WO2025242413A1 - Systems, methods, and software for phase-based alignment sensors - Google Patents

Abstract

Disclosed is a metrology system having an optical module configured to receive signals from a target of interest. The optical module includes phase shifting optics configured to displace at least a portion of the signals such that a phase shift in the signals is introduced. Also disclosed is a metrology system that includes an array of phase masks configured to receive signals having multiple wavelengths. The array of phase masks provides dedicated phase retardances to the multiple wavelengths such that the signals passing through the array of phase masks combine into a single wavelength signal having discrete phase components corresponding to the multiple wavelengths.

Description

SYSTEMS, METHODS, AND SOFTWARE FOR PHASE-BASED ALIGNMENT SENSORS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63/649,836 which was filed on May 20, 2024 and which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

[0002] The description herein relates generally to metrology of patterns produced by lithographic processes. More particularly, the disclosure includes apparatus, methods, and computer programs for obtaining multiple wavelength probing signals with a reduced number of acquisitions by leveraging various phase shifting components, order shifting components, etc.

BACKGROUND

[0003] In manufacturing processes of integrated circuits (ICs), unfinished or finished circuit components are inspected to ensure that they are manufactured according to design and are free of defects. Inspection systems utilizing optical microscopes or charged particle (e.g., electron) beam microscopes, such as a scanning electron microscope (SEM) can be employed. As the physical sizes of IC components continue to shrink, and their structures continue to become more complex, accuracy and throughput in defect detection and inspection become more important.

[0004] Digital holographic microscopy (DHM) is being explored as a candidate platform for next generation overlay metrology due to its potential benefits for aberration correction and sensitivity to weak signals (low DE stacks and/or small targets). These benefits emerge from the fact that holographic microscopy encodes the full complex field, including both amplitude and phase of the 1st diffraction order signal and the linear amplification characteristic to holography.

SUMMARY

[0005] Systems, methods, and computer programs for improved metrology are disclosed along with methods of use in the manufacture of semiconductor devices. In a first aspect, a metrology system includes an optical module configured to receive signals from a target of interest. The optical module includes phase shifting optics configured to displace at least a portion of the signals such that a phase shift in the signals is introduced.

[0006] In some variations, the signals can include 0^th order signals and higher order signals diffracted from the target of interest. The optical module can include a first lens element configured to direct the 0^th order signals to the phase shifting optics that include a variable 0^th order attenuator. The variable 0^th order attenuator can further include a first mirror to receive the 0^th order signals and a shutter mounted after the first mirror. The shutter can be coupled to a controller to move the shutter to attenuate a portion of the 0^th order signals and create attenuated 0^th order signals. A second lens element can be configured to receive the attenuated 0^th order signals and direct the attenuated 0^th order signals to a detector.

[0007] In some variations, the shutter can be configured to perform a variable attenuation of the 0^th order signals to reduce contrast between the 0^th order signals and the higher order signals. The shutter can have a variable thickness to cause the variable attenuation based on a shutter position, with the shutter position and the variable attenuation driven by an amplitude of the 0^th order signals.

[0008] In some variations, the first mirror can be partially transparent such that a portion of the 0^th order signals arrive at an optical sensor and are utilized to drive a movement of the shutter. The driving of the shutter can be based on the intensity of the 0^th order signals at the optical sensor. The optical sensor can include a photodiode that converts the portion of the 0^th order signals to an electrical signal that controls the driving of the shutter. The 0^th order signal can be a reference signal and the system is configured to perform phase shifting to acquire multiple wavelengths from the target of interest. The optical module can introduce a phase shift in the 0^th order signals. For example, variable 0^th order attenuator can be coupled to a second controller to move the variable 0^th order attenuator and modify a path length of the 0^th order signals. The variable 0^th order attenuator can include a piezoelectric stage to drive the variable 0^th order attenuator.

[0009] In some variations, the system can have a second mirror, where the first mirror and the second mirror form a corner reflector configured to cause the phase shift of the 0^th order signals.

[0010] In some variations, the phase shifting optics can displace the 0^th order signals at the second lens element. The phase shifting optics can displace the 0^th order signals to be at a different angle at the second lens element than the higher order signals. There can be a third mirror and a fourth mirror, with the variable 0^th order attenuator in an optical path between the third mirror and the fourth mirror. The fourth mirror can be disposed after the variable 0^th order attenuator and displaced to be off an optical axis of the second lens element. The phase shifting optics can be configured to locate the 0^th order signal outside locations of a + 1^st order signal or a -1^st order signal.

[0011] In an interrelated aspect, a metrology system can include an array of phase masks configured to receive signals having multiple wavelengths, the array of phase masks providing dedicated phase retardances to the multiple wavelengths such that the signals passing through the array of phase masks combine into a single wavelength signal having discrete phase components corresponding to the multiple wavelengths.

[0012] In some variations, the array of phase masks can correspond to pixels providing a first resolution at a detector, and a single wavelength signal can be captured by a pixel providing a second resolution that is lower than the first resolution. The array of phase masks can be configured to simultaneously acquire N wavelengths utilizing M (2N + 1) phase masks. The M phase masks can be arranged in an /W X /W square formation corresponding to the pixels providing the first resolution. [0013] In some variations, optical module can be configured to receive 0^th order signals and higher order signals diffracted from the target of interest. The optical module can include an array of phase masks configured to provide dedicated phase retardances to corresponding pixels of a detector. A first lens element can be configured to direct the 0^th order signals to the array of phase masks. A second lens element can be configured to receive the retarded 0^th and higher order signals and direct the retarded 0^th and higher order signals to the detector.

[0014] In an interrelated aspect, a semiconductor device manufacturing method can include, receiving a substrate with a photoresist layer, directing radiation from radiation source to transfer a pattern from a mask onto the photoresist layer, removing a portion of the photoresist layer to form the pattern over the substrate, and performing metrology on the substrate with a metrology system. The metrology system can include an optical module configured to receive signals from the substrate. The optical module can have phase shifting optics configured to displace at least a portion of the signals such that a phase shift in the signals is introduced.

[0015] In an interrelated aspect, a semiconductor device manufacturing method can include receiving a substrate with a photoresist layer, directing radiation from radiation source to transfer a pattern from a mask onto the photoresist layer, removing a portion of the photoresist layer to form the pattern over the substrate, and performing metrology on the substrate with a metrology system. The metrology system can include an array of phase masks configured to receive signals having multiple wavelengths, the array of phase masks providing dedicated phase retardances to the multiple wavelengths such that the signals passing through the array of phase masks combine into a single wavelength signal having discrete phase components corresponding to the multiple wavelengths.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which are incorporated in and constitute a part of this specification, show certain aspects of the subject matter disclosed herein and, together with the description, help explain some of the principals associated with the disclosed implementations. In the drawings,

Figure 1 depicts a schematic representation of holistic lithography, representing a cooperation between three technologies to optimize semiconductor manufacturing, according to an embodiment of the present disclosure.

Figure 2 depicts a schematic diagram of an exemplary optical module having a mechanically driven attenuator, according to an embodiment of the present disclosure.

Figure 3 depicts a schematic diagram of an attenuator coupled to an optical sensor, according to an embodiment of the present disclosure.

Figure 4 depicts a schematic diagram of wavelength-dependent phase shifts caused by a change in optical path length, according to an embodiment of the present disclosure.

Figure 5 depicts a diagram of a displaced 0^th order signal on a pupil of a metrology system, according to an embodiment of the present disclosure. Figure 6 depicts a diagram of a metrology system where phase shifting optics are part of a folded pupil.

Figure 7 depicts a diagram of a metrology system that includes an array of phase masks in front of a detector, according to an embodiment of the present disclosure.

Figure 8 depicts a diagram of an array of phase masks combing signals with different phases into a single pixel, according to an embodiment of the present disclosure.

Figure 9 is a block diagram of an example computer system, according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

[0017] Embodiments of the present disclosure are described in detail with reference to the drawings, which are provided as illustrative examples of the disclosure so as to enable those skilled in the art to practice the disclosure. Notably, the figures and examples below are not meant to limit the scope of the present disclosure to a single embodiment, but other embodiments are possible by way of interchange of some or all of the described or illustrated elements. Moreover, where certain elements of the present disclosure can be partially or fully implemented using known components, only those portions of such known components that are necessary for an understanding of the present disclosure will be described, and detailed descriptions of other portions of such known components will be omitted so as not to obscure the disclosure. Embodiments described as being implemented in software should not be limited thereto, but can include embodiments implemented in hardware, or combinations of software and hardware, and vice-versa, as will be apparent to those skilled in the art, unless otherwise specified herein. In the present specification, an embodiment showing a singular component should not be considered limiting; rather, the disclosure is intended to encompass other embodiments including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein. Moreover, applicants do not intend for any term in the specification or the claims to be ascribed an uncommon or special meaning unless explicitly set forth as such. Further, the present disclosure encompasses present and future known equivalents to the known components referred to herein by way of illustration.

[0018] Although specific reference may be made in this text to the manufacture of ICs, it should be explicitly understood that the description herein has many other possible applications. For example, it may be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid-crystal display panels, thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” in this text should be considered as interchangeable with the more general terms “substrate” and “target portion”, respectively.

[0019] Figure 1 depicts a schematic representation of holistic lithography, representing a cooperation between three technologies to optimize semiconductor manufacturing. A patterning device can comprise, or can form, one or more patterns. The patterns can be generated utilizing CAD (computer- aided design) programs, based on a pattern or design layout, this process often being referred to as EDA (electonic design automation). Typically, the patterning process in a lithographic apparatus LA is one of the most critical steps in the processing which requires high accuracy of dimensioning and placement of structures on the substrate. To ensure this high accuracy, three systems (in this example) may be combined in a so called “holistic” control environment as schematically depicted in Figure 3. One of these systems is the lithographic apparatus LA which is (virtually) connected to a metrology apparatus (e.g., a metrology tool) MT (a second system), and to a computer system CL (a third system). A “holistic” environment may be configured to optimize the cooperation between these three systems to enhance the overall process window and provide tight control loops to ensure that the patterning performed by the lithographic apparatus LA stays within a process window. The process window defines a range of process parameters (e.g., dose, focus, overlay) within which a specific manufacturing process yields a defined result (e.g., a functional semiconductor device) - typically within which the process parameters in the lithographic process or patterning process are allowed to vary.

[0020] The computer system CL may use (part of) the design layout to be patterned to predict which resolution enhancement techniques to use and to perform computational lithography simulations and calculations to determine which mask layout and lithographic apparatus settings achieve the largest overall process window of the patterning process (depicted in Figure 2 by the double arrow in the first scale SCI). Typically, the resolution enhancement techniques are arranged to match the patterning possibilities of the lithographic apparatus LA. The computer system CL may also be used to detect where within the process window the lithographic apparatus LA is currently operating (e.g., using input from the metrology tool MT) to predict whether defects may be present due to, for example, sub-optimal processing (depicted in Figure 1 by the arrow pointing “0” in the second scale SC2). [0021] The metrology apparatus (tool) MT may provide input to the computer system CL to enable accurate simulations and predictions and may provide feedback to the lithographic apparatus LA to identify possible drifts, e.g., in a calibration status of the lithographic apparatus LA (depicted in Figure 3 by the multiple arrows in the third scale SC3).

[0022] In lithographic processes, it is desirable to make frequent measurements of the structures created, e.g., for process control and verification. Different types of metrology tools MT for making such measurements are known, including scanning electron microscopes or various forms of optical metrology tools, image based or scatterometery-based metrology tools, and interferometers. Interferometers can be utilized to obtain information about reflected light that can then be analyzed to determine shifts, rotations, etc. for substrate alignment. Scatterometery tools can be utilized to detect scattered light that can then be analyzed to quantify aspects of the substrate such as overlay between layers of the substrate. [0023] As used herein, the term “layer” refers to a process layer, e.g., a region of the printed object (e.g., a semiconductor device or wafer) that was created with the patterning processes. Layers can be made of different materials or may be different regions that are processed (e.g., when performing an etch, the area with material removed may be considered one layer and the area below it without material removed may be considered another layer).

[0024] As used herein, the term “alignment” (AL) means the alignment of a substrate (e.g., a wafer) to be correctly positioned for subsequent metrology or for processing/exposure. Alignment measurements can be performed with an AL sensor that can utilize, for example, scattered light from the substrate. The position of the substrate can be encoded in the phase shift of the scattered light and used to determine alignment corrections.

[0025] From the above, “alignment” refers to determining the position of a substrate and “overlay” refers to determining error in the positioning of substrate layers.

[0026] The present disclosure provides various systems and methods for an improved alignment sensor that has reduced sensitivity to vibration, allows parallel acquisition of multiple channels (e.g., wavelengths, and polarizations), etc. Scattered or reflected light from the target of interest (e.g., a wafer or other substrate) can be detected and analyzed to determine the position of the target by calculating positional shifts in structural features of the target (e.g., alignment marks or other reference points). Deviation of the expected position can indicate a misalignment. Embodiments of the improved alignment sensor can utilize several features, in various combinations, to achieve numerous improvements over the state of the art.

[0027] Embodiments of the disclosed improved alignment sensor can utilize the 0^th order signal as a reference signal for several reasons. The 0^th order signal is generated coherently with the 1^st order signal and therefore vibration induced errors in the phase of 0^th order signal are correlated to vibration induced errors in phase of 1^st order (or other orders which carry signal of interest). Also, the 0^th order signal is typically stronger than the 1^st order signal, enabling linear amplification of the holographic signal and therefore allowing marks in stacks with low diffraction efficiency to be measured (in fact, 0^th order can often times be too strong, such that the resulting bright field fringe image may suffer from poor contrast). Further, the 0^th order signal is identically common to both +l^st order signal and - 1^st order signal, thereby reducing the burden on calibration and the risk of drift or mechanical vibration between the holograms of the two orders. The present disclosure refers to “higher order signals,” and while this can refer to 1^st order signals, it is also contemplated that higher order signals can include 2^nd order, 3^rd order, etc. Similarly, rather than using the 0^th order signal, other orders can be used. For example, the reference signal could be 1^st order instead of 0^th order, and as such the higher order signals could be 2^nd order, 3^rd order, etc.

[0028] Phase shifting interferometry (PSI) can be used for measuring extremely precise phase maps of the signal field, with a resolution as low as Z/l 000. where I is the wavelength of measurement. PSI is an interferometric imaging technique which captures a series of interferograms with specific phase shifts of the reference beam (e.g., 0, 0.5TI, 71, 1 ,5n) and thus encodes the quadrature components of the complex fields. This technique can be generalized to multiple wavelengths in which arbitrary but symmetric phase shifts are introduced in the reference path and 2N+1 holograms are sufficient to solve for the complex field at N wavelengths. For example, a 12 color (wavelength) sensor can use 25 holographic fringe images to record the complex field of the 1st order diffraction signals for all wavelengths.

[0029] Improved stability and throughput can be realized by, for example, reducing the number of camera acquisitions. In holography, the signal content can be encoded in the 2D angular frequency space, and therefore can be separated if the fringes are oriented at different angles.

[0030] As explained in further detail by the disclosed embodiments, the aspects above can be realized in, for example, an optical module that utilizes zeroth and higher order signals, can shift and/or attenuate the 0^th order reference signal to allow simultaneous acquisition with the higher-order signals. Other embodiments can include phase shifting of higher order signals at different wavelengths to allow them to be simultaneously acquired, thus reducing or eliminating perturbations that may occur were they acquired at different times.

[0031] Figure 2 depicts a schematic diagram of an exemplary optical module having a mechanically driven attenuator, according to an embodiment of the present disclosure. The depicted optical module 200 can serve two basic purposes. The optical module can act to move various components to cause a wavelength-dependent phase shift in the light reflected from a substrate (so that multiple wavelengths can be measured at a detector). Another purpose can include causing an intensity-dependent attenuation of the reflected light, which can aid in reducing excessive contrast between 0^th order and higher order fringes reaching the detector (so that the higher order fringes are not overwhelmed by the bright 0^th order light). While both functions can be included in the same embodiment, and hence for simplicity the moving mirrors and/or shutter are collectively referred to as an “optical module,” it is contemplated that some embodiments may only facilitate one of them (e.g., either the phase shifting or the variable attenuation).

[0032] The depicted portion of a metrology system can include an optical module 200 configured to receive signals (e.g., light) from a target of interest 210 (e.g., an alignment mark, grating, or other reference point/feature), where optical module 200 can include phase shifting optics 220 configured to displace at least a portion of the signals such that a phase shift in the signals can be introduced. This can be performed by second controller 246 that can move various optical components (e.g., including first mirror 222, etc.) in the ‘Y’ direction to increase the path length. As also shown in the example of Figure 2, the signals can include 0^th order signals 211 and higher order signals 212 diffracted from target of interest 210. Optical module 200 can include a first lens element 230 configured to direct the 0^th order signals to the phase shifting optics that can include a variable 0^th order attenuator 240. Variable 0^th order attenuator 240 can include a first mirror 222 to receive the 0^th order signals to second mirror 224 and a shutter 242 mounted after the first mirror. Shutter 242 can be coupled to controller 244 to move shutter 242 to attenuate at least a portion of 0^th order signals 211 and create attenuated 0^th order signals. Second lens element 232 can be configured to receive the attenuated 0^th order signals and direct the attenuated 0^th order signals to detector 250.

[0033] Figure 3 depicts a schematic diagram of an attenuator coupled to an optical sensor, according to an embodiment of the present disclosure. In some embodiments, the attenuator can be in the form of a shutter (e.g., a variable thickness material moved as needed to attenuate the 0^th order signals). For example, shutter 242 can be configured to perform a variable attenuation of the 0^th order signals to reduce the contrast between the 0^th order signals reaching the detector and the higher order signals. While different types of variable attenuators can be utilized, in one example, shutter 242 can have a variable thickness to cause a variable attenuation based on the shutter position. In other embodiments, the shutter can incorporate material of varying opacity to the light desired to be attenuated.

[0034] In one example use, the shutter position and the variable attenuation can be driven by the amplitude of the 0^th order signals. In the example of Figure 3, first mirror 222 can be partially transparent (e.g., transmitting through the mirror 50%, 10%, 1%, etc. of the incident light) such that a portion 311 of 0^th order signals 211 arrive at optical sensor 320 and are utilized by controller 244 to drive the movement of shutter 242. The driving of shutter 242 can be based on an intensity of the 0^th order signals at optical sensor 320. In some embodiments, optical sensor 320 coupled to the controller can include a photodiode that converts the portion of the 0^th order signals to an electrical signal (e.g., a current delivered to controller circuitry 330) that controls the driving of shutter 242. [0035] The shutter can, for example, be manufactured as a MEMS device. In some embodiments, the response time can be as little as 2.5ms for attenuation of 50dB. Furthermore, in some embodiments, the shutter only needs to be driven once per layer (not for each mark measurement), and its accuracy can be relaxed since attenuating reference beam optimizes fringe contrast and does not affect phase retrieval accuracy. A particularly desirable advantage of such MEMS devices over optical devices (e.g. ND filters) is that fact that they provide low insertion loss, extremely wide bandwidth and polarization insensitivity. This can be useful as any optical element in the path of the Oth order beam can introduce further phase delay and hence change the desired phase shift.

[0036] Figure 4 depicts a schematic diagram of wavelength-dependent phase shifts induced by the optical module varying the path length of detected light, according to an embodiment of the present disclosure. Phase shifting of the reflected light can be performed by, for example, controlling some optical components to move to different locations, thereby introducing a wavelength dependent phase shift in the signal received at detector 250. The principle of this phase shift is depicted in Figure 3, showing examples of a first curve 410 and a second curve 420 corresponding to two wavelengths of light li and F, where because of their different wavelengths, a given change in pathlength (DL) causes a corresponding change in phase (DF). This phase shifting encodes the quadrature components of the complex signal fields and thus can be decoded to recover information carried by signals at the various wavelengths (e.g., information in the signal light reflected from the alignment mark). [0037] As shown in Figure 2, in some embodiments, the 0^th order signal can be used as a reference signal and the system can thus be configured to perform phase shifting to acquire multiple wavelengths from the target of interest. For example, the optical module can introduce a phase shift in 0^th order signals 211. In some embodiments, variable 0^th order attenuator 240 can be coupled to second controller 246 to move variable Oth order attenuator 240 (e.g., in the ‘y’ direction) and modify a path length of 0^th order signals 211 (e.g., causing the DL shown in Figure 4). While any drive mechanism can be utilized for this (e.g., a stepper motor), in some embodiments, variable Oth order attenuator 240 can include a piezoelectric stage to drive the variable Oth order attenuator 240. The shifting in path length can be performed by moving numerous combinations of the disclosed optical components. For example, in some embodiments, movement of first mirror 222 (e.g., in the y- direction) can be sufficient to induce the path length change. In other embodiments, there can be second mirror 224, where first mirror 222 and second mirror 224 form a corner reflector configured to cause the phase shift of 0^th order signals 211.

[0038] As shown in Figure 2, there can also be third mirror 226 and fourth mirror 228, with variable Oth order attenuator 240 in the optical path between third mirror 226 and fourth mirror 228. Fourth mirror 228 can be disposed after variable Oth order attenuator 240 and displaced to be off the optical axis of second lens element 232. This can also facilitate the shifting of the 0^th order signal as described further herein.

[0039] Figure 5 depicts a diagram of a displaced 0^th order signal on a pupil of a metrology system, according to an embodiment of the present disclosure. Phase shifting optics 220 can displace the Oth order signals 211 at second lens element 232 off axis (i.e., off the optical axis of the lens). Also, the phase shifting optics 220 can displace 0^th order signals 211 to be at a different angle 530 at second lens element 232 than the higher order signals. This causes the 0^th order signal to be at a different angular location at pupil 500 (which may correspond to a portion of second lens element 232). Instead of the fringes from positive and negative orders overlapping with each other, the shifted 0^th order signal enables them to be recorded with different angular frequencies in the hologram, and hence be separated in computational post processing. An example of this is shown in Figure 5, with the -1^st order signals 513 form -1^st order fringes 523 in an exemplary fringe pattern 520, seen as being spaced further apart due to the increased separation from 0^th order signal 211. Similarly, the +l^st order signals 514 form +l^st order fringes 524, seen as being closer together due to the decreased separation from 0^th order signal 211. This can allow both +l^st and -1^st order signals to be detected simultaneously at different angular spatial carrier frequencies so that they can also be easily separated by fringe processing.

[0040] Figure 6 depicts a diagram of a metrology system where phase shifting optics are part of a folded pupil. While the depicted physical layout of this embodiment is different than the example shown in Figure 2, many components and aspects can be similar or equivalent, and as such, the same reference numbers will be used, where appropriate. Folded pupils can be used to extend an optical path length. In some embodiments, space can be limited so some of the phase shifting optics (e.g., including first mirror 222 and second mirror 224) can be located outside of the space between third mirror 226 and fourth mirror 228. In this example, third mirror 226 can have a mirror segment 610 displaced from third mirror 226. Such configurations can cause the 0^th order signals to be located outside the +l^st order signal and/or the -1^st order signal (illustrated by the dashed circle 620 superimposed on second lens element 232).

[0041] Figure 7 depicts a diagram of a metrology system that includes an array of phase masks in front of a detector, according to an embodiment of the present disclosure. Additionally, or alternatively to the other embodiments disclosed herein, a metrology system can include an array of phase masks 710 configured to receive signals having multiple wavelengths. Such receiving can be simultaneous so that errors due to system perturbances (e.g., that might occur between successive acquisitions) can be avoided. Figure 7 again uses similar reference numbers for components such as shown and described with reference to Figure 2. Target of interest 210 (e.g., a grating of an alignment mark) can provide 0^th order signals 211 and higher order signals 212 to first lens element 230. The light can then subsequently arrive at second lens element 232, with array of phase masks 710 interposed to provide phase shifting similar to that described with reference to the embodiment of Figure 2. Here however, all wavelengths (each with 0^th order and + 1^st order light) can be acquired at the same time, with array of phase masks 710 providing wavelength-dependent and order-dependent phase shifts to the light going to detector 250. As such, the phase shifts encode the 0^th order and higher order signals, which can then be decoded to extract the individual information for each wavelength of light.

[0042] Figure 8 depicts a diagram of an array of phase masks combing signals with different phases into a single pixel, according to an embodiment of the present disclosure. An expanded view of the array of phase masks 710 is shown with, in this embodiment, the array comprising individual phase masks 810 (e.g., corresponding to a pixel) each providing potentially different phase shifts to light reaching second lens element 232. In some embodiments, array of phase masks 710 can provide dedicated phase retardances to the multiple wavelengths such that the signals passing through array of phase masks 710 combine into a single wavelength signal having discrete phase components corresponding to the multiple wavelengths.

[0043] In the example of Figure 8, array of phase masks 710 correspond to pixels providing a first resolution at the detector. By combining some of the pixels, a single wavelength signal can be captured by a pixel 820, however providing a second resolution that is lower than the first resolution. For example, the array of phase masks 710 can be configured to simultaneously acquire N (e.g., 12) wavelengths utilizing M (2N + 1) phase masks. In the illustrated embodiment, the M (25) phase masks are arranged in an A/M (5) x A/M (5) square formation corresponding to the pixels providing the first resolution. [0044] In certain embodiments, some of the concepts above can be combined to provide alternative systems for improved metrology. For example, the optical module can be configured to receive 0^th order signals and higher order signals diffracted from a target of interest. Such an optical module can include an array of phase masks configured to provide dedicated phase retardances to corresponding pixels of a detector. A first lens element can be configured to direct the 0^th order signals to an array of phase masks. A second lens element can be configured to receive the retarded 0^th and higher order signals and direct the retarded 0^th and higher order signals to the detector. Accordingly, in some embodiments, the simultaneous acquisition embodiment of Figure 8 can be utilized instead of the stepping embodiment of Figure 2. In such an alternative embodiment, it can be combined with the 0^th order shifting of Figure 5. In other words, such an embodiment could include array of phase masks 710, with displaced optical elements such as first mirror 222 to provide the off-axis 0^th order signal as shown in Figure 5.

Figure 9 is a block diagram of an example computer system CS, according to an embodiment of the present disclosure.

[0045] The embodiments may further be described using the following clauses:

1. A metrology system comprising: an optical module configured to receive signals from a target of interest, the optical module comprising: phase shifting optics configured to displace at least a portion of the signals such that a phase shift in the signals is introduced.

2. The metrology system of clause 1 , wherein the signals comprise 0^th order signals and higher order signals diffracted from the target of interest, the optical module comprising: a first lens element configured to direct the 0^th order signals to the phase shifting optics that include a variable 0^th order attenuator, the variable 0^th order attenuator comprising: a first mirror to receive the 0^th order signals; and a shutter mounted after the first mirror, the shutter coupled to a controller to move the shutter to attenuate a portion of the 0^th order signals and create attenuated 0^th order signals; and a second lens element configured to receive the attenuated 0^th order signals and direct the attenuated 0^th order signals to a detector.

3. The metrology system of clause 2, wherein the shutter is configured to perform a variable attenuation of the 0^th order signals to reduce a contrast between the 0^th order signals and the higher order signals.

4. The metrology system of clause 3, wherein the shutter has a variable thickness to cause the variable attenuation based on a shutter position, the shutter position and the variable attenuation driven by an amplitude of the 0^th order signals. 5. The metrology system of clause 3, wherein the first mirror is partially transparent such that a portion of the 0^th order signals arrive at an optical sensor and are utilized to drive a movement of the shutter.

6. The metrology system of clause 2, wherein the driving of the shutter is based on an intensity of the 0^th order signals at the optical sensor.

7. The metrology system of clause 6, wherein the optical sensor comprises a photodiode that converts the portion of the 0^th order signals to an electrical signal that controls the driving of the shutter.

8. The metrology system of clause 2, wherein the 0^th order signal is a reference signal and the system is configured to perform phase shifting to acquire multiple wavelengths from the target of interest.

9. The metrology system of clause 8, wherein the optical module introduces a phase shift in the 0^th order signals.

10. The metrology system of clause 9, the variable 0^th order attenuator being coupled to a second controller to move the variable 0^th order attenuator and modify a path length of the 0^th order signals.

11. The metrology system of clause 10, wherein the variable 0^th order attenuator includes a piezoelectric stage to drive the variable 0^th order attenuator.

12. The metrology system of clause 9, further comprising a second mirror, wherein the first mirror and the second mirror form a corner reflector configured to cause the phase shift of the 0^th order signals.

13. The metrology system of clause 2, wherein the phase shifting optics displace the 0^th order signals at the second lens element.

14. The metrology system of clause 13, wherein the phase shifting optics displaces the 0^th order signals to be at a different angle at the second lens element than the higher order signals.

15. The metrology system of clause 2, further comprising a third mirror and a fourth mirror, with the variable 0^th order attenuator in an optical path between the third mirror and the fourth mirror, the fourth mirror disposed after the variable 0^th order attenuator and displaced to be off an optical axis of the second lens element.

16. The metrology system of clause 2, wherein phase shifting optics are configured to locate the 0^th order signal outside locations of a +l^st order signal or a -1^st order signal.

17. A metrology system comprising: an array of phase masks configured to receive signals having multiple wavelengths, the array of phase masks providing dedicated phase retardances to the multiple wavelengths such that the signals passing through the array of phase masks combine into a single wavelength signal having discrete phase components corresponding to the multiple wavelengths. 18. The metrology system of clause Error! Reference source not found., wherein the array of phase masks correspond to pixels providing a first resolution at a detector, and a single wavelength signal can be captured by a pixel providing a second resolution that is lower than the first resolution.

19. The metrology system of clause Error! Reference source not found., wherein the array of phase masks is configured to simultaneously acquire N wavelengths utilizing M (2N + 1) phase masks.

20. The metrology system of clause Error! Reference source not found., wherein the M phase masks are arranged in an VM X A/M square formation corresponding to the pixels providing the first resolution.

21. The metrology system of clause 1, the optical module configured to receive 0^th order signals and higher order signals diffracted from the target of interest, the optical module comprising: an array of phase masks configured to provide dedicated phase retardances to corresponding pixels of a detector; a first lens element configured to direct the 0^th order signals to the array of phase masks; and a second lens element configured to receive the retarded 0^th and higher order signals and direct the retarded 0^th and higher order signals to the detector.

22. A semiconductor device manufacturing method comprising: receiving a substrate with a photoresist layer; directing radiation from radiation source to transfer a pattern from a mask onto the photoresist layer; removing a portion of the photoresist layer to form the pattern over the substrate; and performing metrology on the substrate with a metrology system comprising: an optical module configured to receive signals from the substrate, the optical module comprising: phase shifting optics configured to displace at least a portion of the signals such that a phase shift in the signals is introduced.

23. A semiconductor device manufacturing method comprising: receiving a substrate with a photoresist layer; directing radiation from radiation source to transfer a pattern from a mask onto the photoresist layer; removing a portion of the photoresist layer to form the pattern over the substrate; and performing metrology on the substrate with a metrology system comprising: an array of phase masks configured to receive signals having multiple wavelengths, the array of phase masks providing dedicated phase retardances to the multiple wavelengths such that the signals passing through the array of phase masks combine into a single wavelength signal having discrete phase components corresponding to the multiple wavelengths.

[0046] Computer system CS includes a bus BS or other communication mechanism for communicating information, and a processor PRO (or multiple processor) coupled with bus BS for processing information. Computer system CS also includes a main memory MM, such as a random access memory (RAM) or other dynamic storage device, coupled to bus BS for storing information and instructions to be executed by processor PRO. Main memory MM also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by processor PRO. Computer system CS further includes a read only memory (ROM) ROM or other static storage device coupled to bus BS for storing static information and instructions for processor PRO. A storage device SD, such as a magnetic disk or optical disk, is provided and coupled to bus BS for storing information and instructions.

[0047] Computer system CS may be coupled via bus BS to a display DS, such as a cathode ray tube (CRT) or flat panel or touch panel display for displaying information to a computer user. An input device ID, including alphanumeric and other keys, is coupled to bus BS for communicating information and command selections to processor PRO. Another type of user input device is cursor control CC, such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to processor PRO and for controlling cursor movement on display DS. This input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), that allows the device to specify positions in a plane. A touch panel (screen) display may also be used as an input device.

[0048] According to one embodiment, portions of one or more methods described herein may be performed by computer system CS in response to processor PRO executing one or more sequences of one or more instructions contained in main memory MM. Such instructions may be read into main memory MM from another computer-readable medium, such as storage device SD. Execution of the sequences of instructions contained in main memory MM causes processor PRO to perform the process steps described herein. One or more processors in a multi-processing arrangement may also be employed to execute the sequences of instructions contained in main memory MM. In an alternative embodiment, hard-wired circuitry may be used in place of or in combination with software instructions. Thus, the description herein is not limited to any specific combination of hardware circuitry and software.

[0049] The term “computer-readable medium” as used herein refers to any medium that participates in providing instructions to processor PRO for execution. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as storage device SD. Volatile media include dynamic memory, such as main memory MM. Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise bus BS. Transmission media can also take the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Computer-readable media can be non-transitory, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge. Non- transitory computer readable media can have instructions recorded thereon. The instructions, when executed by a computer, can implement any of the features described herein. Transitory computer- readable media can include a carrier wave or other propagating electromagnetic signal.

[0050] Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to processor PRO for execution. For example, the instructions may initially be borne on a magnetic disk of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to computer system CS can receive the data on the telephone line and use an infrared transmitter to convert the data to an infrared signal. An infrared detector coupled to bus BS can receive the data carried in the infrared signal and place the data on bus BS. Bus BS carries the data to main memory MM, from which processor PRO retrieves and executes the instructions. The instructions received by main memory MM may optionally be stored on storage device SD either before or after execution by processor PRO.

[0051] Computer system CS may also include a communication interface CI coupled to bus BS. Communication interface CI provides a two-way data communication coupling to a network link NDL that is connected to a local network LAN. For example, communication interface CI may be an integrated services digital network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, communication interface CI may be a local area network (LAN) card to provide a data communication connection to a compatible LAN. Wireless links may also be implemented. In any such implementation, communication interface CI sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information.

[0052] Network link NDL typically provides data communication through one or more networks to other data devices. For example, network link NDL may provide a connection through local network LAN to a host computer HC. This can include data communication services provided through the worldwide packet data communication network, now commonly referred to as the “Internet” INT. Local network LAN (Internet) both use electrical, electromagnetic or optical signals that carry digital data streams. The signals through the various networks and the signals on network data link NDL and through communication interface CI, which carry the digital data to and from computer system CS, are exemplary forms of carrier waves transporting the information.

[0053] Computer system CS can send messages and receive data, including program code, through the network(s), network data link NDL, and communication interface CL In the Internet example, host computer HC might transmit a requested code for an application program through Internet INT, network data link NDL, local network LAN and communication interface CL One such downloaded application may provide all or part of a method described herein, for example. The received code may be executed by processor PRO as it is received, and/or stored in storage device SD, or other nonvolatile storage for later execution. In this manner, computer system CS may obtain application code in the form of a carrier wave. [0054] The lithographic apparatus LA and radiation source SO described herein can be used in a method for manufacturing a semiconductor device. A semiconductor device manufacturing method comprises receiving a substrate W with a photoresist layer. The method further comprises directing a radiation beam from radiation source SO to transfer a pattern from a mask onto the photoresist layer. This could be achieved by a patterning device which is configured to form a patterned radiation beam, imparting the patterned radiation beam onto the photoresist layer. The method for manufacturing a semiconductor device further comprises the step of removing a portion of the photoresist layer to form the pattern over the substrate W.

[0055] The substrate W may be made of silicon or other semiconductor materials. Alternatively or additionally, the substrate W may include other semiconductor materials such as germanium (Ge) or carbon (C). In some embodiments, the semiconductor substrate is made of a compound semiconductor such as III-V compound semiconductors, II-V compound semiconductors, and/or any suitable integration of Group IV materials. In some embodiments, the substrate W may be a silicon-on- insulator (SOI) or a germanium-on-insulator (GOI) substrate.

[0056] The semiconductor device made from the substrate W may have various device elements. Examples of semiconductor device elements that are formed over the substrate W include transistors (e.g., planar or non-planar metal oxide semiconductor field effect transistors (MOSFET), bipolar junction transistors (BJT), high-voltage transistors, high-frequency transistors, etc.), diodes, CMOS image sensors, passive devices, and/or other applicable elements. Various processes may be performed to form the semiconductor device elements, such as deposition, etching, implantation, epitaxial growth, polishing, thermal treatment, and/or other suitable processes. In some embodiments, the substrate W is coated with a photoresist layer sensitive to the EUV light.

[0057] While the concepts disclosed herein may be used for imaging on a substrate such as a silicon wafer, it shall be understood that the disclosed concepts may be used with any type of lithographic imaging systems, e.g., those used for imaging on substrates other than silicon wafers.

[0058] The combinations and sub-combinations of the elements disclosed herein constitute separate embodiments and are provided as examples only. Also, 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 as described without departing from the scope of the claims set out below.

Claims

1. A metrology system comprising: an optical module configured to receive signals from a target of interest, the optical module comprising: phase shifting optics configured to displace at least a portion of the signals such that a phase shift in the signals is introduced.

2. The metrology system of claim 1 , wherein the signals comprise 0^th order signals and higher order signals diffracted from the target of interest, the optical module comprising: a first lens element configured to direct the 0^th order signals to the phase shifting optics that include a variable 0^th order attenuator, the variable 0^th order attenuator comprising: a first mirror to receive the 0^th order signals; and a shutter mounted after the first mirror, the shutter coupled to a controller to move the shutter to attenuate a portion of the 0^th order signals and create attenuated 0^th order signals; and a second lens element configured to receive the attenuated 0^th order signals and direct the attenuated 0^th order signals to a detector.

3. The metrology system of claim 2, wherein the shutter is configured to perform a variable attenuation of the 0^th order signals to reduce a contrast between the 0^th order signals and the higher order signals.

4. The metrology system of claim 3, wherein the shutter has a variable thickness to cause the variable attenuation based on a shutter position, the shutter position and the variable attenuation driven by an amplitude of the 0^th order signals.

5. The metrology system of claim 3, wherein the first mirror is partially transparent such that a portion of the 0^th order signals arrive at an optical sensor and are utilized to drive a movement of the shutter.

6. The metrology system of claim 2, wherein the driving of the shutter is based on an intensity of the 0^th order signals at the optical sensor.

7. The metrology system of claim 6, wherein the optical sensor comprises a photodiode that converts the portion of the 0^th order signals to an electrical signal that controls the driving of the shutter.

8. The metrology system of claim 2, wherein the 0^th order signal is a reference signal and the system is configured to perform phase shifting to acquire multiple wavelengths from the target of interest.

9. The metrology system of claim 8, wherein the optical module introduces a phase shift in the 0^th order signals.

10. The metrology system of claim 9, the variable 0^th order attenuator being coupled to a second controller to move the variable 0^th order attenuator and modify a path length of the 0^th order signals.

11. The metrology system of claim 10, wherein the variable 0^th order attenuator includes a piezoelectric stage to drive the variable 0^th order attenuator.

12. The metrology system of claim 9, further comprising a second mirror, wherein the first mirror and the second mirror form a corner reflector configured to cause the phase shift of the 0^th order signals.

13. The metrology system of claim 2, wherein the phase shifting optics displace the 0^th order signals at the second lens element.

14. The metrology system of claim 13, wherein the phase shifting optics displaces the 0^th order signals to be at a different angle at the second lens element than the higher order signals.

15. The metrology system of claim 2, further comprising a third mirror and a fourth mirror, with the variable 0^th order attenuator in an optical path between the third mirror and the fourth mirror, the fourth mirror disposed after the variable 0^th order attenuator and displaced to be off an optical axis of the second lens element.