Method of etching substrate
By using a combination of Faraday cage and mask in a plasma etching apparatus, it is possible to simultaneously etch multiple surface relief diffraction gratings with different angles and orientations in a single step, solving the problem of multi-step etching in the prior art and improving the etching rate and efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-10
- Publication Date
- 2026-03-24
AI Technical Summary
Existing techniques require multiple separate patterning and etching steps when etching surface relief diffraction gratings on waveguide assemblies or coupler lenses, and the etching rate is low, making it difficult to simultaneously achieve multiple gratings with different angles and orientations.
A Faraday cage is used to position the mask in a plasma etching apparatus. By aligning the discrete regions of the Faraday cage with the substrate, multiple surface relief diffraction gratings can be etched simultaneously. The ICP system provides high-density plasma and a high etching rate.
This technology enables the simultaneous generation of multiple surface relief diffraction gratings with different angles and orientations in a single etching step, thereby improving the etching rate, simplifying the process flow, and reducing the number of vacuum destruction and patterning steps.
Smart Images
Figure CN121721777A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for etching a substrate, and more particularly to a method for etching a substrate to produce a plurality of surface relief diffraction gratings. The invention also relates to an associated plasma etching apparatus. Background Technology
[0002] Surface-embossed diffraction gratings on waveguide combiners or coupler lenses are important components of augmented reality (AR) and virtual reality (VR) systems. Surface-embossed diffraction gratings are typically composed of high-refractive-index (RI) glass (usually including silicon oxide) etched at different angles and orientations. Figure 1 A substrate 10 containing multiple waveguide coupler lenses 12 is shown. The substrate 10 is typically high-RI glass. Figure 2 A more detailed view of the individual waveguide coupler lens 12. For example... Figure 2 As shown, the waveguide coupler lens 12 includes three different surface-embossed diffraction gratings 20, 22, and 24, each etched at a different angle and orientation. In use, the image to be viewed is projected onto the first grating 20, which guides the light through total internal reflection to the second grating 22, which in turn guides the light to the third grating 24, where the image is projected onto the user's eye. It is important that all lenses 12 on the substrate 10 are etched in a similar manner. Figure 1 and 2 In the example illustrated, this involves providing three different surface-embossed diffraction gratings 20, 22, and 24 for each coupler lens 12. The first, second, and third gratings 20, 22, and 24 are formed by etching features into the substrate 10 at different angles and orientations. The etching can be performed to etch a "master" for nanoimprint lithography (NIL) printing or directly onto the substrate to etch the final product.
[0003] Established methods for etching angular features use ion beam etching to create patterned substrates. However, these methods have several significant drawbacks. Specifically, etching three different surface relief diffraction gratings (e.g., using a conventional ion beam etching system) can be challenging. Figure 1 and 2 The surface relief diffraction grating shown in the image requires three separate patterning and etching steps. Furthermore, the etching rate associated with ion beam etching is typically low. The reasons for these drawbacks will now be explained.
[0004] Conventional ion beam systems use a plasma source with an extraction grating to project a small beam of ions toward a substrate. To achieve acceptable uniformity, the substrate needs to be placed at a considerable distance from the source, resulting in relatively low etch rates. Typical ion beam etch rates are approximately 10 to 30 nm / min, which is disadvantageous compared to the approximately 100 to 1000 nm / min etch rates easily achievable with conventional ICP etch systems. Another factor is that the beam is typically projected at low pressure (less than 1 mTorr) to minimize unwanted ion scattering. Therefore, ion beam systems are typically large and complex, and suffer from relatively low etch rates. Furthermore, multiple angled diffraction gratings with different angles and orientations require adjusting the angle of the ion beam system for each region on the waveguide combiner. This can be achieved through multiple patterning steps involving using a mask formed by submicron lithography on the substrate, followed by exposing the substrate to the selected ion beam angle and orientation to etch the diffraction gratings. However, only one angle can be etched into the mask substrate at a time without compromising open features. Because more than one angle and orientation are required to generate different types of surface relief diffraction gratings, the substrate must be removed from the vacuum system and repatterned before subsequent features can be generated at different angles and / or orientations. From a process point of view, using multiple vacuum destruction and patterning steps is highly undesirable. It is highly desirable to provide a manufacturing technology that enables the fabrication of multiple surface relief diffraction gratings with different angles and orientations at excellent etching rates without the need for separate patterning steps. Summary of the Invention
[0005] The present invention addresses the aforementioned problems and desires in at least some of its embodiments. Specifically, the present invention provides a method and associated apparatus that enables the simultaneous etching of multiple surface relief diffraction gratings with different angles and orientations. While the present invention is well-suited for producing structures such as waveguide combiners or coupler lenses, it can be used to provide a wide range of surface relief diffraction gratings.
[0006] According to a first aspect of the present invention, a method is provided for etching a substrate to produce a plurality of surface relief diffraction gratings, the method comprising the steps of:
[0007] A dielectric substrate is provided having a mask formed on its upper surface, the mask comprising a plurality of apertures;
[0008] The substrate is positioned on a substrate support in the chamber of a plasma etching apparatus;
[0009] A Faraday cage is positioned such that its upper portion is disposed above the upper surface of the substrate, and an electrical connection is maintained between the Faraday cage and the substrate support, wherein the upper portion of the Faraday cage includes a plurality of discrete regions having open areas through which the substrate can be plasma-etched; and
[0010] The substrate is plasma-etched to produce a plurality of surface relief diffraction gratings, wherein the plurality of surface relief diffraction gratings comprises at least two subsets having different angles and / or orientations;
[0011] in:
[0012] The Faraday cage is aligned with the discrete region of the upper portion of the mask through the aperture of the mask, such that the plurality of surface relief diffraction gratings are generated by plasma etching of the open region; and
[0013] The discrete region includes at least two subsets, wherein different subsets have open regions with different angles and / or orientations relative to the upper surface of the substrate, such that plasma etching of the at least two subsets of the discrete region produces the at least two subsets of surface relief diffraction gratings with different angles and / or orientations.
[0014] In this way, multiple surface relief diffraction gratings with different angles and / or orientations can be generated in a single etching step. The method can be performed at relatively high etching rates. Another advantage is that existing plasma etching equipment can be easily modified with Faraday cages to provide the apparatus according to the invention.
[0015] Without being bound by any particular theory or conjecture, it is believed that a plasma sheath forms parallel to the surface of the Faraday cage during etching. It is further believed that a dark space region forms above the Faraday cage, allowing ions to enter the Faraday cage only perpendicular to its surface (via open regions in the discrete area). This results in directional anisotropic etching of the substrate.
[0016] Each discrete region may comprise a grid. The grid provides an open area through which plasma can etch the substrate. It should be understood that a Faraday cage is a structure that generally or entirely comprises a conductive material, and the grid is envisioned to be composed of a conductive material. In principle, other structures or arrangements with open areas can be considered, such as perforated structures. Perforated structures can be perforated metal grids.
[0017] The upper portion of the Faraday cage may include a lid portion. At least a subset of discrete regions may be housed in at least one walled shell suspended from the lid portion. Typically, the walled shell is suspended upward from the lid portion, but in principle, the walled shell may be suspended downward from the lid portion.
[0018] The Faraday cage may further include a skirt portion that hangs downwards from the upper portion. Positioning the Faraday cage may include bringing the skirt portion into contact with or close to the substrate support. In practice, the skirt portion should be sufficiently close to the substrate support to prevent plasma from impacting the Faraday cage.
[0019] At least one discrete region may include a zigzag arrangement of repeating structures. Each repeating structure may include a first and a second opposing inclined surface. The first surface may contain an open region, and the second surface may be solid.
[0020] Electrical connection between the Faraday cage and the substrate support can be maintained at least partially via a conductive flexible connection structure. Alternatively, electrical connection can be maintained through direct contact between the Faraday cage and the substrate support. A good ohmic contact between the Faraday cage (including the discrete region) and the substrate support is desirable.
[0021] During plasma etching of the substrate, an RF electrical signal can be applied to the substrate support.
[0022] Inductively coupled plasma (ICP) is used to perform plasma etching. ICP systems are advantageous because they can generate high-density plasma and provide high etching rates. ICP etching is particularly advantageous for etching oxides, where high energy is required. However, other plasma etching techniques, such as capacitively coupled plasma etching, can be used.
[0023] The dielectric substrate can be glass.
[0024] The dielectric substrate may include silicon dioxide or borosilicate glass. However, the invention is not limited in this respect, and other materials that can be etched to provide a surface-embossed diffraction grating may be used. For example, the dielectric substrate may include SiC or LiNbO3.
[0025] The Faraday cage can be formed of aluminum. Other conductive materials, such as other metals or metal alloys, are conceivable. The open region of the discrete zone is the only part of the Faraday cage through which ions in the plasma intend to pass. In practice, the rest of the Faraday cage structure typically consists of solid walls.
[0026] The Faraday cage may be provided as a one-piece structure. Alternatively, the Faraday cage may be provided as more than one piece, such as a two-piece structure. The two-piece structure may include a cover portion and separate side edge portions, wherein the cover portion contacts the side edge portions during use.
[0027] The substrate support can be an electrostatic chuck (ESC).
[0028] According to a second aspect of the present invention, a plasma etching apparatus is provided for etching a substrate to produce a plurality of surface relief diffraction gratings, the apparatus comprising:
[0029] chamber;
[0030] A substrate support, which is disposed within the cavity;
[0031] A plasma generating device for generating plasma in the chamber;
[0032] A Faraday cage comprising an upper portion disposed above an upper surface of a dielectric substrate positioned on a substrate support, wherein the upper portion includes a plurality of discrete regions having open areas through which the substrate can be plasma-etched, the discrete regions comprising at least two subsets, wherein different subsets have open areas having different angles and / or orientations relative to the upper surface of the substrate support; and
[0033] A controller configured to control the device to perform the method according to the first aspect of the invention.
[0034] Each of the discrete regions may include a grid or a perforated structure.
[0035] The upper portion of the Faraday cage may include a cover portion.
[0036] The discrete region of at least one subset may be contained in at least one walled shell that is suspended from the cover portion.
[0037] The Faraday cage may further include side edge portions that hang downwards from the upper portion.
[0038] At least one discrete region may include a zigzag arrangement of repeating structures. Each repeating structure may include a first and a second opposing inclined surface. The first surface may contain an open region, and the second surface may be solid. In this way, etching uniformity within a given discrete region can be improved. The first and second opposing inclined surfaces may be inclined at an angle of 90° or close to 90°. In this way, the loss of ions that have passed through the first surface by colliding with the second surface is minimized. This loss may occur through the scattering and shielding of ions by the second surface, which would otherwise bombard the substrate.
[0039] The upper portion of the Faraday cage may have a master level. Subsets of discrete regions with different angles may be raised to different degrees relative to the master level to reduce variations in ion path lengths associated with etching through different subsets of the discrete regions. These variations can be referenced to variations associated with raising all discrete regions to the same degree to determine whether a reduction has been achieved. In this way, etching uniformity between different discrete regions with different angles relative to the upper surface of the substrate support can be improved. Ideally, the discrete regions are raised such that the average ion path length through each discrete region is the same or substantially the same.
[0040] The device may further include a lifting mechanism for raising the Faraday cage relative to the substrate support and lowering the Faraday cage to contact or be adjacent to the substrate support. The lifting mechanism may include any suitable components, such as one or more actuators and / or one or more lifting pins. Generally, the device further includes a separate lifting mechanism for the substrate, which may be part of a conventional handling mechanism for introducing the substrate into and removing the substrate from the chamber.
[0041] According to a third aspect of the invention, a method is provided to modify a plasma etching apparatus to provide a plasma etching apparatus according to a second aspect of the invention, the method comprising the steps of: providing a Faraday cage for the apparatus, the Faraday cage including an upper portion disposed above an upper surface of a dielectric substrate positioned on a substrate support, wherein the upper portion includes a plurality of discrete regions having open areas through which the substrate can be plasma etched, the discrete regions including at least two subsets, wherein different subsets have open areas having different angles and / or orientations relative to the upper surface of the substrate support; and adjusting the controller to control the operation of the Faraday cage.
[0042] The modification method may further include providing a lifting mechanism for the device, the lifting mechanism being used to lift the Faraday cage relative to the substrate support and to lower the Faraday cage to contact or be adjacent to the substrate support.
[0043] To avoid ambiguity, whenever the context allows, the invention is also to be understood to include further restrictive terms, such as "comprises" and "essentially constitutes," whenever the term "comprising" or "including" and similar terms are used herein.
[0044] While the invention has been described above, it extends to any inventive combination of features set forth in the foregoing or in the following description, drawings, or claims. Any feature disclosed with respect to the first aspect of the invention may be combined with any feature disclosed with respect to the second aspect of the invention, and vice versa, as appropriate. Attached Figure Description
[0045] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, wherein:
[0046] Figure 1 It is a plan view of a substrate with multiple waveguide coupler lenses;
[0047] Figure 2 It is a plan view of a waveguide coupler lens with three surface-embossed diffraction gratings;
[0048] Figure 3 This is a half-sectional schematic diagram of the plasma etching apparatus of the present invention;
[0049] Figure 4 This is a cross-sectional side view of the first Faraday cage and the substrate;
[0050] Figure 5 This is a cross-sectional side view of the second Faraday cage and the substrate; and
[0051] Figure 6 This demonstrates the changes in path length caused by the height, grid angle, and length of the Faraday cage. Detailed Implementation
[0052] This invention utilizes a Faraday cage in a plasma etching apparatus to etch more than one angle and orientation in a single etching cycle. In this way, different surface relief diffraction gratings can be produced simultaneously. Compared to ion beam etching systems, the method of this invention can be performed at a higher etching rate.
[0053] Figure 3 The plasma etching apparatus 300 of the present invention is illustrated. The plasma etching apparatus 300 is an inductively coupled plasma (ICP) device, such as the Adaptive Omega Synapse available from SPTS Technologies Limited in Newport, UK. TM Tools. The generation of plasma in such plasma etching equipment is well known in this art and will not be described herein except as necessary for understanding the invention.
[0054] Figure 3 The plasma etching apparatus 300 shown includes substrate supports 302a / 302b housed within a chamber 304 for supporting a substrate 306. Bias power can be supplied to the substrate via an RF power supply 308 through an impedance matching network 310. The RF frequency can be any convenient value, such as 13.56 MHz, or alternatively, a lower frequency, such as 400 kHz or 2 MHz. Process gas is delivered to the chamber via a central gas ejector through conduit 312 and an annular radial series of ejectors 314, which receive independent gas flows from conduit 312. The gas can be removed from the chamber 304 to a pumping system (not shown) via an isolation valve 316 in a conventional manner. Plasma is generated and sustained within the chamber 304 using an ICP coil 318. The ICP coil 318 is enclosed in a ceramic container 320. As known in the art, the ICP coil 318 receives RF power from a 13.56 MHz power supply 322 via a matching network 324.
[0055] like Figure 3As shown, the substrate support is an electrostatic chuck (ESC) 302a attached to a metal pressure plate 302b. The wafer substrate 306 is placed on the ESC 302a using conventional methods, employing a vacuum robot and lifting pins (not shown). The Faraday cage 326 is in an elevated position using an actuator 328. After loading, the actuator 328 lowers the Faraday cage 326 to a surface adjacent to or in contact with the ESC 302a to prevent the initiation of plasma within the Faraday cage 326. A conductive strip 330 electrically connects the Faraday cage 326 to the pressure plate 302b. The ESC 302a can be of any suitable type. In a particular, but not limiting, example, a bipolar ESC using a helium backside gas at a pressure of approximately 10 Torr is employed. A cooling unit may be provided to control the substrate temperature. As mentioned above, the device 300 is an adaptive commercially available tool. The adaptive tool primarily consists of providing the Faraday cage and a lifting mechanism for the Faraday cage. It should be understood that device 300 further includes a microprocessor-based controller ( Figure 3 (Not shown in the text), its control equipment operation, and the controller is adapted to separately control the Faraday cage and its lifting mechanism.
[0056] Figure 4 A configuration of a two-piece Faraday cage that can be used in conjunction with this invention is shown. Figure 4 The exhibition also showcases substrates 40a / 40b on the ESC. The substrates consist of a SiO2 layer on a silicon wafer (in... Figure 4 The common feature is shown as 40a), wherein an aluminum mask 40b is formed on a SiO2 layer. The Faraday cage includes a metal cap having a central section 42, the metal cap being... Figure 4 The image shows a lowered position used in the etching step. This lowered position is achieved by lowering the cover, including the central section 42, onto the side edge of the Faraday cage to provide a housing for electrical contact with the RF drive platen. The central section of the cover 42 includes apertures, each covered by a grid in ohmic contact with the body of the cover 42. A first grid 44a is attached parallel to the surface of the cover, while a second grid 44b is at a 30° angle to the surface of the cover, and a third grid 44c is at a 45° angle to the surface of the cover. The second and third grids are accommodated using a walled housing that hangs upwards from the cover at a desired angle of inclination relative to the surface of the cover. Figure 4The rear walls 46b and 46c are visible, but it should be understood that each walled shell further includes a pair of sidewalls (not shown). The walls of the walled shells are made of a suitable material (e.g., Al). Due to this configuration, the only path for ions to reach the substrate is through the pores in the grid. A representative gap between the cover 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, which are substantially aligned with the orientation of the grid. Etching rates up to 100 nm / min can be easily achieved. It should be understood that the Faraday cage has multiple distinct zones through which etching can occur to provide multiple different diffraction grating structures. In this way, for example, it is possible to produce Figure 2 The image shows a coupler lens of this type, which has discrete areas etched at different angles and orientations. For the sake of simplicity, Figure 4 The side rims of the Faraday cage and the periphery of the cover are not shown. In practice, a suitable lifting mechanism (e.g., a lifting pin extending through the wall of the side rim or through the substrate support into the interior of the side rim) is used to raise and lower the cover. In any case, the lifting mechanism for the substrate needs to be adapted to ensure that the substrate can be raised above the level of the side rim so that the substrate can be loaded and unloaded.
[0057] Conduct research to characterize the use of roughly corresponding Figure 4 The Faraday cage shown in SPTS Synapse TM The SiO2 film on the silicon layer is etched using an ICP tool. The Faraday cage has square apertures, each 25x25mm in size, and is covered with an aluminum mesh with three different orientations and angles (380-micron openings / 250-micron line diameters).
[0058] Typical process conditions are:
[0059] ESC temperature 0℃.
[0060] ICP power 1.9kW (13.56MHz)
[0061] Bias power 325W (13.56MHz)
[0062] C4F8 flow rate: 50 sccm
[0063] O2 flow rate: 8 sccm.
[0064] Ion energy decreases with increasing path length within the Faraday cage. Therefore, an increase in path length within the Faraday cage can be expected to cause a decrease in etching rate. Consequently, variations in ion path length within the Faraday cage can be expected to cause etching non-uniformity. In practice, the degree of etching rate non-uniformity will be determined by many factors, including ion path length, process conditions, and the properties of the material being etched. For more chemical etching processes, variations in path length become less significant. However, the inventors have determined that, regarding… Figure 4 For the 25x25mm aperture type described, the etching uniformity can vary by >10% depending on the process parameters used. Alternative Faraday cage configurations can be used to address these issues. These alternative Faraday cage configurations offer greater process flexibility and enhance the large-scale implementation of the invention by utilizing a mesh height that can be tuned to minimize the inhomogeneities of the etched grating. Figure 5 An alternative Faraday cage configuration including a side edge portion 50 and a cap portion 52 is shown. The side edge portion 50 is placed on an ESC 54. The ESC supports a substrate 56. The cap portion includes a serrated arrangement of repeating structures 52a / 52b, each repeating structure including a first opposing inclined surface 52a and a second opposing inclined surface 52b, wherein the first surface 52a is a mesh and the second surface 52b is a solid back wall. Each repeating structure further includes a pair of sidewalls (not shown). There is a 90° angle between the mesh 52a and the corresponding back wall 52b of the repeating structure, which minimizes the scattering and shielding of ions impacting the wafer substrate 56. By tuning the process conditions and H (height of the Faraday cage to the cap) and h (height to the vertex of the feature), the etching rate and non-uniformity can be optimized by acting on the ion path length. Figure 5 The repeating structures 52a / 52b shown correspond to a single inclined grid / back wall structure, for example... Figure 4 The diagram shows structures 44b / 46b or 44c / 46c. A serrated arrangement can include any suitable number of repeating structures of any suitable size. For example, Figure 4 The 25mm width mentioned can instead be provided as a serrated arrangement comprising three 8.3mm segments. This significantly reduces the difference in ion path length when comparing ions incident on the top of the grid with ions incident on the lower portion of the grid near the surface of the Faraday cage. In other words, this arrangement reduces the difference in ion path length associated with etching through a single discrete region. Figure 5 The grid arrangement in the middle leads to the formation of a diffraction grating. By doing so, the etching uniformity is improved in the etching of a given diffraction grating.
[0065] The discussion will now focus on what can affect, for example... Figure 5 The detailed design factors of the sawtooth arrangement shown in the image. Figure 6A Faraday cage 60 is shown, having multiple toothed shells 62, each having a length X and an angle (α). It should be understood that the variation in ion path length is determined by components L1 and L2, where L1 depends on the height H and angle α, and L2 depends on the angle α and length X. It can be seen that the additional path length L2 can be reduced by decreasing X. For example, by reducing X by one-third, L2 is also reduced by one-third. This will lead to an improvement in etching rate uniformity. Furthermore, it can be seen that differences in etching uniformity between different discrete regions can occur due to differences in the average ion path length that can occur between different discrete regions. Figure 6 It also shows discrete regions where the grid is parallel to the surface of the cover. To ensure uniformity at different angles, it is important to maintain the same path length. Therefore, parallel to Figure 6 The plane of the grid on the surface of the cover 60 rises to the average path length associated with the outer shell 62. For example... Figure 6 As shown, this raised configuration can be achieved by housing the mesh within a housing 64, which holds the mesh parallel to the surface of the cover 60, but the mesh is raised by a height L3 above the main surface of the cover 60. The degree to which any given mesh is raised will depend on the angle α.
[0066] It will be apparent that the present invention can be implemented in various ways. While ICP etching is an attractive option because relatively high etching rates can be easily achieved, etching systems using devices such as capacitive coupling, helical waves, RIE, or microwaves can also be used. Skilled readers will understand that the present invention is applicable to a wide range of diffraction grating production and end applications.
Claims
1. A method for etching a substrate to produce a plurality of surface relief diffraction gratings, comprising the following steps: A dielectric substrate is provided having a mask formed on its upper surface, the mask comprising a plurality of apertures; The substrate is positioned on a substrate support in the chamber of a plasma etching apparatus; Positioning a Faraday cage such that the upper portion of the Faraday cage is disposed above the upper surface of the substrate, and maintaining an electrical connection between the Faraday cage and the substrate support, wherein the upper portion of the Faraday cage includes a plurality of discrete regions having open areas, through which the substrate can be plasma etched; and The substrate is plasma-etched to produce a plurality of surface relief diffraction gratings, wherein the plurality of surface relief diffraction gratings comprises at least two subsets having different angles and / or orientations; in: The Faraday cage is aligned with the aperture of the mask and the discrete region of the upper portion of the Faraday cage, such that the plurality of surface relief diffraction gratings are generated by plasma etching of the open region. and The discrete region includes at least two subsets, wherein different subsets have open regions with different angles and / or orientations relative to the upper surface of the substrate, such that plasma etching of the at least two subsets of the discrete region produces the at least two subsets of surface relief diffraction gratings with different angles and / or orientations.
2. The method of claim 1, wherein each of the discrete regions comprises a mesh or perforated structure.
3. The method according to claim 1 or claim 2, wherein the upper portion of the Faraday cage includes a cover portion.
4. The method of claim 3, wherein at least a subset of the discrete regions is housed in at least one walled housing suspended from the cover portion.
5. The method according to claim 1 or claim 2, wherein the Faraday cage further comprises a side edge portion that hangs downward from the upper portion.
6. The method of claim 5, wherein the step of positioning the Faraday cage includes bringing the side edge portion into contact with or adjacent to the substrate support.
7. The method of claim 1 or claim 2, wherein at least one discrete region comprises a zigzag arrangement of repeating structures, each repeating structure comprising a first and a second opposing inclined surface, wherein the first surface contains an open region and the second surface is solid.
8. The method of claim 1 or claim 2, wherein at least part of the electrical connection is maintained between the Faraday cage and the substrate support via a conductive flexible connection structure.
9. The method of claim 1 or claim 2, wherein an RF electrical signal is applied to the substrate support during plasma etching of the substrate.
10. The method of claim 1 or claim 2, wherein inductively coupled plasma (ICP) is used to perform the plasma etching.
11. The method according to claim 1 or claim 2, wherein the dielectric substrate is glass.
12. The method according to claim 1 or claim 2, wherein the dielectric substrate comprises silicon dioxide or borosilicate glass.
13. The method according to claim 1 or claim 2, wherein the Faraday cage is formed of aluminum.
14. The method according to claim 1 or claim 2, wherein the substrate support is an electrostatic chuck (ESC).
15. A plasma etching apparatus for etching a substrate to produce a plurality of surface relief diffraction gratings, the apparatus comprising: chamber; A substrate support, which is disposed within the cavity; A plasma generating device for generating plasma in the chamber; A Faraday cage comprising an upper portion capable of being disposed above an upper surface of a dielectric substrate positioned on a substrate support, wherein the upper portion comprises a plurality of discrete regions having open areas, the substrate being capable of being plasma etched through the open areas, the discrete regions comprising at least two subsets, wherein different subsets have open areas having different angles and / or orientations relative to the upper surface of the substrate support. and A controller configured to control the device to perform the method according to claim 1.
16. The plasma etching apparatus of claim 15, wherein each of the discrete regions comprises a mesh or perforated structure.
17. The plasma etching apparatus of claim 15 or claim 16, wherein the upper portion of the Faraday cage includes a cover portion.
18. The plasma etching apparatus of claim 17, wherein at least a subset of the discrete regions are each housed in a walled housing suspended from the cover portion.
19. The plasma etching apparatus of claim 15 or claim 16, wherein the Faraday cage further comprises a side edge portion that hangs downward from the upper portion.
20. The plasma etching apparatus of claim 15 or claim 16, wherein at least one discrete region comprises a serrated arrangement of repeating structures, each repeating structure comprising a first and a second opposing inclined surface, wherein the first surface contains an open region and the second surface is solid.
21. The plasma etching apparatus of claim 20, wherein the first and second opposing inclined surfaces are inclined at an angle of 90° or close to 90°.
22. The plasma etching apparatus of claim 15 or claim 16, wherein the upper portion of the Faraday cage has a main level, and subsets of discrete regions with different angles relative to the upper surface of the substrate support are raised to different degrees relative to the main level in order to reduce variations in ion path length associated with etching through different subsets of the discrete regions.
23. The plasma etching apparatus of claim 15 or claim 16, further comprising a lifting mechanism for lifting the Faraday cage relative to the substrate support and lowering the Faraday cage to contact or be adjacent to the substrate support.