WO2025221665A1 - Methods for forming staircase and blazed grating structures using nanoimprint lithography - Google Patents

Abstract

Embodiments described herein provide for methods of forming optical device structures. The methods relate to forming staircase or blazed angle grating structures using nanoimprint lithography (NIL) in combination with other forming techniques. In certain embodiment, the methods provide for forming staircase or blazed angle grating structures for optical devices without the need for multiple repeated lithographic patterning and etch processes.

Description

METHODS FOR FORMING STAIRCASE AND BLAZED GRATING STRUCTURES USING NANOIMPRINT LITHOGRAPHY

BACKGROUND

Field

[0001] Embodiments of the present disclosure generally relate to optical devices for augmented, virtual, and mixed reality. More specifically, embodiments described herein provide for forming blazed and staircase optical device structures.

Description of the Related Art

[0002] Virtual reality is generally considered to be a computer generated simulated environment in which a user has an apparent physical presence. A virtual reality experience can be generated in 3D and viewed with a head-mounted display (HMD), such as glasses or other wearable display devices that have near-eye display panels as lenses to display a virtual reality environment that replaces an actual environment.

[0003] Augmented reality, however, enables an experience in which a user can still see through the display lenses of the glasses or other HMD device to view the surrounding environment, yet also see images of virtual objects that are generated for display and appear as part of the environment. Augmented reality can include any type of input, such as audio and haptic inputs, as well as virtual images, graphics, and video that enhances or augments the environment that the user experiences. As an emerging technology, there are many challenges and design constraints with augmented reality.

[0004] One such challenge is displaying a virtual image overlaid on an ambient environment. Optical devices including waveguide combiners, such as augmented reality waveguide combiners, and flat optical devices, such as metasurfaces, are used to assist in overlaying images. Generated light is propagated through an optical device until the light exits the optical device and is overlaid on the ambient environment. Optical devices may require staircase stepped structures or structures having blazed angles relative to the surface of the optical device substrate. Conventionally, fabricating such staircase or blazed angle optical device structures requires multiple lithographic patterning and etch steps. The multiple lithographic patterning and etch steps increase fabrication time and increase cost. [0005] Therefore, there is a need for improved methods of manufacturing augmented reality display devices.

SUMMARY

[0006] The present disclosure generally relates to a method and apparatus for use in a display apparatus or in other applications. More specifically, the disclosure relates to forming staircase or blazed angle grating structure for use in a waveguide using nanoimprint lithography (NIL) in combination with other forming techniques. The method herein may also form a waveguide structure that is used as part of a master mold for forming master stamps used in nanoimprint lithography.

[0007] In one embodiment, a method for forming an optical device is provided. The method includes fabricating a master mold having a grating pattern formed therein and forming a stamp using the master mold. The stamp includes an inverse grating pattern corresponding to an inverse of the grating pattern of the master mold. The method also includes imprinting the stamp into a nanoimprint resist disposed on a device layer, curing the nanoimprint resist, and releasing the stamp from the nanoimprint resist to form a patterned nanoimprint resist. After the stamp is released, a plurality of staircase grating structures is formed in the device layer by performing an etch process using the patterned nanoimprint resist as an etch mask.

[0008] In one embodiment, a method for forming a master mold for use in a nanoimprint lithography process is provided. The method includes disposing a mold resin on a substrate, forming a hardmask over the mold resin, and patterning the hardmask to define selected regions for patterning the mold resin. Then the mold resin is patterned with a grating pattern using the hardmask, the grating pattern comprising a plurality of grating structures in the selected regions of the mold resin. The method also includes forming a gray-tone resist over the patterned hardmask and the plurality of grating structures in the selected regions of the mold resin, patterning the gray-tone resist using gray-tone lithography to form a gray-tone pattern in the graytone resist; and performing a transfer etch process to vary a grating depth of one or more of the plurality of grating structures in the master mold.

[0009] In one embodiment, a method for forming an optical device is provided. The method includes providing a master mold having a plurality of staircase grating structures formed therein in which each of the plurality of staircase grating structures comprises a bottom surface disposed between a side wall and a stepped surface of each of the plurality of staircase grating structures, and a bottom critical dimension corresponding to a width of the bottom surface configured for contacting and molding a stamp. The method also includes depositing a coating over the master mold and the plurality of the staircase grating structure to form a coated master mold, forming a stamp with the coated master mold, imprinting the stamp into a nanoimprint resist disposed on a device layer, and curing the nanoimprint resist and releasing the stamp from the nanoimprint resist to form a patterned nanoimprint resist. Lastly, the method includes performing an etch process using the patterned nanoimprint resist as an etch mask to form a plurality of staircase grating structures in the device layer, wherein a bottom critical dimension of each of the plurality of staircase grating structures in the device layer is less than the width of the bottom surface of the master mold.

[0010] In one embodiment, a method for forming an optical device is provided. The method includes fabricating a master mold having a grating pattern formed therein and forming a stamp using the master mold. The stamp formed includes an inverse grating pattern corresponding to an inverse of the grating pattern of the master mold. The method also includes imprinting the stamp into a nanoimprint resist disposed on a device layer, curing the nanoimprint resist and releasing the stamp from the patterned resist to form a patterned nanoimprint resist, and performing an etch process using the patterned nanoimprint resist as an etch mask to form a plurality of blazed grating structures in the device layer.

[0011] In one embodiment, a method for forming an optical device is provided. The method includes forming a hardmask on a device layer disposed on a substrate, patterning the hardmask to define selected regions of the device layer for patterning, and patterning the device layer to form a negative grating pattern in the selected regions of the device layer. The negative grating pattern formed in the device layer includes a plurality of blazed grating structures. The method also includes forming a gray-tone resist over the patterned hardmask and the plurality of blazed grating structures, patterning the gray-tone resist using gray-tone lithography to form a graytone pattern in the gray-tone resist, and performing a transfer etch process to vary the a depth of one or more of the plurality of blazed grating structures in the device layer. [0012] In one embodiment, a method for forming an optical device is provided. The method includes etching one or more structures extending from a top surface of an imprintable layer having regions of varying thicknesses and imprinting a stamp having an inverse grating pattern comprising a plurality of blazed grating structures in one or more of the regions of the imprintable layer. The method also includes curing the imprintable layer and releasing the stamp from the imprintable layer to form a patterned layer having a plurality of blazed grating structures with varying grating depths. A grating depth of each of the plurality of blazed grating structures of the patterned layer corresponds with a thickness of the respective region of the imprintable layer in which each of the plurality of blazed grating structures is formed in.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments and are therefore not to be considered limiting of its scope, and may admit to other equally effective embodiments.

[0014] FIGs. 1 A and 1 B are schematic, cross-sectional views of an optical device having a plurality of staircase grating structures, according to certain embodiments;

[0015] FIGs. 1 C and 1 D are schematic, cross-sectional views of an optical device having a plurality of blazed grating structures, according to certain embodiments;

[0016] FIG. 2 is a perspective, frontal view of a waveguide combiner, according to certain embodiments;

[0017] FIGs. 3A - 3H are schematic, cross-sectional views of various stages of manufacturing an optical device according to the method of FIG. 4, according to certain embodiments;

[0018] FIG. 4 is a flow diagram of a method for forming an optical device, according to certain embodiments; [0019] FIG. 5 is a flow diagram of a method for forming a master mold and a stamp for nanoimprint lithography, according to certain embodiments;

[0020] FIGs. 6A - 60 are schematic, cross-sectional views of various stages of manufacturing the master mold according to the method of FIG. 5, according to certain embodiments;

[0021] FIG. 7 is a flow diagram of a method for forming a master mold for nanoimprint lithography, according to certain embodiments;

[0022] FIGs. 8A - 8G are schematic, cross-sectional views of various stages of manufacturing the master mold according to the method of FIG. 7, according to certain embodiments;

[0023] FIG. 9 is a flow diagram of a method for forming a master mold for nanoimprint lithography, according to certain embodiments;

[0024] FIGs. 10A - 10D are schematic, cross-sectional views of various stages of manufacturing the master mold according to the method of FIG. 9, according to certain embodiments;

[0025] FIG. 11 is a flow diagram of a method for forming an optical device, according to certain embodiments;

[0026] FIGs. 12A - 12F are schematic, cross-sectional views of various stages of manufacturing an optical device according to the method of FIG. 11 , according to certain embodiments;

[0027] FIG. 13 is a flow diagram of a method for forming an optical device, according to certain embodiments; and

[0028] FIGs. 14A - 14C are schematic, cross-sectional views of various stages of manufacturing an optical device according to the method of FIG. 13, according to certain embodiments.

[0029] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

DETAILED DESCRIPTION

[0030] Embodiments of the present invention generally relate to optical devices for augmented, virtual, and mixed reality. More specifically, embodiments described herein provide methods and apparatus for manufacturing staircase or blazed optical device structures on a substrate using nanoimprint lithography (NIL). In some embodiments, the method utilizes NIL in combination with other forming techniques, such as a dry etch process or gray-tone lithography, to form the staircase or blazed optical device structures without the need for multiple repeated lithographic patterning and etch processes. The methods and implementations discussed herein can therefore provide a means for fabricating staircase optical device structures and blazed optical device structures with high throughput while also reducing costs.

[0031] NIL generally includes imprinting a surface pattern of a master stamp into a film by mechanical contact and three-dimensional material displacement. In some embodiments, the imprinting process can be performed by shaping a liquid followed by a curing process for hardening, by variation of the thermomechanical properties of a film by heating and cooling, or by any other kind of shaping process using the difference in hardness of a mold and a moldable material. The local thickness contrast of the resulting imprinted film may then be used as a means to pattern an underlying device layer or substrate at the wafer level by standard pattern transfer methods.

[0032] Optical device waveguides including waveguide combiners include a plurality of diffraction gratings. As discussed herein, a diffraction grating can be referred to as a “grating” or “gratings” and can include a plurality of staircase optical device structures or a plurality of blazed optical device structures formed from a material layer disposed on a substrate. Each of the plurality of staircase optical device structures includes a plurality of steps each with a step height and step width. In some embodiments, the steps within a grating can be uniform in step width or vary in step width between steps. In some embodiments, each of the staircase optical device structures can be uniform in one or more step height, step width, grating width, or grating height with respect to a normal plane of the substrate. In another example, each of the staircase optical device structures can differ in one or more step height, step width, grating width, or grating height with respect to a normal plane of the substrate. Each of the plurality of blazed optical device structures include a blazed angle, a grating height, and a grating width. In some embodiments, each of the optical device structures can be uniform in one or more blazed angle, grating height, or grating width with respect to a normal plane of the substrate. In some embodiments, each of the blazed optical device structures can differ in one or more blazed angle, grating height, and grating width with respect to a normal plane of the substrate.

[0033] As discussed in various embodiments herein, the present disclosure provides methods for using NIL to form optical device structures including a plurality of staircase optical device structures or a plurality of blazed optical device structures. In some embodiments, the present disclosure provides for using NIL in combination with other forming techniques, such as lithography patterning and etch processes to form the optical device structures. The optical device structures may be formed from a material layer disposed on a substrate. The method includes imprinting a stamp into a nanoimprint resist disposed on material layers of substrates. The imprinting stamp has an optical device pattern corresponding to an inverse of the staircase optical device structure or the blazed optical device structure to be formed on the substrate. In some embodiments, the method provides for forming optical device structures with a constant duty cycle (DC) (i.e. the ratio of the step height to the step width in staircase optical device structures, or the ratio of the grating height to the grating width in blazed optical device structures). In certain embodiments, optical device structure designs with a wide range of duty cycles are desirable. As such, in some embodiments, the method provides for forming optical device structures with varying duty cycles using a single imprint operation.

[0034] FIGs. 1 A-1 D illustrate schematic, cross-sectional views of an optical device having a plurality of grating structures formed on a substrate, according to certain embodiments of the present disclosure. In certain embodiments, the plurality of grating structures depicted in FIGs. 1A-1 D may be formed for an optical device such as the optical device 200 depicted in FIG. 2.

[0035] FIG. 1A illustrates a schematic, cross-sectional view of an optical device 100 having a plurality of staircase grating structures 102 formed on a substrate 104, according to certain embodiments of the present disclosure. In some embodiments, the plurality of staircase grating structures 102 define an input coupling region of a waveguide combiner. The plurality of staircase grating structures 102 are formed in a device layer 106 disposed on the substrate 104. In some embodiments, the substrate 104 can be selected to transmit a suitable amount of light of a desired wavelength or wavelength range, such as one or more wavelengths from about 100 to about 3000 nanometers. The substrate 104 can be configured such that the substrate 104 transmits greater than or equal to about 50% to about 100% of an I R to UV region of the light spectrum. The substrate 104 may be formed from any suitable material, provided that the substrate 104 can adequately transmit light in a desired wavelength or wavelength range and can serve as an adequate support for the staircase grating structures 102 (when the staircase grating structures 102 are formed in the device layer 106) described herein. Substrate selection may include substrates of any suitable material, including, but not limited to, amorphous dielectrics, non- amorphous dielectrics, crystalline dielectrics, silicon oxide, polymers, and combinations thereof. The substrate 104 includes a transparent material. Suitable examples may include an oxide, sulfide, phosphide, telluride or combinations thereof. In one example, the substrate 104 includes silicon (Si), silicon dioxide (SiC>2), germanium (Ge), silicon germanium (SiGe), sapphire, and high-index transparent materials such as high-refractive-index glass.

[0036] As shown in FIG. 1A, each of the staircase grating structures 102 includes a step surface 132 having a plurality of steps 134, a sidewall 136, a top surface 138, a bottom surface 140 between the sidewall 136 and the plurality of steps 134, a grating depth “h”, a top width “Tw”, a step width “Sw”, a step number “Ns”, a bottom width “Bw”, a step depth “SD”, and a grating period A. The grating depth h corresponds to the height of the sidewall 136 and in some embodiments can be from about 10 nanometers to about 500 nanometers; for example, from about 80 nanometers to about 150 nanometers; or from about 20 nanometers to about 70 nanometers. In some embodiments, the number of steps Ns of the step surface 132 includes between 2 steps and about 100 steps; such as about 3 steps and about 10 steps. In one embodiment, the step surface 132 includes six steps, as illustrated. In one embodiment, the step surface 132 forms a staircase angle “S.” The staircase angle S can be from about 40 degrees to about 80 degrees relative to an axis perpendicular to the bottom surface 140, for example, from about 60 degrees to about 70 degrees from perpendicular.

[0037] A top duty cycle of each of the staircase grating structures 102 is defined as ^{top Wldth Tw} . The top duty cycle can be from about 0% to about 40%, for example, grating period from about 15% to about 35%. In one embodiment, the grating period can be from about 200 nanometers to about 400 nanometers; for example, from about 230 nanometers and about 280 nanometers; or from about 300 nanometers and about 370 nanometers. A bottom duty cycle is defined as ^{bottom Wldth Bw} The bottom duty grating period cycle can be from about 60% to about 100%, for example, from about 70% to about 90%.

[0038] In one embodiment, which can be combined with other embodiments described herein, the step depth SD corresponds to the distance between a top surface of adjacent steps 134 in a staircase grating structure 120. In one embodiment, which can be combined with other embodiments described herein, the step depth SD of two or more steps 134 are different. In another embodiment, which can be combined with other embodiments described herein, the step depth SD of two or more steps 134 are the same. In one embodiment, which can be combined with other embodiments described herein, the step width Sw corresponds to the width of the top surface of each step 134 between the top surface 138 and the bottom surface 140 of each staircase grating structure 120. In one embodiment, which can be combined with other embodiments described herein, the step depth SD of two or more steps 134 are different. In another embodiment, which can be combined with other embodiments described herein, the step depth SD of two or more steps 134 are the same.

[0039] In the embodiment shown in FIG. 1A, the plurality of staircase grating structures 102 are formed having a constant or uniform duty cycle. In other embodiments, the plurality of staircase grating structures formed may have varying duty cycles.

[0040] FIG. 1 B illustrates a schematic, cross-sectional view of an optical device 150 having a plurality of non-uniform staircase grating structures formed on a substrate, according to certain embodiments. The optical device 150 may be similar to the optical device 100 in which the plurality of non-uniform staircase grating structure are formed in the device layer 106 disposed on the substrate 104. In some embodiments, the non-uniform staircase grating structures depicted in FIG. 1 B define an input coupling region of a waveguide combiner. In certain embodiments, the plurality of non-uniform staircase grating structure include a first staircase grating structure 152 and a second staircase grating structure 154 formed in the device layer 106. As shown, the first and second staircase grating structures 152, 154 may be formed with varying duty cycles.

[0041] Figure 1 C illustrates a schematic, cross-sectional view of an optical device 160 having a plurality of blazed grating structures 118, according to certain embodiments of the present disclosure. The optical device 160 may be similar to the optical device 100 in which the plurality of blazed grating structures 118 are formed in the device layer 106 disposed on the substrate 104. In some embodiments, the plurality of blazed grating structures 118 defines an input coupling region of a waveguide combiner.

[0042] In certain embodiments, each of the blazed grating structures 118 includes a blazed surface 124, a top surface 126, a sidewall 128, a grating depth “h”, a top width “Tw”, a bottom width “Bw,” and a grating period A (shown in Figure 1 B). The grating depth “h” corresponds to the height of the sidewall 128 and in some embodiments can be from about 10 nanometers to about 500 nanometers; for example, from about 80 nanometers to about 150 nanometers; or from about 20 nanometers to about 70 nanometers. The blazed surface 124 forms a blaze angle “A.” The blaze angle A can be from about 50 degrees to about 80 degrees relative to the sidewall 128, for example, from about 60 degrees to about 70 degrees from perpendicular.

[0043] A top duty cycle of each of the blazed grating structures 118 is defined as top width TW _uty _Cy_C|_e can be from about 0% to about 40%, for example, grating period from about 15% to about 35%. In one embodiment, the grating period can be from about 250 nanometers to about 500 nanometers; for example, from about 300 nanometer to about 400 nanometers. A bottom duty cycle is defined as ^bo g^t r^t a^o t^m ing ^W p^ld e^t r^h io ^B d^w The bottom duty cycle can be from about 60% to about 100%, for example, from about 70% to about 90%.

[0044] In the embodiment shown in FIG. 10, the plurality of blazed grating structures 118 are formed having a constant or uniform duty cycle. In other embodiments, the plurality of blazed grating structures formed may have varying duty cycles.

[0045] FIG. 1 D illustrates a schematic, cross-sectional view of an optical device 170 having a plurality of non-uniform blazed grating structures formed on a substrate, according to certain embodiments. The optical device 170 may be similar to the optical device 160 in which the plurality of non-uniform blazed angle grating structures are formed in the device layer 106 disposed on the substrate 104. In some embodiments, the non-uniform blazed grating structures depicted in FIG. 1 D define an input coupling region of a waveguide combiner. In certain embodiments, the plurality of non-uniform blazed grating structures include a first blazed grating structure 172 and a second blazed grating structure 172 formed in the device layer 106. As shown, the first and second blazed grating structures 172, 174 may be formed with varying duty cycles resulting in different blazed angles. As shown, the first blazed grating structure 172 includes a blaze angle “A” between a first blazed surface 176 and a first side wall 178. The second blazed grating structure 174 includes a blaze angle “B” between a second blazed surface 180 and a second side wall 182.

[0046] FIG. 2 is a perspective, frontal view of an optical device 200. It is to be understood that the optical device 100 described below is an exemplary optical device. In one embodiment, which can be combined with other embodiments described herein, the optical device 200 is a waveguide combiner, such as an augmented reality waveguide combiner. In another embodiment, which can be combined with other embodiments described herein, the optical device 200 is a flat optical device, such as a metasurface.

[0047] The optical device 200 includes a plurality of device structures 203 disposed in or on a substrate 201 . The optical device 200 includes an input coupling region 202 defined by a plurality gratings 208, an intermediate region 204 defined by a plurality of gratings 210, and an output coupling region 206 defined by a plurality of gratings 212. The input coupling region 202 receives incident beams of light (a virtual image) having an intensity from a microdisplay.

[0048] In some embodiments, each of the plurality of gratings 208, 210 comprise blazed angle gratings. Each grating of the plurality of gratings 208 splits the incident beams into a plurality of modes, each beam having a mode. Zero-order mode (TO) beams are refracted back or lost in the optical device 200, positive first-order mode (T1 ) beams are coupled through the intermediate region 204 to the output coupling region 206, and negative first-order mode (T-1 ) beams propagate in the optical device 200 a direction opposite to the T1 beams. Ideally, the incident beams are split into T1 beams that have all of the intensity of the incident beams in order to direct the virtual image to the output coupling region 206. One approach to split the incident beam into T1 beams that have all of the intensity of the incident beams is to optimize the blazed angle of each grating of the plurality of gratings 208 to suppress the T-1 beams and the TO beams. In some embodiments, a portion of the input coupling region 202 may have gratings 208 with a blazed angle different from the blazed angle of gratings 208 from an adjacent portion of the input coupling region 202.

[0049] The T1 beams contact a grating of the plurality of gratings 210 in the intermediate region 204. The T1 beams are split into TO beams that are refracted back or lost in the optical device 200, T1 beams that undergo TIR in the intermediate region 204 until the T1 beams contact another grating of the plurality of gratings 210, and T-1 beams that are coupled through the optical device 200 to the output coupling region 206.

[0050] The T-1 beams pass through the optical device 200 to the output coupling region 206 and undergo TIR in the optical device 200 until the T-1 beams contact a grating of the plurality of gratings 212 where the T-1 beams are split. Specifically, the T01 beams are split into TO beams that are refracted back or lost in the optical device 200, T1 beams that undergo TIR in the output coupling region 206 until the T1 beams contact another grating of the plurality of gratings 212, or T-1 beams that pass out of the optical device 200 and therefore also lost. The T1 beams that undergo TIR in the output coupling region 206 continue to contact gratings of the plurality of gratings 212 until the either the intensity of the T-1 beams passing through the optical device 200 to the output coupling region 206 is depleted, or remaining T1 beams propagating through the output coupling region 206 have reached the end of the output coupling region 206 The plurality of gratings 212 must be tuned to control the T-1 beams passed through the optical device 200 to the output coupling region 206 in order to control the intensity of the T-1 beams passed out of the optical device 200 to further modulate the field of view of the virtual image produced from the microdisplay from the user's perspective and further increase the viewing angle from which the user can view the virtual image.

[0051] One approach to control the T-1 beams passed through the optical device 200 to the output coupling region 206 is to optimize the blazed angle of each grating of the plurality of gratings 212 to further modulate the field of view and increase the viewing angle. A portion of the output coupling region 206 may have gratings 212 with a blazed angle different than the blazed angle of gratings 212 from an adjacent portion of the output coupling region 206. Furthermore, the gratings 212 may have blazed angles different than the blazed angles of the gratings 208. In other embodiments, each of the plurality of gratings 208, 212 may alternatively comprise staircase gratings

[0052] The depth of the gratings 208, 210, or 212 may vary across the coupling or intermediate regions in embodiments described herein. In some embodiments, the depth of the gratings may vary smoothly over the grating area. In one example embodiment, the depth may range from about 10 nm to about 400 nm across the grating area. The grating area in an example embodiment can range from approximately 20 mm to approximately 50 mm on a given side. Therefore, as one example, the angle of the change in the depth of the gratings may be on the order of 0.0005 degrees.

[0053] FIG. 4 is a flow diagram of a method 400 for forming an optical device 300, shown in FIGs. 3A - 3H, having a plurality of staircase grating structures, according to certain embodiments. In an embodiments, the plurality of staircase grating structures of the optical device 300 may correspond with the plurality of staircase grating structures 102 of optical device 100 depicted in FIGs. 1A and/or 1 B. In other embodiments, method 400 may be used to form an optical device having a plurality of blazed grating structures. [0054] At operation 401 , a device layer 302 is formed on a substrate 304, as shown in FIG. 3A. The device layer 302 may be formed by a film deposition process. Any suitable method for deposition of the device layer 302 can be used. Examples of suitable thin film deposition methods include a physical vapor deposition (PVD) process (e.g., ion beam sputtering, magnetron sputtering, e-beam evaporation), a chemical vapor deposition (CVD) process, a plasma enhanced chemical vapor deposition (PECVD) process, an atomic layer deposition (ALD) process, an inkjet printing process, or a three-dimensional (3D) printing process.

[0055] The device layer 302 includes, but is not limited to, one or more of silicon oxycarbide (SiOC), titanium dioxide (TiC ), silicon dioxide (SiC>2), vanadium (IV) oxide (VOx), aluminum oxide (AI2O3), aluminum-doped zinc oxide (AZO), indium tin oxide (ITO), tin dioxide (SnO2), zinc oxide (ZnO), tantalum pentoxide (Ta2Os), silicon nitride (SisN4), zirconium dioxide (ZrO2), niobium oxide (Nb20s), cadmium stannate (Cd2SnO4), or silicon carbon-nitride (SiCN) containing materials. The material of the device layer 302 can have a refractive index of about 1 .5 to about 4.0. For example, the material of the device layer 302 can have a refractive index of 2.65 to about 4.0.

[0056] In operation 402, an optional adhesion layer 306 may be disposed over the device layer 302, as shown in FIG. 3B. In some embodiments, the adhesion layer 306 may be a silicon dioxide (SiO2) layer disposed on the device layer 302 by a PVD process. In other embodiments, no adhesion layer 306 may be used.

[0057] In operation 403, a nanoimprint resist 308 is formed on the adhesion layer 306, as shown in FIG. 3C. The nanoimprint resist 308 may be formed using a liquid material pour casting process, a spin-on coating process, a liquid spray coating process, a jet deposition process (e.g., inkjet deposition), a dry powder coating process, a screen printing process, a physical vapor deposition (PVD) process, a chemical vapor deposition (CVD) process, a flowable CVD (FCVD) process, or an atomic layer deposition (ALD) process.

[0058] The nanoimprint resist 308 may include at least one of spin on glass (SOG), flowable SOG, solgel, organic, inorganic, and hybrid (organic and inorganic) nanoimprintable materials that may contain at least one of silicon oxycarbide (SiOC), titanium dioxide (TiO2), silicon dioxide (SiO2), vanadium (IV) oxide (VOx), aluminum oxide (AI2O3), indium tin oxide (ITO), zinc oxide (ZnO), tantalum pentoxide (Ta2O5), silicon nitride (Si3N4), titanium nitride (TiN), and zirconium dioxide (ZrO2) containing materials.

[0059] In operation 404, the nanoimprint resist 308 disposed on the substrate 304 is imprinted by a stamp 310, as shown in FIG. 3D. In some embodiments, the stamp 310 includes a positive grating pattern having a plurality of inverse gratings 314. The plurality of inverse gratings 314 corresponds to the inverse of a plurality of grating structures desired to be imprinted in the device layer 302. In one embodiment, the nanoimprint resist 308 may be heated before the stamp 310 is imprinted.

[0060] In certain embodiments, the stamp 310 may be cast from a master mold made from a semi-transparent material, such as fused silica or polydimethylsiloxane (PDMS) material, or a transparent material, such as a glass material or a plastic material, to allow the nanoimprint resist to be cured by exposure to electromagnetic radiation, such as infrared (IR) radiation or ultraviolet (UV) radiation. As shown in FIG. 3D, in one embodiment, the stamp 310 may comprise a backing sheet 318, such as a sheet of glass, to add mechanical strength to the stamp 310. In certain embodiments, each stamp 310 may be used to create up to 100 imprints via NIL.

[0061] Operation 404 generally includes imprinting the stamp 310 into a top surface 322 of the nanoimprint resist 308 to form a plurality of staircase grating structures, according to certain embodiments. In an embodiment, the imprinting by the stamp 310 in operation 404 forms a patterned nanoimprint resist 312 (as shown in Fig. 3F) having a negative grating pattern. In an embodiment, the patterned nanoimprint resist 312 includes a plurality of staircase grating structures. In other embodiments, such as for imprinting a plurality of blazed grating structures in the nanoimprint resist 308 (e.g., the plurality of blazed grating structures 118 shown in FIG. 1 C) the plurality of inverse gratings 314 of the stamp 310 may include a plurality of corresponding inverse blazed grating structures.

[0062] In some embodiments in which the stamp 310 comprises a plurality of grating structures having varying grating depths, a profile or a top surface of the nanoimprint resist 308 may be varied prior to imprinting by the stamp 310 in operation 404 so as to achieve a uniform residual layer thickness when the plurality of grating structures are imprinted in the nanoimprint resist 308. For example, a thickness of certain regions of the nanoimprint resist 308 may be formed thicker than other regions if the inverse grating 314 of the stamp 310 to be imprinted in such regions have a greater grating depth (that is, the inverse grating on the stamp extends farther from the backing sheet 318 than other inverse gratings). A uniform residual layer thickness in the nanoimprint resist 308 is desirable as it provides improved pattern transfer to the device layer 302 disposed below the nanoimprint resist 308. In some embodiments, the varying of the profile of the nanoimprint resist 308 may also assist in balancing out a filling factor when imprinting the nanoimprint resist 308 with the stamp 310.

[0063] After the stamp 310 is imprinted in the nanoimprint resist 308 in operation 404, the nanoimprint resist 308 is cured to stabilize the nanoimprint resist 308 in operation 405. Curing the nanoimprint resist 308 may include, for example, an ultraviolet (UV) ray irradiation (for UV NIL) or an annealing process (for thermal NIL).

[0064] At operation 406, the stamp 310 is released resulting in the patterned nanoimprint resist 312. In one embodiment, the stamp 310 can be mechanically removed by a machine tool or by hand peeling as the stamp 310 may be coated with a mono-layer of anti-stick surface treatment coating, such as a fluorinated coating. In another embodiment, the stamp 310 may comprise a polyvinyl alcohol (PVA) material that is water soluble in order for the stamp 310 to be removed by dissolving the stamp 310 in water. In yet another embodiment, the stamp 310 comprises a rigid backing sheet, such as a sheet of glass, to add mechanical strength.

[0065] As shown in FIG. 3F, the patterned nanoimprint resist 312 includes a negative grating pattern comprising a plurality of staircase gratings 319 that is the inverse of the plurality of inverse gratings 314 in the stamp 310. Each of the plurality of staircase gratings 319 in the patterned nanoimprint resist 312 extends a grating depth 320 from the top surface 322 of the patterned nanoimprint resist 312 to a bottom surface 324.

[0066] In operation 407, a etch process is performed into the device layer 302 to pattern the device layer 302 and form a patterned device layer 326. The results of operation 407 is shown in FIG. 3G. In some embodiments, the patterned nanoimprint resist 312 may be used as an etch mask in a dry etching process to form the patterned device layer 326. For example, the dry etch process in operation 407 may include performing a cyclic etch process in which a first etch, selective to the nanoimprint resist material and the adhesion layer 306, is performed to etch the patterned nanoimprint resist 312 and the adhesion layer 306 and expose a portion of the device layer 302. A second etch process, selective to the device layer 302 is then performed to selectively etch the exposed portion of the device layer 302 for a predetermined amount of time to form the bottom surface 324 of each of the plurality of staircase gratings 319. The cyclic etching process (first and second etch) may then be repeated for forming the first step of each of the plurality staircase gratings 319. For example, the first etch process may be repeated to expose a second portion of the device layer 302. The second etch process may then be performed to selectively etch the exposed first and second portions of the device layer 302 to form the first step 330 adjacent to the bottom surface 324. The cyclic etching process may be repeated for forming each of the steps formed in each of the plurality of staircase gratings 319 in the patterned nanoimprint resist 312.

[0067] In some embodiments, which may be combined with other embodiments described herein, the etch processes in operation 407 including the first and second etch processes described above, may comprise an anisotropic (i.e., vertical) etch process. The anisotropic etch process may include at least one of ion implantation, IBE, RIE, plasma etching, thermal atomic layer etching, or laser ablation. The etching process in operation 407 may therefore be performed into the device layer 302 until the grating pattern of the patterned nanoimprint resist 312 is transferred to the device layer 302. In the example shown, the etch process forms a plurality of staircase grating structures

[0068] In another embodiment, operation 407 transfers a pattern corresponding to a plurality of blazed grating structures formed in the patterned nanoimprint resist 312 to the device layer 302.

[0069] In operation 408, the adhesion layer 306 and any remaining nanoimprint resist material may be removed from the device layer 302. As shown in FIG. 3H, stripping the adhesion layer 306 yields the optical device 300 with the patterned device layer 326 on the substrate 304.

[0070] FIG. 5 is a flow diagram of a method 500 for forming a master mold 600 and a stamp 608, shown in FIGS. 6A - 6E, for use in a NIL process to form an optical device, according to certain embodiments. The master mold 600 may be used after it is formed to form the stamp 608 which may then be utilized in a NIL process, such as in method 400 described above, to form optical devices. As mentioned above, depending on processing conditions and the device layer the stamp 608 is imprinted into, each stamp 608 may be used to create up to about 100x imprints. In an embodiment, method 500 may be performed prior to method 400 to form a master mold for forming the stamp 310 used in operation 404.

[0071] In an embodiment, method 500 begins in operation 501 with disposing a mold resin 602 on a substrate 604, as shown in FIG. 6A. In some embodiments, the mold resin 602 includes without limitation, semi-transparent materials, such as fused silica or polydimethylsiloxane (PDMS) material, or transparent materials, such as a glass material or a plastic material.

[0072] In operation 502, the mold resin 602 is patterned to form a grating pattern 606 for the master mold 600. In some embodiments, the grating pattern 606 includes a plurality of staircase grating structures formed as a negative grating pattern in the master mold 600, as shown in FIG. 6B. In other embodiments, the grating pattern 606 includes a plurality of blazed angle structures. In other embodiments, the grating pattern 606 may be a positive grating pattern extending outwards from a top surface of the master mold 600.

[0073] In some embodiments, the grating pattern 606 is formed in the master mold 600 using standard lithography processes. For example, the master mold 600 may be formed by repeating a cyclic lithography patterning and etch process to form the grating pattern 606 in the mold resin 602. In other embodiments, the master mold 600 may be formed using other forming techniques, including without limitation, graytone lithography, digital lithography, and laser ablation. In some embodiments, the grating pattern 606 includes a plurality of staircase grating structures having constant or varying duty cycles. In other embodiments, the grating pattern 606 includes a plurality of blazed grating structures having constant or varying duty cycles.

[0074] In some embodiments, the master mold 600 may be formed of, for example, silicon. As the master mold 600 will be used to cast a stamp which in turn may be used in NIL to imprint a plurality of grating structures of an optical device, the plurality of staircase grating structures of the grating pattern 606 in the master mold 600 corresponds to the plurality of staircase grating structures grating structures desired to be imprinted and formed for the optical device.

[0075] In operation 503, a stamp 608 is cast from the master mold 600, as shown in FIG. 6C. In some embodiments, operation 503 includes disposing a flowable material over the grating pattern 606 of the master mold 600 to form the stamp 608. In some embodiments, the flowable material for forming the stamp 608 may be a thermally curable material or a UV-curable material. After the flowable material is disposed on the master mold 600, a rigid backing sheet 610 for supporting the stamp 608 may be applied over the flowable material and cured, as shown in FIG. 6D. Depending on the flowable material used, in some embodiments, a compressive force may be applied to the rigid backing sheet 610 to improve an adhesive force between the backing sheet 610 and the flowable material. In other embodiments, an adhesive layer may alternatively be applied between the backing sheet 610 and the flowable material. When the flowable material is cured, the flowable material may harden to form the stamp 608 having a positive inverse grating pattern 612 protruding outwards from the rigid packing sheet 610. In the example shown, the inverse grating pattern 612 comprises a plurality of staircase grating structures inverse of the grating pattern 606 of the master mold 600.

[0076] In operation 504, after pressing the backing sheet 610 against the flowable material and curing the flowable material, the stamp 608 may then be released from the master mold 600, as shown in FIG. 6E.

[0077] As shown in FIGs. 1A and 1 B, it may be desirable to form optical device structure designs with a wide range of duty cycles, as well as optical device structures with constant and varying duty cycles. In some embodiments, a top and/or bottom duty cycle for each of the staircase grating structures formed in the master mold may be in a range between about 30% and about 70%. As such, in certain embodiments, operation 502 of method 500 may therefore be tailored to correspondingly pattern the mold resin 602 to form a stamp for imprinting staircase grating structures with a constant duty cycle, or imprinting staircase grating structures with varying duty cycles.

[0078] As the grating pattern 606 of the master mold 600 corresponds to the desired optical structures to be formed on the optical device substrate, the usually complex and time consuming cyclic lithography and etch process (i.e. angled beam etch to form blazed grating structures) that would otherwise normally be repeated to form the optical structures for each substrate during fabrication may instead just be performed once to form the master mold 600. Furthermore, while the plurality of grating structures imprinted and formed on an optical device using the stamp 608 in NIL may be the same as or highly similar to the original grating pattern 606 of the master mold 600, the grating structures formed on the optical device via NIL can be consistently and accurately formed using the stamp 608 more efficiently and at a lower cost, as compared to when the process used to form the grating pattern 606 in the master mold 600 is repeated. In some embodiments, the same master mold 600 may also be repeatedly used to form additional stamps as the stamp 608 wears out due to use.

[0079] FIG. 7 is a flow diagram of a method 700 for forming a master mold 800, shown in FIGs. 8A-8G, having a plurality of staircase grating structures with varied grating depths, according to certain embodiments. In some embodiments, the grating depths of the plurality of staircase grating structures (e.g., constant or varying duty cycles) formed in the master mold 800 may be varied using gray-tone lithography in combination with other forming techniques. Gray-tone lithography is a one-step process used to create three-dimensional profiles in a resist layer using an optical gray-tone (or grayscale) mask. Gray-tone masks let varying amounts of light pass through during photolithography to create depth-modulated profiles in the gray-tone resist.

[0080] As discussed above, conventionally, the grating pattern for a master mold may be formed using standard lithography and etch processes. As such, forming multiple grating structures with varying grating depths on the master mold using conventional techniques requires multiple complex lithography and etch processes to be performed. In certain embodiments, method 700 therefore provides for forming a master mold having a plurality of grating structures with varying grating depths. In the example shown, method 700 may be performed to form a plurality of staircase grating structures having varying grating depths in a master mold. In other embodiments, method 700 may similarly be performed to form a plurality of blazed grating structures having varying grating depths in a master mold. [0081] In an embodiment, method 700 begins with operation 701 in which a mold resin 802 is disposed on a substrate 804, as shown in FIG. 8A. In some embodiments, the mold resin 802 is similar to the mold resin 602 which may include without limitation, semi-transparent materials, such as fused silica or polydimethylsiloxane (PDMS) material, or transparent materials, such as a glass material or a plastic material.

[0082] In operation 702, a patterned hardmask 805 is formed over the mold resin 802. As shown in FIG. 8B, the patterned hardmask 805 exposes a plurality of selected regions 806 of the mold resin 802. The patterned hardmask 805 provides for the selected regions 806 of the mold resin 802 to be etched for forming a plurality of staircase grating structures in the mold resin 802. The patterned hardmask 805 may be formed from any suitable material, for example titanium nitride (TiN) or tantalum nitride (TaN), among others, provided that the patterned hardmask 805 is resistant to the etching processes described herein in method 700.

[0083] In operation 703, a plurality of grating structures with uniform grating depths is formed in the selected regions 806 of the mold resin 802. In the example shown, the plurality of grating structures includes a first staircase grating structures 808 and a second staircase grating structures 810. In some embodiments, the first and second staircase grating structures 808, 810 are formed with uniform grating depths D1 , as shown in FIG. 8C.

[0084] In operation 704, a gray-tone resist 812 is formed over the patterned hardmask 805 including within the first and second staircase grating structures 808, 810 of the master mold 800, as shown in FIG. 8D. In operation 705, the gray-tone resist 812 is patterned with gray-tone pattern 814. FIG. 8E shows the results of operation 705.

[0085] In one embodiment, forming and patterning the gray-tone resist 812 in operations 704 and 705 include disposing the gray-tone resist 812 over the master mold 800 and developing the gray-tone resist 812 to form the gray-tone pattern 814 of the gray-tone resist 812. In some embodiments, the gray-tone resist 812 may include but is not limited to, light-sensitive polymer containing materials. Developing the gray-tone resist 812 may include performing a lithography process, such as graytone photolithography, digital lithography, or by performing laser ablation. [0086] In one embodiment, the gray-tone resist 812 is developed using a gray-tone photolithography process to form the gray-tone pattern 814 of the gray-tone resist 812. The gray-tone photolithography process can include applying radiation through a gray-tone mask to expose the gray-tone resist 812 to the radiation. The gray-tone mask is a mask that is configured to allow varying amounts of radiation to pass through different portions of the mask when the different portions of the mask (i.e. , different portions in the XY plane of the mask) are exposed to radiation having the same properties (e.g., intensity, wavelength, frequency, duration, etc.). The varying amount of radiation directed through the gray-tone mask enables the gray-tone resist 812 to be altered to varying depths in the Z-direction. After exposure of portions of the graytone resist 812 to radiation using the resist 812 mask, the gray-tone resist 812 can be developed to remove portions of the gray-tone resist 812, such as uncured portions of the gray-tone resist 812. Removal of these portions the gray-tone resist 812 leaves the gray-tone pattern 814, as shown in FIG. 8E.

[0087] In the example shown, photolithography has been performed to pattern the gray-tone resist 812 with a sloped profile (e.g., inclined shape) to provide for increasing a grating depth for the second staircase grating structure 810. The varying of thickness in the sloped profile of the gray-tone pattern 814 provides for tuning the grating depth of the plurality of grating structures formed in the mold resin 802 in operation 703. In the example shown, the sloped profile of the gray-tone pattern 814 provides for an increase in the grating depth of the second staircase grating structure 810 in which the increase corresponds to a difference in the thickness of the graytone pattern 814 formed over the first and second staircase grating structures 808, 810.

[0088] In operation 706, a transfer etch process into the selected regions 806 of the pattered mold resin 802 is performed. The patterned hardmask 805 on the mold resin 802 prevents the transfer etch process from etching other portions of the master mold 800.

[0089] The results of operation 706 are illustrated in FIG. 8F. In this example embodiment, the transfer etch increases a grating depth of the second staircase grating structure 810 from D1 to D2, the increase of the grating depth to D2 corresponding to a difference in the thickness of the gray-tone pattern 814 disposed over the first staircase grating structure 808 and the second staircase grating structure 810. As shown in FIG. 8E, the gray-tone pattern 814 was formed with a thickness T1 over the first staircase grating structure 808, and a thickness of T2 over the second staircase grating structure 810. In some embodiments, the transfer etch process may be performed for a predetermined amount time. In an embodiment, the transfer etch process was performed until all the gray-tone pattern was etched away.

[0090] In an embodiment, the transfer etch process may include performing a cyclic etch process with varying hardmasks to selectively etch the staircase grating structures so as to separately etch each step and increase a grating depth in the first and second staircase grating structure 808, 810.

[0091] As the profile of the gray-tone resist 812 directly correlates with the extent of the etching for each of the grating structures of the hardmask, which in turn provides for varying the grating depth, the gray-tone photolithography process for forming of the gray-tone pattern 814 in operation 705 therefore provides control for tuning and varying the grating depth of the plurality of grating structures in a master mold, as desired.

[0092] In operation 707, the patterned hardmask 805 is removed. As shown in FIG. 8G, stripping the patterned hardmask 805 yields the master mold 800 in which the first and second staircase grating structures 808, 810 are formed with varying grating depths.

[0093] In another embodiment, method 700 may similarly be performed for varying a grating depth for a plurality of blazed angle gratings formed in a master mold. As discussed above, the plurality of grating structures formed in a master mold corresponds with the gratings structures to be formed from imprints by the corresponding stamp formed using the respective master mold. Accordingly, method 700 described herein for varying the grating depth of the grating structures (staircase or blazed angle) in a master mold in turn provides for varying the grating depth of the grating structures for the optical devices to be formed using the corresponding stamp in a NIL process.

[0094] FIG. 9 is a flow diagram of a method 900 for forming a master mold 1000, shown in FIGs. 10A - 10D, having a reduced bottom critical dimension, according to certain embodiments. In an embodiment, which may be combined with other embodiments herein, method 900 provides for modifying a grating pattern of a master mold having a plurality of staircase grating structures to reduce a bottom critical dimension (CD) of each of the plurality of staircase grating structures in the grating. That is, the method 900 provides for reducing a width of a bottom surface of each of the plurality of staircase grating structures. Reducing the bottom CD of each of the plurality of grating structures in the master mold 600 in turn reduces the bottom CD of the grating structures imprinted by the stamp 608 formed from the master mold 600.

[0095] In certain embodiments, which may be combined with other embodiments herein, method 900 provides for modifying a grating pattern of a pre-existing master mold, such as the grating pattern 606 of the master mold 600, to reduce the bottom critical dimension of the plurality of staircase grating structures formed therein. As forming staircase grating structures with a smaller bottom critical dimension in a master mold requires less material to have originally been etched when forming the master mold, forming a master mold with a reduced critical dimension conventionally requires fabrication of a new master mold. Method 900 described herein enables using and modifying a preexisting master mold to form similar grating structures with a reduced bottom critical dimension.

[0096] Method 900 for forming the master mold 1000 begins in operation 901 with disposing a master mold having a negative grating pattern formed therein in a deposition process chamber. In an embodiment, the deposition process chamber may be an atomic layered deposition (ALD) process chamber. In the example shown in FIG. 10A, the master mold 1000 is formed using the master mold 600 with the grating pattern 606 formed therein. The grating pattern 606 of the master mold 600 includes a plurality of staircase grating structures 1004. Each of the plurality of staircase grating structures 1004 includes a stepped surface 1006 having a plurality of steps 1008, a sidewall 1010, a top surface 1012, and a bottom surface 1014 between the sidewall 1010 and the plurality of steps 1008 having a bottom critical dimension 1016. When a stamp is cast from the master mold 600, the stamp comprises an inverse positive staircase grating structure in which a width of a top step of the inverse staircase grating on the stamp substantially matches the bottom critical dimension 1016. [0097] In operation 902, a deposition process is performed using the process chamber to form a coating 1002 over the grating pattern 606 and the master mold 600, as shown in FIG. 10B. In some embodiments, the coating 1002 is deposited on the master mold 600 by an ALD process. In some embodiments, the coating 1002 is deposited so that the thickness of the coating is substantially uniform. In some embodiments, the coating 1002 comprises a thickness between about 1 nm and about 20 nm. In some embodiments, the coating 1002 comprises a material including without limitation, TiOx, TiNx, SiN, or SiOx. When the coating 1002 is disposed over the plurality of staircase grating structures 1004, a top surface of the coating 1002 steps in and becomes the molding surface of the master mold 1000 for forming the stamp.

[0098] Due to the inherent thickness of the coating 1002 deposited on the staircase grating structures of the master mold 600, an inverse staircase grating structure of a stamp formed from master mold 1000 with the coating 1002 as the molding surface is smaller than the corresponding inverse staircase grating structure of the stamp formed from the original master mold 600 without the coating 1002 thereon. A bottom critical dimension 1020 of the coating 1002 disposed over the bottom surface 1014 for forming the stamp is less than the bottom critical dimension 1016. Specifically, the bottom critical dimension 1020 corresponds to the bottom critical dimension 1016 reduced by a thickness of the coating 1002 disposed over the sidewall 1010 and a sidewall 918 of a step 1008 opposite the sidewall 1010. As such, tuning the thickness of the coating 1002 provides control over the extent of the reduction when forming the bottom critical dimension 1020 for the master mold 1000.

[0099] In operation 903, a stamp 1022 is formed from the master mold 1000, as shown in FIG. 10C. The master mold 1000 having the reduced bottom critical dimension 1020 in turn enables the stamp 1022 to be formed in which a width of a top step 1024 of the corresponding inverse staircase grating on the stamp 1022 is also correspondingly reduced to that of the bottom critical dimension 1020. In some embodiments, the bottom critical dimension 1020 is in a range from about 0 nm to about 40 nm. Accordingly, adding the A LD coating 1002 provides an efficient method for tuning and modifying a bottom critical dimension of an existing master mold. The addition of the ALD coating for further reducing the bottom CD may also advantageous provide for overcoming CD limitations of the lithography process performed for initially forming grating structures in a master mold.

[0100] In operation 904, a curing process may be performed to cure and harden the stamp 1022. After the stamp 1022 hardens, the stamp 1022 may then be released from the master mold 600, as shown in FIG. 10D.

[0101] FIG. 11 is a flow diagram of a method 1100 for forming an optical device 1200, shown in FIGs. 12A - 12F, having a plurality of blazed angle gratings with varying depths, according to certain embodiments. In certain embodiments, which may be combined with other embodiments herein, method 1100 provides for forming the plurality of blazed angle gratings in a device layer 1204 on a substrate 1202 and varying the grating depth of the plurality of blazed angle gratings thereafter using a gray-tone lithography process in combination with other forming process. In some embodiments, the plurality of blazed angle gratings initially formed in the device layer 1204 may be formed with constant grating depths.

[0102] In an embodiment, method 1100 begins in operation 1101 with disposing the device layer 1204 over the substrate 1202, as shown in FIG. 12B. In operation 1102, a patterned hardmask 1207 is formed over a top surface of the device layer 1204. The patterned hardmask 1207 exposes a plurality of selected regions 1206 of the device layer 1204.

[0103] In operation 1103, a plurality grating structures 1208 is formed in the device layer 1204, according to certain embodiments. The plurality of grating structures 1208 includes a plurality of blazed angle gratings formed in the plurality of selected regions 1206 of the device layer 1204, as shown in FIG. 12C. As shown, the plurality of grating structures 1208 includes a first blazed angle grating 1208A, a second blazed angle grating 1208B, and a third blazed angle grating 1208C. In some embodiments, the plurality of grating structures 1208 is formed in the device layer 1204 using standard lithography patterning and etches processes. For example, operation 1103 may include forming a resist layer and performing a photolithography patterning and angled etch process to form each of the plurality of grating structures 1208 in the device layer 1204. In other embodiments, the plurality of grating structures 1208 formed in operation 1103 may be formed using a NIL and etch process. [0104] In operation 1104, a gray-tone resist 1210 is formed over the device layer 1204 including each of the plurality of grating structures 1208, as shown in FIG. 12D. In operation 1105, the gray-tone resist 1210 is patterned with a gray-tone pattern 1212. Operations 1104 and 1105 may be similar to operations 704 and 705 described herein. The gray-tone resist 1210 can be deposited and patterned to enable etching the desired grating depth for each of the plurality of grating structures 1208. In one embodiment, forming and patterning the gray-tone resist 1210 includes disposing a gray-tone resist material over the device layer 1204 and developing the resist material utilizing a photolithography process to form the gray-tone pattern 1212. In some embodiments, the gray-tone resist material may include but is not limited to, lightsensitive polymer containing materials. Developing the resist material may include performing a lithography process, such as photolithography, digital lithography, or by performing laser ablation.

[0105] FIG. 12E shows the results of operation 1105. In the example shown, photolithography has been performed to vary the grating depth of each of the plurality of grating structures 1208 formed in the device layer 1204. Patterning or forming the profile (e.g. varying of thickness) or gray-tone pattern 1212 of the gray-tone resist 1210 therefore provides for selectively tuning the grating depth of each of the plurality of grating structures 1208 in the device layer 1204.

[0106] In operation 1106, a transfer etch process into the device layer 1204 is performed. The results of operation 1106 are illustrated in FIG. 12F. In this example embodiment, the transfer etch increases a grating depth of each of the plurality of grating structures 1208 based on the gray-tone pattern 1212 or corresponding to the differences in thickness in the gray-tone resist 1210 disposed over each of the plurality of grating structures 1208. In one embodiment, which can be combined with other embodiments, the gray-tone resist 1210 is entirely removed such that the grating depth of each of the plurality of grating structures 1208 is increased by a difference in thickness between the thickness of the gray-tone resist 1210 formed thereon and the thickness of the thickest portion of the gray-tone resist 1210 formed over any one of the plurality of angle gratings 1208A, 1208B, and 1208C. As shown in FIG. 12C, a thickness T1 , T2, and T3 of the gray-tone resist 1210 is formed over grating structures 1208A-C, respectively, with T1 being the thinnest, T3 being the thickest, and each of the grating structures 1208A-C having a grating depth D1. [0107] In one embodiment, the transfer etch process in operation 1106 is stopped as soon as the gray-tone resist 1210 is entirely removed from the third blazed angle grating 1208C so as to maintain the grating depth D1 of the third blazed angle grating 1208C. As shown in FIG. 12f , the transfer etch process however increased the grating depth of the first blazed angle grating 1208A to a grating depth D2, and the grating depth of the second blazed angle grating 1208B to a grating depth D3. In an embodiment, as the transfer etch process was stopped as soon as the gray-tone resist 1210 was entirely removed from the third blazed angle grating 1208C, the increase in grating depth of the first blazed angle grating 1208A (i.e. the difference between D2 and D1 ) may correspond to the difference between T1 and T3 of the gray-tone resist 1210 prior to the transfer etch process. Similarly, the increase in grating depth of the second blazed angle grating 1208B (i.e. the difference between D3 and D1 ) may correspond to the difference between T2 and T3 of the gray-tone resist 1210 disposed over the second and third grating structures 1208B-C prior to the transfer etch process.

[0108] In operation 1107, the patterned hardmask 1207 is removed. As shown in FIG. 12E, stripping the patterned hardmask 1207 yields the optical device 1200 in which the first, second, and third staircase angle gratings 1208A, 1208B, and 1208C are formed with varying grating depths.

[0109] As forming a plurality of blazed angle gratings in the device layer 1204 with varying grating depths using conventional techniques requires performing more complex lithography patterning and angled etch operations than gratings with uniform grating depths, method 1100 described herein provides for forming the simpler operation of forming gratings with uniform grating depths, and then varying the grating depths as desired by performing just the additional gray-tone lithography process described above in operations 1104 and 1105 on the device layer 1204.

[0110] FIG. 13 is a flow diagram of a method 1300 for forming an optical device 1400, shown in FIGS. 14A - 14C, according to certain embodiments. In an embodiment, method 1300 provides for forming a plurality of blazed grating structures with varying top surface heights using an imprintable layer having structures formed thereon with varying residual layer thicknesses. [0111] Method 1300 begins in operation 1301 with disposing an imprintable layer 1402 having a plurality of structures formed thereon and varying residual layer thicknesses T1 , T2, and T3, as shown in FIG. 14A. The imprintable layer 1402 is disposed over a device layer 1403 on a substrate 1401. The imprintable layer 1402 includes a first portion 1404 with structures extending from a first residual layer 1406 having a thickness T1 , a second portion 1408 with structures extending from a second residual layer 1410 having a thickness T2, and a third portion 1412 with structures extending from a third residual layer 1414 having a thickness T3. In some embodiments, the imprintable layer 1402 may be an uncured imprintable polymer or resist material that may be patterned by a nanoimprint process including but not limited to, an UV curable adhesive, an UV curable resist, a thermoplastic material, or other polymer material.

[0112] In operation 1302, an etch process is performed to remove the structures on each of the first, second, and third portions 1404, 1408, 1412 of the imprintable layer 1402. In some embodiments, the etch process in operation 1302 includes an anisotropic (i.e. , vertical) etch process. The anisotropic etch process may include, but is not limited to, at least one of ion implantation, IBE, RIE, plasma etching, thermal atomic layer etching, or laser ablation. FIG. 14B shows the results of operation 1302 in which only the first, second, and third residual layers 1406, 1410, 1414 remain for the imprintable layer 1402 after the etching process is performed.

[0113] In operation 1303, as shown in FIG. 14C, the imprintable layer 1402 is imprinted with a stamp 1416 having a plurality of inverse blazed angle gratings 1418. In operation 1304, after the stamp 1416 is imprinted into the imprintable layer 1402, the imprintable layer 1402 is cured and the stamp 1416 is released to form a patterned layer 1420. FIG. 14D shows the results of operation 1304 in which the patterned layer 1420 includes a plurality of blazed angle gratings 1422 formed with grating depths corresponding to the thickness of the respective residual layer each of the blazed angle gratings 1422 is formed in.

[0114] In an embodiment, method 1300 provides for using a stamp comprising a plurality of blazed angle gratings with uniform grating depth to form a plurality of blazed angle gratings with varying grating depths utilizing a film having varying thicknesses. [0115] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

What is claimed is:

1 . A method for forming an optical device, comprising: fabricating a master mold having a grating pattern formed therein; forming a stamp using the master mold, the stamp comprising an inverse grating pattern corresponding to an inverse of the grating pattern of the master mold; imprinting the stamp into a nanoimprint resist disposed on a device layer; curing the nanoimprint resist; releasing the stamp from the nanoimprint resist to form a patterned nanoimprint resist; and performing an etch process using the patterned nanoimprint resist as an etch mask to form a plurality of staircase grating structures in the device layer.

2. The method of claim 1 , wherein fabricating the master mold comprises patterning the master mold with a plurality of staircase grating structures with uniform duty cycles to form the grating pattern.

3. The method of claim 1 , wherein fabricating the master mold comprises patterning the master mold with a plurality of staircase grating structures with varied duty cycles to form the grating pattern.

4. The method of claim 1 , wherein each of the plurality of staircase grating structures comprises a plurality of steps, and performing the etch process comprises cyclically etching the patterned nanoimprint resist and the device layer to form each of the plurality of steps in each of the plurality of staircase grating structures in the device layer.

5. A method for forming a master mold, comprising: disposing a mold resin on a substrate; forming a hardmask over the mold resin; patterning the hardmask to form a patterned hardmask for defining selected regions of the mold resin for patterning; patterning the mold resin with a grating pattern, the grating pattern comprising a plurality of grating structures disposed in the selected regions of the mold resin; forming a gray-tone resist over the patterned hardmask and the plurality of grating structures; patterning the gray-tone resist using gray-tone lithography to form a gray-tone pattern in the gray-tone resist; and performing a transfer etch process to vary a grating depth of one or more of the plurality of grating structures in the master mold.

6. The method of claim 5, wherein the plurality of grating structures comprises a plurality of staircase grating structures.

7. The method of claim 5, wherein the plurality of grating structures comprises a plurality of blazed angle structures.

8. The method of claim 5, wherein the grating pattern comprises a negative grating pattern comprising the plurality of grating structures formed in the mold resin.

9. A method of forming an optical device, comprising: providing a master mold comprising a plurality of staircase grating structures wherein each of the plurality of staircase grating structures comprises a bottom surface disposed between a side wall and a stepped surface of each of the plurality of staircase grating structures, and a bottom critical dimension corresponding to a width of the bottom surface configured for contacting and molding a stamp; depositing a coating over the master mold and the plurality of the staircase grating structure to form a coated master mold; forming a stamp with the coated master mold; imprinting the stamp into a nanoimprint resist disposed on a device layer; curing the nanoimprint resist and releasing the stamp from the nanoimprint resist to form a patterned nanoim print resist; and performing an etch process using the patterned nanoimprint resist as an etch mask to form a plurality of staircase grating structures in the device layer, wherein a bottom critical dimension of each of the plurality of staircase grating structures in the device layer is less than the width of the bottom surface of the master mold.

10. The method of claim 9, wherein depositing the coating comprises performing an ALD deposition process.

11 . The method of claim 9, wherein the plurality of staircase grating structures is formed as a negative grating pattern in the master mold.

12. The method of claim 9, wherein a thickness of the coating on the master mold is substantially uniform.

13. The method of claim 12, wherein the bottom critical dimension of the master mold is greater than the bottom critical dimension of the coated master mold by about twice the thickness of the coating on the coated master mold.

14. A method for forming an optical device, comprising: fabricating a master mold having a grating pattern formed therein; forming a stamp using the master mold, the stamp comprising an inverse grating pattern corresponding to an inverse of the grating pattern of the master mold; imprinting the stamp into a nanoimprint resist disposed on a device layer; curing the nanoimprint resist and releasing the stamp from the nanoimprint resist to form a patterned nanoim print resist; and performing an etch process using the patterned nanoimprint resist as an etch mask to form a plurality of blazed grating structures in the device layer.

15. The method of claim 14, wherein fabricating the master mold comprises patterning the master mold with the grating pattern having a plurality of blazed grating structures with uniform duty cycles.

16. The method of claim 14, wherein fabricating the master mold comprises patterning the master mold with a plurality of blazed grating structures with varied duty cycles to form the grating pattern.

17. A method for forming an optical device, comprising: forming a hardmask on a device layer disposed on a substrate; patterning the hardmask to form a patterned hardmask for defining selected regions of the device layer for patterning; patterning the device layer to form a negative grating pattern in the selected regions of the device layer, the negative grating pattern comprising a plurality of blazed grating structures; forming a gray-tone resist over the patterned hardmask and the plurality of blazed grating structures; patterning the gray-tone resist using gray-tone lithography to form a gray-tone pattern in the gray-tone resist; and performing a transfer etch process to vary the a depth of one or more of the plurality of blazed grating structures in the device layer.

18. The method of claim 17, wherein patterning the device layer to form the negative grating pattern comprises forming plurality of blazed grating structures with uniform grating depths.

19. A method for forming an optical device, comprising: etching one or more structures extending from a top surface of an imprintable layer having regions of varying thicknesses; imprinting a stamp having in the top surface of one or more of the regions of the imprintable layer, the stamp having an inverse grating pattern comprising a plurality of blazed grating structures; curing the imprintable layer; and releasing the stamp from the imprintable layer to form a patterned layer having a plurality of blazed grating structures with varying grating depths, wherein a grating depth of each of the plurality of blazed grating structures of the patterned layer corresponds with a thickness of the respective region of the imprintable layer each of the plurality of blazed grating structures is formed in.

20. The method of claim 19, wherein etching one or more structures comprises performing an anisotropic etch process to remove each of the one or more structures extending from a corresponding residual layer in each of the regions of the imprintable layer.