Method for removing silicon nitride on back surface of silicon wafer
Through the combination of dry etching and wet etching, the problem of long removal time of silicon nitride on the back of the silicon wafer and unstable process is solved, and an efficient and controllable silicon nitride removal effect is achieved.
Patent Information
- Application Number
- CN202311769049.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-12-20
- Publication Date
- 2025-06-20
AI Technical Summary
The prior art has problems such as long time consumption, high corrosion risk for front silicon nitride and unstable drug liquid when removing silicon nitride on the back of the silicon wafer.
Using a combination of dry etching and wet etching, a part of the second silicon nitride layer is first removed by dry etching, and then the remaining part is removed by wet etching to form a protective layer to prevent frontal damage.
It effectively shortens the removal time of the silicon nitride layer, reduces the consumption of the drug liquid and the loss during the liquid replacement process, and improves the controllability and smoothness of the process.
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Figure CN120174336A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of semiconductor technology, and particularly to a method for removing silicon nitride on the back side of a silicon wafer. Background Art
[0002] Optical waveguides are used to transmit optical signals on silicon optical chips. Waveguides can be divided into silicon waveguides and silicon nitride waveguides. The low non-linearity of silicon nitride (Si3N4) enables silicon nitride waveguides to handle higher optical powers than silicon waveguides. Moreover, the low temperature coefficient of silicon nitride results in little influence by temperature. The refractive index ratio of silicon to silicon nitride is less than that of silicon to silicon dioxide, making the roughness requirement of the sidewall of the silicon nitride waveguide lower than that of the silicon waveguide, that is, the silicon nitride waveguide is easier to process. There are two processes for depositing silicon nitride in silicon nitride waveguides. One is the plasma-enhanced deposition method (PECVD), and the other is the low-pressure chemical vapor deposition method in a furnace tube (LPCVD). In optical communication applications, the loss of LPCVD is much lower than that of PECVD. Therefore, in optical communication applications, LPCVD is often used to deposit silicon nitride, and the thickness of the deposited silicon nitride is controlled to be 300–400 nm.
[0003] However, when using LPCVD to deposit silicon nitride, silicon nitride is deposited on both the front and back sides of the silicon wafer. Therefore, it is necessary to remove the silicon nitride on the back side of the silicon wafer. The traditional process for removing the silicon nitride on the back side of the silicon wafer is to use a hot phosphoric acid solution for removal, but this method has the following problems:
[0004] (1) Since the rate of removing silicon nitride by hot phosphoric acid It takes 1.5 - 2 hours to remove, for example, 400 nm of silicon nitride, which takes a long time;
[0005] (2) The silicon wafer needs to be immersed in the hot phosphoric acid solution, and the chemical liquid flowing between the silicon wafers is likely to cause corrosion defects on the silicon nitride on the front side of the silicon wafer;
[0006] (3) Due to the service life of the chemical liquid and the instability caused by the volatilization of the water content at high temperature, the concentration of the hot phosphoric acid solution will change, which causes great difficulties in precisely controlling the corrosion rate and corrosion selectivity. Summary of the Invention
[0007] The purpose of the present invention is to provide a method for removing silicon nitride on the back side of a silicon wafer. By combining dry etching and wet etching, the second silicon nitride layer on the back side of the silicon wafer can be removed with high quality, and the removal time of the second silicon nitride layer can be effectively shortened. It can effectively reduce the instability of the chemical liquid caused by the consumption of the chemical liquid during the long-time removal of the second silicon nitride layer by the traditional process, avoid frequent replacement of the chemical liquid, reduce the loss of the chemical liquid during the liquid replacement process, etc. Moreover, the process is more controllable and saves the amount of the chemical liquid used.
[0008] To achieve the above object, the method for removing silicon nitride on the back side of a silicon wafer according to the present invention includes the following steps:
[0009] S0. Provide a silicon wafer, where the silicon wafer includes a substrate and a silicon waveguide disposed on the top surface of the substrate, and a first silicon nitride layer and a second silicon nitride layer are respectively deposited on the front and back sides of the silicon wafer by LPCVD;
[0010] S1. Form a protective layer on the top surface of the first silicon nitride layer;
[0011] S2. Perform dry etching treatment on the second silicon nitride layer to remove part of the second silicon nitride layer;
[0012] S3. Immerse the silicon wafer processed in step S2 in a treatment solution for wet etching treatment to remove the remaining part of the second silicon nitride layer.
[0013] The beneficial effects of the method for removing silicon nitride on the back side of a silicon wafer according to the present invention are as follows: By step S1, a protective layer is formed on the top surface of the first silicon nitride layer to protect the first silicon nitride layer on the front side of the silicon wafer, avoiding damage to the first silicon nitride layer and the silicon waveguide in subsequent steps; By step S2, dry etching treatment is performed on the second silicon nitride layer to remove part of the second silicon nitride layer, that is, by first removing part of the second silicon nitride layer by dry etching, the removal time of the second silicon nitride layer can be effectively shortened, the instability of the treatment solution caused by the consumption of the treatment solution during the long-time removal of the second silicon nitride layer by hot phosphoric acid in the traditional process can be effectively reduced, frequent replacement of the treatment solution is avoided, the loss of the treatment solution during the solution replacement process is reduced, etc., and the process is more controllable and the consumption of the treatment solution is saved; By S3, the silicon wafer processed in step S2 is immersed in a treatment solution for wet etching treatment to remove the remaining part of the second silicon nitride layer, so as to avoid defects such as high roughness and poor smoothness on the back side of the silicon wafer caused by the complete removal of the second silicon nitride layer by dry etching, that is, the second silicon nitride layer on the back side of the silicon wafer can be removed with high quality by a combination of dry etching and wet etching.
[0014] Preferably, in step S2, the step of performing dry etching treatment on the second silicon nitride layer includes: etching the second silicon nitride layer with a mixed etching gas composed of trifluoromethane, oxygen, carbon tetrafluoride and argon. The beneficial effect is that it can quickly remove part of the second silicon nitride layer, and this parameter is beneficial to improving the etching effect on the second silicon nitride layer, thereby shortening the etching time.
[0015] Preferably, in the step S2, the step of performing dry etching on the second silicon nitride layer further includes: controlling the flow rate of trifluoromethane to be 10-100 sccm, the flow rate of oxygen to be 30–200 sccm, the flow rate of carbon tetrafluoride to be 10–500 sccm, and the flow rate of argon to be 100-2000 sccm. The beneficial effect is that this parameter is beneficial to improving the etching effect on the second silicon nitride layer, thereby shortening the etching time.
[0016] Preferably, in the step S2, the step of performing dry etching on the second silicon nitride layer further includes: controlling the etching time to be 50–100 s. The beneficial effect is that it avoids the second silicon nitride layer being completely removed by dry etching, resulting in defects such as high roughness and poor smoothness on the back of the silicon wafer. Compared with directly using hot phosphoric acid to remove the second silicon nitride layer in the traditional process, the dry etching time is short, and the removal time of the second silicon nitride layer can be effectively shortened.
[0017] Preferably, in the step S1, the step of forming a protective layer on the top surface of the first silicon nitride layer includes: sequentially forming a silicon dioxide protective layer and a silicon nitride protective layer on the top surface of the first silicon nitride layer. The beneficial effect is that the silicon nitride protective layer is beneficial to improving the protection effect on the first silicon nitride layer and the silicon waveguide. The silicon nitride protective layer will be removed in the wet etching process of the step S3. Adding a silicon dioxide protective layer between the first silicon nitride layer and the silicon nitride protective layer can effectively avoid damaging the first silicon nitride layer and the silicon waveguide during the wet etching process, and this silicon dioxide protective layer can be used as an isolation medium for the subsequently formed silicon nitride waveguide.
[0018] Preferably, in the step S1, the step of sequentially forming a silicon dioxide protective layer and a silicon nitride protective layer on the top surface of the first silicon nitride layer includes: controlling the silicon dioxide protective layer to cover the top surface of the first silicon nitride layer, and controlling the thickness of the silicon dioxide protective layer to be 50-100 nm. The beneficial effect is that it is beneficial to improving the protection effect on the first silicon nitride layer and the silicon waveguide, and avoiding damaging the first silicon nitride layer and the silicon waveguide during the wet etching process.
[0019] Preferably, in the step S1, the step of sequentially forming a silicon dioxide protective layer and a silicon nitride protective layer on the top surface of the first silicon nitride layer includes: controlling the silicon nitride protective layer to cover the top surface of the silicon dioxide protective layer, and controlling the thickness of the silicon nitride protective layer to be 30-50 nm. The beneficial effect is that it is beneficial to protecting the silicon dioxide protective layer and avoiding the treatment liquid from corroding the silicon dioxide protective layer, so that the silicon dioxide protective layer can be used as an isolation medium for the subsequently formed silicon nitride waveguide.
[0020] Preferably, in the step S2, the step of performing dry etching on the second silicon nitride layer includes: controlling the ratio of the thickness of the second silicon nitride layer etched away to the thickness of the original second silicon nitride layer to be 85%-93%. The beneficial effect is that by first removing most of the second silicon nitride layer through dry etching, the removal time of the second silicon nitride layer can be effectively shortened, and the remaining second silicon nitride layer can prevent the entire second silicon nitride layer from being removed by dry etching, which may cause defects such as high roughness and poor smoothness on the back of the silicon wafer.
[0021] Preferably, in the step S3, the step of immersing the silicon wafer processed in the step S2 in a treatment solution for wet etching to remove the remaining second silicon nitride layer includes:
[0022] S31. Immerse the silicon wafer processed in the step S2 in a DHF solution to remove the silicon oxynitride formed by oxidation on the surface of the second silicon nitride layer;
[0023] S32. Immerse the silicon wafer processed in the step S31 in a hot phosphoric acid solution for wet etching to remove the remaining second silicon nitride layer. The beneficial effect is that it is conducive to removing the remaining second silicon nitride layer with high quality, and can avoid affecting the silicon dioxide protective layer, as well as prevent the entire second silicon nitride layer from being removed by dry etching, which may cause defects such as high roughness and poor smoothness on the back of the silicon wafer.
[0024] Preferably, in the step S3, the step of immersing the silicon wafer processed in the step S2 in a treatment solution for wet etching to remove the remaining second silicon nitride layer includes: controlling the temperature of the hot phosphoric acid solution to be 160-165°C and the treatment time to be 15-30 min. The beneficial effect is that it is conducive to removing the remaining second silicon nitride layer with high quality and can avoid affecting the silicon dioxide protective layer. Description of the Drawings
[0025] Figure 1 It is a flowchart of the method for removing silicon nitride on the back of a silicon wafer in an embodiment of the present invention;
[0026] Figure 2 It is a structural schematic diagram of a silicon wafer in an embodiment of the present invention;
[0027] Figure 3 It is for Figure 2 The structural schematic diagram after forming a protective layer on the top surface of the first silicon nitride layer in the shown silicon wafer;
[0028] Figure 4 It is for Figure 3Schematic diagram of the structure after the silicon wafer is flipped and part of the second silicon nitride layer is removed;
[0029] Figure 5 is Figure 4 Schematic diagram of the structure after the remaining second silicon nitride layer and the silicon nitride protective layer in the shown silicon wafer are removed. Specific embodiments
[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein shall have the ordinary meanings understood by those of ordinary skill in the art to which the present invention pertains. The words such as "including" used herein mean that the elements or objects appearing before this word cover the elements or objects listed after this word and their equivalents, without excluding other elements or objects.
[0031] To overcome the problems existing in the prior art, an embodiment of the present invention provides a method for removing silicon nitride on the back of a silicon wafer. By combining dry etching and wet etching, the second silicon nitride layer on the back of the silicon wafer can be removed with high quality, and the removal time of the second silicon nitride layer can be effectively shortened. It can effectively reduce the instability of the chemical solution caused by the consumption of the chemical solution during the long-term removal of the second silicon nitride layer directly using hot phosphoric acid in the traditional process, avoid frequent replacement of the chemical solution, reduce the loss of the chemical solution during the solution replacement process, etc., and the process is more controllable and saves phosphoric acid usage.
[0032] Figure 1 Flow chart of the method for removing silicon nitride on the back of a silicon wafer in an embodiment of the present invention; Figure 2 Schematic diagram of the structure of a silicon wafer in an embodiment of the present invention; Figure 3 is in Figure 2 Schematic diagram of the structure after a protective layer is formed on the top surface of the first silicon nitride layer in the shown silicon wafer; Figure 4 is Figure 3 Schematic diagram of the structure after the shown silicon wafer is flipped and part of the second silicon nitride layer is removed; Figure 5 is Figure 4 Schematic diagram of the structure after the remaining second silicon nitride layer and the silicon nitride protective layer in the shown silicon wafer are removed.
[0033] In some embodiments of the present invention, referring to Figures 1 to 5 , the method for removing silicon nitride on the back of a silicon wafer includes the following steps:
[0034] S0. Provide a silicon wafer 1, where the silicon wafer 1 includes a substrate 11 and a silicon waveguide 12 disposed on the top surface of the substrate 11, and a first silicon nitride layer 2 and a second silicon nitride layer 3 are respectively deposited on the front and back surfaces of the silicon wafer 1 by LPCVD;
[0035] S1. Form a protective layer 4 on the top surface of the first silicon nitride layer 2;
[0036] S2. Perform a dry etching process on the second silicon nitride layer 3 to remove part of the second silicon nitride layer 3;
[0037] S3. Immerse the silicon wafer processed in step S2 in a treatment solution for wet etching treatment to remove the remaining part of the second silicon nitride layer 3.
[0038] Specifically, through step S1, a protective layer 4 is formed on the top surface of the first silicon nitride layer 2 to protect the first silicon nitride layer 2 on the front surface of the silicon wafer 1 and avoid damage to the first silicon nitride layer 2 and the silicon waveguide 12 in subsequent steps; through step S2, a dry etching process is performed on the second silicon nitride layer 3 to remove part of the second silicon nitride layer 3, that is, by first removing part of the second silicon nitride layer 3 through dry etching, the removal time of the second silicon nitride layer 3 can be effectively shortened, the instability of the treatment solution caused by the consumption of the treatment solution during the long - time removal of the second silicon nitride layer 3 using hot phosphoric acid in the traditional process can be effectively reduced, frequent replacement of the treatment solution can be avoided, the loss of the treatment solution during the solution replacement process can be reduced, etc., and the process is more controllable and the consumption of the treatment solution is saved; through S3, the silicon wafer processed in step S2 is immersed in a treatment solution for wet etching treatment to remove the remaining part of the second silicon nitride layer 3 to avoid defects such as high roughness and poor smoothness on the back surface of the silicon wafer 1 caused by the complete removal of the second silicon nitride layer 3 through dry etching, that is, the second silicon nitride layer 3 on the back surface of the silicon wafer 1 can be removed with high quality by combining dry etching and wet etching.
[0039] In some specific embodiments of the present invention, refer to Figures 2 to 5 , the silicon wafer is a SOI silicon wafer, the SOI silicon wafer further includes a first insulating layer 13 disposed on the bottom surface of the substrate 11, and a second insulating layer 14 disposed on the top surface of the substrate 11. The silicon waveguide 12 is disposed on the top surface of the second insulating layer 14. An isolation medium 15 is formed on the surface of each unit structure of the silicon waveguide 12 during processing. The first insulating layer 13, the second insulating layer 14, and the isolation medium 15 are all made of silicon dioxide. The first silicon nitride layer 2 is disposed on the top surface of the isolation medium 15, and the second silicon nitride layer 3 is disposed on the bottom surface of the first insulating layer 13.
[0040] In some embodiments of the present invention, refer to Figure 2 andFigure 3 In step S1, the step of forming the protective layer 4 on the top surface of the first silicon nitride layer 2 includes: sequentially forming a silicon dioxide protective layer 41 and a silicon nitride protective layer 42 on the top surface of the first silicon nitride layer 2. Providing the silicon nitride protective layer 42 is beneficial to improving the protection effect on the first silicon nitride layer 2 and the silicon waveguide 12. The silicon nitride protective layer 42 will be removed in the wet etching process of step S3. Adding the silicon dioxide protective layer 41 between the first silicon nitride layer 2 and the silicon nitride protective layer 42 can effectively avoid damaging the first silicon nitride layer 2 and the silicon waveguide 12 during the wet etching process, and this silicon dioxide protective layer 41 can be used as the isolation medium for the subsequently formed silicon nitride waveguide.
[0041] In some embodiments of the present invention, referring to Figure 2 and Figure 3 in step S1, the step of sequentially forming the silicon dioxide protective layer 41 and the silicon nitride protective layer 42 on the top surface of the first silicon nitride layer 2 includes: controlling the silicon dioxide protective layer 41 to cover the top surface of the first silicon nitride layer 2, and controlling the thickness of the silicon dioxide protective layer 41 to be 50 - 100 nm. This is beneficial to improving the protection effect on the first silicon nitride layer 2 and the silicon waveguide 12, avoiding damaging the first silicon nitride layer 2 and the silicon waveguide 12 during the wet etching process, and setting the silicon dioxide protective layer 41 on the top surface of the first silicon nitride layer 2 can effectively prevent the first silicon nitride layer 2 from contacting with oxygen and being oxidized.
[0042] In some specific embodiments of the present invention, in step S1, the step of sequentially forming the silicon dioxide protective layer and the silicon nitride protective layer on the top surface of the first silicon nitride layer includes: controlling the silicon dioxide protective layer to cover the top surface of the first silicon nitride layer, and controlling the thickness of the silicon dioxide protective layer to be any one of 50 nm, 65 nm, 80 nm, 85 nm, and 100 nm.
[0043] In some embodiments of the present invention, referring to Figure 2 and Figure 3 in step S1, the step of sequentially forming the silicon dioxide protective layer 41 and the silicon nitride protective layer 42 on the top surface of the first silicon nitride layer 2 includes: controlling the silicon nitride protective layer 42 to cover the top surface of the silicon dioxide protective layer 41, and controlling the thickness of the silicon nitride protective layer 42 to be 30 - 50 nm. This is beneficial to protecting the silicon dioxide protective layer 41 and avoiding the treatment liquid from corroding the silicon dioxide protective layer 41, so that the silicon dioxide protective layer 41 can be used as the isolation medium for the subsequently formed silicon nitride waveguide.
[0044] In some specific embodiments of the present invention, in step S1, the steps of sequentially forming a silicon dioxide protective layer and a silicon nitride protective layer on the top surface of the first silicon nitride layer include: controlling the silicon nitride protective layer to cover the top surface of the silicon dioxide protective layer, and controlling the thickness of the silicon nitride protective layer to be any one of 30 nm, 35 nm, 40 nm, 43 nm, 47 nm, and 50 nm.
[0045] In some embodiments of the present invention, referring to Figure 4 , in step S2, the steps of dry-etching the second silicon nitride layer 3 include: etching the second silicon nitride layer 3 with a mixed etching gas composed of trifluoromethane, oxygen, carbon tetrafluoride, and argon. This enables rapid removal of part of the second silicon nitride layer 3, and this parameter is beneficial to improving the etching effect on the second silicon nitride layer 3, thereby shortening the etching time.
[0046] Specifically, before etching the second silicon nitride layer 3, the silicon wafer 1 needs to be flipped so that the second silicon nitride layer 3 faces upward for easy etching.
[0047] In some embodiments of the present invention, in step S2, the steps of dry-etching the second silicon nitride layer further include: controlling the flow rate of trifluoromethane to be 10 - 100 sccm, the flow rate of oxygen to be 30–200 sccm, the flow rate of carbon tetrafluoride to be 10–500 sccm, and the flow rate of argon to be 100 - 2000 sccm. This parameter is beneficial to improving the etching effect on the second silicon nitride layer, thereby shortening the etching time.
[0048] In some specific embodiments of the present invention, in step S2, the steps of dry-etching the second silicon nitride layer further include: controlling the flow rate of trifluoromethane (CHF3) to be any one of 10 sccm, 20 sccm, 50 sccm, 70 sccm, 85 sccm, and 100 sccm.
[0049] In some specific embodiments of the present invention, in step S2, the steps of dry-etching the second silicon nitride layer further include: controlling the flow rate of oxygen (O2) to be any one of 30 sccm, 50 sccm, 100 sccm, 120 sccm, 150 sccm, and 200 sccm.
[0050] In some specific embodiments of the present invention, in the step S2, the step of performing dry etching on the second silicon nitride layer further includes: controlling the flow rate of carbon tetrafluoride (CF4) to be any one of 10 sccm, 20 sccm, 80 sccm, 150 sccm, 300 sccm, 350 sccm, 400 sccm, 450 sccm, and 500 sccm.
[0051] In some specific embodiments of the present invention, in the step S2, the step of performing dry etching on the second silicon nitride layer further includes: controlling the flow rate of argon (Ar) to be any one of 100 sccm, 300 sccm, 600 sccm, 9000 sccm, 1200 sccm, 1600 sccm, 1800 sccm, and 2000 sccm.
[0052] In some embodiments of the present invention, in the step S2, the step of performing dry etching on the second silicon nitride layer further includes: controlling the etching time to be 50–100 s. Avoiding the complete removal of the second silicon nitride layer by dry etching, which may lead to defects such as high roughness and poor smoothness on the back side of the silicon wafer. Compared with the traditional process of directly removing the second silicon nitride layer with hot phosphoric acid, the dry etching process has a shorter etching time, which can effectively shorten the removal time of the second silicon nitride layer.
[0053] In some specific embodiments of the present invention, in the step S2, the step of performing dry etching on the second silicon nitride layer further includes: controlling the etching time to be any one of 50 s, 60 s, 75 s, 88 s, and 100 s.
[0054] In some embodiments of the present invention, in the step S2, the step of performing dry etching on the second silicon nitride layer includes: controlling the ratio of the thickness of the second silicon nitride layer removed by etching to the thickness of the original second silicon nitride layer to be 85% - 93%. That is, by first removing most of the second silicon nitride layer through dry etching, the removal time of the second silicon nitride layer can be effectively shortened, and the remaining part of the second silicon nitride layer can avoid the complete removal of the second silicon nitride layer by dry etching, which may lead to defects such as high roughness and poor smoothness on the back side of the silicon wafer.
[0055] In some specific embodiments of the present invention, in the step S2, the step of performing dry etching on the second silicon nitride layer includes: controlling the ratio of the thickness of the second silicon nitride layer removed by etching to the thickness of the original second silicon nitride layer to be any one of 85%, 87.5%, 89%, 80%, 82.5%, and 93%.
[0056] In some embodiments of the present invention, in step S2, after the dry etching treatment of the second silicon nitride layer, the thickness of the remaining second silicon nitride layer is 30 - 50 nm, so as to prevent the entire second silicon nitride layer from being removed by dry etching, which may cause defects such as high roughness and poor smoothness on the back side of the silicon wafer.
[0057] In some embodiments of the present invention, referring to Figure 5 , in step S3, the step of immersing the silicon wafer 1 processed in step S2 in a treatment solution for wet etching to remove the remaining second silicon nitride layer includes:
[0058] S31: Immerse the silicon wafer processed in step S2 in a DHF solution to remove the silicon oxynitride formed by oxidation on the surface of the second silicon nitride layer;
[0059] S32: Immerse the silicon wafer processed in step S31 in a hot phosphoric acid solution for wet etching to remove the remaining second silicon nitride layer.
[0060] Since the second silicon nitride layer is easily oxidized to form silicon oxynitride when contacting with oxygen, and silicon oxynitride does not react with the hot phosphoric acid solution, it is necessary to use hydrofluoric acid solution (DHF solution) to remove the silicon oxynitride formed on the surface of the second silicon nitride layer before immersing the silicon wafer 1 processed in step S31 in the hot phosphoric acid solution for wet etching. This is beneficial to the high-quality removal of the remaining second silicon nitride layer 3, and can avoid affecting the silicon dioxide protection layer 41, as well as prevent the entire second silicon nitride layer 3 from being removed by dry etching, which may cause defects such as high roughness and poor smoothness on the back side of the silicon wafer 1. Among them, on the top surface of the first silicon nitride layer 2, not only the silicon dioxide protection layer 41 is provided, but also the silicon nitride protection layer 42 is provided, in order to protect the silicon dioxide protection layer 41 with the silicon nitride protection layer 42 to prevent the DHF solution from removing the silicon dioxide protection layer 41. In step S3, the hot phosphoric acid solution will only synchronously remove the silicon nitride protection layer 42, while the silicon dioxide protection layer 41 will be retained as the isolation medium for the subsequently formed silicon nitride waveguide. At the same time, due to the provision of the silicon dioxide protection layer 41 on the top surface of the first silicon nitride layer 2, the hot phosphoric acid solution will not damage the first silicon nitride layer 2.
[0061] In some embodiments of the present invention, in step S3, the step of immersing the silicon wafer processed in step S2 in a treatment solution for wet etching to remove the remaining portion of the second silicon nitride layer includes: controlling the temperature of the hot phosphoric acid (H3PO4) solution to be 160 - 165 °C and the treatment time to be 15 - 30 min. This is beneficial for removing the remaining portion of the second silicon nitride layer with high quality and can avoid affecting the silicon dioxide protective layer.
[0062] In some specific embodiments of the present invention, in step S3, the step of immersing the silicon wafer processed in step S2 in a treatment solution for wet etching includes: controlling the temperature of the hot phosphoric acid solution to be any one of 160 °C, 162 °C, 164 °C, and 165 °C.
[0063] In some specific embodiments of the present invention, in step S3, the step of immersing the silicon wafer processed in step S2 in a treatment solution for wet etching includes: controlling the treatment time of the hot phosphoric acid solution to be any one of 15 min, 18 min, 20 min, 25 min, 27 min, and 30 min.
[0064] Although the embodiments of the present invention have been described in detail above, it is obvious to those skilled in the art that various modifications and changes can be made to these embodiments. However, it should be understood that such modifications and changes are all within the scope and spirit of the present invention as described in the claims. Moreover, the present invention described herein can have other embodiments and can be implemented or realized in various ways.
Claims
1. A method for removing silicon nitride on the back side of a silicon wafer, characterized in that, It includes the following steps: S0. Provide a silicon wafer, the silicon wafer includes a substrate and a silicon waveguide disposed on the top surface of the substrate, and a first silicon nitride layer and a second silicon nitride layer are respectively deposited on the front and back surfaces of the silicon wafer by LPCVD; S1. Form a protective layer on the top surface of the first silicon nitride layer; S2. Perform dry etching treatment on the second silicon nitride layer to remove part of the second silicon nitride layer; S3. Immerse the silicon wafer processed in step S2 in a treatment solution for wet etching treatment to remove the remaining part of the second silicon nitride layer.
2. The method for removing silicon nitride on the back side of a silicon wafer according to claim 1, characterized in that, In step S2, the step of performing dry etching treatment on the second silicon nitride layer includes: Etch the second silicon nitride layer with a mixed etching gas composed of trifluoromethane, oxygen, carbon tetrafluoride and argon.
3. The method for removing silicon nitride on the back side of a silicon wafer according to claim 2, characterized in that, In step S2, the step of performing dry etching treatment on the second silicon nitride layer further includes: Control the flow rate of the trifluoromethane to be 10 - 100 sccm, the flow rate of the oxygen to be 30–200 sccm, the flow rate of the carbon tetrafluoride to be 10–500 sccm, and the flow rate of the argon to be 100 - 2000 sccm.
4. The method for removing silicon nitride on the back side of a silicon wafer according to claim 1 or 2, characterized in that, In step S2, the step of performing dry etching treatment on the second silicon nitride layer further includes: Control the etching time to be 50–100 s.
5. The method for removing silicon nitride on the back side of a silicon wafer according to claim 1, characterized in that, In step S1, the step of forming a protective layer on the top surface of the first silicon nitride layer includes: Sequentially form a silicon dioxide protective layer and a silicon nitride protective layer on the top surface of the first silicon nitride layer.
6. The method for removing silicon nitride on the back side of a silicon wafer according to claim 5, characterized in that, In step S1, the step of sequentially forming a silicon dioxide protective layer and a silicon nitride protective layer on the top surface of the first silicon nitride layer includes: Control the silicon dioxide protective layer to cover the top surface of the first silicon nitride layer, and control the thickness of the silicon dioxide protective layer to be 50 - 100 nm.
7. The method for removing silicon nitride on the back side of a silicon wafer according to claim 5, characterized in that, In step S1, the step of sequentially forming a silicon dioxide protective layer and a silicon nitride protective layer on the top surface of the first silicon nitride layer includes: Control the silicon nitride protective layer to cover the top surface of the silicon dioxide protective layer, and control the thickness of the silicon nitride protective layer to be 30 - 50 nm.
8. The method for removing silicon nitride on the back side of a silicon wafer according to claim 1, characterized in that, In step S2, the step of performing dry etching treatment on the second silicon nitride layer includes: Control the ratio of the thickness of the second silicon nitride layer etched away to the thickness of the original second silicon nitride layer to be 85% - 93%.
9. The method for removing silicon nitride on the back side of a silicon wafer according to claim 1, characterized in that, In step S3, the step of immersing the silicon wafer processed in step S2 in a treatment solution for wet etching treatment to remove the remaining part of the second silicon nitride layer includes: S31. Immerse the silicon wafer processed in step S2 in a DHF solution to remove the silicon oxynitride formed by oxidation on the surface of the second silicon nitride layer; S32. Immerse the silicon wafer processed in step S31 in a hot phosphoric acid solution for wet etching treatment to remove the remaining part of the second silicon nitride layer.
10. The method for removing silicon nitride on the back side of a silicon wafer according to claim 9, characterized in that, In step S3, the step of immersing the silicon wafer processed in step S2 in a treatment solution for wet etching treatment to remove the remaining part of the second silicon nitride layer includes: Control the temperature of the hot phosphoric acid solution to be 160 - 165 °C, and the treatment time to be 15 - 30 min.