Large-thickness silicon nitride waveguide preparation method based on wafer bonding
By employing wafer bonding and plasma activation methods, thick silicon nitride waveguides were fabricated, solving the cracking problem caused by stress accumulation. This resulted in high-quality and low-loss silicon nitride waveguides, simplifying the process and reducing costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-15
- Publication Date
- 2026-03-17
AI Technical Summary
Existing processes for fabricating thick silicon nitride waveguides suffer from defects such as cracks caused by stress accumulation, leading to a decrease in waveguide quality and an increase in transmission loss. Furthermore, existing processes are complex and costly, making it difficult to achieve large-scale production.
A wafer-based bonding method is adopted, in which silicon nitride wafers are directly bonded after plasma activation treatment, combined with chemical mechanical polishing and wet etching processes to fabricate thick silicon nitride waveguides, avoiding the cracking problem caused by stress accumulation and simplifying the process flow.
This achievement enables the fabrication of thick, high-quality, and low-loss silicon nitride waveguides, simplifies the process, reduces costs, and lays the foundation for large-scale production.
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Figure CN121679804A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of photonic integrated chip technology, and more specifically, to a method for fabricating thick silicon nitride waveguides based on wafer bonding. Background Technology
[0002] With the rapid development of silicon-based optoelectronics, the integration requirements of silicon photonic chips are constantly increasing, and the complexity of devices is also becoming increasingly higher. To adapt to advanced optoelectronic integrated devices, materials with better performance than traditional silicon or InGaAsP waveguides are needed to achieve higher integration and better device performance. Compared with traditional silicon photonic materials, silicon nitride has the advantage of compatibility with complementary metal-oxide-semiconductor (CMOS) processes, while also exhibiting superior performance. Silicon nitride has a wide transparency window, a wider bandgap, almost no two-photon absorption, and a low thermo-optical coefficient, resulting in minimal transmission loss. For fields such as precision computing, quantum communication, nonlinear optics, and heterogeneous integrated narrow-linewidth lasers, low-loss silicon nitride waveguides and high-Q silicon nitride microring resonators are of great interest. Therefore, more and more research is dedicated to optimizing the fabrication process of silicon nitride waveguides to meet the needs of complex optoelectronic chips. However, existing manufacturing processes struggle to achieve thick, high-quality silicon nitride waveguides, mainly due to the high stress accumulation in the silicon nitride thin film, which increases the generation of defects such as cracks.
[0003] The existing methods have the following problems when preparing thick silicon nitride waveguides: (1) When preparing thick silicon nitride waveguides using plasma enhanced chemical vapor deposition (PECVD) process, the bombardment of the silicon nitride surface by plasma will cause significant damage to the waveguide layer, which will lead to structural looseness, non-stoichiometry (Si / N≠1.33) problems, and increase intrinsic absorption and scattering loss. The deposition process will introduce high stress concentration, which will lead to film cracking or even peeling (especially serious when the thickness is greater than 500 nm), resulting in low quality of thick film, high defect density and increased transmission loss. The process has insufficient step coverage capability and it is difficult to achieve uniform coverage in high aspect ratio structures, which will increase the roughness of the waveguide sidewall and significantly increase the sidewall scattering loss. (2) When using low-pressure chemical vapor deposition (LPCVD) to fabricate thick silicon nitride waveguides, huge stress is easily generated during the deposition of thick films, leading to film cracking, peeling, or wafer warping, which limits the maximum depositable thickness. Thick film growth requires a long high-temperature process, resulting in reduced production efficiency, increased costs, and decreased yield, making large-scale production difficult. Deposition uniformity is difficult to control, and as the film thickness increases, uniformity is easily deteriorated, leading to increased surface roughness and scattering loss. (3) Using photonic damascus to fabricate thick silicon nitride waveguides has high process complexity: it involves multiple etching, polishing, and deposition steps, which is costly, thus limiting the large-scale production and further development of thick silicon nitride waveguide devices. Compared with LPCVD and PECVD processes, this manufacturing process has a relatively low maturity. Summary of the Invention
[0004] The purpose of this invention is to overcome the shortcomings of existing technologies in the manufacturing process of thick silicon nitride waveguides, which inevitably face defects such as cracks caused by stress accumulation in the silicon nitride waveguide film, leading to a decrease in waveguide quality. This invention provides a method for fabricating thick silicon nitride waveguides based on wafer bonding, which effectively avoids problems such as cracks caused by stress accumulation, realizes the fabrication of thick silicon nitride waveguides, improves the quality of thick silicon nitride waveguides, and simplifies the process flow.
[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for fabricating thick silicon nitride waveguides based on wafer bonding is provided, comprising: S1. Select at least two silicon nitride wafers of the required size; S2. Clean the silicon nitride wafer; S3. Perform plasma activation treatment on the cleaned silicon nitride wafer; S4. Bond the activated silicon nitride wafer; S5. Remove the substrate, retain the target layer, and obtain the desired thick silicon nitride wafer; S6. Waveguide design and fabrication on thick silicon nitride wafers.
[0006] This invention discloses a method for fabricating thick silicon nitride waveguides based on wafer bonding. This method only requires plasma activation treatment of commercially available low-thickness silicon nitride wafers followed by direct bonding to obtain high-performance thick silicon nitride waveguides. It effectively avoids the problems of reduced yield and increased optical transmission loss caused by structural defects such as cracks due to stress accumulation in the silicon nitride thin film during deposition-based fabrication of thick silicon nitride waveguides. The method of this invention enables the fabrication of thick silicon nitride waveguides, improves their quality and performance, and simplifies the process flow.
[0007] Further, step S2 specifically includes: removing organic contaminants from the surface of the silicon nitride wafer using a cleaning agent, and cleaning particulate contaminants from the surface of the silicon nitride wafer using megaphonic cleaning. Cleaning agents include acetone, isopropanol, ethanol, and deionized water, etc.
[0008] Further, in step S2, the silicon nitride wafer is rinsed sequentially with acetone, isopropanol, ethanol and deionized water to remove organic contaminants.
[0009] Further, step S3 specifically includes: plasma bombarding the surface of silicon nitride wafers with ions to form unsaturated chemical bonds on the wafer surface.
[0010] Furthermore, step S4 specifically includes: S41. Room temperature bonding: Under room temperature conditions, the silicon nitride layer of one silicon nitride wafer is aligned with the silicon nitride layer of another silicon nitride wafer. S42. Bonding in the bonding machine: Place the aligned silicon nitride wafer into the bonding machine, set the bonding parameters and annealing temperature, and perform the bonding and annealing operations in sequence.
[0011] Further, step S5 includes: removing the substrate layer of one of the silicon nitride wafers, leaving the silicon nitride layer.
[0012] Furthermore, the silicon nitride wafer comprises, from bottom to top, a silicon substrate, a silicon dioxide buried layer, and a silicon nitride layer.
[0013] Furthermore, step S5 specifically includes: Chemical mechanical polishing is used to remove the silicon substrate layer: first, the silicon substrate layer is thinned to 45-55 micrometers; then, the remaining thickness of the silicon substrate layer is thoroughly removed using tetramethylammonium hydroxide solution. The silica buried layer was removed by wet etching: buffered hydrofluoric acid was used to perform wet etching to remove the silica buried layer; During the removal process, another silicon nitride wafer is simultaneously protected.
[0014] Further, step S6 includes: The thick silicon nitride wafer after step S5 is subjected to inductively coupled plasma oxygen plasma activation treatment. Electron beam photoresist is spin-coated onto the silicon nitride layer surface of a thick silicon nitride wafer; Waveguide patterns are defined using electron beam lithography. Waveguide structures are etched using reactive ion etching. A silicon dioxide layer was prepared by chemical vapor deposition as the upper cladding of the waveguide.
[0015] Furthermore, step S1 also includes cleaving the silicon nitride wafer to obtain a silicon nitride wafer of the target size.
[0016] Compared with the prior art, the beneficial effects of the present invention are: This invention discloses a method for fabricating thick silicon nitride waveguides based on wafer bonding, overcoming the shortcomings of existing thick silicon nitride thin film deposition processes that suffer from defects such as cracks due to stress accumulation. This method successfully achieves a silicon nitride waveguide integrating "large thickness, high quality, and low loss." Furthermore, the plasma-activated direct bonding process for fabricating thick silicon nitride waveguides is relatively simple and low-cost, providing a simpler and more industrially feasible solution for the large-scale fabrication of thick, high-quality, and low-loss silicon nitride waveguides. Attached Figure Description
[0017] Figure 1 This is a schematic flowchart of a method for fabricating a thick silicon nitride waveguide based on wafer bonding in one embodiment; Figure 2 This is a schematic diagram of the fabrication process of a thick silicon nitride waveguide based on wafer bonding in one embodiment; Figure 3 This is a schematic diagram of the waveguide structure in one embodiment.
[0018] In the attached diagram: 100, upper bonding wafer; 200, lower bonding wafer; 1, silicon nitride layer; 2, silicon dioxide buried layer; 3, silicon substrate; 4, electron beam photoresist; 5, waveguide structure; 6, upper cladding. Detailed Implementation
[0019] The present invention will be further described below with reference to specific embodiments. The accompanying drawings are for illustrative purposes only, representing schematic diagrams rather than actual physical objects, and should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.
[0020] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.
[0021] Example 1 This embodiment is a first embodiment of a method for fabricating a thick silicon nitride waveguide based on wafer bonding. This embodiment is based on plasma-activated direct bonding to fabricate a thick silicon nitride waveguide, including cutting a low-thickness silicon nitride wafer to obtain a silicon nitride wafer of the target size for bonding; cleaning the silicon nitride wafer to be bonded to ensure its surface cleanliness; performing plasma activation treatment on the cleaned silicon nitride wafer to generate sufficient hydroxyl groups (-OH) required for bonding on the surface of the silicon nitride wafer; after the activated silicon nitride wafer is bonded at room temperature, bonding and annealing are completed by a bonding machine; removing the substrate of the thick silicon nitride wafer after bonding; since most commercially available silicon nitride wafers are silicon nitride-on-insulator structures, the upper silicon nitride wafer substrate needs to be removed before subsequent waveguide design and manufacturing can be carried out; waveguide structure 5 is designed and manufactured on the silicon nitride wafer after substrate removal, and through processes such as photolithography, etching and oxide layer deposition, a thick, high-quality, low-loss silicon nitride waveguide is finally obtained.
[0022] In this embodiment, as Figure 1 As shown, the specific implementation steps include the following: Step S1. Select two commercially available silicon nitride wafers of suitable size. Commercially available silicon nitride wafers are mostly 300nm or 400nm low-thickness specifications. Silicon nitride wafers of the required size can be obtained through dicing process, and bonding between small silicon nitride wafers can be performed. Alternatively, the dicing step can be skipped and wafer-level bonding can be performed directly.
[0023] Step S2. Clean the silicon nitride wafer; the cleanliness and flatness of the silicon nitride wafer surface are crucial for achieving direct bonding. This step typically involves conventional cleaning and megasonic cleaning. Conventional cleaning involves sequentially rinsing the silicon nitride wafer with acetone (ACE), isopropanol (IPA), ethanol (EtOH), and deionized water (DI water) to primarily remove surface organic contaminants. Megasonic cleaning uses a transducer to generate megahertz-level high-energy sound waves to effectively remove micro-particulate contaminants adsorbed on the silicon nitride wafer surface, thus achieving a highly efficient and precise cleaning effect. After this cleaning step, the surface cleanliness of the silicon nitride wafer to be bonded is significantly improved.
[0024] Step S3. Perform plasma activation treatment on the cleaned silicon nitride wafer; the plasma bombards the wafer surface with ions, causing unsaturated chemical bonds to form on the wafer surface. These chemical bonds can adsorb water molecules and form a sufficient number of hydroxyl groups (-OH) on the wafer surface, providing bonding strength and bonding quality assurance for wafer bonding.
[0025] Step S4. Bond the activated silicon nitride wafers; this process typically includes room temperature bonding, machine bonding, and annealing. Room temperature bonding aims to ensure precise alignment of the two silicon nitride wafers to be bonded, providing a pretreatment basis for subsequent machine bonding annealing. Machine bonding annealing involves placing the room temperature bonded silicon nitride wafers in a bonding machine and setting key parameters such as pressure, pressure application time, annealing temperature, annealing environment, and annealing time to ensure bonding quality. The core mechanism of this step lies in the dehydration condensation reaction between hydroxyl groups on the silicon nitride wafer surface, which promotes the formation of more covalent bonds at the bonding interface during subsequent annealing, thereby achieving high-strength bonding and ultimately obtaining a thick silicon nitride waveguide layer (twice the thickness of a single layer).
[0026] Step S5. Remove the substrate, retaining the target layer, to obtain the desired thick silicon nitride wafer. The core objective of this step is to remove the silicon substrate 3 and the silicon dioxide buried layer 2 from the insulator. When removing the silicon substrate 3, it is first thinned to approximately 50 micrometers using chemical mechanical polishing. Then, the remaining thickness of the silicon substrate 3 is thoroughly removed using tetramethylammonium hydroxide solution. The reaction mechanism is that when the silicon surface is exposed to the tetramethylammonium hydroxide solution, hydroxide ions (OH-) in the solution react with silicon to form silicon hydroxide (Si(OH)4), thereby dissolving the silicon layer. Similarly, for the silicon dioxide buried layer 2, wet etching using buffered hydrofluoric acid is employed. Buffered hydrofluoric acid is prepared by mixing ammonium fluoride and hydrofluoric acid in a specific ratio. The main reaction is between hydrofluoric acid and silicon dioxide, with the reaction mechanism being: 6HF + SiO2 → H2SiF6 + 2H2O. This buffer system allows for precise control of the hydrogen ion concentration, enabling controlled etching of silicon dioxide (SiO2). Although substrate removal can also be achieved using dry etching, wet etching is chosen in this embodiment because it has a higher etching selectivity and is easier to control the process.
[0027] Step S6. Waveguide design and fabrication on a thick silicon nitride wafer; this step uses electron beam lithography (EBL) to define the waveguide pattern, followed by reactive ion etching (RIE) to etch the waveguide structure 5, and finally uses chemical vapor deposition (CVD) to fabricate a silicon dioxide layer as the waveguide cladding 6. At this point, the fabrication of the thick silicon nitride waveguide is complete.
[0028] This embodiment proposes a method for fabricating thick silicon nitride waveguides based on wafer bonding. It innovatively employs a direct bonding process involving plasma activation to firmly bond two commercially available low-thickness silicon nitride wafers, successfully fabricating a silicon nitride waveguide with significant thickness (equivalent to twice the thickness of a single layer), high quality, and low transmission loss. Compared to other existing thick silicon nitride manufacturing processes, this embodiment offers significant advantages: First, the direct bonding process fundamentally avoids the inherent defects such as cracks caused by stress accumulation during the fabrication of thick silicon nitride waveguides using traditional methods. Second, its process steps are simple and efficient, requiring only a single bonding operation to simultaneously achieve the three key performance indicators of increased thickness, improved quality, and reduced loss. This method not only provides a groundbreaking new path for the fabrication of thick silicon nitride materials but, more importantly, opens up a highly promising new direction for the large-scale industrial production of thick silicon nitride waveguide devices and their in-depth research and application in related fields (such as high-performance integrated photonic chips and low-loss optical interconnects).
[0029] In summary, the core objective of the thick silicon nitride waveguide manufacturing method designed in this embodiment is to efficiently and reliably fabricate silicon nitride waveguide structures that possess both large thickness (twice the thickness of a single layer), high-quality optical properties, and ultra-low transmission loss. This method offers several significant advantages: the process flow is simple and direct, easy to operate, and highly repeatable; the resulting thick silicon nitride waveguide structure is intact, has low defect density, and excellent quality; the waveguide optical transmission loss is low; and simultaneously, the process inherently possesses good scalability, easily integrating into existing production lines, laying a solid foundation for achieving stable, mass-produced, and large-scale manufacturing.
[0030] Example 2 This embodiment is a second embodiment of a method for fabricating thick silicon nitride waveguides based on wafer bonding. This embodiment is similar to the first embodiment. Figure 2 As shown, the specific steps include: Step S1. Silicon nitride wafer dicing: A commercially available 8-inch (300nm thick) silicon nitride-on-insulator wafer is used. The structure from bottom to top consists of a silicon substrate 3, a silicon dioxide buried layer 2, and a silicon nitride layer 1. It is diced to a specified size by laser cutting: as shown in 2, a 10mm × 10mm silicon nitride wafer is used as the upper bonding wafer 100. Figure 2 The 15mm×15mm silicon nitride wafer shown is used as the lower bonding wafer 200.
[0031] Step S2. Cleaning: The wafer surface is rinsed sequentially with acetone (ACE), isopropanol (IPA), ethanol (EtOH), and deionized water (DIWater) to remove organic contaminants; then, the EVG mega-frequency ultrasonic cleaning equipment is used to remove micro-particle contaminants adsorbed on the surface to achieve high-precision cleaning requirements and ensure that the wafer surface cleanliness meets the direct bonding standards (sub-nanometer flatness and cleanliness).
[0032] Step S3. Plasma Activation Treatment: Place the upper bonded wafer 100 and the lower bonded wafer 200 in an EVG plasma activation device. Surface activation is performed using oxygen plasma (argon [Ar] or nitrogen [N] plasma can also be used). The plasma activation process is as follows: opening the cavity for wafer placement → closing the cavity for startup → evacuating the device → filling with oxygen → glow discharge → purification → equilibration → opening the cavity for wafer removal. The activation effect is as follows: Figure 2 As shown in the intermediate ion activation treatment step, a large number of hydroxyl groups (-OH) are adsorbed on the surfaces of the upper bonded wafer 100 and the lower bonded wafer 200.
[0033] Step S4. Bonding: After activation treatment, room temperature bonding is performed. The silicon nitride layer 1 of the upper bonding wafer 100 is precisely aligned with the silicon nitride layer 1 of the lower bonding wafer 200. Then, it is transferred to the EVG bonding equipment, a specific pressure F is applied, the annealing temperature and environmental parameters are set, and the bonding and annealing processes are executed. After bonding and annealing are completed, the bonded wafer is removed.
[0034] Step S5. Substrate Removal: The substrate of the upper bonded wafer 100 is removed. When removing the silicon substrate 3, a chemical mechanical polishing (CMP) process is first used to thin the silicon substrate 3 to approximately 50 μm. Subsequently, the remaining silicon substrate 3 is thoroughly removed using a tetramethylammonium hydroxide (TMAH) solution. Note that increasing the TMAH concentration decreases the etching rate of silicon, while increasing the temperature increases the etching rate. Under conditions of 80°C and 25% TMAH solution, the etching rate of the silicon crystal orientation is approximately 50 μm / h. For the silicon dioxide buried layer 2, wet etching is performed using buffered oxygen ether (BOE). It is worth noting that, given the symmetrical structure of the upper bonded wafer 100 and the lower bonded wafer 200, protective measures must be taken for the lower bonded wafer 200 during the removal of the upper bonded wafer 100 substrate to prevent accidental etching of its substrate.
[0035] Step S6. After wet etching to remove the substrate, spin-coat electron beam photoresist 4 onto the surface of the bonding wafer (the wafer after bonding). Before spin-coating, perform inductively coupled plasma (ICP) oxygen plasma activation treatment on the surface of the bonding wafer to enhance the adhesion of the photoresist.
[0036] Step S7. Waveguide Fabrication: Electron beam lithography is performed to define the waveguide pattern. After lithography, the waveguide structure 5 is etched using reactive ion etching (RIE). Next, acetone is used to remove residual electron beam photoresist 4, fully exposing the waveguide morphology. Wherein, as... Figure 3 As shown, waveguide structure 5 is an adiabatic tapered waveguide structure with a length of 1 μm. Its left port has a height of 600 nm and a width of 0.5 μm; the right port connects to a strip waveguide with a height of 600 nm and a width of 1.2 μm. These structural parameters meet the single-mode transmission conditions of the silicon nitride waveguide prepared by this process. In this embodiment, waveguide structure 5 can also be etched using a dry etching process, followed by ICP oxidation to remove residual electron beam photoresist 4.
[0037] The method for fabricating thick silicon nitride waveguides employs a direct bonding process based on plasma activation treatment. After successfully fabricating and confirming that the waveguide morphology is correct, a silicon dioxide cladding layer with a thickness of 2 μm is deposited using chemical vapor deposition (CVD) to finally obtain a complete chip structure.
[0038] This embodiment proposes a wafer-bonded silicon nitride waveguide with large thickness (equivalent to twice the thickness of a single layer), high quality, and low transmission loss characteristics. Compared with existing thick silicon nitride waveguide fabrication processes, this embodiment effectively avoids the problems of reduced yield and increased optical transmission loss caused by structural defects such as cracks due to stress accumulation in the silicon nitride thin film during the deposition method for thick silicon nitride waveguides. This embodiment only requires plasma activation treatment of commercially available low-thickness silicon nitride wafers followed by a direct bonding process to obtain the aforementioned high-performance thick silicon nitride waveguide. The method has a simple process route, is convenient to operate, and has good repeatability; the fabricated thick silicon nitride waveguide has good structural integrity, low defect density, excellent quality, and low optical transmission loss characteristics. At the same time, this process naturally has good scalability and is easy to integrate into existing production lines, laying a solid foundation for stable, large-scale manufacturing.
[0039] Example 3 This embodiment is the third embodiment of a method for fabricating thick silicon nitride waveguides based on wafer bonding. Similar to Embodiment Two, this embodiment uses two commercial silicon nitride wafers of different thicknesses, which are directly bonded after plasma activation treatment to achieve the superposition of different thicknesses. For example, a 300 nm thick commercial silicon nitride wafer is bonded to a 400 nm thick commercial silicon nitride wafer. This bonding process is performed at the wafer level, thus eliminating the need for cleaving the silicon nitride wafers. The subsequent fabrication steps of the thick silicon nitride waveguide are essentially the same as in Embodiment Two, ultimately obtaining a silicon nitride waveguide with a thickness of 700 nm (composed of the superposition of 300 nm and 400 nm). Unlike Embodiment Two, the thickness of the thick silicon nitride waveguide obtained by this method is not limited to twice the base thickness, but rather achieves a thicker waveguide structure by superimposing different thicknesses. Based on this example, silicon nitride wafers of other thicknesses can be used to fabricate diverse thick silicon nitride waveguides.
[0040] Example 4 This embodiment is a third embodiment of a method for fabricating thick silicon nitride waveguides based on wafer bonding. This embodiment is similar to Embodiment Two, except that in this embodiment, three commercial silicon nitride wafers are bonded to obtain a silicon nitride waveguide with a thickness at least three times that of a single layer. In this embodiment, in step S1, three silicon nitride wafers of the same or different thicknesses are selected. Steps S2-S5 are the same as in Embodiment Two, during which two silicon nitride wafers are bonded to obtain a first bonded wafer. After completing step S5, step S4 is performed, aligning the silicon nitride layer 1 of the third silicon nitride wafer with the silicon nitride layer 1 of the first bonded wafer, and bonding is performed again. After bonding, steps S5-S7 are continued. This embodiment differs from Embodiment Two in that it is not limited to bonding two silicon nitride wafers, but multiple silicon nitride wafers can be bonded as needed to obtain a silicon nitride waveguide structure with greater thickness.
[0041] In the specific implementation of the above embodiments, the technical features can be combined in any non-contradictory way. For the sake of brevity, not all possible combinations of the above technical features are described. However, as long as the combination of these technical features is not contradictory, it should be considered to be within the scope of this specification.
[0042] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.
Claims
1. A method for fabricating thick silicon nitride waveguides based on wafer bonding, characterized in that, The method comprises the following steps: S1. Selecting at least two silicon nitride wafers with desired sizes; S2. Cleaning the silicon nitride wafers; S3. Performing plasma activation treatment on the cleaned silicon nitride wafers; S4. Bonding the silicon nitride wafers after the activation treatment; S5. Removing the substrate and retaining the target layer to obtain a large-thickness silicon nitride wafer; S6. Designing and preparing a waveguide on the large-thickness silicon nitride wafer.
2. The method of claim 1, wherein the method further comprises: The step S2 specifically comprises: removing organic contaminants on the surface of the silicon nitride wafer by a cleaning agent, and removing particulate contaminants on the surface of the silicon nitride wafer by megasonic cleaning.
3. The method of claim 2, wherein the method further comprises: In step S2, the silicon nitride wafer is sequentially rinsed with acetone, isopropyl alcohol, ethanol and deionized water to remove organic contaminants.
4. The method of claim 1, wherein the method further comprises: The step S3 specifically comprises: the plasma performs ion bombardment on the surface of the silicon nitride wafer to form unsaturated chemical bonds on the surface of the wafer.
5. The method of claim 1, wherein the method further comprises: The step S4 specifically comprises: S41. Room temperature bonding: aligning the silicon nitride layer of one silicon nitride wafer with the silicon nitride layer of another silicon nitride wafer at room temperature; S42. Bonding in a bonder: placing the aligned silicon nitride wafers into a bonder, setting bonding parameters and annealing temperature, and sequentially performing bonding operation and annealing operation.
6. The method of claim 1, wherein the method further comprises: The step S5 comprises: removing the substrate layer of one silicon nitride wafer and retaining the silicon nitride layer.
7. The method of claim 6, wherein the method further comprises: The silicon nitride wafer comprises, from bottom to top, a silicon substrate, a silicon dioxide buried layer and a silicon nitride layer.
8. The method of claim 7, wherein the method further comprises: In step S5, specifically comprising: Chemical mechanical polishing is used to remove the silicon substrate layer: first, the silicon substrate layer is thinned to 45-55 microns; then, the residual thickness of the silicon substrate layer is completely removed by using tetramethylammonium hydroxide solution; Wet etching is used to remove the silicon dioxide buried layer: buffer hydrofluoric acid is used for wet etching to remove the silicon dioxide buried layer; During the removal process, the other silicon nitride wafer is simultaneously protected.
9. The method of claim 1, wherein the method further comprises: The step S6 comprises: Performing inductively coupled plasma oxygen plasma activation treatment on the large-thickness silicon nitride wafer after step S5; Spinning electron beam resist on the surface of the silicon nitride layer of the large-thickness silicon nitride wafer; Defining a waveguide pattern by using electron beam lithography technology; Etching the waveguide structure by using reactive ion etching; Preparing a silicon dioxide layer as a cladding layer on the waveguide by using chemical vapor deposition.
10. The method of claim 1 to 9, wherein, In step S1, the silicon nitride wafer is also subjected to splitting treatment to obtain a silicon nitride wafer with a desired size.