WO2025162589A1

WO2025162589A1 - Method and apparatus for etching a sample

Info

Publication number: WO2025162589A1
Application number: PCT/EP2024/052593
Authority: WO
Inventors: Yuansen CHEN; Andre Nauen
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2024-02-02
Filing date: 2024-02-02
Publication date: 2025-08-07
Anticipated expiration: 2026-08-02

Abstract

A method (200) and an apparatus for etching a sample is disclosed. The method (200) comprises cooling (201) a surface of the sample, wherein the surface of the sample is covered with a layer of etchant material or is being covered with etchant material for forming a layer of etchant material on the surface of the sample. The surface of the sample and the layer of etchant material are cooled to a cooling temperature below an activation temperature of the etchant material. Moreover, the method (200) comprises heating (203), i.e. activating the layer of cooled, i.e. inactive etchant material and the surface of the sample at one or more selected locations for activating the etchant material and for etching the surface of the sample at the one or more selected locations with the activated etchant material. The method (200) allows performing micro-fabrication or nano- fabrication with a precise control for locally etching structures in a sample without having to use a photoresist material or a liftoff process, because the layer of etchant material is an inactive solid film at cryogenic conditions.

Description

METHOD AND APPARATUS FOR ETCHING A SAMPLE

TECHNICAL FIELD

The present disclosure relates to material fabrication and machining. More specifically, the present disclosure relates to a method and an apparatus for etching a sample, for instance, a semiconductor material sample.

BACKGROUND

Conventional semiconductor device fabrication techniques often involve an etching process, which usually requires prior to the etching a lithography process for defining an etching pattern on a photoresist layer. After a lift-off process, which removes (or keeps) the exposed positive (or negative) resist, wet etching or dry etching is performed with a controllable etching depth. In material micro-machining, laser molding or laser-assisted etching is adopted to perform 3D machining. Due to the strong laser-induced local heating, the sample can be processed either physically or chemically with a spatial resolution of micrometer length scale.

Laser etching is a process that creates marks on parts and products by melting their surface. It is part of the broader category called laser marking which also includes laser engraving and laser annealing. Highly versatile, it can be used with most metals. To produce a raised mark, a laser beam delivers a high amount of energy to a small area. As a result, the surface of the material melts and expands. This can color the material in black, white or gray. For laser etching and/or engraving the resolution is typically larger than 10 pm and this process is limited to metal materials.

Wet etching is an economic, straightforward but in most cases an isotropic machining technique, and thus it is hard to obtain an etching profile with a high aspect ratio. Dry etching is anisotropic and, thus, can achieve a much higher aspect ratio, but it is much more complicated and expensive. Both wet and dry etching are based on lithography and thus need to rely on photoresist materials.

Laser-assisted selective etching (LSE) benefits from the substantial difference of etching rates between the laser-heating area and the unexposed area, of which the surface is nevertheless slightly etched. The heating diffusion in a liquid also degrades the etching resolution beyond the optical resolution. LSE is generally limited to a few types of glass materials, because the sample materials need to be almost inactive for chemical reactions at room temperature. In addition, the sample surface is also destructed even it is not exposed to the laser. Thirdly, the laser-induced heating has a noticeable diffusion length, and therefore the etching resolution is clearly lower than the optical resolution.

SUMMARY

It is an objective of the present disclosure to provide an improved method and an improved apparatus for etching a sample, for instance, a semiconductor material sample.

The foregoing and other objectives are achieved by the subject matter of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

According to a first aspect a method for etching a sample is provided. The method according to the first aspect comprises a step of cooling a surface of the sample, wherein the surface of the sample is covered with a layer of etchant material or is being covered with etchant material for forming a layer of etchant material on the surface of the sample. The surface of the sample and the layer of etchant material are cooled to a cooling temperature below an activation temperature of the etchant material.

Moreover, the method according to the first aspect comprises a step of heating, i.e. activating the layer of cooled, i.e. inactive etchant material and the surface of the sample at one or more selected locations for activating the etchant material and for etching the surface of the sample at the one or more selected locations with the activated etchant material.

The method according to the first aspect allows performing micro-fabrication or nano-fabrication with a precise control for locally etching structures in a sample without having to use a photoresist material or a liftoff process, because the layer of etchant material is an inactive solid film at cryogenic conditions. The method according to the first aspect may be used for micro-fabrication and nano-fabrication of chip-level products, such as electronics chips, photonics chips, laser chips, waveguide chips, meta-optics, Nano-/Micro Electro Mechanical Systems, micro-LED arrays, holography optical elements, Fresnel optics, and the like.

In a further possible implementation form, the step of heating, i.e. activating the layer of cooled, i.e. inactive etchant material and the surface of the sample at the one or more selected locations comprises heating, i.e. activating the layer of cooled, i.e. inactive etchant material and the surface of the sample at the one or more selected locations with a heating tip by thermal transfer, such as an atomic force microscopy (AFM) or any scanning probe microscopy, heating tip. This allows to efficiently heat and activate the layer of cooled, i.e. inactive etchant material and the surface of the sample at the one or more selected locations, e.g. a resolution of below 10 nm may be achieved.

In a further possible implementation form, the method further comprises measuring the etching depth in real time, for instance, by atomic force microscopy or any scanning probe microscopy technique. This allows to precisely monitor and control the etching depth in real time, e.g. an accuracy of below 1 nm may be achieved.

In a further possible implementation form, the method further comprises controlling one or more of the following parameters: the distance from the surface of the layer of the etchant material to the tip; the etching depth; the heating duration; the tip temperature; the heating power for heating the tip; and/or the scanning rate of the tip. This allows to control the etching rate and adapt the etching resolution as needed.

In a further possible implementation form, the method further comprises scanning the heating tip along the one or more selected locations, for instance, by atomic force microscopy or any scanning probe microscopy technique. This allows to etch any selected location of the sample with a specified etching depth.

In a further possible implementation form, the step of heating, i.e. activating the layer of cooled, i.e. inactive etchant material and the surface of the sample at the one or more selected locations comprises heating, i.e. activating the layer of cooled, i.e. inactive etchant material and the surface of the sample at the one or more selected locations with laser radiation from a laser. This allows to remotely heat and activate the layer of cooled, i.e. inactive etchant material and the surface of the sample at the one or more selected locations.

In a further possible implementation form, the method further comprises guiding, i.e. focusing the laser radiation from the laser to the one or more selected locations by an optical assembly for heating the layer of cooled, i.e. inactive etchant material and the surface of the sample at the one or more selected locations. This allows to efficiently heat and activate the layer of cooled, i.e. inactive etchant material and the surface of the sample at the one or more selected locations, e.g. a resolution on the order of 100 nm may be achieved. In a further possible implementation form, the method further comprises measuring the etching depth in real time by an optical means, e.g. an optical interferometer. This allows the etching depth to be in real time monitored and precisely controlled, e.g. an accuracy of below 10 nm may be achieved.

In a further possible implementation form, guiding the laser radiation from the laser to the one or more selected locations of the layer of cooled etchant material and the surface of the sample comprises projecting the laser radiation from the laser through an etching pattern or etching mask onto the one or more selected locations of the layer of cooled etchant material and the surface of the sample. As will be appreciated, the etching pattern or etching mask does not have to be in contact with the surface of the sample or the layer of the etchant material. As used herein, projecting the laser radiation through the etching pattern or etching mask means guiding the laser onto the etching mask which only allows selected parts of the laser light to hit the layer of the etchant material and the surface of the sample at the one or more selected locations.

In a further possible implementation form, the method further comprises controlling one or more of the following parameters: a power of the laser radiation; an exposure time of the laser radiation; a beam size of the laser radiation; a beam shape of the laser radiation; a pulse shape of the laser radiation; a pulse repetition rate of the laser radiation; and/or a power density of the laser radiation. This allows to control the etching rate and adapt the etching resolution as needed.

In a further possible implementation form, guiding the laser radiation from the laser to the one or more selected locations of the layer of cooled, i.e. inactive etchant material and the surface of the sample comprises scanning the one or more selected locations of the layer of etchant material and the surface of the sample with the laser radiation from the laser. This allows to etch any selected location of the sample with a specified etching depth.

In a further possible implementation form, the method according to the first aspect further comprises controlling the cooling temperature.

In a further possible implementation form, cooling the surface of the sample and the layer of etchant material to a cooling temperature below the activation temperature of the etchant material comprises cooling the surface of the sample covered or to be covered by the layer of etchant material to a cooling temperature below the activation temperature of the etchant material with a cryostat, in particular a liquid or cold nitrogen cryostat, a liquid or cold helium cryostat or a thermoelectric cryostat.

In a further possible implementation form, the sample comprises a semiconductor sample material, a metal sample material, an alloy sample material, a glass sample material, a solid-state sample material and/or any combination of these materials.

In a further possible implementation form, the surface of the sample is being covered with etchant material for forming the layer of etchant material on the surface of the sample by evaporating the etchant material and guiding the evaporated etchant material via a feedthrough, if needed, onto the surface of the sample for depositing the etchant material on the cooled surface of the sample.

In a further possible implementation form, the surface of the sample is being covered with etchant material for forming the layer of etchant material on the surface of the sample by spray coating the etchant material onto the surface of the sample.

In a further possible implementation form, the etchant material comprises an acid etchant material and/or an alkali etchant material. In a further possible implementation form, the step of heating the layer of cooled etchant material and the surface of the sample at the one or more selected locations for activating the cooled etchant material and for etching the surface of the sample at the one or more selected locations with the activated etching material comprises heating the layer of cooled etchant material and the surface of the sample at the one or more selected locations for activating the cooled etchant material and for performing anisotropic etching of the surface of the sample at the one or more selected locations with the activated etching material.

According to a second aspect an apparatus for etching a sample is provided. The apparatus according to the second aspect comprises a cooling device configured to cool a surface of the sample, wherein the surface of the sample is covered with a layer of etchant material or is being covered with etchant material for forming a layer of etchant material on the surface of the sample and wherein the surface of the sample and the layer of etchant material are cooled by the cooling device to a cooling temperature below an activation temperature of the etchant material.

Moreover, the apparatus according to the second aspect comprises a heating device configured to heat, i.e. activate the layer of cooled, i.e. inactive etchant material and the surface of the sample at one or more selected locations for activating the etchant material and for etching the surface of the sample at the one or more selected locations with the activated etching material.

The apparatus according to the second aspect allows performing micro-fabrication or nano-fabrication with a precise control for locally etching structures in a sample without having to use a photoresist material or a liftoff process, because the layer of etchant material is an inactive solid film at cryogenic conditions. The apparatus according to the second aspect may be used for micro-fabrication and nano-fabrication of chip-level products, such as electronics chips, photonics chips, laser chips, waveguide chips, meta-optics, Nano-/Micro Electro Mechanical Systems, micro-LED arrays, holography optical elements, Fresnel optics, and the like.

In a further possible implementation form, the heating device comprises a heating tip configured to heat, i.e. activate the layer of cooled, i.e. inactive etchant material and the surface of the sample at the one or more selected locations by thermal transfer. The heating tip may be an atomic force microscopy, AFM, heating tip.

In a further possible implementation form, the device further comprises a sensor device for measuring the etching depth in real time by atomic force microscopy or any scanning probe microscopy technique.

In a further possible implementation form, the device further comprises a control unit configured to control one or more of the following parameters: the distance from the etchant surface to the tip; the etching depth; the heating duration; the tip temperature; the heating power for the tip; and/or the scanning rate.

In a further possible implementation form, the apparatus comprises a device configured to scan the heating tip along the one or more selected locations, for instance, by atomic force microscopy or any scanning probe microscopy technique. This allows to etch any selected location of the sample with a specified etching depth.

In a further possible implementation form, the heating device comprises a laser configured to heat, i.e. activate the layer of cooled, i.e. inactive etchant material and the surface of the sample at the one or more selected locations with laser radiation from the laser.

In a further possible implementation form, the apparatus further comprises an optical assembly configured to guide, i.e. focus the laser radiation from the laser to the one or more selected locations of the layer of cooled etchant material and the surface of the sample for heating the layer of cooled, i.e. inactive etchant material and the surface of the sample at the one or more selected locations.

In a further possible implementation form, the apparatus further comprises a sensor device configured to measure the etching depth in real time by optical means, e.g. an optical interferometer.

In a further possible implementation form, the apparatus comprises a control unit configured to control one or more of the following parameters: a power of the laser radiation; an exposure time of the laser radiation; a beam size of the laser radiation; a beam shape of the laser radiation; a pulse shape of the laser radiation; a pulse repetition rate of the laser radiation; and/or a power density of the laser radiation.

In a further possible implementation form, the optical assembly is configured to scan the one or more selected locations of the layer of etchant material and the surface of the sample with the laser radiation from the laser.

In a further possible implementation form, the optical assembly is configured to project the laser radiation from the laser through an etching pattern onto the one or more selected locations of the layer of etchant material and the surface of the sample.

In a further possible implementation form, the apparatus comprises a control unit configured to control the cooling temperature.

In a further possible implementation form, the cooling device comprises a cryostat, in particular a liquid or cold nitrogen cryostat, a liquid or cold helium cryostat or a thermoelectric cryostat, configured to cool the surface of the sample and the layer of etchant material to a cooling temperature below the activation temperature of the etchant material.

In a further possible implementation form, the sample comprises a semiconductor sample material, a metal sample material, an alloy sample material, a glass sample material, a solid-state sample material, and/or any combination of these materials.

In a further possible implementation form, the apparatus comprises a depositing device configured to cover the surface of the sample with etchant material for forming the layer of etchant material on the surface of the sample by evaporating the etchant material and guiding the evaporated etchant material via a feedthrough onto the surface of the sample.

In a further possible implementation form, the apparatus comprises a depositing device configured to cover the surface of the sample with etchant material for forming the layer of etchant material on the surface of the sample by spray coating the etchant material onto the surface of the sample.

In a further possible implementation form, the etchant material comprises an acid etchant material and/or an alkali etchant material.

In a further possible implementation form, the heating device is configured to heat, i.e. activate the layer of cooled, i.e. inactive etchant material and the surface of the sample at one or more selected locations for activating the etchant material and for performing anisotropic etching of the surface of the sample at the one or more selected locations with the activated etching material.

Details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

In the following, embodiments of the present disclosure are described in more detail with reference to the attached figures and drawings, in which:

Fig. la shows a schematic diagram illustrating an apparatus for etching a sample according to an embodiment based on etchant material activation by laser radiation;

Fig. lb shows a schematic diagram illustrating an apparatus for etching a sample according to a further embodiment based on etchant material activation by laser radiation;

Fig. 1c shows a schematic diagram illustrating an apparatus for etching a sample according to a further embodiment based on etchant material activation by a heating tip; and

Fig. 2 shows a flow diagram illustrating a method for etching a sample according to an embodiment.

In the following, identical reference signs refer to identical or at least functionally equivalent features.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description, reference is made to the accompanying figures, which form part of the disclosure, and which show, by way of illustration, specific aspects of embodiments of the present disclosure or specific aspects in which embodiments of the present disclosure may be used. It is understood that embodiments of the present disclosure may be used in other aspects and comprise structural or logical changes not depicted in the figures. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims.

For instance, it is to be understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g. functional units, to perform the described one or plurality of method steps (e.g. one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps), even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g. functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g. one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units), even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary embodiments and/or aspects described herein may be combined with each other, unless specifically noted otherwise.

Figure la shows a schematic diagram illustrating an apparatus 100 for etching a sample 150 according to an embodiment. In an embodiment, the sample 150 may comprise a semiconductor sample material, such as a silicon wafer, a metal sample material, an alloy sample material, a glass sample material, and/or a solid-state sample material.

As illustrated in figure la, the apparatus 100 comprises a cooling device 110 configured to cool at least one surface of the sample 150, preferably the whole sample 150. In the embodiment shown in figure la the cooling device 110 comprises a cryostat cooling device 110 with a cooling unit 110a for generating a cooling temperature and a cooling or sample chamber 110b housing the sample 150. In an embodiment, the cryostat cooling device 110 may be a cryostat cooling device 110 with low vibration, of which the magnitude is clearly below the etching resolution. In an embodiment, the cryostat cooling device 110 may comprises, for instance, a liquid or cold nitrogen cryostat 110, a liquid or cold helium cryostat 110 or a thermoelectric cryostat 110 configured to generate cooling temperatures of, for instance, down to about 77 Kelvin and about 4 Kelvin, respectively. As will be described in more detail in the following, the at least one surface of the sample 150 is covered with a layer 140 of etchant material and/or is being covered with etchant material for forming the layer 140 of etchant material on the surface of the sample 150. The surface of the sample 150 and the layer 140 of etchant material are cooled by the cooling device 110 to a cooling temperature below an activation temperature of the etchant material. In an embodiment, the etchant material may comprise an acid etchant material and/or an alkali etchant material. A possible etchant material for a silicon sample 150 is a KOH 45% solution, for which the melting point is 243 Kelvin. A possible etchant material for a GaAs sample is H3PO4 75% solution, for which the melting point is 255.8 Kelvin) In an embodiment, the activation temperature of the etchant material may be the melting point of the etchant material.

As illustrated in figure la, the apparatus 100 further comprises a heating device 120 in the form of a laser 120 configured to generate laser radiation, i.e. a highly focused laser beam 120a. The heating device 120, e.g. laser 120 is configured to locally heat, i.e. activate by means of the laser radiation the layer 140 of cooled, i.e. solid and inactive etchant material and the surface of the sample 150 at one or more selected locations for activating the etchant material, e.g. by locally changing the etchant material into a liquid phase and for locally etching the surface of the sample 150 at the one or more selected locations with the activated, e.g. liquified etching material. This activates the local etching process while keeping the neighboring non-exposed areas fully unaffected or little affected. Thus, in an embodiment, due to local heating and the on-going cooling of the surrounding material the apparatus 100 may perform an anisotropic etching of the surface of the sample 150 allowing for etching structures with very high aspect ratio, which can be only done for most semiconductor materials by dry etching in semiconductor industry.

As will be appreciated, for conventional anisotropic etching it is known to use materials such as SiO2, Si3N4, GaAs, InGaAs, AlGaAs, A12O3, Si [non-(100) crystalline] and the like. These materials are often very expensive and cannot be used for wet etching, but only for dry etching, which further requires a RIE equipment and a lithography system. Thus a complete conventional system for anisotropic etching can easily cost up to a few Million Euros. Embodiments disclosed herein allow to substantially reduce these costs, while still providing anisotropic etching, because less expensive wet etching materials, such as any chemical liquid solvents, may be used, a lithography system is not necessary, and/or the maintenance and the safety of using massive volume of toxic gases is no longer required.

In the embodiment shown in figure la, the apparatus 100 further includes a cryogenic optical assembly 130, such as an objective 130 configured to guide, i.e. focus the laser radiation 120a from the laser 120 to the one or more selected locations of the surface of the sample 150 and/or the layer 140 of cooled etchant material for locally heating the surface of the sample 150 and/or the layer 140 of cooled, i.e. solid and inactive etchant material at the one or more selected locations with the laser radiation 120a. In an embodiment, the optical assembly 130 may comprise one or more optical elements, such as lenses or objectives, and be located inside or outside of the cooling chamber 110b of the cooling device 110.

In the embodiment of figure la, the optical assembly 130 is configured to scan the one or more selected locations of the surface of the sample 150 and/or the layer 140 of etchant material with the laser radiation 120a from the laser 120, for instance, by tilting and/or moving the optical assembly 130 and/or the laser 120 relative to the sample 150. A variant of this embodiment for achieving a desired pattern of etched sample material on the surface of the sample 150 is shown in figure lb, where the laser 120 and/or the optical assembly 130 are configured to project the laser radiation 120a from the laser through an etching pattern 125 onto the one or more selected locations of the surface of the sample 150 and/or the layer 140 of etchant material. In other words, by projecting the laser radiation 120a via the etching pattern 125 so that the projected laser radiation 120a has a high energy density, it is possible heat the layer 140 of etchant material to a liquid phase, so that the projected structure is etched, as illustrated in figure lb. As the etching is thermally activated, the etching depth may be controlled by tuning either the laser power or the exposure time. After the etching stage described above, the etched surface of the sample 150 may be rinsed with DI water at room temperature. As the unexposed portions of the surface of the sample 140 are protected by the remaining layer 140 of solid, i.e. frozen etchant material, which is chemically not reactive, no residual contamination will occur because of the rinsing.

While in the embodiments shown in figures la and lb the local heating is achieved by means of the laser radiation 120a that is generated by the laser 120 and absorbed by the sample 150 and/or the layer 140 of etchant material, in a further embodiment as illustrated in figure 1c the heating device may comprise a heating tip 121, a device 122 for moving the heating tip 121, i.e. for vertically adjusting the height of the heating tip 121 and/or horizontally scanning the heating tip 121 along the selected locations of the surface of the sample 150 and the layer 140 of the etchant material, and a unit 123 for heating the heating tip 121. In other words, in the embodiment illustrated in figure 1c, the heating of the selected locations of the layer 140 of etchant material and the surface of the sample 150 is performed based on thermal transfer with the heating tip 121, such as by means of an atomic force microscopy, AFM, heating tipl21 , configured to locally heat, i.e. activate the layer 140 of cooled, i.e. solid and inactive etchant material and the surface of the sample 150 at the one or more selected locations by thermal transfer. In such an embodiment, the heating tip 121 may be applied, i.e. brought into proximity or context to locally heat the layer 140 of etchant material to a liquid phase. This activates a local etching process while keeping the neighboring non-melt areas, which are still cooled by the cooling device 110, fully unaffected. The etching thickness may be measured in-real time and controlled by a control unit 160 of the apparatus 100 based on atomic force measurements or any other scanning probe technique, e.g. magnetic force microscopy, tunneling microscopy, Kelvin force microscopy, and the like. By performing a scanning motion of the heating tip 121 (due to the device 122) with depth control, a dedicated pattern of etched sample material may be formed within the sample 150. The fabrication may be finished by solving a further protection layer on the surface of the sample 150 and rinsing the surface of the sample 150.

As illustrated in figures la-c and already mentioned above, in an embodiment, the apparatus 100 may further comprise a control unit 160 configured to control one or more of the following parameters: a power of the laser radiation 120a: an exposure time of the laser radiation 120a; a beam size of the laser radiation 120a; a beam shape of the laser radiation 120a; a pulse shape of the laser radiation 120a; a pulse repetition rate of the laser radiation 120a; and/or a power density of the laser radiation 120a. Thus, by means of the control unit 160, for instance, the beam size, shape, pulse shape, pulse repetition rate and power density of the laser radiation 120a can be optimized for any given target structure to achieve best fidelity of the etching result. In an embodiment, the control unit 160 may be further configured to control the cooling temperature generated by the cooling device 100. For the embodiment shown in figure 1c the control unit 160 may be configured to control one or more of the following parameters: the distance from the surface of the layer 140 of the etchant material to the tip 121 ; the etching depth; the heating duration; the tip temperature; the heating power for heating the tip 121; and/or the scanning rate of the tip 121.

As will be appreciated, in comparison with conventional lithography-based etching techniques the etching techniques disclosed herein provide, in particular, the following advantages. Firstly, there is no need for coating a mask and, thus, no resist is needed. All related lithography-related processes are avoided, including lithography, resist development and lift-off. Secondly, the etching techniques disclosed herein allow to flexibly define and adjust the etching pattern, while for the conventional etching technique the etching pattern is defined during the lithography process, i.e. it cannot be modified afterwards. Thirdly, the with the etching techniques disclosed herein the etching depth can be controlled at different sample locations, and further it can be locally monitored in-real time during the etching process. For the conventional etching technique, the etching depth is determined by the etching recipe and protocol, in which all parameters are defined and the etching depth cannot be varied. Moreover, the etching rate is the same over the whole sample. It is impossible to achieve different etching depths at different sample locations, as it is possible with the etching techniques disclosed herein.

For the laser-activated etching technique described above in the context of figures la and lb the resolution may be on the order of a few 100 nm. The scanning speed may be up to 10 micrometer/microsecond, and an etching pattern may be directly projected to perform pattern-level etching at one time. Thus, this etching technique may be especially suitable for chip mass production.

For the heating tip-activated etching technique described above in the context of figure 1c the resolution may be better than 10 nm. The achievable scanning speeds may be slower than for the laser-activated etching technique, for instance, on the order of 1 micrometer/second, and an etching pattern may be achieved by scanning the tip from one location to another one. Therefore, this etching technique may be especially suitable for producing devices which demand very high spatial resolution and accuracy, i.e. single-electron/molecule quantum device or other devices which cannot be done by optical /SEM lithography.

In the embodiments shown in figures la, lb, and 1c, the apparatus 100 further comprises a depositing device configured to cover the surface of the sample 150 with etchant material for forming the layer 140 of etchant material on the surface of the sample 150 by evaporating liquid etchant material, for instance, by means of heating the liquid etchant material to room temperature and guiding the evaporated etchant material via a feedthrough 115 or another type of capillary system onto the surface of the sample 150, where the evaporated etchant material quickly solidifies as an etchant film, i.e. the layer 140 of etchant material on the cold surface of the sample 150. In a further embodiment, the depositing device may be configured to cover the surface of the sample 150 with etchant material for forming the layer 140 of etchant material on the surface of the sample 150 by spray coating the etchant material onto the surface of the sample 150. As will be appreciated, the etchant material may be deposited as a layer 140 on the surface of the sample 150 using other deposition processes, as long as these processes allow for the de-activation of the etchant material by freezing, which inhibits chemical reactions, either by reaching a temperature below the activation temperature, i.e. the thermal activation energy or by suppressing transport of active species to the boundary layer between the layer 140 of the etchant material and the surface of the sample 150. In an embodiment, the control unit 160 of the apparatus 100 may be configured to control the depositing device for controlling the thickness of the layer 140 of etchant material on the surface of the sample 150. In an embodiment, tailoring the thickness of the etchant material layer 140 by the control unit 160 may be used to limit the etching process, in particular the etching depth due to depletion of etchant material.

In an embodiment, the depositing of the etchant material onto the surface of the sample 150, for instance, by means of the depositing device described above may occur before, during or after the stage of cooling the surface of the sample 150. In an embodiment, the order of these processing stages may depend on the properties of the selected etchant material. For instance, a dry etchant material may be deposited prior to the cooling stage, while a liquid etchant material may be deposited after the sample 150 already has been cooled, for instance, by means of crystallization from a vapor phase and/or by spray coating. As will be appreciated, however, the different possible orders of the depositing stage and the cooling stage should make sure that eventually both the surface of the sample 150 and the layer 140 of etchant material are being cooled to a temperature below the activation temperature of the etchant material.

In an embodiment, a further material layer may be located between the surface of the sample 150 and the layer 140 of etchant material, such as a protection layer or a highly optical absorptive material for increasing the optical absorption of the laser radiation and, thus, the local heating. As will be appreciated, for semiconductor chips so-called “protection” or “protective” layers may be used to protect or enhance some properties (e.g. adhesion) of the wafer surface during the processing. The “protection” layer may be organic or inorganic, which can be both insulating, semi-insulating or conductive. Typically, such layers may include materials, such as HMDS, MgO, A12O3, and the like. Figure 2 shows a flow diagram illustrating a method 200 for etching the sample 150 illustrated in figures la and lb according to an embodiment. The method 200 comprises a step 201 of cooling a surface of the sample 150, wherein the surface of the sample 150 is covered with the layer 140 of etchant material and/or is being covered with etchant material for forming the layer 140 of etchant material on the surface of the sample 150, As already described above, the surface of the sample 150 and the layer 140 of etchant material are cooled to a cooling temperature below the activation temperature of the etchant material. Moreover, the method 200 comprises a step 203 of locally heating, i.e. activating the layer 140 of cooled, i.e. solid and inactive etchant material and the surface of the sample 150 at one or more selected locations for activating the etchant material and for locally etching the surface of the sample 150 at the one or more selected locations with the activated etchant material.

The method 200 can be performed by the apparatus 100. Thus, further features of the method 200 result directly from the functionality of the apparatus 100 as well as the different embodiments thereof described above and below.

The person skilled in the art will understand that the "blocks" ("units") of the various figures (method and apparatus) represent or describe functionalities of embodiments of the present disclosure (rather than necessarily individual "units" in hardware or software) and thus describe equally functions or features of apparatus embodiments as well as method embodiments (unit = step).

In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus, and method may be implemented in other manners. For example, the described embodiment of an apparatus is merely exemplary. For example, the unit division is merely a logical function division and may be another division in an actual implementation. For example, a plurality of units or components may be combined or integrated into another system, or some features may be ignored or not performed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections may be implemented by using some interfaces. The indirect couplings or communication connections between the apparatuses or units may be implemented in electronic, mechanical, or other forms.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one position, or may be distributed on a plurality of network units. Some or all of the units may be selected according to actual needs to achieve the objectives of the solutions of the embodiments.

In addition, functional units in the embodiments of the disclosure may be integrated into one processing unit, or each of the units may exist alone physically, or two or more units may be integrated into one unit.

Claims

1. A method (200) for etching a sample (150), wherein the method (200) comprises: cooling (201) a surface of the sample (150), wherein the surface of the sample (150) is covered with a layer (140) of etchant material and/or is being covered with etchant material for forming a layer (140) of etchant material on the surface of the sample (150) and wherein the surface of the sample (150) and the layer (140) of etchant material are cooled to a cooling temperature below an activation temperature of the etchant material; and heating (203) the layer (140) of etchant material and the surface of the sample (150) at one or more selected locations for activating the etchant material and for etching the surface of the sample (150) at the one or more selected locations with the activated etchant material.

2. The method (200) of claim 1, wherein heating (201) the layer (140) of etchant material and the surface of the sample (150) at the one or more selected locations comprises heating the layer (140) of etchant material and the surface of the sample (150) at the one or more selected locations with a heating tip (121) by thermal transfer.

3. The method (200) of claim 2, wherein the method (200) further comprises measuring the etching depth in real time by a scanning probe microscopy technique.

4. The method (200) of claim 2 or 3, wherein the method (200) further comprises controlling one or more of the following parameters: the distance from the surface of the layer (140) of etchant material to the heating tip (121); the etching depth; the heating duration; the heating tip ( 121 ) temperature; the heating power for the heating tip ( 121 ); the scanning rate of the heating tip (121).

5. The method (200) of any one of claims 2 to 4, wherein the method further comprises scanning the heating tip (121) along the one or more selected locations by a scanning probe microscopy technique.

6. The method (200) of any one of the preceding claims, wherein heating (201 ) the layer (140) of etchant material and the surface of the sample (150) at the one or more selected locations comprises heating the layer (140) of etchant material and the surface of the sample (150) at the one or more selected locations with laser radiation (120a) from a laser (120).

7. The method (200) of claim 6, wherein the method (200) further comprises guiding the laser radiation (120a) from the laser (120) to the one or more selected locations of the layer (140) of cooled etchant material by an optical assembly (130).

8. The method (200) of claim 7, wherein guiding the laser radiation (120a) from the laser (120) to the one or more selected locations of the layer (140) of cooled etchant material comprises scanning the one or more selected locations of the layer (140) of cooled etchant material with the laser radiation (120a) from the laser (120).

9. The method (200) of claim 7, wherein guiding the laser radiation (120a) from the laser (120) to the one or more selected locations of the layer (140) of cooled etchant material comprises projecting the laser radiation (120a) from the laser (120) through an etching pattern (125) onto the one or more selected locations of the layer (140) of cooled etchant material.

10. The method (200) of any one of claims 6 to 9, wherein the method (200) further comprises controlling one or more of the following: a power of the laser radiation (120a); an exposure time of the laser radiation (120a); a beam size of the laser radiation (120a); a beam shape of the laser radiation (120a); a pulse shape of the laser radiation (120a); a pulse repetition rate of the laser radiation (120a); and/or a power density of the laser radiation (120a).

11. The method (200) of any one of the preceding claims, wherein the method (200) further comprises controlling the cooling temperature.

12. The method (200) of any one of the preceding claims, wherein cooling (201) the surface of the sample (150) and the layer (140) of etchant material to a cooling temperature below the activation temperature of the etchant material comprises cooling the surface of the sample (150) and the layer (140) of etchant material to a cooling temperature below the activation temperature of the etchant material with a cryostat (110).

13. The method (200) of any one of the preceding claims, wherein the sample (150) comprises a semiconductor sample material, a metal sample material, an alloy sample material, a glass sample material, and/or a solid-state sample material.

14. The method (200) of any one of the preceding claims, wherein the surface of the sample (150) is being covered with etchant material for forming the layer (140) of etchant material on the surface of the sample (150) by evaporating the etchant material and guiding the etchant material via a feedthrough (115) onto the surface of the sample (150).

15. The method (200) of any one of the preceding claims, wherein the surface of the sample (150) is being covered with etchant material for forming the layer of etchant material on the surface of the sample (150) by spray coating the etchant material onto the surface of the sample (150).

16. The method (200) of any one of the preceding claims, wherein the etchant material comprises an acid etchant material and/or an alkali etchant material.

17. The method (200) of any one of the preceding claims, wherein heating (203) the layer (140) of cooled etchant material and the surface of the sample (150) at the one or more selected locations for activating the cooled etchant material and for etching the surface of the sample (150) at the one or more selected locations with the activated etching material comprises heating the layer (140) of cooled etchant material and the surface of the sample (150) at the one or more selected locations for activating the cooled etchant material and for performing anisotropic etching of the surface of the sample (150) at the one or more selected locations with the activated etching material.

18. The method (200) of any one of the preceding claims, wherein the method further comprises measuring the etching depth in real time by an optical sensor device.

19. An apparatus (100) for etching a sample (150), wherein the apparatus (100) comprises: a cooling device (110) configured to cool a surface of the sample (150), wherein the surface of the sample (150) is covered with a layer (140) of etchant material and/or is being covered with etchant material for forming a layer (140) of etchant material on the surface of the sample (150) and wherein the surface of the sample (150) and the layer (140) of etchant material are cooled by the cooling device (110) to a cooling temperature below an activation temperature of the etchant material; and a heating device (120, 121) configured to heat the layer (140) of etchant material and the surface of the sample (150) at one or more selected locations for activating the etchant material and for etching the surface of the sample (150) at the one or more selected locations with the activated etching material.

20. The apparatus (100) of claim 19, wherein the heating device (120; 121) comprises a heating tip (121) configured to heat the layer (140) of etchant material and the surface of the sample (150) at the one or more selected locations by thermal transfer.

21. The apparatus (100) of claim 20, wherein the apparatus (100) comprises a device (122) configured to scan the heating tip (121) along the one or more selected locations.

22. The apparatus (100) of claim 20 or 21, wherein the apparatus (100) further comprises a sensor device configured to measure the etching depth in real time by a scanning probe microscopy technique.

23. The apparatus (100) of any one of claims 20 to 22, wherein the apparatus (100) further comprises a control unit (160) configured to control one or more of the following parameters: the distance from the surface of the layer (140) of the etchant material to the heating tip (121); the etching depth; the heating duration; the heating tip (121) temperature; the heating power for the heating tip (121); the scanning rate of the heating tip (121).

24. The apparatus (100) of any one of claims 19 to 23, wherein the heating device (120; 121) comprises a laser (120) configured to heat the layer (140) of etchant material and the surface of the sample (150) at the one or more selected locations with laser radiation (120a) from the laser (120).

25. The apparatus (100) of claim 24, wherein the apparatus (100) further comprises an optical assembly (130) configured to guide the laser radiation (120a) from the laser (120) to the one or more selected locations of the layer (140) of etchant material and the surface of the sample (150).

26. The apparatus (100) of claim 25, wherein the optical assembly (130) is configured to scan the one or more selected locations of the layer (140) of etchant material and the surface of the sample (150) with the laser radiation (120a) from the laser (120).

27. The apparatus (100) of claim 25, wherein the optical assembly (130) is configured to project the laser radiation (120a) from the laser (120) through an etching pattern (125) onto the one or more selected locations of the layer (140) of etchant material and the surface of the sample (150).

28. The apparatus (100) of any one of claims 24 to 27, wherein the apparatus (100) comprises a control unit (160) configured to control one or more of the following: a power of the laser radiation (120a); an exposure time of the laser radiation (120a); a beam size of the laser radiation (120a); a beam shape of the laser radiation (120a); a pulse shape of the laser radiation (120a); a pulse repetition rate of the laser radiation (120a); and/or a power density of the laser radiation (120a).

29. The apparatus (100) of any one of claims 19 to 28, wherein the apparatus (100) comprises a control unit (160) configured to control the cooling temperature.

30. The apparatus (100) of any one of claims 19 to 29, wherein the cooling device (110) comprises a cryostat (110) configured to cool the surface of the sample (150) and the layer (140) of etchant material to a cooling temperature below the activation temperature of the etchant material.

31. The apparatus (100) of any one of claims 19 to 30, wherein the sample (150) comprises a semiconductor sample material, a metal sample material, an alloy sample material, a glass sample material, and/or a solid-state sample material.

32. The apparatus (100) of any one of claims 19 to 31, wherein the apparatus (100) comprises a depositing device configured to cover the surface of the sample (150) with etchant material for forming the layer (140) of etchant material on the surface of the sample (150) by evaporating the etchant material and guiding the etchant material via a feedthrough (115) onto the surface of the sample (150).

33. The apparatus (100) of any one of claims 19 to 32, wherein the apparatus (100) comprises a depositing device configured to cover the surface of the sample (150) with etchant material for forming the layer (140) of etchant material on the surface of the sample (150) by spray coating the etchant material onto the surface of the sample (150).

34. The apparatus (100) of any one of claims 19 to 33, wherein the etchant material comprises an acid etchant material and/or an alkali etchant material.

35. The apparatus (100) of any one of claims 19 to 34, wherein the heating device (120, 121) is configured to heat the layer (140) of etchant material and the surface of the sample (150) at one or more selected locations for activating the etchant material and for performing anisotropic etching of the surface of the sample (150) at the one or more selected locations with the activated etching material.

36. The apparatus (100) of any one of claims 19 to 35, wherein the apparatus (100) further comprises an optical sensor device configured to measure the etching depth in real time.