim 2 or claim 3, further comprising:

a. a first position measurement module configured to measure a position of the first

substrate support when the first substrate support is in the clearing station, and b. a second position measurement module configured to measure a position of the first substrate support when the first substrate support is in the measurement station, wherein the second position measurement module is configured to measure the position of the first substrate support with a higher precision than the first position measurement module.

5. Apparatus according to one or more of the preceding claims, wherein the clearing tool further comprises:

a. an image sensor configured to capture an image of at least a part of the first substrate, b. a processing unit configured to determine a position of at least one of the one or more marks below the mask layer based on said image, and to determine the area of the mask layer to be cleared based on the position of said mark.

6. Apparatus according to one or more of the preceding claims, wherein the clearing tool comprises a laser ablation tool configured to clear the area of the mask layer by emitting laser pulses on the mask layer.

7. Apparatus according to claim 6, wherein the laser pulses emitted on the mask layer have a size which is substantially equal to the area of the mask layer which is to be cleared.

8. Apparatus according to claim 6 or claim 7, wherein the laser ablation tool further comprises, in an optical path of the emitted laser pulses:

a. at least one mirror, which mirror is configured to be adjustable to control the direction of the laser pulses emitted on the mask layer, and/or

b. at least one size shaper configured to control the size of the laser pulses emitted on the mask layer.

9. Apparatus according to one or more of the preceding claims, wherein the clearing tool further comprises:

a. a feedback camera configured to capture an image during the clearing of at least a part of the first substrate comprising at least the area of the mask layer which is being cleared, b. a processing unit configured to determine at least one clearing process parameter based on said image, wherein said processing unit is further configured to, based on said clearing process parameter, control or stop the clearing.

10. Apparatus according to claim 9 when dependent on any one of claims 6 to 8, wherein the clearing comprises sequentially emitting multiple laser pulses on the area of the mask layer with the laser ablation tool, wherein

a. the feedback camera is configured to capture the image after at least a first laser pulse has been emitted on the mask layer, b. the processing unit is configured to control the clearing by controlling for a subsequently emitted laser pulse

i. a position of the first substrate, and/or

ii. a location on the mask layer on which the laser pulse is emitted, and/or iii. a size of the laser pulse.

11. System comprising the apparatus according to one or more of the preceding claims, and a

lithographic apparatus which comprises:

i. an apparatus substrate support configured to hold the first substrate,

ii. a mask support constructed to support a patterning device and connected to a first apparatus positioner configured to position the patterning device,

iii. a projection system configured to project a pattern imparted to a radiation beam by the patterning device onto the first substrate while the first substrate is arranged on the apparatus substrate support, and

iv. a second apparatus positioner configured to position the apparatus substrate support,

wherein at least one of the first apparatus positioner and the second apparatus positioner is configured to position the patterning device or the apparatus substrate support, respectively, based on measurements obtained by the measurement tool of the apparatus.

12. Method for processing at least a first substrate, which first substrate comprises a mask layer and one or more marks arranged below said mask layer, the method comprising the following steps: a. arranging the first substrate on a first substrate support,

b. clearing at least one of the marks with a clearing tool by clearing an area of the mask layer above said mark while the first substrate is arranged on the first substrate support, c. determining a position of at least one of the cleared marks with a measurement tool while the first substrate is arranged on the first substrate support.

13. Method according to claim 12, further comprising the steps of:

a. arranging a second substrate on a second substrate holder, which second substrate

comprises a mask layer and one or more marks arranged below said mask layer, b. clearing at least one of the marks of the second substrate with the clearing tool by

clearing an area of the mask layer of above said marks, said second substrate being arranged on the second substrate support, while determining a position of the at least one of the cleared marks of the first substrate with the measurement tool, said first substrate being arranged on the first substrate support.

14. Method according to claim 12 or claim 13, further comprising the steps of:

a. capturing an image of at least a part of the first substrate

b. determining a position of at least one of the one or more marks below the mask layer based on said image, and

c. determining the area of the mask layer to be cleared based on the position of said mark.

15. Method according to one or more of the claims 12-14, further comprising the steps of:

a. capturing an image with a feedback camera during the clearing of at least of part of the first substrate comprising at least the area of the mask layer which is being cleared, b. determining at least one clearing process parameter based on said image,

c. controlling or stopping the clearing based on said clearing process parameter.