Patent Publication Number: US-2022212983-A1

Title: Methods for encapsulating silver mirrors on optical structures

Description:
BACKGROUND 
     Field 
     Embodiments of the present disclosure generally relate to optical devices and methods for fabricating optical devices, and more specifically, to encapsulated optical devices and methods for fabricating the encapsulated optical devices. 
     Description of the Related Art 
     In optical devices, such as a virtual reality (VR) device or an augmented reality (AR) device, a waveguide combiner is often used to couple a virtual image, transport light inside a glass substrate through total internal reflection, and then couple the image when reaching the position of viewer&#39;s eye. For light coupling and decoupling, slanted features and trenches in the waveguide combiner are usually applied as gratings for light diffraction. The orientation of lines (fins) controls the light propagation direction, whereas the tilted angle controls the efficiency of desired orders of diffraction. Mirrors are used to reflect the light on a controlled manner. 
     In many applications, mirrors having silver layers are used in these optical devices. To protect the silver from long term oxidation, an encapsulation layer is often deposited on or over the silver layer. However, when the silver layer is exposed to an oxidizing environment, such as oxygen in a plasma reactor, the silver atoms often migrate into neighboring layers and or the substrate damaging the optical device. Migration is especially a problem to silicon oxide layers as well as glass or quartz substrates or wafers. 
     Therefore, there is a need for improved optical devices having mirrors and methods for fabricating such optical devices. 
     SUMMARY 
     Embodiments of the present disclosure generally relate to encapsulated optical devices and methods for fabricating the encapsulated optical devices. In one or more embodiments, a method for encapsulating an optical device includes depositing a metallic silver layer on a substrate, depositing a barrier layer on the metallic silver layer, where the barrier layer contains silicon nitride, one or more metallic elements, one or more metal nitrides, or any combination thereof, and depositing an encapsulation layer containing silicon oxide on the barrier layer. 
     In some embodiments, a method for encapsulating an optical device includes depositing a first barrier layer on a substrate, depositing a metallic silver layer on the first barrier layer, depositing a second barrier layer on the metallic silver layer, and depositing an encapsulation layer containing silicon oxide on the second barrier layer by a physical vapor deposition (PVD) process. Each of the first and second barrier layers independently contains silicon nitride, one or more metallic elements, one or more metal nitrides, or any combination thereof. 
     In other embodiments, an encapsulated optical device contains a first barrier layer disposed on a substrate, a metallic silver layer disposed on the first barrier layer, a second barrier layer disposed on the metallic silver layer, and an encapsulation layer containing silicon oxide disposed on the second barrier layer. The substrate is or contains glass, quartz, silicon dioxide, or fused silica. Each of the first and second barrier layers independently contains silicon nitride, one or more metallic elements, one or more metal nitrides, or any combination thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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, may admit to other equally effective embodiments. 
         FIG. 1  depicts a schematic cross-sectional view of an encapsulated optical device, according to one or more embodiments described and discussed herein. 
         FIG. 2  depicts a schematic cross-sectional view of another encapsulated optical device, according to one or more embodiments described and discussed herein. 
     
    
    
     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 or more embodiments may be beneficially incorporated in other embodiments. 
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure generally relate to encapsulated optical devices and methods for fabricating the encapsulated optical devices. The encapsulated optical devices can be or include devices or film stacks used as virtual reality (VR) devices, augmented reality (AR) devices, as well as other devices, including optical devices, display devices, and/or microelectronic devices. 
       FIG. 1  depicts a schematic cross-sectional view of an encapsulated optical device  100 , according to one or more embodiments described and discussed herein. The encapsulated optical device  100  contains a barrier layer  110  (e.g., a first or intermediate barrier layer) disposed on a substrate  102 , a metallic silver layer  120  disposed on the barrier layer  110 , a barrier layer  130  (e.g., a second barrier layer) disposed on the metallic silver layer  120 , and an encapsulation layer  140  disposed on the second barrier layer  130 . In one or more embodiments, an optical device  132  contains the substrate  102 , the first barrier layer  110 , the metallic silver layer  120 , and the second barrier layer  130 . The optical device  132  is encapsulated by the encapsulation layer  140  in order to produce the encapsulated optical device  100 . The method for producing the encapsulated optical device  100  includes depositing the barrier layer  110  on the substrate  102 , depositing a metallic silver layer  120  directly on the barrier layer  110 , depositing the barrier layer  130  on the metallic silver layer  120 , and depositing the encapsulation layer  140  containing silicon oxide on the barrier layer  130 . 
       FIG. 2  depicts a schematic cross-sectional view of an encapsulated optical device  200 , according to one or more embodiments described and discussed herein. The encapsulated optical device  200  is similar to the encapsulated optical device  100 , but lacks the barrier layer  110 . As such, the encapsulated optical device  200  contains the metallic silver layer  120  disposed on the substrate  102 , the barrier layer  130  disposed on the metallic silver layer  120 , and the encapsulation layer  140  containing silicon oxide disposed on the second barrier layer  130 . In one or more embodiments, an optical device  232  contains the substrate  102 , the metallic silver layer  120 , and the barrier layer  130 . The optical device  232  is encapsulated by the encapsulation layer  140  in order to produce the encapsulated optical device  200 . The method for producing the encapsulated optical device  200  includes depositing the metallic silver layer  120  on the substrate  102 , depositing the barrier layer  130  on the metallic silver layer  120 , and depositing the encapsulation layer  140  containing silicon oxide on barrier layer  130 . 
     For the encapsulated optical device  100 , the barrier layer  110  protects the substrate  102  from being contaminated by silver atoms defusing from the metallic silver layer  120  during the subsequent deposition, plasma, and/or thermal processes. Without the barrier layer  110 , silver atoms from the silver layer  120  would migrate into the substrate  102  damaging the optical device. However, with the barrier layer  110  disposed between the substrate  102  and the metallic silver layer  120 , the barrier layer  110  reduces or eliminates silver migration into the substrate  102 . For both of the encapsulated optical devices  100 ,  200 , the barrier layer  130  protects the metallic silver layer  120  from plasma exposure and/or one or more oxidizing agents (e.g., ozone, oxygen plasma, or oxygen radicals) during the deposition of the encapsulation layer  140 . In some examples, the plasma exposure and/or oxidizing agent can be generated while encapsulating the metallic silver layer  120 . Without the barrier layer  130 , once the silver layer  120  is exposed to plasma and/or an oxidizing agent, silver atoms from the silver layer  120  would migrate into neighboring layers and or the substrate damaging the optical device. However, with the barrier layer  130  disposed on or over the metallic silver layer  120 , the metallic silver layer  120  is protected from silver migration. 
     In one or more embodiments, the substrate  102  is or contains glass, quartz, silicon dioxide, fused silica, one or more polymeric materials, or any combination thereof. In some examples, the substrate  102  is or contains a high refractive index (HRI) glass, an HRI polymeric material, or other HRI material. Exemplary HRI glass, the HRI polymeric material, or other HRI material can have a refractive index of greater than 1.5, such as about 1.6, about 1.7, about 1.8, about 1.9, or about 2 to about 2.1, about 2.2, about 2.3, about 2.4, about 2.5, about 2.6, about 2.7, about 2.8, or greater. In one or more examples, the HRI glass, the HRI polymeric material, or other HRI material can have a refractive index of about 1.6 to about 2.8, about 1.6 to about 2.5, about 1.6 to about 2.3, about 1.6 to about 2.2, about 1.6 to about 2.1, about 1.8 to about 2.8, about 1.8 to about 2.5, about 1.8 to about 2.3, about 1.8 to about 2.2, about 1.8 to about 2.1, about 2 to about 2.8, about 2 to about 2.5, about 2 to about 2.3, or about 2 to about 2.2. 
     In some embodiments, the substrate  102  can include a wafer or panel substrate capable of having material, layers, films, mirrors, and/or the like deposited thereon. The substrate  102  can include silicon (doped or undoped), crystalline silicon (e.g., Si&lt;100&gt; or Si&lt;111&gt;), strained silicon, silicon oxide, doped or undoped polysilicon, or the like, a germanium substrate, a silicon germanium substrate, a Group III-V compound substrate, such as a gallium arsenide substrate, a gallium nitride substrate, a silicon carbide substrate, a patterned or non-patterned semiconductor-on-insulator (SOI) substrate, a carbon-doped oxide, a silicon nitride, glass, sapphire, quartz, one or more polymeric materials, reflective materials (e.g., mirrors), an optical device, a virtual reality (VR) device, an augmented reality (AR) device, a solar array, solar or photovoltaic (PV) panel, a light emitting diode (LED) substrate, or any other materials such as metals, metal alloys, and other conductive materials, or any combination thereof. In some examples, the substrate  102  can include a plurality of layers or films, such as a semi-insulating material and a semiconducting material, where the semi-insulating material has a higher resistivity than the semiconducting material. The substrate  102  is not limited to any particular size or shape (e.g., round, rectangular, or square), or may have various dimensions. In some examples, the substrate  102  is round and has a diameter of 100 mm, 200 mm, 300 mm, 450 mm, or other diameter substrates. 
     Each of the barrier layers  110 ,  130  independently contains one or more materials, such as silicon nitride, one or more metallic elements, one or more metal nitrides, or combination thereof. In one or more examples, each of the barrier layers  110 ,  130  independently contains silicon nitride which can be deposited by PVD or another vapor deposition process (e.g., CVD or ALD). In some examples, each of the barrier layers  110 ,  130  independently contains metallic titanium, metallic chromium, metallic tantalum, metallic tungsten, metallic molybdenum, metallic vanadium, silicon, alloys thereof, dopants thereof, or any combination thereof. In other examples, each of the barrier layers  110 ,  130  independently contains titanium nitride, tantalum nitride, tungsten nitride, chromium nitride, molybdenum nitride, vanadium nitride, silicon nitride, alloys thereof, dopants thereof, or any combination thereof. The barrier layers  110 ,  130  can be deposited or otherwise formed by one or more processes or techniques, such as CVD, plasma-enhanced CVD (PE-CVD), sub-atmospheric CVD (SA-CVD), high density plasma CVD (HDP-CVD), flowable CVD (FCVD® processes), ALD, furnace or thermal ALD, thermal ALD, plasma-enhanced ALD (PE-ALD), PVD, sputtering, evaporation deposition, ion beam deposition, or any combination thereof. 
     Each of the barrier layers  110 ,  130  can independently have a thickness of about 1 nm, about 2 nm, about 5 nm, about 8 nm, about 10 nm, about 12 nm, or about 15 nm to about 18 nm, about 20 nm, about 25 nm, about 30 nm, about 35 nm, about 40 nm, about 45 nm, or about 50 nm. For example, each of the barrier layers  110 ,  130  can independently have a thickness of about 1 nm to about 50 nm, about 1 nm to about 40 nm, about 1 nm to about 30 nm, about 1 nm to about 35 nm, about 1 nm to about 30 nm, about 1 nm to about 25 nm, about 1 nm to about 20 nm, about 1 nm to about 15 nm, about 1 nm to about 12 nm, about 1 nm to about 10 nm, about 1 nm to about 5 nm, about 2 nm to about 25 nm, about 5 nm to about 50 nm, about 5 nm to about 40 nm, about 5 nm to about 30 nm, about 5 nm to about 35 nm, about 5 nm to about 30 nm, about 5 nm to about 25 nm, about 5 nm to about 20 nm, about 5 nm to about 15 nm, about 5 nm to about 12 nm, about 5 nm to about 10 nm, about 5 nm to about 8 nm, about 10 nm to about 50 nm, about 10 nm to about 40 nm, about 10 nm to about 30 nm, about 10 nm to about 35 nm, about 10 nm to about 30 nm, about 10 nm to about 25 nm, about 10 nm to about 20 nm, about 10 nm to about 15 nm, or about 10 nm to about 12 nm. 
     The metallic silver layer  120  contains metallic silver, which has a zero oxidation state. The metallic silver layer  120  can include other elements, but generally contains substantially or completely silver. In some embodiments, the metallic silver layer  120  contains at least 50 atomic percent (at %) metallic silver, such as about 60 at %, about 75 at %, about 80 at %, or about 85 at % to about 90 at %, about 95 at %, about 97 at %, about 98 at %, about 99 at %, about 99.5 at %, about 99.9 at %, or greater amount of metallic silver. 
     The metallic silver layer  120  can be deposited or otherwise formed by one or more processes or techniques, such as CVD, plasma-enhanced CVD (PE-CVD), sub-atmospheric CVD (SA-CVD), high density plasma CVD (HDP-CVD), flowable CVD (FCVD® processes), ALD, furnace or thermal ALD, thermal ALD, plasma-enhanced ALD (PE-ALD), PVD, sputtering, evaporation deposition, ion beam deposition, or any combination thereof. In one or more examples, the metallic silver layer  120  can be deposited or otherwise formed from a silver target or silver alloy target by PVD or sputtering. 
     The metallic silver layer  120  has a thickness of about 10 nm, about 15 nm, about 20 nm, about 25 nm, about 30 nm, about 35 nm, about 40 nm, about 45 nm, or about 50 nm to about 55 nm, about 60 nm, about 70 nm, about 80 nm, about 90 nm, about 100 nm, about 120 nm, about 135 nm, about 150 nm, about 180 nm, about 200 nm, or thicker. For example, the metallic silver layer  120  has a thickness of about 10 nm to about 200 nm, about 10 nm to about 180 nm, about 10 nm to about 150 nm, about 10 nm to about 120 nm, about 10 nm to about 100 nm, about 10 nm to about 80 nm, about 10 nm to about 60 nm, about 10 nm to about 50 nm, about 10 nm to about 40 nm, about 10 nm to about 20 nm, about 20 nm to about 200 nm, about 20 nm to about 180 nm, about 20 nm to about 150 nm, about 20 nm to about 120 nm, about 20 nm to about 100 nm, about 20 nm to about 80 nm, about 20 nm to about 60 nm, about 20 nm to about 50 nm, about 20 nm to about 40 nm, about 40 nm to about 200 nm, about 40 nm to about 180 nm, about 40 nm to about 150 nm, about 40 nm to about 120 nm, about 40 nm to about 100 nm, about 40 nm to about 80 nm, about 40 nm to about 60 nm, about 40 nm to about 50 nm, or about 50 nm to about 60 nm. 
     The encapsulation layer  140  contains one or more materials for encapsulating or protecting the underlying layers, namely the optical devices  132 ,  232 . In one or more embodiments, the encapsulation layer  140  contains silicon oxide (e.g., silicon dioxide), aluminum oxide, magnesium oxide, dopants thereof, or any combination thereof. In some examples, the encapsulation layer  140  is deposited or otherwise formed by one or more vapor deposition processes which utilize plasma, such as a PVD or sputtering process, a furnace CVD (FCVD) process, a PE-CVD process, a PE-ALD process, or other plasma process. During the deposition of the encapsulation layer  140 , a silicon source (e.g., a silicon target or a silicon precursor) is reacted with an oxygen source, oxygen precursor, and/or oxidizing agent (e.g., ozone, atomic oxygen, oxygen-plasma, oxygen (O 2 ), water, hydrogen peroxide, or any combination thereof). In one or more examples, the encapsulation layer  140  is deposited by a PVD process which includes generating ozone or an oxygen plasma while depositing the encapsulation layer  140 . For example, silicon oxide is deposited in a magnetron sputtering PVD chamber using a silicon target and depositing reactively with a plasma containing argon and oxygen (Ar/O 2 ). In other examples, the encapsulation layer  140  is deposited by RF sputtering of a dielectric target. An exemplary PVD chamber or system for depositing the encapsulation layer  140 , as well as other layers described and discussed herein, is the PVD Endura® tool, commercially available from Applied Materials, Inc. 
     The encapsulation layer  140  has a thickness of about 10 nm, about 15 nm, about 20 nm, about 25 nm, about 30 nm, about 35 nm, about 40 nm, about 45 nm, or about 50 nm to about 55 nm, about 60 nm, about 70 nm, about 80 nm, about 90 nm, about 100 nm, about 120 nm, about 135 nm, about 150 nm, about 180 nm, about 200 nm, or thicker. For example, the encapsulation layer  140  has a thickness of about 10 nm to about 200 nm, about 10 nm to about 180 nm, about 10 nm to about 150 nm, about 10 nm to about 120 nm, about 10 nm to about 100 nm, about 10 nm to about 80 nm, about 10 nm to about 60 nm, about 10 nm to about 50 nm, about 10 nm to about 40 nm, about 10 nm to about 20 nm, about 15 nm to about 50 nm, about 20 nm to about 200 nm, about 20 nm to about 180 nm, about 20 nm to about 150 nm, about 20 nm to about 120 nm, about 20 nm to about 100 nm, about 20 nm to about 80 nm, about 20 nm to about 60 nm, about 20 nm to about 50 nm, about 20 nm to about 40 nm, about 20 nm to about 30 nm, about 40 nm to about 200 nm, about 40 nm to about 180 nm, about 40 nm to about 150 nm, about 40 nm to about 120 nm, about 40 nm to about 100 nm, about 40 nm to about 80 nm, about 40 nm to about 60 nm, about 40 nm to about 50 nm, about 50 nm to about 60 nm, about 50 nm to about 150 nm, about 80 nm to about 120 nm, or about 90 nm to about 110 nm. 
     Embodiments of the present disclosure further relate to any one or more of the following paragraphs 1-23: 
     1. A method for encapsulating an optical device, comprising: depositing a metallic silver layer on a substrate; depositing a barrier layer on the metallic silver layer, wherein the barrier layer comprises silicon nitride, a metallic element, a metal nitride, or any combination thereof; and depositing an encapsulation layer comprising silicon oxide on the barrier layer. 
     2. The method according to paragraph 1, wherein the encapsulation layer is deposited by a physical vapor deposition process. 
     3. The method according to paragraph 2, wherein the physical vapor deposition process comprises generating ozone or an oxygen plasma while depositing the encapsulation layer. 
     4. The method according to any one of paragraphs 1-3, wherein the metallic silver layer has a thickness of about 10 nm to about 200 nm. 
     5. The method according to any one of paragraphs 1-4, wherein the barrier layer comprises silicon nitride deposited by physical vapor deposition. 
     6. The method according to any one of paragraphs 1-5, wherein the barrier layer comprises metallic titanium, metallic chromium, metallic tantalum, metallic tungsten, metallic molybdenum, metallic vanadium, silicon, alloys thereof, dopants thereof, or any combination thereof. 
     7. The method according to any one of paragraphs 1-6, wherein the barrier layer comprises titanium nitride, tantalum nitride, tungsten nitride, chromium nitride, molybdenum nitride, vanadium nitride, silicon nitride, alloys thereof, dopants thereof, or any combination thereof. 
     8. The method according to any one of paragraphs 1-7, wherein the barrier layer has a thickness of about 1 nm to about 50 nm. 
     9. The method according to any one of paragraphs 1-8, wherein the encapsulation layer has a thickness of about 10 nm to about 200 nm. 
     10. The method according to any one of paragraphs 1-9, wherein the substrate comprises glass, quartz, silicon dioxide, or fused silica. 
     11. The method according to any one of paragraphs 1-10, further comprising: depositing an intermediate barrier layer on the substrate, wherein the intermediate barrier layer comprises silicon nitride, a metallic element, a metal nitride, or any combination thereof; and depositing the metallic silver layer directly on the intermediate barrier layer. 
     12. The method according to paragraph 11, wherein the intermediate barrier layer has a thickness of about 1 nm to about 50 nm. 
     13. A method for encapsulating an optical device, comprising: depositing a first barrier layer on a substrate, wherein the first barrier layer comprises silicon nitride, a metallic element, a metal nitride, or any combination thereof; depositing a metallic silver layer on the first barrier layer; depositing a second barrier layer on the metallic silver layer, wherein the second barrier layer comprises silicon nitride, a metallic element, a metal nitride, or any combination thereof; and depositing an encapsulation layer comprising silicon oxide on the second barrier layer by a physical vapor deposition process. 
     14. An encapsulated optical device, comprising: a first barrier layer disposed on a substrate, wherein the substrate comprises glass, quartz, silicon dioxide, or fused silica, and wherein the first barrier layer comprises silicon nitride, a metallic element, a metal nitride, or any combination thereof; a metallic silver layer disposed on the first barrier layer; a second barrier layer disposed on the metallic silver layer, wherein the second barrier layer comprises silicon nitride, a metallic element, a metal nitride, or any combination thereof; and an encapsulation layer comprising silicon oxide disposed on the second barrier layer. 
     15. The encapsulated optical device according to paragraph 14, wherein the encapsulation layer is deposited by a physical vapor deposition process. 
     16. The encapsulated optical device according to paragraph 14 or 15, wherein the physical vapor deposition process comprises generating ozone or an oxygen plasma while depositing the encapsulation layer. 
     17. The encapsulated optical device according to any one of paragraphs 14-16, wherein the metallic silver layer has a thickness of about 10 nm to about 200 nm. 
     18. The encapsulated optical device according to any one of paragraphs 14-17, wherein the first barrier layer and/or the second barrier layer independently comprises silicon nitride deposited by physical vapor deposition. 
     19. The encapsulated optical device according to any one of paragraphs 14-18, wherein each of the first barrier layer and the second barrier layer independently comprises metallic titanium, metallic chromium, metallic tantalum, metallic tungsten, metallic molybdenum, metallic vanadium, silicon, alloys thereof, dopants thereof, or any combination thereof. 
     20. The encapsulated optical device according to any one of paragraphs 14-19, wherein each of the first barrier layer and the second barrier layer independently comprises titanium nitride, tantalum nitride, tungsten nitride, chromium nitride, molybdenum nitride, vanadium nitride, silicon nitride, alloys thereof, dopants thereof, or any combination thereof. 
     21. The encapsulated optical device according to any one of paragraphs 14-20, wherein each of the first barrier layer and the second barrier layer independently has a thickness of about 1 nm to about 50 nm. 
     22. The encapsulated optical device according to any one of paragraphs 14-21, wherein the encapsulation layer has a thickness of about 10 nm to about 200 nm. 
     23. The encapsulated optical device according to any one of paragraphs 14-22, wherein the substrate comprises glass, quartz, silicon dioxide, or fused silica. 
     While the foregoing is directed to embodiments of the disclosure, other and further embodiments may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. All documents described herein are incorporated by reference herein, including any priority documents and/or testing procedures to the extent they are not inconsistent with this text. As is apparent from the foregoing general description and the specific embodiments, while forms of the present disclosure have been illustrated and described, various modifications can be made without departing from the spirit and scope of the present disclosure. Accordingly, it is not intended that the present disclosure be limited thereby. Likewise, the term “comprising” is considered synonymous with the term “including” for purposes of United States law. Likewise, whenever a composition, an element, or a group of elements is preceded with the transitional phrase “comprising”, it is understood that the same composition or group of elements with transitional phrases “consisting essentially of”, “consisting of”, “selected from the group of consisting of”, or “is” preceding the recitation of the composition, element, or elements and vice versa, are contemplated. As used herein, the term “about” refers to a +/−10% variation from the nominal value. It is to be understood that such a variation can be included in any value provided herein. 
     Certain embodiments and features have been described using a set of numerical upper limits and a set of numerical lower limits. It should be appreciated that ranges including the combination of any two values, e.g., the combination of any lower value with any upper value, the combination of any two lower values, and/or the combination of any two upper values are contemplated unless otherwise indicated. Certain lower limits, upper limits and ranges appear in one or more claims below.