Method for manufacturing silicon nitride waveguide by using side wall

Abstract

The invention relates to the technical field of silicon nitride waveguides, in particular to a method for manufacturing a silicon nitride waveguide by using a side wall, which comprises the following steps of: S1, growing a substrate on a wafer; s2, a deep groove is formed in the substrate, then silicon nitride is deposited, the depth H2 of the groove needs to be larger than the sum of the thickness H1 of the waveguide target, the width W1 of the waveguide target and the deposition thickness H3 of the silicon nitride, namely H2 is larger than H1 + W1 + H3; s3, etching the silicon nitride and stopping on the substrate to form a side wall, and completing a waveguide target width at the moment; and S4, depositing a cladding layer and an upper cladding layer. The stress of the silicon nitride film layer can be dispersed by arranging the deep groove to manufacture the step, and crack diffusion caused by common stress can be stopped in front of the step; the deep groove can be used for manufacturing the side wall, and the crack diffusion does not extend to the side wall, so that the waveguide without cracks can be manufactured by using the side wall; the grooves can be designed into grooves with very low depth-to-width ratio, so that the filling problem of high depth-to-width ratio is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon nitride waveguides, and in particular to a method for manufacturing a silicon nitride waveguide by utilizing side walls. Background Art

[0002] Low-pressure chemical vapor deposition (LPCVD) silicon nitride waveguides are increasingly being used in silicon photonic chips due to their low transmission loss. LPCVD silicon nitride has strong stress and is prone to cracks at the weak points of the film after the deposition thickness is generally greater than 300nm, such as the edge of the wafer and foreign matter inside the wafer. Cracks will originate from the weak points and spread in a certain direction throughout the wafer until they stop at the edge of the wafer. Cracks can cause waveguide breakage and increase transmission loss, so this problem needs to be prevented.

[0003] At present, the common solution in the industry is to disperse stress and add multi-step deposition. For example, patents, patent CN110441860A discloses a method for preparing grooves for thick-film silicon nitride waveguides, and patent CN112680715A discloses a method for growing silicon nitride films and a method for preparing thick-film silicon nitride waveguide devices. The similarities are that a groove of sufficient depth is first etched on the substrate to disperse the film stress, and then LPCVD is used to deposit a certain thickness of silicon nitride to ensure that it will not crack. The chemical mechanical polishing (CMP) process is used to remove the silicon nitride film in some areas to ensure that stress will not accumulate. Repeat the LPCVD deposition and CMP removal steps to achieve the target thickness and the silicon nitride film will not crack. Finally, photolithography, etching and other processes can be performed to make the silicon nitride waveguide.

[0004] Patent CN116299854A discloses a method for preparing silicon nitride devices based on stress dispersion and crack blocking patterns. Compared with the above two patents, the method further disperses stress and blocks crack diffusion by designing a dummy pattern, and can deposit the target silicon nitride thickness in one go, improving the disadvantages of multi-step deposition. It does not require the final photolithography and etching process to make waveguides, and the process steps are simpler. However, when we make silicon nitride waveguides with a high aspect ratio (for example, a waveguide with a thickness of 800nm ​​and a width of 90nm), the silicon nitride deposited by LPCVD cannot fill this extreme case well. Summary of the invention

[0005] The purpose of the present invention is to provide a method for manufacturing silicon nitride waveguides using side walls, so as to solve the technical problem in the prior art that silicon nitride deposited by LPCVD cannot be well filled when manufacturing silicon nitride waveguides with a high aspect ratio (for example, a waveguide with a thickness of 800nm ​​and a width of 90nm).

[0006] The present invention discloses a method for manufacturing a silicon nitride waveguide by using a side wall, comprising the following steps: S1. Growing a substrate on a wafer; S2. A deep groove is formed on the substrate, and then silicon nitride is deposited, wherein the groove depth H2 needs to be greater than the sum of the waveguide target thickness H1, the waveguide target width W1 and the silicon nitride deposition thickness H3, that is, H2>H1+W1+H3; S3. Etching silicon nitride and stopping at the substrate to form a sidewall. At this time, the target width of the waveguide is completed; S4. Deposited cladding and upper cladding are annealed again.

[0007] By setting deep grooves to make steps, the stress of the silicon nitride film layer can be dispersed. Generally, the crack propagation caused by stress will stop before the step. The deep grooves can be used to make side walls. Since the crack propagation will not extend to the side walls, we can use the side walls to make crack-free waveguides. The trenches can be designed to have a very low aspect ratio to solve the filling problem of high aspect ratios.

[0008] Furthermore, the waveguide is formed by photolithography and etching using a mask to obtain a waveguide profile.

[0009] Furthermore, when preparing a non-closed-loop waveguide, after the target width of the waveguide is completed in step S3, photolithography and etching using a mask are further performed at least twice according to the shape of the waveguide.

[0010] Furthermore, the silicon nitride is anisotropically etched by a dry method.

[0011] Furthermore, the silicon nitride deposition thickness H3 is not less than the target width of the waveguide, that is, H3≥W1.

[0012] Furthermore, the width W2 of the side wall is equal to the target width W1 of the waveguide, that is, W2=W1.

[0013] Furthermore, the ratio of the waveguide target thickness to the waveguide target width is not less than 4, that is, H1 / W1≥4.

[0014] Furthermore, the silicon nitride is deposited by low pressure chemical vapor deposition.

[0015] Furthermore, after the cladding is deposited, chemical mechanical polishing is performed until the thickness of the silicon nitride waveguide reaches the target thickness of the waveguide. At this time, the target thickness of the waveguide is achieved and a complete waveguide is manufactured.

[0016] Furthermore, the cladding layer is deposited and annealed before depositing the upper cladding layer.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1.Silicon nitride grown by LPCVD has a large internal stress. The thicker the film and the larger the surface area, the greater the internal stress. The thickness of the film cannot be changed according to the process requirements, but the stress of the silicon nitride film can be dispersed by setting deep grooves to make steps and dividing the surface of the film into small blocks. The crack propagation caused by general stress will stop before the steps. The deep groove steps can control the cracks in a certain block to reduce losses. The deep grooves can be used to make side walls. Since the crack propagation will not extend to the side walls, we can use the side walls to make waveguides without cracks. The trenches can be designed to have a very low aspect ratio to solve the filling problem of high aspect ratios.

[0018] 2. Use LPCVD to deposit the thickness of silicon nitride film and etching to define the waveguide width. After silicon nitride is deposited and etched, an arc-shaped structure generally appears on the top. Add the CMP process to remove the top arc structure, use the groove depth and CMP process to define the thickness of the waveguide, and make a waveguide with a cross-sectional view that is approximately rectangular.

[0019] 3. If it is a closed-loop waveguide such as a circle, we can use only one mask to define the outer contour and indirectly define the inner contour by controlling the waveguide width. Therefore, the closed-loop waveguide does not need to use two masks. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only represent some embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0021] Figure 1 It is a schematic diagram of the use process of the photomask of the present invention, wherein Figure a is a cross-sectional view of Figure b along the AA axis, and Figure b is a top view outline view.

[0022] Figure 2 It is a schematic diagram of the deep groove structure of the present invention, wherein Figure c is a cross-sectional view of Figure DD, and Figure d is a top view contour view.

[0023] Figure 3 This is a schematic diagram of the structure after silicon nitride is deposited in the present invention, wherein Figure e is a cross-sectional view of Figure f EE, and Figure f is a top view outline view.

[0024] Figure 4 This is a schematic diagram of the rear structure of the side wall obtained by the present invention, wherein Figure g is a cross-sectional view of Figure h GG, and Figure h is a top view outline view.

[0025] Figure 5 This is a schematic diagram of the non-closed-loop waveguide structure prepared in the present invention, wherein Figure i is a cross-sectional view of Figure j and Figure j is a top view.

[0026] Figure 6 It is a schematic diagram of the structure after the cladding is deposited in the present invention, wherein Figure k is a cross-sectional view of Figure lLL, and Figure l is a top view outline view.

[0027] Figure 7 It is a schematic diagram of the structure after depositing the upper cladding layer of the present invention, wherein figure m is a cross-sectional view of figure n MM, and figure n is a top view outline view.

[0028] In the above drawings, the meanings of the various marks are: 001 - first mask, 002 - second mask, 101 - wafer, 102 - substrate, 103 - deep trench, 104 - silicon nitride, 105 - side wall, 106 - complete waveguide, 107 - cladding, 108 - upper cladding. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0030] In the embodiment, the target waveguide thickness is H1, the target waveguide width is W1, the deep trench depth is H2, the silicon nitride deposition thickness is H3, and the sidewall width is W2.

[0031] Example 1 A method for making a silicon nitride waveguide using a side wall of the above device used in this embodiment is as follows: Figure 1-Figure 3 , Figure 5-Figure 7 As shown, the following steps are included: 1. A substrate 102 is grown on a wafer 101, and a first mask 001 is used for photolithography and etching to form a deep groove 103 on the substrate 102, such as Figure 2 As shown, the groove depth needs to be greater than the sum of the waveguide target thickness, waveguide target width and silicon nitride deposition thickness, that is, H2>H1+W1+H3; 2. LPCVD deposits silicon nitride 104, the thickness of which must be no less than the target waveguide width, i.e. H3 ≥ W1, e.g. Figure 3 The dry etching of silicon nitride 104 stops at the substrate to form a sidewall 105. At this time, the width of the sidewall 105 after etching is equal to the target width of the waveguide, that is, W2=W1. At this time, the target width of the waveguide is completed, as shown in FIG. Figure 4 As shown; 3. Use the second mask 002, photolithography, etching, and determine the waveguide target contour at this time, such as Figure 5 As shown; 4. Deposit the cladding layer and CMP until the silicon nitride waveguide thickness reaches the target waveguide thickness. At this point, the target waveguide thickness is achieved and a rectangular waveguide is made, such as Figure 6As shown, 106 is a complete waveguide, and the ratio of the target waveguide thickness to the target waveguide width is not less than 4, that is, H1 / W1≥4; 5. Annealing, deposit the upper cladding and then anneal, such as Figure 7 .

[0032] Example 2 In this embodiment, as a preferred embodiment of the present invention, a method for making a silicon nitride waveguide using a sidewall is provided. Figure 4 As shown, the following steps are included: 1. A substrate 102 is grown on a wafer 101, and a first mask 001 is used for photolithography and etching to form a deep groove 103 on the substrate 102. The groove depth must be greater than the sum of the waveguide target thickness, the waveguide target width and the silicon nitride deposition thickness, that is, H2>H1+W1+H3; 2. LPCVD deposits silicon nitride 104, the thickness of which must be no less than the target waveguide width, i.e. H3 ≥ W1. Dry etching of silicon nitride 104 stops at the substrate to form a sidewall 105. At this time, the width of the etched sidewall 105 is equal to the target waveguide width, i.e. W2 = W1. At this time, the target waveguide width is completed, such as Figure 4 As shown; 3. Deposit the cladding layer 107, and CMP until the silicon nitride waveguide thickness reaches the target waveguide thickness. At this time, the target waveguide thickness is achieved and a complete waveguide 106 is made. Figure 4 As shown, the ratio of the waveguide target thickness to the waveguide target width is not less than 4, that is, H1 / W1≥4; 4. Annealing, deposition of upper cladding layer 108, such as Figure 7 .

[0033] The above are the implementation methods listed in this embodiment, but this embodiment is not limited to the above optional implementation methods. Those skilled in the art can arbitrarily combine the above methods to obtain other various implementation methods. Anyone can derive other various forms of implementation methods under the inspiration of this embodiment. The above specific implementation methods should not be understood as limiting the scope of protection of this embodiment. The scope of protection of this embodiment shall be based on the definition in the claims, and the description can be used to interpret the claims.

Claims

1. A method for making a silicon nitride waveguide using a sidewall, characterized in that: The following steps are involved: S1. Growing a substrate (102) on a wafer (101); S2. forming a deep groove (103) on the substrate (102), and then depositing silicon nitride (104), wherein the groove depth H2 needs to be greater than the sum of the waveguide target thickness H1, the waveguide target width W1 and the silicon nitride (104) deposition thickness H3, that is, H2>H1+W1+H3; S3. Etching silicon nitride (104) and stopping at the substrate (102) to form a sidewall (105). At this time, the target width of the waveguide is completed; S4. The deposited cladding (107) and the upper cladding (108) are annealed again.

2. The method for fabricating a silicon nitride waveguide using a sidewall according to claim 1, characterized in that: The waveguide is patterned by photolithography and etching using a mask to obtain a waveguide profile.

3. The method for manufacturing a silicon nitride waveguide using a sidewall according to claim 2, characterized in that: When preparing a non-closed-loop waveguide, after the target width of the waveguide is completed in step S3, photolithography and etching using a mask are further performed at least twice according to the shape of the waveguide.

4. The method for manufacturing a silicon nitride waveguide using a sidewall according to claim 1, characterized in that: The silicon nitride (104) is anisotropically etched by a dry method.

5. The method for manufacturing a silicon nitride waveguide using a sidewall according to claim 1, characterized in that: The silicon nitride (104) deposition thickness H3 is not less than the target waveguide width, that is, H3≥W1.

6. The method for manufacturing a silicon nitride waveguide using a sidewall according to claim 1, characterized in that: The width W2 of the side wall (105) is equal to the target width W1 of the waveguide, that is, W2=W1.

7. The method for manufacturing a silicon nitride waveguide using a sidewall according to claim 1, characterized in that: The ratio of the waveguide target thickness to the waveguide target width is not less than 4, that is, H1 / W1≥4.

8. The method for manufacturing a silicon nitride waveguide using a sidewall according to claim 1, characterized in that: The silicon nitride (104) is deposited by low pressure chemical vapor deposition.

9. The method for manufacturing a silicon nitride waveguide using a sidewall according to claim 1, characterized in that: After the deposition of the cladding layer (107), chemical mechanical polishing is performed until the thickness of the silicon nitride (104) waveguide reaches the target thickness of the waveguide. At this time, the target thickness of the waveguide is achieved and a complete waveguide (106) is manufactured.

10. The method for manufacturing a silicon nitride waveguide using a sidewall according to claim 9, characterized in that: After the complete waveguide (106) is manufactured, annealing is performed, and after the upper cladding (108) is deposited, annealing is performed again.

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