Patent ID: 12249489

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

Embodiments of the present disclosure relate to improved optical devices and methods of improving the optical properties of one or more surface regions of optical devices. Optical device structures (e.g., optical gratings for a waveguide combiner) are often formed of silicon carbide due to the refractive index and other optical properties of silicon carbide. These silicon carbide optical device structures are often formed on substrates formed of silicon carbide. Forming the optical device structures on silicon carbide substrates using methods, such as ion-beam etching (IBE), can result in regions near the surface of the optical device structures and substrate being formed of silicon oxycarbide due to gases (e.g., oxides) used in the process. These silicon oxycarbide regions can cause high levels of optical loss and diminish the optical performance of the optical device.

Disclosed herein are methods and related process equipment that can substantially reduce the carbon content of these silicon oxycarbide regions (e.g., >50% reduction) formed over the optical device structures and the substrate, so that the optical loss caused by the silicon oxycarbide regions is substantially reduced. In one embodiment, a plasma treatment process is performed to substantially reduce the carbon content in the surface regions of the optical device structures and substrate. In another embodiment, an annealing process is performed with one or more process gases to substantially reduce the carbon content in the surface regions of the optical device structures and substrate. These methods can be used to improve the optical performance of the optical device and restore the optical loss to levels substantially the same as optical loss levels of the material (e.g., silicon carbide) before the process (e.g., IBE) used to form the optical device structures is performed. In some embodiments, these methods can improve the optical device efficiency for red light, green light, and blue light by at least 50%, such as by at least 70%. In some embodiments, these methods can improve the optical device efficiency for green light by at least 100%, such as by at least 149%. In some embodiments, these methods can improve the optical device efficiency for green light by at least 100%, such as by at least 260%.

FIG.1is a cross-sectional view of an optical device100, according to one embodiment. The optical device100includes an optical device substrate101and an optical device film105. The optical device substrate101includes a first surface101A and an opposing second surface101B. The optical device film105is disposed over the first surface101A of the optical device substrate101. In some embodiments, the optical device film105is disposed directly on the first surface101A of the substrate101.

In some embodiments, which can be combined with other embodiments described herein, the optical device substrate101can be formed of an optically transparent material. In some embodiments, the optical device substrate101can be formed of silicon carbide.

The optical device film105can also be formed of silicon carbide. In some embodiments, the optical device film105can be formed of another optically transparent material, for example another optically transparent material including silicon and/or carbon. In some embodiments, the optical device film105can be formed over the optical device substrate101using chemical vapor deposition (CVD), plasma-enhanced CVD, or physical vapor deposition among other techniques. In other embodiments, there is not a separate film105and the optical device structures described below can be formed by etching a silicon carbide substrate.

FIG.2is a cross-sectional view of an optical device200, according to one embodiment. The optical device200is formed by modifying the optical device film105from the optical device100ofFIG.1. In one embodiment, which can be combined with other embodiments described herein, the optical device200is a waveguide combiner, such as an augmented reality waveguide combiner. In another embodiment, which can be combined with other embodiments described herein, the optical device200is a flat optical device, such as a metasurface. Other optical devices that can be formed from the optical device film105include optical filters and dielectric mirrors.

The optical device200includes a plurality of optical device structures202disposed over (e.g., directly on) the first surface101A of the substrate101. The optical device structures202can be spaced apart from each other in the X-direction by trenches211. In some embodiments, the trenches211extend down to the first surface101A of the optical device substrate101. The optical device structures202can each include a top surface203and side surfaces204. The optical device structures202can each further include a bulk region205and surface regions206. The optical device structures202are formed from the optical device film105fromFIG.1, and thus the bulk regions205of the optical device structures202are formed of silicon carbide. In some embodiments, the optical device structures202can be formed of another optically transparent material, for example another optically transparent material including silicon and/or carbon. In one embodiment, the optical device structures202are gratings for a waveguide combiner configured for use in an augmented reality device.

The surface regions206are formed of silicon oxycarbide. The surface regions206can extend along the top surface203and the side surfaces204of each optical device structure202. Although the surface regions206are shown having a uniform thickness, the thickness of the surface regions206can vary along the top surface203and the side surfaces204. The thickness of the surface regions206can be from about 0.1 nm to about 50 nm, such as from about 1 nm to about 10 nm, such as about 3 nm. Furthermore, the carbon content can vary within the surface regions206along any dimension. The accumulation of carbon in the surface regions206can reduce the optical performance of the optical device200compared to the same optical device200that does not include the accumulated carbon in the surface regions206.

In some embodiments, surface regions212are formed over the first surface101A of the optical device substrate101at the bottom of the trenches211as a result of the process used to form the optical device structures202(e.g., an IBE process). Although only one example of the surface regions212is shown, in some embodiments, the surface regions212are formed at the bottom of each trench211. In one embodiment, the surface regions212can have a similar composition (e.g., formed of silicon oxycarbide) and dimensions as the surface regions206described above.

The plurality of optical device structures202can be spaced apart from each other in a direction (e.g., the X-direction) parallel to the first surface101A of the substrate101. The optical device structures202include sub-micron critical dimensions, e.g., nanosized dimensions, corresponding to the widths of the optical device structures202in the X-direction. In some embodiments, the optical device structures202may be binary structures (not shown) with side surfaces204perpendicular to the first surface101A of the substrate101. In other embodiments, the optical device structures202may be angled structures with at least one of the side surfaces204angled relative to the first surface101A of the substrate101. The optical device structures202can be formed from the optical device film105via one or more lithography and/or etch processes, such as an ion beam etching process on the optical device film105.

FIG.3is a side cross-sectional view of a plasma processing system300, according to one embodiment. The plasma processing system300includes a process chamber301, a radio frequency power source305, an optional remote plasma source307, and a controller355for controlling processes performed by the processing system300. The plasma processing system300can be used to generate a plasma in the process chamber301or supply a plasma to the process chamber301. The optical device200fromFIG.2can be exposed to the plasma to remove the carbon or substantially reduce the carbon content of the surface regions206,212of the optical device200.

The process chamber301includes a chamber body302having a bottom317aand one or more sidewalls317bthat are disposed around a processing volume311(also referred to as interior volume). The process chamber301includes a substrate support350disposed in the processing volume311. The substrate support350is adapted to support the optical device200on a top surface351of the substrate support350during processing.

The process chamber301further includes an actuator338and a shaft337. The substrate support350is coupled to the actuator338by the shaft337. The actuator338is configured to move the substrate support350at least vertically to (1) facilitate transfer of the optical device200into and out of the chamber body302and/or (2) adjust a distance D between the optical device200and a showerhead assembly303.

The process chamber301can include a heater360in the substrate support350configured to provide heat to the optical device200during processing. In some embodiments, the heater360is a resistive heater embedded in the substrate support350. In some embodiments, the process chamber301includes a temperature sensor365, such as a thermocouple, configured to measure a temperature of the substrate supporting surface351of the substrate support350. The controller355can use measurements from the temperature sensor365to adjust the power provided to the heater360to control the temperature of the top surface351of the substrate support350. In some embodiments, the process chamber301can include an electrode361embedded in the substrate support350. In some of these embodiments, the electrode361can be connected to an electrical ground to provide a return path for RF energy provided to the showerhead for generating the plasma in the process chamber301as described in further detail below.

The process chamber301includes a showerhead assembly303that is configured to supply gases to the processing volume311from a plurality of gas sources322. The plasma processing system300also includes an exhaust system318configured to apply vacuum pressure to the processing volume311. The showerhead assembly303is generally disposed opposing the substrate support350, for example directly above the substrate support350, in a substantially parallel relationship.

The showerhead assembly303includes a gas distribution plate314and a backing plate316. The backing plate316may function as a blocker plate to enable formation of a gas volume331between the gas distribution plate314and the backing plate316. The gas sources322are connected to the gas distribution plate314by a conduit334. In one embodiment, an optional remote plasma source307is coupled to the conduit334for supplying a plasma through the gas distribution plate314to the processing volume311.

The gas distribution plate314, the backing plate316, and the conduit334are generally formed from electrically conductive materials and are in electrical communication with one another. The chamber body302is also formed from an electrically conductive material. The chamber body302is electrically insulated from the showerhead assembly303. In one embodiment, the showerhead assembly303can be suspended below a top of the chamber body302by attaching the showerhead assembly303to an insulator335that electrically separates the showerhead assembly303from the chamber body302.

In one embodiment, the substrate support350is also electrically conductive. The electrically conductive substrate support350and the showerhead assembly303can be configured as opposing electrodes for generating a plasma308abetween the substrate support350and the showerhead assembly303during plasma processes. In one embodiment, the electrode361in the substrate support350can be connected to electrical ground of the RF power source described below.

The plasma processing system300can include the radio frequency (RF) power source305that can be used to generate the plasma308abetween the showerhead assembly303and the substrate support350during processing. The RF power source305may also be used to maintain energized species or further excite gases supplied from the remote plasma source307. The plasma generated by the RF power source305or provided from the remote plasma source307can help remove carbon from the surface regions206,212of the optical device200(seeFIG.2), which can improve the optical performance of the optical device200.

The RF power source305can be coupled to the showerhead assembly303to supply RF power for generating the plasma. The RF power source305can also be connected to the chamber body302and the electrode361embedded in the substrate support350to allow for a return path for the RF circuit. The RF power source305can make these corresponding connections to the showerhead assembly303, the chamber body302, and the electrode361through an impedance matching circuit321.

The controller355can be any type of controller used in an industrial setting, such as a programmable logic controller (PLC). The controller355includes a processor357, a memory356, and input/output (I/O) circuits358. The controller355can further include one or more of the following components (not shown), such as one or more power supplies, clocks, communication components (e.g., network interface card), and user interfaces typically found in controllers for semiconductor equipment.

The memory356can include non-transitory memory. The non-transitory memory can be used to store the programs and settings described below. The memory356can include one or more readily available types of memory, such as read only memory (ROM) (e.g., electrically erasable programmable read-only memory (EEPROM), flash memory, floppy disk, hard disk, or random access memory (RAM) (e.g., non-volatile random access memory (NVRAM).

The processor357is configured to execute various programs stored in the memory356, such as a programs configured to execute the methods4000,6000described below in reference to correspondingFIGS.4and6. During execution of these programs, the controller355can communicate to I/O devices through the I/O circuits358. For example, during execution of these programs and communication through the I/O circuits358, the controller355can control outputs (e.g., pumps and valves) and monitor inputs (e.g., sensors). The memory356can further include various operational settings used to control the processing system300(FIG.3) and the processing system500(FIG.5). For example, the settings can include settings for controlling the operating conditions (e.g., temperature, pressure, and gas concentrations) inside the process chamber301(FIG.3) and process chamber501(FIG.5).

FIG.4is a process flow diagram of a method4000of performing a plasma process on the optical device200shown inFIG.2, according to one embodiment. The method4000can be performed on the optical device200using the processing system300described above in reference toFIG.3.

The method4000begins at block4002. At block4002, the optical device200is positioned on the substrate support350in the processing volume311of the process chamber301.

At block4004, heat is provided by the heater360to heat the substrate support350and the optical device200on the substrate support350. The heater360can be used to heat the substrate supporting surface351to a temperature setpoint (e.g., 200° C. to 500° C.) as measured by the temperature sensor365. Also, at block6004one or more process gases are provided to the process volume311from the gas sources322. In some embodiments, the process gases can include one or more of hydrogen, steam, nitrogen, and oxygen. In some of these embodiments, an inert gas, such as argon, can also be provided from the gas sources322. The controller355can be used to adjust power provided to the heater360during block4004to maintain the top surface351of the substrate support350at the temperature setpoint. Block4004can be performed for a duration extending from about five seconds to about five minutes, such as for about one minute.

At block4006, the gases provided to the processing volume311during block4004continue to be provided to the processing volume311and a plasma is generated from the gases provided to the processing volume311from the gas sources322. In one embodiment, RF power can be provided from the RF power source305to the showerhead assembly303to generate the plasma308abetween the showerhead assembly303and the substrate support350. In one embodiment, the electrode361in the substrate support350is connected to electrical ground for the RF power source305, so that the capacitively coupled plasma308acan be generated in the processing volume311by the RF power provided to the showerhead assembly303from the RF power source305. In some embodiments, the RF power provided by the RF power source305has a frequency of about 13.56 MHz and a power level from about 100 Watts to about 1000 Watts.

The plasma and heat provided to the interior volume311of the process chamber301during blocks4004,4006can substantially reduce the carbon content in the surface regions206,212of the optical device200(FIG.2) by at least 50%, such as by at least 80% (e.g., ⅚ of the carbon being removed), such as by at least 90%, such as by at least 99%. By reducing the carbon content in the surface regions206by a substantial amount, the surface regions206of the optical device structures202obtain optical properties significantly more similar to silicon oxide. These substantially lower levels of carbon in the regions206,212improve the optical performance of the optical device200and cause substantially lower levels of optical loss when compared to the optical device200including the silicon oxycarbide regions206,212with higher levels of carbon.

In some embodiments, the plasma308acan alternatively be generated in the remote plasma source307and provided to the processing volume311to expose the optical device200to the plasma308ainstead of being generated in the processing volume311by the RF power provided by the RF power source305.

At block4008, the plasma generation and the heat provided by the heater360is stopped, and the processing volume311of the process chamber301is cooled to a reduced temperature. In some embodiments, the process gas and/or the inert gas can be provided during the execution of block6008.

FIG.5is a top cross-sectional view of a batch processing system500, according to one embodiment. The batch processing system500includes a batch processing chamber501, a plurality of gas sources520, an exhaust pump525, and the controller355described above in reference toFIG.3.

The batch processing chamber501includes a chamber body502enclosing an interior volume505. The batch processing chamber501includes a support550and a plurality of stands551on the support550. The optical devices200can each be positioned between the stands551to enable the optical devices200to each be oriented in a vertical direction, for example with the surfaces101A,101B of the optical device substrate101(seeFIG.2) facing in the plus and minus X-directions.

The batch processing chamber501further includes a plurality of heating coils530on opposing sides of the support550. In some embodiments, the coils530can each be positioned behind an infrared-transparent window535, such as a quartz window. Power can be provided to the coils530during processing to heat the optical devices200to temperatures from about 600° C. to about 2000° C. during processing. The batch processing chamber501can further include a temperature sensor560, such as a thermocouple, positioned on the support550near the optical devices200to monitor and control the temperature of the interior volume505during processing. The controller355can be configured to receive measurements from the temperature sensor560and modulate power provided to the coils530to control the temperature of the interior volume505during processing. In some embodiments, the batch processing chamber501can include two or more temperature sensors, such as five temperature sensors or ten temperature sensors (e.g., one temperature sensor for each coil530, so that the temperature measured by each sensor can be controlled by one coil530).

FIG.6is a process flow diagram of a method6000of performing a batch annealing process on a plurality of the optical devices200shown inFIG.2, according to one embodiment. The method6000can be performed on the optical devices200using the batch processing system500described above in reference toFIG.5.

The method6000begins at block6002. At block6002, a plurality of the optical devices200(e.g., ten optical devices200as shown inFIG.5) are positioned on the support550in the interior volume505of the batch process chamber501. The optical devices200can be positioned and vertically oriented within the stands551. The optical devices200can be spaced apart from each other, for example in the X-direction ofFIG.5, so that the optical device structures202(FIG.2) can be exposed to the gases provided to the interior volume505.

At block6004, heat is provided from the coils530to increase the interior volume505of the process chamber501to a temperature setpoint. In some embodiments, the temperature of the interior volume505is heated to a temperature from about 600° C. to about 2000° C., such as from about 900° C. to about 1400° C.

One or more process gases (e.g., hydrogen, steam, oxygen, and nitrogen) can be provided to the interior volume505of the process chamber501from the gas sources520during block6004. In some embodiments, an inert gas (e.g., argon) can be used as a carrier gas to assist in flowing the one or more process gases over surfaces of the optical devices200.

At block6006, the controller355can use measurements from the temperature sensor560to control the power provided to the coils530, so that the temperature measured by the temperature sensor560can be maintained within a specified threshold (0.5 degrees ° C.) of the temperature setpoint during processing.

The duration of block6006can be from about one minute to about three hours, such as from about five minutes to about one hour, such as about ten minutes. The one or more process gases and the optional inert gas from the gas sources520can be provided to the interior volume505of the process chamber501during block6006.

In some embodiments, the process gas can be hydrogen (H2). In some of these embodiments, the flowrate (e.g., sccm) of H2can be from about 0.1% to about 10%, such as from about 1% to about 5% (e.g., 2.8%) of the total gas flowrate (e.g., sccm) provided to the interior volume505of the process chamber501during blocks6004and6006. In some of these embodiments, the remainder of the gas flowrate is provided by an inert gas, such as argon. In other of these embodiments, the remainder of the gas flowrate is provided by nitrogen.

During blocks6004and6006, the pressure in the interior volume505of the process chamber501can be maintained at a pressure from about 250 Torr to about 1000 Torr, such as from about 300 Torr to about 760 Torr, such as about 400 Torr to about 500 Torr.

The heat and process gases provided to the interior volume505of the process chamber501during blocks6004,6006can substantially reduce the carbon content in the surface regions206,212of the optical device200(FIG.2) by at least 50%, such as by at least 80% (e.g., ⅚ of the carbon being removed), such as by at least 90%, such as by at least 99%. By reducing the carbon content in the surface regions206by a substantial amount, the surface regions206,212of the optical device200obtain optical properties significantly more similar silicon oxide. which improves the optical performance of the optical device200. These substantially lower levels of carbon in the regions206,212improve the optical performance of the optical device200and cause substantially lower levels of optical loss when compared to the optical device200including the silicon oxycarbide regions206,212with higher levels of carbon.

At block6008, the interior volume505of the process chamber501is cooled to a reduced temperature. In some embodiments, the process gas and/or the inert gas can be provided during some or all of the cooling down period at block6008.

While the foregoing is directed to examples of the present disclosure, other and further examples of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.