Systems and methods for bidirectional thin film deposition to produce etching mask features with tailorable spacing and duty cycle

Abstract

A method is disclosed for creating a metasurface in a substrate material. A photoresist material layer (PRM) is formed on a surface of the substrate material having a plurality of spaced apart photoresist material features which define a pattern to be etched into the substrate material. Next a first additional quantity of material is deposited at a first angle, which is not normal to the upper surface, over a portion of the upper surface of the PRM. Next a second deposition operation is performed at a second angle to deposit a second additional quantity of material onto the PRM. The two quantities of additional material cooperate to form a new mask feature which is located between the spaced apart features. The substrate is then etched to create a pattern in the substrate in accordance with the photoresist material layer, with the pattern forming the metasurface.

Description

SYSTEMS AND METHODS FOR BIDIRECTIONAL THIN FILM DEPOSITION TO PRODUCE ETCHING MASK FEATURES WITH TAILORABLE SPACING AND DUTY CYCLECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a PCT International Application of United States Patent Application No. 63 / 702,922 filed on October 3, 2024. The entire disclosure of the above application is incorporated herein by reference.FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] This invention was made with Government support under Contract No. DE-AC52-07NA27344 awarded by the United States Department of Energy. The Government has certain rights in the invention.FIELD

[0003] The present disclosure relates to systems and methods for creating metasurfaces, and more particularly to systems and methods which use a bidirectional thin film deposition operation to create parallel, linear, etching mask features which can be readily tailored both in spacing (i.e., period) and in duty cycle (i.e., overall fill factor).BACKGROUND

[0004] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0005] Laser systems often utilize waveplates to control the polarization of the light, and, when used in conjunction with other optical elements, they can be used to control the transmitted laser power. However, conventional birefringent materials have some limitations, namely: (1 ) optical materials exhibiting natural birefringence often have a low laser-induced damage threshold, placing an upper limit on the laser power the system can safely use before the waveplate, and (2) these specialized materials exhibiting bulk birefringence tend to be pricier for shorter wavelengths.

[0006] One prior-art technique uses Glancing Angle Deposition (GLAD) to form tilted rods. While this technique can use more robust materials than those exhibiting bulk birefringence, a downside of this technique (and other techniques based on deposition) is that the deposited material, while having similar optical properties,typically has weaker laser damage durability due to defects that accumulate during the deposition process.

[0007] One known method that uses angled etching through metal nanoparticle masks addresses the durability and short-wavelengths limitations mentioned previously. However, the metasurface birefringence is linked to the depth of the metasurface, which can introduce limitations due to challenges associated with etching deep enough.

[0008] Another prior art method demonstrated the ability to replenish metal etching masks for continued etching and increased obtainable etching depths. This method used self-assembly of quasi-linear metallic features as an etching mask for fabrication of a grating-like structure for birefringent applications. However, the deviation of this structure from the ideal one-dimensional case decreased the birefringence per unit etch depth, which introduces challenges associated with etching deep enough for the desired polarization rotation.

[0009] Other optical components that are used frequently are gratings. Gratings enable the incident light to be resolved into the spectral components. These components are typically fabricated through either lithographic techniques or optical interference. For most lithographic fabrication processes, scaling the final product up to length scales used with high power lasers (e.g., optics of ~ meter length scales) becomes technologically challenging. For optical interference processes, scaling up to large apertures is not as challenging, but fabrication of the small periods demonstrated here is not possible with lasers available today.

[0010] Accordingly, there remain needs for the ability to form large area coverage of metal lines to function as etching masks, originating from a photoresist etch mask template, and which provides a metasurface having period length scales of the resultant metal linear etch mask which are tailorable, and also smaller than the initial photoresist mask, and where a duty cycle is larger than that of the initial photoresist mask, and also tailorable.SUMMARY

[0011] This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

[0012] In one aspect the present disclosure relates to a method for creating a metasurface in a substrate material. The method may comprise forming a photoresistmaterial layer on a surface of the substrate material having a plurality of spaced apart photoresist material features, the photoresist material layer defining a pattern to be etched into the substrate material. The method may further include performing a first deposition operation at a first angle relative to an upper surface of the photoresist material layer, the first angle being not normal to the upper surface, to deposit a first additional quantity of material over a portion of the upper surface of the photoresist material layer. The method may further include performing a second deposition operation at a second angle relative to the upper surface of the photoresist material layer, to deposit a second additional quantity of material onto the photoresist material layer. The first and second quantities of additional material cooperate to form a new mask feature for the photoresist material layer which is located between the spaced apart features. The method may further include etching the substrate to create a pattern in the substrate in accordance with the photoresist material layer, with the pattern forming the metasurface.

[0013] In another aspect of the present disclosure the first angle and the second angle are the same, relative to the upper surface of the photoresist material.

[0014] In another aspect of the present disclosure the first angle and the second angle are different, relative to the upper surface of the photoresist material.

[0015] In another aspect of the present disclosure the first deposition is performed with the substrate at a first orientation, and the second deposition is performed with the substrate at a second orientation different from the first orientation.

[0016] In another aspect of the present disclosure the second orientation is rotated 180 degrees from the first orientation, and the first and second angles are identical relative to the upper surface of the photoresist material.

[0017] In another aspect of the present disclosure the second orientation is rotated 180 degrees from the first orientation, and the first and second angles are different relative to the upper surface of the photoresist material.

[0018] In another aspect of the present disclosure the first additional quantity of material deposited and the second additional quantity of material deposited are the same quantities.

[0019] In another aspect of the present disclosure the first additional quantity of material deposited and the second additional quantity of material deposited are different quantities.

[0020] In another aspect of the present disclosure the first additional quantity of material differs from the second additional quantity of material in terms of material type.

[0021] In another aspect of the present disclosure the first additional quantity of material is the same as the second additional quantity of material in terms of material type.

[0022] In another aspect of the present disclosure the etching creates spaced apart features in the substrate having a common height.

[0023] In another aspect of the present disclosure the etching is performed using an etching beam directed normal to the upper surface of the substrate material.

[0024] In another aspect of the present disclosure at least one of the first additional quantity of material or the second additional quantity of material may comprise at least one of Au, Pt or Ni.

[0025] In still another aspect the present disclosure relates to a method for creating a mask to be used in forming a periodic metasurface in a substrate material. The method may comprise forming a photoresist material layer on a surface of the substrate material having a plurality of linear, spaced apart photoresist material features. The photoresist material layer defines a pattern to be etched into the surface of the substrate material. The method may also involve depositing a first additional quantity of material at a first angle relative to an upper surface of the photoresist material layer, the first angle being not normal to the upper surface. The first additional quantity of material is deposited over a portion of the surface of the photoresist material layer and also forms shadow areas where no portion of the first additional quantity of material is deposited. The method also includes altering an orientation of the substrate material within an X / Y plane, and then depositing a second additional material at a second angle relative to the upper surface of the photoresist material layer. The second additional quantity of material is deposited on portions of the substrate and portions of the first additional quantity of material. The first and second additional quantities of materials cooperate to form a new mask having a new mask feature located between an adjacent pair of the linear, spaced apart photoresist material features. The new mask feature alters a period of the linear, spaced apart photoresist material features.

[0026] In another aspect of the present disclosure the method further comprises performing an etching operation on the new mask to form the periodic metasurface.

[0027] In another aspect of the present disclosure, the operation of altering an orientation of the substrate material comprises rotating the substrate 180 degrees with the X / Y plane.

[0028] In another aspect of the present disclosure the first angle is equal to the second angle, relative to the surface of the substrate.

[0029] In another aspect of the present disclosure the first angle is different from the second angle, relative to the surface of the substrate.

[0030] In another aspect of the present disclosure at least one of the first additional quantity of material or the second additional quantity of material may comprise at least one of Au, or Pt, or Ni.

[0031] In another aspect of the present disclosure a method is disclosed for creating a metasurface in a substrate material. The method may comprise initially forming a photoresist material layer on a surface of the substrate material, which has a plurality of spaced apart photoresist material features with spacings forming a first period. The method may further include performing a first deposition operation at a first angle relative to an upper surface of the photoresist material layer. The first angle is not normal to the upper surface, such that a first additional quantity of material is deposited over first portions of the upper surface of the photoresist material layer. The method may further include performing a second deposition operation at a second angle relative to the upper surface of the photoresist material layer, to deposit a second additional quantity of material onto second portions of the photoresist material layer. The first and second quantities of additional material cooperate to form a new mask having new features between adjacent ones of the plurality of spaced apart photoresist material features. The method may also involve etching the new mask to create a metasurface in the substrate. The metasurface defines a pattern of linear features which have a second period different from the first period.

[0032] Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

[0034] Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

[0035] Figure 1 a is a plan view of a planar substrate with a plurality of parallel, linear, photoresist ridges formed thereon, prior to a metallic deposition process being performed thereon;

[0036] Figure 1 b is a side view of the structure of Figure 1 a after a first deposition operation has been performed at an angle 01 to coat the photoresist ridges with a metallic coating of height hi, where the deposition is performed at an angle which is not normal to an upper surface of the substrate, and which creates a shadow region which does not receive any metallic coating;

[0037] Figure 1 c is a side view of the structure of Figure 1 b after performing a second deposition operation at an angle of 02, which is the same as 01 , and where the substrate has been rotated 180 degrees prior to the second deposition operation being performed, which creates a metallic ridge intermediate the two pre-existing photoresist ridges, and where the intermediate metallic ridge has a height double that of hi (i.e. , hz) and is perfectly centered between the two pre-existing photoresist ridges;

[0038] Figure 2a is a plan view of a substrate with a planar substrate with a plurality of parallel, linear, photoresist ridges formed thereon, prior to a metallic deposition process being performed thereon;

[0039] Figure 2b shows the substrate after having performed a first deposition operation at a first angle 01 , which deposits a first metallic material coating over a portion of the substrate but which also creates a shadow region where no metallic material is deposited;

[0040] Figure 2c shows the substrate after having performed a second deposition operation to deposit metallic material at a second angle 02 which is different from 01 , and after the substrate has been rotated 180 degrees, which creates a ridge having a height of h2, but which is off center relative to the two adjacent photoresist ridges;

[0041] Figures 3a 1 -3a3 show an etching operation performed on the substrate and photoresist mask of Figure 1 c, illustrating how the channels are formed in the substrate as defined by the photoresist mask, with the photoresist mask having been completely removed in Figure 3a3;

[0042] Figures 3b 1 -3b3 show an etching operation performed on the substrate and photoresist mask of Figure 2c, illustrating how channels having non-uniform depths and different widths are formed in the substrate, and with the photoresist mask completely removed in Figure 3b3;

[0043] Figures 4a and 4b are illustrations of prior art operation where a conventional dry etching process is used to produce channels of uniform width and depth (Figure 4b) from the photoresist mask (shown in Figure 4a);

[0044] Figures 4c-4e show a methodology in accordance with the present disclosure where two deposition / etching sequences are performed to obtain a finally etch substrate with channels having significantly increased depths (Figure 4e) as compared to after only the first deposition / etching operation (Figure 4d);

[0045] Figures 5a-5c are scanning electron microscope (SEM) images of an initial photoresist layer formed on a substrate (Figure 5a), and after a platinum coating has been deposited on the photoresist material to form a finished mask (Figure 5b), and after an etching operation has been performed to etch the substrate using the finished mask, and where a remaining residual portion of the finished mask is left after the etching operation;

[0046] Figure 6 is a highly enlarged SEM image showing how continuing the etching operation after the etching mask has been fully etched through can produce controlled modulated height ridges / features, and / or ridge / feature tip sharpening if desired;

[0047] Figure 7 is a high level block diagram drawing of one example of a system for controlling, for example, movement within the X / Y plane of one or more of the substrate or a blocking plate to either eliminate a slight degree of variability in the period of the created photoresist ridges, or to introduce a controlled variability in the period of the created photoresist ridges;

[0048] Figure 8 is a high level flowchart of basic operations that may be performed in accordance with one example of the methodology of the present disclosure to create a metasurface;

[0049] Figures 9a and 9b are perspective and cross sectional scanning electron microscope (SEM) images, respectively, showing a prior art structure where photoresist ridges were created on a glass substrate using just a traditional photoresist process; and

[0050] Figures 10a and 10b are perspective and cross sectional SEM images, respectively, showing a new structure created using the teachings of the present disclosure, which enable new, additional features to be created at the very top of each of a plurality of photoresist ridges.DETAILED DESCRIPTION

[0051] Example embodiments will now be described more fully with reference to the accompanying drawings.

[0052] The present disclosure, in various embodiments and implementations, provides methods for forming large-area coverage of metal lines to function as etching masks, originating from a photoresist etch mask template. A significant advantage is that the period length scales of the resultant metal linear etch mask are smaller than the initial photoresist mask, and duty cycle may be even larger than that of the initial photoresist mask. The methods described herein in some implementations are based on bidirectional thin film deposition that uses shadowing from an initial photoresist mask to generate additional periodic etch mask features. As the spacing between resultant adjacent etched features is, by definition, smaller than the initial photoresist mask, this technique is limited only by the spacing of the initial photoresist mask and the number of times the user cares to repeat the process. Not only can this technique be used to create new etch mask features, but the new features increase the duty cycle of the resultant etched structure, yielding another advantage.

[0053] Referring now to Figure 1 , the methods of the present disclosure involve forming nanoscale metal lines using the following described process. As shown in Figure 1 a, initially a substrate 10 is provided which has a photoresist material deposited thereon forming upstanding photoresist features 12. In this example the features 12 form ridges, and hereinafter will be referred to simply as “photoresist ridges 12”.

[0054] The photoresist ridges 12 may comprise a pattern which was previously produced using any suitable method, for example and without limitation, through a conventional photoresist etching mask or periodic etch mask self-imaging, i.e., displacement Talbot lithography. An enlarged cross-section of a portion of the substrate 10 with the photoresist ridges 12 thereon is also illustrated in Figure 1 a.

[0055] Figure 1 b shows a deposition operation to deposit a first quantity of additional material 14. The deposited first quantity of additional material 14 could be, without limitation, a few nanometers or tens of nanometers of a material, for example a metal. In some instances the metal may be, for example and without limitation, Au, Pt, or Ni. This first quantity of additional material 14 is deposited at a first angle 91 with respect to the substrate 10 surface normal, where the projection of the deposition angle 01 to the substrate surface is not parallel to the walls 12a of the existing photoresist ridges 12. In doing this, the photoresist ridge 12 casts a shadowed region 16 where noadditional material 14 is deposited between the adjacent pair of photoresist ridges 12. A layer 14a of the additional material 14 having a thickness “hr is now present between the pair of adjacent photoresist ridges 12, but the layer 14a does not extend fully between the adjacent pair of photoresist ridges 14 because of the shadow region 16 that was created during the deposition of the additional material 14.

[0056] The substrate 10 may then be rotated about its original position (i.e., within the X / Y plane) before performing a further deposition operation. Figure 1 c shows the substrate having been rotated by 180° within the X / Y plane. However, this is but one example and other rotation angles may be advantageous for some applications, and the present disclosure is therefore not limited to any specific rotation angle. In this example, however, with respect to the rotated substrate 10, when a further deposition operation is performed at a deposition angle 02 to deposit a second quantity of the additional material 14, more of the material is deposited making an angle with respect to the substrate 10 surface normal. The second quantity of additional material 14 deposited does not need to be deposited such that the material thickness and deposition angle are exactly the same as the thickness and deposition angle when depositing the first quantity of the additional material 14 as described in connection with Figure 1 b. This second deposition, when performed at angle 02 to deposit the second quantity of additional material 14, forms a shadow 18 in the opposing direction relative to the shadow 16 shown in Figure 1 b, while producing a planar coating 14b adjacent the rightmost photoresist ridge 12. This planar coating 14b of deposited material immediately adjacent to the rightmost photoresist ridge 12 has a thickness equal to the deposited material thickness shown in Figure 1 b (i.e., equal to hi). This second deposition operation advantageously creates a central 'overlap' region that creates a central ridge 20 of deposited material having a thickness equal to the sum of the two material deposition processes, that is two hi thicknesses, or “h2”. As depicted in Figure 1 c, appropriate selections of the deposition angles and deposited thicknesses yield the new deposited material ridge 20 in between the photoresist ridges 12. The new material ridge 20 is a feature that cuts the initial period (i.e., the spacing of photoresist ridges 12) in half yet preserves the feature width of coated ridges 12 and the new material ridge 20. By this it is meant that the width of the new material ridge 20, in this example, is the same as the width of the photoresist ridges 12 when they are coated with the first and second quantities of additional material 14.

[0057] Referring now to Figures 2a, 2b and 2c, it can be seen how different selections of deposited material thicknesses and / or deposition angles can create a custom period and / or duty cycle for the photoresist features 12. Accordingly, it should be understood from Figures 2a-2c that a newly created etching mask 22 (Figure 2c) has an intermediate ridge 20’ feature which does not need to be centered between the preexisting photoresist ridges 12. Still further, the overall material heights to the immediate left and right of the intermediate ridge 20’ feature do not need to be the same. Any suitable, conventional etching operation can be used to transfer the newly deposited intermediate ridge 20’, in addition to the initial photoresist mask features, to the underlying substrate 10 through etching to create the new etching mask 22. For both cases shown in Figures 1 and 2, etching through some of the deposited first and / or first and second quantities of additional material 14 must occur before the underlying substrate 10 is exposed to etching.

[0058] Figures 3a1 -3a3 depict directional dry etching of the period halving structure with the etching beam 30 directed normal to the substrate 10, to produce a new metasurface 50, as shown in Figure 3a1 . Figure 3a2 shows the channels 32 etched into the substrate 10 with an hi thickness of the additional material 14 having been removed during the etching operation. Figure 3a3 shows the mask 12 and the remaining hi thickness of additional material 14 fully removed, leaving just the fully etched substrate 10. The channels 32 define parallel, linear, upstanding ridges 34. The ridges 34 have the same width as the photoresist ridges of the new mask 22 after the photoresist ridges 12 are coated with an hi thickness layer of the additional material 14, and the intermediate ridge 20 after the ridges 12 have been coated with one or more quantities of the additional material 14. The intermediate ridge 20, once the etching process is complete, forms the center ridge 34 in Figure 3a3, which has the same thickness as the other ridges 34.

[0059] Figures 3b 1 -3b3 show a new metasurface 60 (Figure 3b3) created from etching using the etch mask 22’ shown in Figure 2c. In this example the etching operation produces channels 38 and 40 which define ridges 42, 44 and 46. In this example, however, the finished metasurface 60 has ridge 44 which defines a different feature width, and which is located off-center between the photoresist ridges 42 and 46, as shown in Figure 3b3. The left-facing and right-facing gaps differ, as indicated by the different widths of the channels 38 and 40. Also, the width of the ridges 42, 44 and 46 are not uniform; ridge 44 can be seen to be wider than ridges 42 and 46. Ridge 44 canalso be thinner than ridges 42 and 46. Thus, both the width and the period of the ridges 42, 44 and 46 can tailored independent of one another.

[0060] In Figures 3b1 -3b3, usage of different material deposition thicknesses also enables different obtainable etch depths by virtue of etching through the deposited additional material 14 prior to etching the underlying substrate 10. If necessary, a mask replenishment process can be used to build up a subsequent etching mask atop the metasurface 60 to enable repeated etching of the substrate 10. In doing this, the limitations associated with etching through sacrificial etching masks (that may erode quickly) are overcome. This approach can be repeated to further increase the density of the ridges 34 or 42 / 44 / 46 in the final metastructure. As this process advantageously makes use of the shadowing deposition technique described in connection with Figures 1 and 2, iterations beyond the first iteration can be used to introduce a modulation in the etched feature (i.e., ridge) height. By “modulation”, it is meant a predetermined, highly controlled variation in the overall height of ridges 34 and / or ridges 42 / 44 / 46. However, this modulated height can be controlled and is expected to be a very small fraction of the application-required feature height.

[0061] Depiction of two iterations of this process is shown in Figures 4c-4e. Initially, however, Figures 4a and 4b depict a single iteration that etches the mask using a conventional dry etch process to transfer the pattern of the photoresist ridges 80, present initially on top of a substrate 82 (e.g., silicon) into the substrate. Channels 84 help define the ridges 80 at the conclusion of a single iteration of the deposition / etch operations.

[0062] As shown in Figures 4c-4e, for the case of photoresist feature width preservation and period halving, two iterations of the deposition / etching operations yield a 3x increase in the duty cycle and a period that is one quarter of the initial period, as visible in the new metasurface 100 having ridges 90. For the cases of preserving the initial resist mask dimensions on the new features, see Figures 3a1 -3a3 and Figures 4c- 4e, the duty cycle, which may also be understood as the “fill factor” (i.e., area percentage of the substrate 10 being covered by the photoresist ridges 14) of the initial resist mask must be smaller than 100 / (n+1 ) %, where 'n' is the number of intended iterations. So for the single iteration shown in Figures 3a1 -3a3, the initial resist duty cycle must be smaller than 50%. For the 2-step process shown in Figures 4c-4e, the initial resist duty cycle must be smaller than 33%.

[0063] Those skilled in the art can appreciate that there is a correlation between the photoresist period, height, and thin film deposition angle. Thus, for a given photoresist mask height and period, there is a range of acceptable deposition angles. Appropriate selection of the deposition angles can be used to significantly increase the duty cycle (i.e., a simple function of geometry). This methodology is not bound by the current lithographic techniques; as technology evolves to make finer etching mask features, this methodology can be used to improve the future 'state-of-the-art' technology.

[0064] With brief reference to Figures 5a-5c, scanning electron microscope (SEM) images of a grating-like metastructure 124 is shown in Figure 5c. The initial photoresist mask 120 (used here for shadowing) is shown in Figure 5a on substrate 1 18. Figure 5b shows the photoresist mask 120 after having been coated with a coating of platinum, to produce a coated photoresist mask 122. Figure 5c shows the resultant etched grating-like metastructure 124 composed of substrate features underneath the residual remaining photoresist mask 122. If desired, etching beyond the point of etch mask depletion for the new etching mask features may result in (1 ) modulated height features, and / or (2) ridge (or feature) tip sharpening. This is shown in the metasurface 200 of Figure 6, where ridges 202 having significantly sharpened tips. Tapering of the features into the layer is a known technique to yield anti-reflectivity. This methodology is scalable, limited only by the aperture of the initial photoresist mask, which can be done on meter length-scales using today's technology.

[0065] Figure 7 illustrates one example of a system 250 for controlling movement of one or more of a movable stage 252 and / or a blocking plate 254 to either eliminate any minute variability in the period between photoresist ridges 12 if a large substrate is being acted on, or to introduce a controlled degree of variability in the period. In this example a deposition subsystem is indicated by reference numeral 256 for depositing the additional quantities of material 14 onto the substrate 10. A motion control subsystem (e.g., linear DC stepper motors, linear actuators, etc.) 258 may be used to controllably move the movable stage, and thus the substrate 10, within the X / Y plane. The motion control subsystem 258 may also be used to implement tilting to generate tunability of the period 44 in Figure 3b3 across substrate 10. Similarly, a separate motion control subsystem 260 may be used to control movement of the blocking plate 254 within the X / Y plane to controlled block a portion of the additional material being deposited from the deposition subsystem 256. An electronic control system 262 (e.g., computer,electronic controller, etc.) may be used to control one or both of the motion control subsystem 258 and 260.

[0066] Referring briefly to Figure 8, a flowchart 300 is shown illustrating one example of a method in accordance with the present disclosure. Initially at operation 302 a substrate is selected (i.e., a planar material piece of a desired material, for example silicon). At operation 304 an initial photoresist material mask is created through any conventional means (e.g., interference lithography). At operation 306 a first deposition operation may be performed to deposit a first additional quantity of metallic material on the photoresist material mask, from a first deposition angle 01 . At operation 308 a second deposition operation may be performed to deposit a second quantity of the additional material onto the photoresist mask at an angle 92 which may be different from angle 01 . In some instances 02 may differ significantly from 01 , but in the great majority of cases will be less than 180 degrees, and in any event will be selected to meet the needs of a particular application. Alternatively, the substrate may instead be rotated a desired angular amount (i.e., within the X / Y plane), while the deposition angle remains the same, to achieve the same shadowing effect as described herein. Also, the material deposited during the second deposition operation may differ from that deposited in the first deposition, and the quantity of material used in the second deposition may also differ from what was used in the first deposition operation.

[0067] At operation 310 an etching operation may be performed to etch a desired pattern into the substrate in accordance with the photoresist and / or deposited material mask. At operation 312 a check is made if the etching of the substrate is complete. If not, then an additional deposition may be performed to deposit still another quantity of additional material onto the photoresist mask, as indicated at operation 314. Etching operation 310 may then be repeated. When the check at operation 312 indicates that the etching is fully completed, then any remaining residual photoresist and deposited masking materials may be removed, as indicated at operation 316, and the process is complete.

[0068] Applications of the systems and methods described herein are expected to include gratings for short wavelengths (i.e., ultraviolet), and metasurfaces that exhibit birefringence. Additional applications are expected to involve ultra-thin waveplate optics, and environmentally stable and laser damage durable metasurfaces for emphasis on short wavelength lasers. Still further applications are expected to involve large area gratings for use with short wavelength applications, or at conventional ultraviolet, visible,and near infrared wavelengths. The systems and methods disclosed herein enable formation of waveplates from durable optical materials, such as but not limited to, fused silica, that do not natively exhibit bulk-state optical birefringence.

[0069] Referring to Figures 9a, 9b, 10a and 10b, still another important feature of the present disclosure will be discussed, which is the ability to form unique geometrical features at just the tops, or even at areas closely adjacent the tops, of each of the phororesist ridges. Figures 9a and 9b show a structure 400 having photoresist ridges 402 created on a fused silica substrate 404 using optical interference lithography. Figures 10a and 10b show a new structure 500 having ridges 502 formed on a fused silica substrate 504. However, with the structure 500, each of the ridges 502 has an enlarged, circumferential feature 502a formed at its uppermost portion. The circumferential feature 502a in this example, is circumferential, although it need not be. Depending on the deposition angles used, as well as the thickness of the deposition layer being deposited and the speed of movement of the deposition component (or the substrate), other shapes (e.g., pyramidal, oval, etc.) may potentially be formed. The circumferential feature 502a (or other shaped feature) may enable further unique etching masks to be created which enable an even greater degree of control over the features formed in the substrate during a subsequently performed etching process.

[0070] In some embodiments, the deposition angles used to form the circumferential features 502a may be between 10 degrees to 85 degrees, and it will be appreciated that the speed of movement of the of the deposition component (or alternatively the substrate) within the X / Y plane may vary while the deposition action is being performed, which will affect the thickness of the deposited material at any point along the upper portions of the ridges 502. These variables will be important factors in achieving the specific shape or type of feature at the top of each ridge 502. Thus, it will be appreciated that movement will permit spatial patterning, and modification of the deposition angle in real time will allow even more control over the deposited geometry. And as per Figure 7, the use of a blocking plate would allow still further additional control over creation of the size and / or shape of the features.

[0071] The features 502a formed at the top of each ridge 502 may provide significant additional benefits. One such benefit is the ability to utilize materials with higher etch selectivity than the underlying materials. Still another important advantage is the increased control over the duty cycle (DC), which is also sometimes referred to as the “fill factor” (FF). The approaches described herein, and particularly that shown inFigures 10a and 10b, allow the duty cycle to be pushed to high values that may be challenging to obtain with scalable conventional photoresist approaches.

[0072] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

[0073] Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

[0074] The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

[0075] When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layersmay be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items. As used herein, the term “about”, when used immediately previous to a specific recited value, denotes the specific recited value as well as all values, inclusive, from + / - 10% of the specific recited value.

[0076] Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

[0077] Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

Claims

AMENDED CLAIMS received by the International Bureau on 26 Feb. 2026 (26.02.2026)CLAIMSWhat is claimed is:

1. A method for creating a metasurface in a substrate material, the method comprising: forming a photoresist material layer directly on a surface of the substrate material having a plurality of spaced apart photoresist material features, the photoresist material layer defining forming an initial mask which defines a pattern to be etched into the substrate material; performing a first deposition operation at a first angle relative to an upper surface of the photoresist material layer, the first angle being not normal to the upper surface, to deposit a first additional quantity of material over a portion of the upper surface of the photoresist material layer; performing a second deposition operation at a second angle relative to the upper surface of the photoresist material layer, to deposit a second additional quantity of material onto the photoresist material layer, and where the first and second quantities of additional material cooperate to form a new mask feature for the photoresist material layer which is located between the spaced apart features of the initial mask; and etching the substrate to create a new pattern in the substrate in accordance with the both the initial mask of the photoresist material layer and the new mask feature, with the new pattern forming the metasurface.

2. The method of claim 1 , wherein the first angle and the second angle are the same, relative to the upper surface of the photoresist material.

3. The method of claim 1 , wherein the first angle and the second angle are different, relative to the upper surface of the photoresist material.

4. The method of claim 1 , wherein the first deposition is performed with the substrate at a first orientation, and the second deposition is performed with the substrate at a second orientation different from the first orientation.

5. The method of claim 4, wherein the second orientation is rotated 180 degrees from the first orientation, and the first and second angles are identical relative to the upper surface of the photoresist material.

6. The method of claim 4, wherein the second orientation is rotated 180 degrees from the first orientation, and the first and second angles are different relative to the upper surface of the photoresist material.

7. The method of claim 1 , wherein the first additional quantity of material deposited and the second additional quantity of material deposited are the same quantities.

8. The method of claim 1 , wherein the first additional quantity of material deposited and the second additional quantity of material deposited are different quantities.

9. The method of claim 1 , wherein the first additional quantity of material differs from the second additional quantity of material in terms of material type.

10. The method of claim 1 , wherein the first additional quantity of material is the same as the second additional quantity of material in terms of material type.1 1 . The method of claim 1 , wherein the etching creates spaced apart features in the substrate having a common height.

12. The method of claim 1 , wherein the etching is performed using an etching beam directed normal to the upper surface of the substrate material.

13. The method of claim 1 , wherein at least one of the first additional quantity of material or the second additional quantity of material comprises at least one of:Au;Pt; orNi.

14. A method for creating a mask to be used in forming a periodic metasurface in a substrate material, the method comprising: forming a photoresist material layer directly on a surface of the substrate material having a plurality of linear, spaced apart photoresist material features, the photoresist material layer defining an initial mask which defines a pattern to be etched into the surface of the substrate material; depositing a first additional quantity of material at a first angle relative to an upper surface of the photoresist material layer, the first angle being not normal to the upper surface, the first additional quantity of material being deposited over a portion of the surface of the photoresist material layer and forming shadow areas where no portion of the first additional quantity of material is deposited; altering an orientation of the substrate material within an X / Y plane; depositing a second additional material at a second angle relative to the upper surface of the photoresist material layer, the second additional quantity of material being deposited on portions of the substrate and portions of the first additional quantity of material; the first and second additional quantities of materials cooperating to form a new mask having a new mask feature located between an adjacent pair of the linear, spaced apart photoresist material features of the initial mask, the new mask feature modifying the initial mask and altering a period of the linear, spaced apart photoresist material features of the initial mask.

15. The method of claim 14, further comprising performing an etching operation on the new mask to form16. The method of claim 14, wherein altering an orientation of the substrate material comprises rotating the substrate 180 degrees with the X / Y plane.

17. The method of claim 14, wherein the first angle is equal to the second angle, relative to the surface of the substrate.

18. The method of claim 14, wherein the first angle is different from the second angle, relative to the surface of the substrate.

19. The method of claim 14, wherein at least one of the first additional quantity of material or the second additional quantity of material comprises at least one of:Au; orPt; orNi.

20. A method for creating a metasurface in a substrate material, the method comprising: creating an initial mask by forming a photoresist material layer directly on a surface of the substrate material having a plurality of spaced apart photoresist material features with spacings forming a first period; performing a first deposition operation at a first angle relative to an upper surface of the photoresist material layer, the first angle being not normal to the upper surface at the start of the first deposition operation, wherein the first angle may change while the first deposition operation is carried out, to deposit a first additional quantity of material having a first thickness over first portions of the upper surface of the photoresist material layer; performing a second deposition operation at a second angle not normal to the upper surface of the photoresist material layer at the start of the second deposition operation, wherein the second angle may change while the second deposition operation is carried out, to deposit c :o second portions of the photoresist material layer, ano wnere me nrsi ano secono quantities of additionalmaterial cooperate to form features between adjacent ones of the plurality of spaced apart photoresist material features, which modifies the initial mask to form a new mask; and etching the new mask to create a metasurface in the substrate, with the metasurface defining a pattern of linear features defining a second period different from the first period.

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