Apparatus and method for etching features at multiple angles

Abstract

The present invention provides a method and apparatus for enabling the simultaneous etching of multiple surface relief diffraction gratings having different angles and orientations. [Solution] A method for creating multiple surface relief diffraction gratings by etching a substrate, comprising the steps of: preparing a dielectric substrate on which a mask having multiple apertures is formed on its upper surface; placing the substrate on a substrate support in the chamber of a plasma etching apparatus; arranging a Faraday cage, which has multiple discrete regions on its upper surface having open areas through which the substrate can be plasma etched, such that the upper part of the Faraday cage is positioned above the upper surface of the substrate and electrical connection between the Faraday cage and the substrate support is maintained; and plasma etching the substrate to create multiple surface relief diffraction gratings forming at least two subsets with different angles and / or orientations.

Description

Technical Field

[0001] The present invention relates to a method for etching a substrate, and more particularly to a method for etching a substrate to create a plurality of surface relief diffraction gratings. The present invention also relates to a related plasma etching apparatus.

Background Art

[0002] Surface relief diffraction gratings on waveguide couplers and coupler lenses are important elements for augmented reality (AR) and virtual reality (VR) systems. Surface relief diffraction gratings are typically made of high refractive index (RI) glass, generally silicon oxide, and are etched at various angles and orientations. FIG. 1 shows a substrate 10 with a plurality of waveguide coupler lenses 12 therein. The substrate 10 is typically high RI glass. FIG. 2 shows the individual waveguide coupler lenses 12 in more detail. As shown in FIG. 2, the waveguide coupler lens 12 includes three different surface relief diffraction gratings 20, 22, 24, each grating being etched at a different angle and orientation. In use, the image to be viewed is projected into the first grating 20, and the light is directed through total internal reflection therein to the second grating 22, and then from there the light is directed to the third grating 24, where the image is projected onto the user's eye. Importantly, all the lenses 12 on the substrate 10 are etched in a similar manner. In the example depicted in FIGS. 1 and 2, as part of this, each coupler lens 12 is provided with three different surface relief diffraction gratings 20, 22, 24. The first, second, and third gratings 20, 22, 24 are formed by etching features at different angular orientations and different angles into the substrate 10. By performing such etching, a "master" for nanoimprint lithography (NIL) printing can be etched, or the final product can be etched directly onto the substrate.

[0003] Established methods for etching angled features include the use of ion beam etching to create patterned substrates. However, these established methods have numerous significant drawbacks. In particular, etching three distinct surface relief diffraction gratings, such as those shown in Figures 1 and 2, using a conventional ion beam etching system requires three separate patterning and etching processes. Furthermore, the etching rate associated with ion beam etching is generally low. The causes of these drawbacks will be explained first.

[0004] In conventional ion beam systems, a plasma source with an extraction grid is used to project an ion beamlet onto the substrate. To achieve acceptable uniformity, the substrate must be placed at a considerable distance from the plasma source, resulting in a relatively low etching rate. Typical ion beam etching rates are approximately 10-30 nm / min, which is inferior to the approximately 100-1000 nm / min that can be easily achieved with conventional ICP etching systems. Another factor is that the beam is usually projected at low pressure (less than 1 mTorr) to minimize unwanted ion scattering. As a result, ion beam systems tend to be large and complex, and are generally plagued by relatively low etching rates. Furthermore, to create multiple angled diffraction gratings with different angles and orientations, it is necessary to adjust the angle of the ion beam system for each region of the waveguide coupler. This can be achieved by etching the diffraction grating by exposing the substrate to ion beams at carefully selected angles and orientations after multiple patterning steps—using masks formed by submicron lithography. However, etching into the masked substrate without damaging the open features can only be performed at one angle at a time. Since multiple angles and orientations are required to create various types of surface relief diffraction gratings, the substrate must be removed from its vacuum system and repatterned before subsequent features can be generated at different angles and / or orientations. From a process perspective, using multiple vacuum break and patterning steps is highly undesirable. It would be highly desirable to provide a production technology that can manufacture multiple surface relief diffraction gratings with different angles and orientations at excellent etching speeds and without the need for separate patterning steps. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2023 / 220480 [Patent Document 2] International Publication No. 2013 / 147966 [Patent Document 3] U.S. Patent Application Publication No. 2021 / 0311229 [Overview of the project] [Problems that the invention aims to solve]

[0006] In at least some of its embodiments, the present invention addresses the aforementioned problems and requirements. In particular, the present invention provides a method and apparatus for enabling the simultaneous etching of multiple surface relief diffraction gratings having different angles and orientations. [Means for solving the problem]

[0007] While the present invention is very well suited for creating structures such as waveguide couplers and coupler lenses, it can also be used to create a wide range of surface relief diffraction gratings.

[0008] According to a first aspect of the present invention, a method for creating a plurality of surface relief diffraction gratings by etching a substrate, A step of preparing a dielectric substrate on which a mask is formed on its upper surface, wherein the mask has a plurality of openings, A step of placing the substrate on a substrate support inside the chamber of a plasma etching apparatus, The process involves arranging a Faraday cage such that the upper part of the Faraday cage is positioned above the upper surface of the substrate and that electrical connections between the Faraday cage and the substrate support are maintained, wherein the upper part of the Faraday cage comprises multiple discrete regions having open areas through which the substrate can be plasma-etched. The process involves plasma etching the substrate to create multiple surface relief diffraction gratings, wherein these multiple surface relief diffraction gratings form at least two subsets having different angles and / or orientations. It has, By aligning the mask opening and the discrete region at the top of the Faraday cage when arranging the Faraday cage, multiple surface relief diffraction gratings are created by plasma etching through the open area, and These discrete regions form at least two subsets, and each of these subsets has open areas with different angles and / or orientations relative to the substrate surface, so that plasma etching through the discrete regions of these at least two subsets generates surface relief diffraction gratings of at least two subsets with different angles and / or orientations. The item is provided.

[0009] This method allows for the creation of multiple surface relief diffraction gratings with different angles and / or orientations in a single etching process. This method can be performed at a relatively high etching speed. Another advantage is that the apparatus according to the present invention can be easily provided by modifying an existing plasma etching apparatus and attaching a Faraday cage.

[0010] While we do not wish to be bound by any particular theory, it is conceivable that during etching, a plasma sheath is formed parallel to the surface of the Faraday cage. Furthermore, because a dark space region is formed above the Faraday cage, it is conceivable that ions can only enter the Faraday cage perpendicular to its surface (through open areas within the discrete region). This results in directional and anisotropic etching of the substrate.

[0011] Each of the discrete regions described above can be provided with a mesh. Through the open areas created by this mesh, the substrate can be etched with plasma. As you can see, a Faraday cage is a structure composed substantially or entirely of conductive material, and it is assumed that its mesh is also composed of conductive material. In principle, other structures or arrangements with open areas, such as perforated structures, can also be considered. One such perforated structure is a porous metal grid.

[0012] The top of the Faraday cage may be equipped with a lid. At least one subset of discrete regions can be housed in at least one walled housing attached to the lid. Typically, the walled housing is attached upward from the lid, but in principle, it could also be attached downward (hanging) from the lid.

[0013] The Faraday cage may further be equipped with a skirt portion hanging down from its upper part. The Faraday cage placement process described above may include a step of bringing the skirt portion into contact with or close to the substrate support. In practice, bringing the skirt portion close enough to the substrate support will prevent plasma impact within the Faraday cage.

[0014] At least one discrete region may have a sawtooth arrangement of repeating structures. Each repeating structure may have a first face and a second face that is in the opposite direction. The first face may have an open area, and the second face may be solid.

[0015] Electrical connections can be maintained between the Faraday cage and the substrate support, at least partially, via a conductive flexible linking structure. Alternatively, these electrical connections can be maintained by direct contact between the Faraday cage and the substrate support. It is desirable to achieve good ohmic contact between the Faraday cage, which has discrete regions, and the substrate support.

[0016] During the plasma etching of the substrate, an RF electrical signal can be applied to the substrate support.

[0017] Plasma etching can be performed using inductively coupled plasma (ICP). The ICP system is advantageous because it can generate a high-density plasma and provide a high etching rate. ICP etching is particularly advantageous for etching oxides, where high energy is required. However, other plasma etching techniques, such as capacitively coupled plasma etching, may also be used.

[0018] The dielectric substrate described above can be made of glass.

[0019] The dielectric substrate described above can contain silicon dioxide or borosilicate glass. However, the present invention is not limited in this regard, and other materials capable of being etched to create a surface relief diffraction grating may also be used. For example, the dielectric substrate can contain SiC or LiNbO3.

[0020] The Faraday cage can be formed of aluminum. Other conductive materials, such as other metals or metal alloys, are also envisioned. The open area of the discrete region is the portion through which in-plasma ions are assumed to pass. In practice, the remainder of the Faraday cage structure is typically assumed to have a solid wall.

[0021] The Faraday cage can be provided as a single-piece structure. Alternatively, the Faraday cage can be provided in a multi-piece configuration, such as a two-piece configuration. The two-piece configuration can include a lid and a separate skirt portion, with the lid contacting the skirt portion during use.

[0022] The substrate support described above can be an electrostatic chuck (ESC).

[0023] According to a second aspect of the present invention, a plasma etching apparatus for etching a substrate to create a plurality of surface relief diffraction gratings, Chamber and, A substrate support installed inside the chamber, A plasma generator that generates plasma inside a chamber, A Faraday cage having an upper part that can be positioned above the upper surface of a dielectric substrate placed on a substrate support, wherein the upper part comprises a plurality of discrete regions having open areas through which the substrate can be plasma-etched, and these discrete regions constitute at least two subsets, each of which has open areas with different angles and / or orientations with respect to the upper surface of the substrate support, A controller that controls this device and causes it to execute the method according to the first embodiment, A device equipped with these features is provided.

[0024] Each of the discrete regions mentioned above may be provided with either a mesh or a perforated structure.

[0025] The top of the Faraday cage can be fitted with a lid.

[0026] At least one subset of discrete regions can be housed within at least one wall-mounted housing attached to its lid.

[0027] The Faraday cage can also be further equipped with a skirt portion that hangs down from its top.

[0028] At least one discrete region may have a sawtooth arrangement of repeating structures. Each repeating structure may have a first surface and a second surface that is in the opposite direction. The first surface may have an open area, and the second surface may be solid. This improves etching uniformity within a given discrete region. The first surface and the second surface can be tilted at an angle of 90° or close to it. This minimizes the loss of ions passing through the first surface due to collisions with the second surface. Such losses could otherwise occur through scattering and blocking by the second surface of ions that would have otherwise collided with the substrate.

[0029] The top of the Faraday cage can have a certain main level (height). Discrete regions of different subsets with different angles can be raised by different amounts relative to the main level to reduce variations in ion path length involved in etching through these discrete regions of different subsets. By defining these variations in relation to the variations that would occur if all discrete regions were raised by the same amount, it becomes possible to determine whether or not reduction has been achieved. In this way, etching uniformity between different discrete regions with different angles relative to the top surface of the substrate support can be improved. The optimal arrangement is to raise the discrete regions so that the average ion path length through each discrete region is the same or substantially the same.

[0030] The apparatus may further include a lifting mechanism for raising the Faraday cage relative to the substrate support and for lowering the Faraday cage to contact or approach the substrate support. This lifting mechanism may comprise any suitable components, such as one or more actuators and / or one or more lift pins. Generally, the apparatus may further include a separate lifting mechanism for the substrate, which may be part of a conventional handling mechanism for placing the substrate into and removing it from the chamber.

[0031] A third aspect of the present invention provides a method for providing a plasma etching apparatus according to a second aspect of the present invention by modifying a plasma etching apparatus, the method comprising the steps of preparing a Faraday cage together with the apparatus, wherein the Faraday cage has an upper part that can be disposed above a dielectric substrate placed on a substrate support, and the upper part has a plurality of discrete regions having open areas through which the substrate can be plasma-etched, and these discrete regions constitute at least two subsets, with different subsets having open areas having different angles and / or orientations with respect to the upper surface of the substrate support; and adapting a controller so as to be able to control the operation of the Faraday cage.

[0032] This modification method may further include a step of preparing a lifting mechanism, in conjunction with the device, for raising the Faraday cage relative to the substrate support and for lowering the Faraday cage to contact or approach the substrate support.

[0033] To avoid any ambiguity, whenever the present invention is referred to in this application by the words “equipped with” or “possessing” and similar terms, it should be understood, where the context allows, that the invention also encompasses more restrictive terms such as “composed of” and “essentially composed of.”

[0034] The present invention, as described above, extends to any original combination of the features described above or contained in the following descriptions, drawings, or claims. Where appropriate, any feature disclosed in connection with the first aspect of the present invention can be combined with any feature disclosed in connection with the second aspect of the present invention, and vice versa.

[0035] Embodiments of the present invention will be described primarily by illustration with reference to the following accompanying drawings. [Brief explanation of the drawing]

[0036] [Figure 1]This is a plan view of a substrate having multiple waveguide coupler lenses. [Figure 2] This is a plan view of a waveguide coupler lens having three surface relief diffraction gratings. [Figure 3] This is a semi-schematic cross-sectional view of the plasma etching apparatus of the present invention. [Figure 4] This is a side cross-sectional view of the first Faraday cage and substrate. [Figure 5] This is a side cross-section of the second Faraday cage and substrate. [Figure 6] This figure shows the variation in path length due to Faraday cage height, mesh angle, and length. [Modes for carrying out the invention]

[0037] In this invention, a Faraday cage is used in a plasma etching apparatus to etch at multiple angles and orientations during a single etching cycle. This allows for the simultaneous creation of various surface relief diffraction gratings. The method of this invention can be performed at a higher etching rate compared to ion beam etching systems.

[0038] Figure 3 shows the plasma etching apparatus 300 of the present invention. The plasma etching apparatus 300 is an inductively coupled plasma (ICP) apparatus, such as an adapted OmegaSynapse® tool available from SPTS Technologies Limited in Newport, UK. Plasma generation in such plasma etching apparatuses is well known in the art and will not be described here unless necessary for understanding the present invention.

[0039] The plasma etching apparatus 300 shown in Figure 3 includes substrate supports 302a / 302b disposed within the chamber 304 to support the substrate 306. Bias power can be supplied to the substrate via an impedance matching network 310 by an RF power supply 308. The RF frequency can be any convenient value, for example 13.56 MHz, or an alternative lower frequency, for example 400 kHz or 2 MHz. Process gases are supplied into the chamber through a central gas injector longitudinal pipe 312 and injectors 314 arranged along the annular diameter and receiving gas flows independent of pipe 312. These gases can be moved back from the chamber 304 to a pumping system (not shown) via a shut-off valve 316 in a conventional manner. An ICP coil 318 is used to generate and maintain plasma within the chamber 304. The ICP coil 318 is enclosed within a ceramic container 320. As is well known in this technical field, the ICP coil 318 receives RF power from the 13.56MHz power supply 322 via the matching network 324.

[0040] As shown in Figure 3, the substrate support is an electrostatic chuck (ESC) 302a, which is attached to a metallic platen 302b. The wafer substrate 306 is placed on the ESC 302a by conventional means using a vacuum robot and lift pins (not shown). A Faraday cage 326 is positioned in an elevated position using an actuator 328. After loading, the actuator 328 lowers the Faraday cage 326 to contact or approach the surface of the ESC 302a, thereby preventing plasma initiation within the Faraday cage 326. The Faraday cage 326 is electrically connected to the platen 302b by a conductive strap 330. The ESC 302a can be of any preferred type. In one specific but non-limiting example, a bipolar ESC using helium backside gas at a pressure of approximately 10 Torr is employed. A chiller unit can be provided to control the temperature of the substrate. As noted earlier, the device 300 is a modified and commercially available tool. This modification, in principle, consists of providing a Faraday cage and a lifting mechanism for the Faraday cage. As you can see, the device 300 further includes a microprocessor-based controller (not shown in Figure 3) that controls its operation, and this controller is modified to additionally control the Faraday cage and its lifting mechanism.

[0041] Figure 4 shows a configuration for a two-piece Faraday cage that can be used in connection with the present invention. Figure 4 also shows substrates 40a / 40b on the ESC. This substrate, together with the SiO2 layer on the silicon wafer (collectively shown as 40a in Figure 4), includes an aluminum mask 40b formed on the SiO2 layer. The Faraday cage has a metal lid 42 with a central portion, shown in Figure 4 in a lowered position used in the etching process. This lowered position is achieved by lowering the lid 42, including the central portion, onto the skirt portion of the Faraday cage, thereby providing an enclosure that can be electrically contacted with the RF drive platen. The central portion of the lid 42 has an opening, each of which is covered by a mesh that is in ohmic contact with the body of the lid 42. A first mesh 44a is mounted parallel to the surface of the lid, while a second mesh 44b is angled 30° to the surface of the lid and a third mesh 44c is angled 45° to the surface of the lid. The second and third meshes are housed in wall-mounted housings attached upward from the lid, at a desired inclination angle with respect to the lid surface. The back walls 46b and 46c can be seen in Figure 4, and as can be seen, each wall-mounted housing is further equipped with a pair of side walls (not shown). The walls of these wall-mounted housings are made of a suitable material, such as Al. As a result of this configuration, the only ion paths that can reach the substrate are those passing through openings in the mesh. The typical gap width between the lid 42 and the surface of the substrate 40b is approximately 40 mm. Etching results in the formation of diffraction grating features 48a, 48b, and 48c that roughly match the orientation of the mesh. Etching rates of up to 100 nm / min can be easily achieved. As can be seen, the Faraday cage has multiple distinct zones, and by etching through them, multiple distinct diffraction grating structures can be provided. In this way, for example, a coupler lens of the type shown in Figure 2, having discrete regions etched at different angles and orientations, can be created. In light of the need for expressive simplification, the skirt and lid periphery of the Faraday cage are not shown in Figure 4.In practice, the lid is raised and lowered using a suitable lifting mechanism, for example, by using lift pins that pass through the walls of the skirt section or through the substrate support into the interior of the skirt section. In any case, the lifting mechanism for the substrate needs to be adapted so that the substrate can be raised above the level (height) of the skirt section for loading and unloading.

[0042] We conducted research and elucidated the etching of the SiO2 film on the silicon layer using the SPTS Synapse™ ICP tool, using a Faraday cage that roughly corresponds to the one shown in Figure 4. The Faraday cage had square openings, each with dimensions of 25 × 25 mm, and was covered with aluminum mesh (380 micron opening / 250 micron wire diameter) in three different orientations and angles (1 micron = 10 -6 m).

[0043] Typical process conditions are: ESC temperature: 0℃. ICP power: 1.9kW (13.56MHz) Bias power: 325W (13.56MHz) C4F8 flow rate: 50sccm O2 flow rate: 8sccm That is the case.

[0044] Ion energy decreases as the path length within the Faraday cage increases. Therefore, a decrease in etching rate can be expected with increasing path length within the Faraday cage. Consequently, etching non-uniformity can be expected with variations in path length within the Faraday cage. Numerous factors effectively determine the degree of non-uniformity in etching rate, including ion path length, process conditions, and the properties of the material being etched. In more chemical etching processes, path length variations become less pronounced. However, as the inventors of this invention have determined, a 25 × 25 mm opening of the type described in relation to Figure 4 can change etching uniformity by more than 10%, depending on the process parameters used. These problems can also be addressed using alternative Faraday cage configurations. These alternative Faraday cage configurations can provide greater process flexibility and enhance the large-scale implementation of the present invention by utilizing the ability to minimize non-uniformity of the etching grid by adjusting the mesh height. Figure 5 shows an alternative Faraday cage configuration comprising a skirt portion 50 and a lid portion 52. The skirt portion 50 is placed on an ESC 54, which supports the substrate 56. The lid portion has a sawtooth arrangement of repeating structures 52a / 52b, each repeating structure having a first surface 52a and an inclined second surface 52b, where the first surface 52a is a mesh and the second surface 52b is a solid back wall. Each repeating structure further comprises a pair of side walls (not shown). There is a 90° angle between the mesh 52a forming the repeating structure and its corresponding back wall 52b, thereby minimizing the scattering and blocking of ions colliding with the wafer substrate 56. By adjusting H (height of the Faraday cage to the lid) and h (height to the vertices of the features) in conjunction with the process conditions, the ion path length can be affected, optimizing the etching rate and non-uniformity. The repeating structures 52a / 52b shown in Figure 5 correspond to single inclined mesh / back wall structures, such as structures 44b / 46b and 44c / 46c shown in Figure 4.The sawtooth arrangement can consist of any number of repeating structures of any suitable size. For example, the 25 mm width described with reference to Figure 4 can be provided instead as a sawtooth arrangement with three 8.3 mm sections. This significantly reduces the difference in ion path length when comparing ions incident on the upper part of the mesh with ions incident on the lower part of the mesh, near the surface of the Faraday cage lid. In other words, this arrangement reduces the difference in ion path length related to etching through a single discrete region; in Figure 5, this is the mesh arrangement that results in the formation of a single diffraction grating. This improves the etching uniformity related to etching a given diffraction grating.

[0045] The following discussion will cover the various factors that may influence the detailed design of the sawtooth arrangement, for example, shown in Figure 5. The Faraday cage lid 60 shown in Figure 6 has multiple toothed enclosures 62, each having a length X and an angle (α). As can be inferred, the variation in ion path length is determined by components L1 and L2, where L1 depends on height H and angle α, and L2 depends on angle α and length X. As can be seen from this, shortening X can shorten its additional path length L2. For example, shortening X by 1 / 3 also shortens L2 by 1 / 3. This results in an improvement in the uniformity of the etching rate. As can also be seen, the difference in etching uniformity between different discrete regions is caused by the difference in average ion path length that can occur between different discrete regions. Figure 6 also shows discrete regions where the mesh is parallel to the surface of the lid. Maintaining the same path length is important in order to ensure uniformity at various angles. Therefore, in Figure 6, the mesh plane parallel to the surface of the lid 60 is raised to the average path length related to the enclosure 62. As shown in Figure 6, this raised arrangement configuration can be achieved by housing the mesh within the enclosure 64, thereby keeping the mesh parallel to the surface of the lid 60, but raising the mesh to a height L3 above the main surface of the lid 60. The amount by which any given mesh is raised will depend on the angle α.

[0046] As is evident, the present invention can be implemented in various ways. ICP etching is an attractive option because relatively high etching rates can be easily achieved, but etching systems such as capacitive coupling, helicon, RIE, or microwave devices can also be used. As will be understood by those skilled in the art, the present invention can be applied to a wide range of diffraction grating fabrication and end-of-process applications.

Claims

1. A method for creating multiple surface relief diffraction gratings by etching a substrate, A step of preparing a dielectric substrate on which a mask is formed on its upper surface, wherein the mask has a plurality of openings, A step of placing the substrate on a substrate support inside the chamber of the plasma etching apparatus, The process involves positioning a Faraday cage such that the upper part of the Faraday cage is positioned above the upper surface of the substrate, and that an electrical connection is maintained between the Faraday cage and the substrate support, wherein the upper part of the Faraday cage comprises a plurality of discrete regions having open areas through which the substrate can be plasma-etched. The process involves plasma etching the substrate to create a plurality of surface relief diffraction gratings, wherein the plurality of surface relief diffraction gratings form at least two subsets having different angles and / or orientations. It has, When arranging the Faraday cage, the opening of the mask and the discrete region at the top of the Faraday cage are aligned so that the plurality of surface relief diffraction gratings are created by plasma etching through the open area, and The discrete region is configured to form at least two subsets, and each of these subsets has open areas with different angles and / or orientations relative to the upper surface of the substrate, thereby generating surface relief diffraction gratings of the at least two subsets with different angles and / or orientations by plasma etching through the discrete regions of the at least two subsets. method.

2. A method according to claim 1, wherein each of the discrete regions comprises a mesh or a perforated structure.

3. A method according to claim 1 or 2, wherein the upper part of the Faraday cage is provided with a lid.

4. A method according to claim 3, wherein at least one subset of the discrete regions is housed in at least one wall-mounted housing attached to the lid.

5. A method according to any one of claims 1 to 4, wherein the Faraday cage further comprises a skirt portion hanging down from the upper part.

6. A method according to claim 5, wherein the Faraday cage placement step includes a step of bringing the skirt portion into contact with or close to the substrate support.

7. A method according to any one of claims 1 to 6, wherein at least one discrete region comprises a sawtooth arrangement of repeating structures, each repeating structure having a first surface and a second surface that is inclined in the opposite direction, the first surface having an open area and the second surface being solid.

8. A method according to any one of claims 1 to 7, wherein the electrical connection between the Faraday cage and the substrate support is maintained at least partially via a conductive flexible linking structure.

9. A method according to any one of claims 1 to 8, wherein an RF electrical signal is applied to the substrate support during plasma etching of the substrate.

10. A method according to any one of claims 1 to 9, wherein plasma etching is performed using inductively coupled plasma (ICP).

11. A method according to any one of claims 1 to 10, wherein the dielectric substrate is glass.

12. A method according to any one of claims 1 to 11, wherein the dielectric substrate contains silicon dioxide or borosilicate glass.

13. A method according to any one of claims 1 to 12, wherein the Faraday cage is made of aluminum.

14. A method according to any one of claims 1 to 13, wherein the substrate support is an electrostatic chuck (ESC).

15. A plasma etching apparatus for etching a substrate to create multiple surface relief diffraction gratings, Chamber and, A substrate support is disposed within the chamber, A plasma generator that generates plasma in the chamber, A Faraday cage having an upper part that can be disposed above the upper surface of a dielectric substrate placed on the substrate support, wherein the upper part comprises a plurality of discrete regions having open areas through which the substrate can be plasma-etched, and these discrete regions constitute at least two subsets, each of which has open areas having different angles and / or orientations with respect to the upper surface of the substrate support, A controller that controls this device and causes it to execute the method according to claim 1, A plasma etching apparatus equipped with the following features.

16. A plasma etching apparatus according to claim 15, wherein each of the discrete regions is a mesh or a perforated structure.

17. A plasma etching apparatus according to claim 15 or 16, wherein a lid portion is provided on the upper part of the Faraday cage.

18. A plasma etching apparatus according to claim 17, wherein at least one subset of the discrete regions in the upper part of the Faraday cage is housed in a walled housing attached to the lid.

19. A plasma etching apparatus according to any one of claims 15 to 18, wherein the Faraday cage further comprises a skirt portion hanging down from the upper part.

20. A plasma etching apparatus according to any one of claims 15 to 19, wherein at least one discrete region comprises a sawtooth arrangement of a repeating structure, each repeating structure having a first surface and a second surface that is inclined in the opposite direction, the first surface having an open area and the second surface being solid.

21. A plasma etching apparatus according to claim 20, wherein the first surface and the second surface which is inclined in the opposite direction are inclined at an angle of 90° or close to it.

22. A plasma etching apparatus according to any one of claims 15 to 21, wherein the upper part of the Faraday cage has a main level, and the discrete regions of various subsets having different angles with respect to the upper surface of the substrate support are arranged to be raised by different amounts relative to the main level in order to reduce ion path length fluctuations related to etching through the discrete regions of the different subsets.

23. A plasma etching apparatus according to any one of claims 15 to 21, further comprising a lifting mechanism for raising the Faraday cage relative to the substrate support and for lowering the Faraday cage to contact or approach the substrate support.

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