Method for reducing stress of high-temperature deposited film and application

Abstract

The invention discloses a method for reducing the stress of a high-temperature deposited film and application, and the method comprises the steps: enabling a substrate to deform through heating when a high-temperature deposited film technology is executed, then depositing a first film on the surface of the deformed substrate, and then carrying out the cooling, thereby obtaining the stress of the high-temperature deposited film. Enabling the substrate with the first thin film to deform and restore, and releasing the first stress existing in the first thin film. According to the invention, the problem that patterning is difficult when a corresponding device is manufactured due to the fact that the film layer of the high-temperature deposited film is likely to crack and peel off from the substrate subsequently can be avoided.

Description

Technical Field

[0001] This invention relates to the field of semiconductor integrated circuit technology, and in particular to a method and application for reducing stress in high-temperature deposited thin films. Background Technology

[0002] Some materials, after being deposited on a substrate using high-temperature furnace tube processes to form a thin film, often exhibit significant stress. If this stress is unintended, it can affect subsequent processes.

[0003] For example, in conventional LPCVD silicon nitride processes using furnace tubes, the NH3 in the reaction gas is typically set to be in excess. This ensures that the atomic ratio of Si to N in the grown silicon nitride film is close to the ideal 3:4, achieving a satisfactory film refractive index during subsequent silicon nitride device fabrication. However, the silicon nitride film grown under these conditions exhibits high stress. When deposited to the required thickness for device fabrication, silicon nitride films with high stress may experience subsequent film cracking and peeling from the substrate, making patterning difficult during the fabrication of corresponding silicon nitride devices. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned defects in the prior art and to provide a method and application for reducing the stress of high-temperature deposited thin films.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: This invention provides a method for reducing stress in high-temperature deposited thin films, comprising: In the high-temperature deposition thin film process, the substrate is first deformed by heating, and then a first thin film is deposited on the surface of the deformed substrate. Then, the substrate with the first thin film is cooled to restore its deformation and release the first stress present in the first thin film.

[0006] Furthermore, by heating, a second stress is applied to the first surface of the substrate, causing the substrate to deform as a whole, and then the first thin film is deposited on the second surface of the substrate opposite to the first surface, wherein the second stress is of the same stress type as the first stress.

[0007] Furthermore, the stress types of the first stress and the second stress include tensile stress.

[0008] Furthermore, before performing the high-temperature deposition thin film process, a second thin film is first formed on the first surface. The coefficient of thermal expansion of the second thin film is smaller than that of the substrate. When the substrate is heated during the high-temperature deposition thin film process, tensile stress is applied to the first surface, causing the substrate to deform due to the smaller deformation on the first surface compared to the second surface. By depositing the first thin film with tensile stress on the second surface of the deformed substrate, and utilizing the deformation recovery of the substrate caused by cooling, the first thin film on the second surface shrinks, thereby releasing the first stress present in the first thin film.

[0009] Furthermore, before forming the second thin film, a third thin film is also formed on the first surface, the second thin film is formed on the surface of the third thin film, the coefficient of thermal expansion of the third thin film is between the coefficient of thermal expansion of the substrate and the coefficient of thermal expansion of the second thin film, and the thickness of the second thin film is greater than the thickness of the third thin film, or the coefficient of thermal expansion of the third thin film is equal to the coefficient of thermal expansion of the second thin film, and / or, a fourth thin film is also formed on the second surface, the first thin film is formed on the surface of the fourth thin film, the coefficient of thermal expansion of the fourth thin film is equal to the coefficient of thermal expansion of the second thin film, and the thickness of the second thin film is greater than the thickness of the fourth thin film, or the coefficient of thermal expansion of the fourth thin film is greater than or equal to the coefficient of thermal expansion of the substrate.

[0010] Further, the substrate includes a silicon substrate or an SOI substrate, the second thin film includes a silicon dioxide thin film, and / or the third thin film and / or the fourth thin film includes a silicon dioxide thin film.

[0011] Furthermore, the thickness of the second film is 0.5~1μm.

[0012] Furthermore, the first thin film includes a silicon nitride thin film, and the high-temperature deposition thin film process includes a furnace tube deposition thin film process, in which the silicon nitride thin film is deposited in a furnace tube using an LPCVD process, and by introducing excess NH3, the atomic ratio of silicon to nitrogen in the formed silicon nitride thin film is close to the ideal 3:4, and / or the process temperature for depositing the silicon nitride thin film is 700~900℃.

[0013] The present invention also provides an application of the above-described method for reducing stress in high-temperature deposited thin films, the application including the fabrication of passive devices using a first thin film after the first stress has been released.

[0014] Furthermore, the passive device includes a silicon nitride waveguide.

[0015] Compared with the prior art, the present invention has the following advantages: (1) When performing high-temperature thin film deposition process (e.g. furnace tube thin film deposition process), the substrate is first deformed by heating to apply prestress to the substrate, and then the required thin film (first thin film) is deposited on the substrate surface. After cooling, the substrate is deformed and recovered, so as to fully release the first stress in the deposited thin film, thereby effectively solving the problem of subsequent possible film cracking and peeling off from the substrate, which makes it difficult to pattern when manufacturing corresponding devices.

[0016] (2) By introducing a second thin film with a low coefficient of thermal expansion on the back side (first surface) of the substrate, the first stress in the first thin film can be released by the heating and cooling process of the furnace tube deposition thin film process itself, which can be achieved by deforming and recovering the substrate. This not only eliminates the need to introduce other complex structures and processes, but also forms the second thin film on the back side of the substrate, which is convenient for subsequent removal.

[0017] (3) When used to prepare silicon nitride thin films, compared with other methods to reduce the stress of LPCVD silicon nitride thin films, the present invention does not require changing the ratio of reaction gases during LPCVD silicon nitride, and will not introduce disordered groups (such as hydrogen bonds) into the silicon nitride thin film, thus maintaining the original chemical composition of the silicon nitride thin film and thus not affecting the properties of the silicon nitride thin film. Attached Figure Description

[0018] Figure 1 This is a flowchart of a preferred embodiment of the present invention for reducing stress in high-temperature deposited thin films.

[0019] Figures 2-7 According to a preferred embodiment of the present invention Figure 1 A schematic diagram illustrating the steps involved in reducing stress in high-temperature deposited thin films. Detailed Implementation

[0020] 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 only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art. The terms "comprising" and similar expressions used herein mean that the element or object preceding the word covers the element or object listed after the word and its equivalents, but does not exclude other elements or objects.

[0021] Some materials, after being deposited on a substrate using high-temperature furnace tube processes to form a thin film, often exhibit significant stress. For example, depending on the furnace tube process conditions, the stress in deposited silicon nitride films can vary between several gigapascals of compressive stress and several gigapascals of tensile stress.

[0022] The stress within the thin film can be classified into intrinsic stress and extrinsic stress according to its source.

[0023] For silicon nitride, intriguing stress (mismatch of thermal expansion coefficients) often leads to tensile stress (tensile stress caused by the thermal expansion coefficient of silicon nitride being greater than that of the substrate silicon).

[0024] The intrinsic stress can be either compressive or tensile: (1) The introduced disordered matter (atoms not composed according to chemical proportions) occupies some abnormal structural positions, which destroys the integrity of the film structure. Because the disordered matter occupies a certain space, the film has a tendency to expand, thereby generating compressive stress.

[0025] (2) If very little disordered material is introduced, the atoms can obtain enough activation energy to rearrange themselves, thereby increasing the density of the film and causing it to tend to contract in space, thus generating tensile stress.

[0026] In furnace tube processing, silicon nitride thin films are normally prepared using an excess of NH3. The resulting silicon nitride thin films have an atomic ratio of Si to N close to the ideal 3:4 stoichiometry, and a refractive index of around 2.0, exhibiting tensile stress. However, the silicon nitride thin films grown under these conditions have relatively high stress, around 1100 MPa.

[0027] To minimize stress, the sum of intrinsic stress and extrinsic stress needs to be close to zero. Therefore, the intrinsic stress should be a compressive stress that can offset the extrinsic tensile stress.

[0028] Essentially, a thick silicon nitride film with a stable growth structure exhibits low stress on a macroscopic scale, but in reality, the strain of the silicon nitride film is coordinated with the strain of the substrate.

[0029] Based on the above, the present invention provides a method for reducing stress in high-temperature deposited thin films, comprising: In the high-temperature deposition thin film process, the substrate is first deformed by heating, and then a first thin film is deposited on the surface of the deformed substrate. Then, the substrate with the first thin film is cooled to restore its deformation and release the first stress present in the first thin film.

[0030] Therefore, without introducing disordered substances (i.e. maintaining the ideal chemical composition of the film) and without changing the properties of the film, the present invention utilizes the temperature rise and fall process of the film itself during high-temperature deposition to introduce prestress into the substrate by causing deformation, thereby reducing the stress of the deposited film and obtaining a low-stress film.

[0031] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0032] refer to Figure 1 The present invention provides a method for reducing stress in high-temperature deposited thin films, comprising the following steps: Step S1: Provide a substrate.

[0033] like Figure 2 As shown in (a), a silicon substrate 10 is used as the substrate for implementing a method of reducing the stress of a high-temperature deposited thin film according to the present invention on the silicon substrate 10. However, it is understood that conventional semiconductor substrates such as SOI substrates can also be used as the substrate.

[0034] The silicon substrate 10 has a first surface 102 and a second surface 101.

[0035] In some embodiments, a third thin film is formed on the first surface 102 of the silicon substrate 10.

[0036] In some embodiments, a fourth thin film is formed on the second surface 101 of the silicon substrate 10.

[0037] In some embodiments, a fourth thin film is formed on the second surface 101 of the silicon substrate 10, while a third thin film is also formed on the first surface 102 of the silicon substrate 10.

[0038] In this embodiment, a fourth thin film 12 is formed on the second surface 101 of the silicon substrate 10, and a third thin film 11 is simultaneously formed on the first surface 102 of the silicon substrate 10, such as... Figure 2 As shown in (b).

[0039] It should be noted that in the method for reducing stress of high-temperature deposited thin films according to the present invention, the high-temperature deposited thin film is a first thin film deposited on the second surface 101 of the silicon substrate 10, and a second thin film needs to be formed on the first surface 102 of the silicon substrate 10 before forming the first thin film. Furthermore, when a fourth thin film 12 is formed on the second surface 101 of the silicon substrate 10, the first thin film is formed on the surface of the fourth thin film 12 away from the silicon substrate 10; when a third thin film 11 is formed on the first surface 102 of the silicon substrate 10, the second thin film is formed on the surface of the third thin film 11 away from the silicon substrate 10.

[0040] In some embodiments, the coefficient of thermal expansion of the second thin film is less than that of the silicon substrate 10.

[0041] In some embodiments, the coefficient of thermal expansion of the third thin film 11 is between that of the silicon substrate 10 and the second thin film, and the thickness of the third thin film 11 is less than that of the second thin film.

[0042] In some embodiments, the coefficient of thermal expansion of the third film 11 is equal to that of the second film.

[0043] In some embodiments, the coefficient of thermal expansion of the fourth film 12 is equal to that of the second film, and the thickness of the fourth film 12 is less than that of the second film.

[0044] In some embodiments, the coefficient of thermal expansion of the fourth thin film 12 is greater than or equal to the coefficient of thermal expansion of the silicon substrate 10.

[0045] In some embodiments, the third thin film 11 and the fourth thin film 12 are made of the same material as the second thin film. That is, the second thin film, the third thin film 11, and the fourth thin film 12 have the same coefficient of thermal expansion, and the coefficients of thermal expansion of the second thin film, the third thin film 11, and the fourth thin film 12 are all less than the coefficient of thermal expansion of the silicon substrate 10. Furthermore, the thickness of the third thin film 11 and the fourth thin film 12 is less than the thickness of the second thin film.

[0046] In some embodiments, based on the silicon substrate 10, a front-end process, such as thermal oxidation, is first performed to simultaneously grow and form silicon dioxide thin films on the second surface 101 and the first surface 102 of the silicon substrate 10, which serve as the fourth thin film 12 and the third thin film 11, respectively. Since the silicon dioxide thin film formed by this thermal oxidation is normally relatively thin, the silicon dioxide thin films formed by the front-end process on the second surface 101 and the first surface 102 of the silicon substrate 10 and serving as the fourth thin film 12 and the third thin film 11 can be considered together with the silicon substrate 10 as part of the substrate of the present invention. Furthermore, to highlight the principle of the present invention, in Figures 3-7 The fourth film 12 and the third film 11 are omitted from the illustration.

[0047] Step S2: Form a second thin film with a low coefficient of thermal expansion on the first surface of the substrate.

[0048] High-temperature thin film deposition processes include furnace tube thin film deposition processes. Before the silicon substrate 10 is fed into the furnace tube for the first thin film elongation, a second thin film with a lower coefficient of thermal expansion than the silicon substrate 10 needs to be formed on the first surface 102 of the silicon substrate 10.

[0049] In this embodiment, the second thin film is formed on the first surface 102 of the silicon substrate 10 by depositing the second thin film on the surface of the third thin film 11 on the first surface 102 of the silicon substrate 10.

[0050] like Figure 3 As shown, using, for example, a CVD process, a further layer of silicon dioxide film is deposited on the surface of the thermally oxidized silicon dioxide third thin film 11 (not shown, the same below) on the first surface of the silicon substrate 10, as the second thin film 13.

[0051] For the silicon substrate 10, the coefficient of thermal expansion of silicon dioxide is less than that of silicon, so the second thin film 13 with the low coefficient of thermal expansion can be a thicker silicon dioxide film.

[0052] In some embodiments, the thickness of the second silicon dioxide film 13 is preferably 0.5~1μm.

[0053] Step S3: Perform a high-temperature thin film deposition process. First, heat the substrate to deform it, and then deposit a first thin film with a first stress on the second surface of the deformed substrate.

[0054] A silicon substrate 10 with a fourth silicon dioxide film 12, a third silicon dioxide film 11, and a second silicon dioxide film 13 is fed into a furnace tube for a high-temperature deposition process (furnace tube deposition process) to deposit a first film with a first stress on the surface of the fourth silicon dioxide film 12 (not shown, the same below) on the second surface 101 of the silicon substrate 10.

[0055] In this embodiment, an LPCVD process is used to deposit a silicon nitride film as the first film on the surface of the fourth silicon dioxide film 12 on the second surface 101 of the silicon substrate 10. However, it is understood that the first film can be a film of other materials that have high stress after deposition.

[0056] The furnace tube deposition process for thin films generally includes a heating stage before deposition, a deposition stage, and a cooling stage after deposition.

[0057] The process temperature for LPCVD silicon nitride is typically 700~900℃. In this embodiment, the preferred process temperature for LPCVD silicon nitride is 750~850℃. That is, before depositing the silicon nitride thin film, it is necessary to heat the silicon substrate 10 to reach the required deposition temperature of 750~850℃.

[0058] The silicon substrate 10 with the second silicon dioxide thin film 13 is heated to generate an applied second stress on the first surface 102 of the silicon substrate 10, causing the silicon substrate 10 to deform as a whole. Then, a silicon nitride thin film as the first thin film is deposited on the second surface 101 of the deformed silicon substrate 10.

[0059] The second stress is of the same type as the first stress that needs to be released. Furthermore, both the first and second stresses are tensile stresses.

[0060] The principle of this invention, which causes deformation of the silicon substrate 10 by heating, is as follows: Before performing the furnace tube deposition thin film process, a second silicon dioxide thin film 13 is first formed on the first surface 102 of the silicon substrate 10. Since the coefficient of thermal expansion of the second silicon dioxide thin film 13 is less than that of the silicon substrate 10, when the silicon substrate 10 is heated during the furnace tube deposition thin film process, the thermal expansion of the silicon substrate 10 is less than that of the silicon substrate 10. That is, by utilizing the difference in thermal expansion between the second silicon dioxide thin film 13 and the silicon substrate 10, the expansion deformation on the first surface 102 of the silicon substrate 10 is less than the expansion deformation on the second surface 101 of the silicon substrate 10, thereby forming a tensile stress applied to the first surface 102 of the silicon substrate 10 as a second stress. Before the deposition of the first silicon nitride film, a prestress is introduced onto the silicon substrate 10. This causes a difference in deformation between the second surface 101 and the first surface 102 of the silicon substrate 10, resulting in an overall deformation of the silicon substrate 10 and a centrally convex (arched) morphology. Figure 4 As shown.

[0061] It is worth noting that for the second thin film 13 of the same material, the greater the thickness of the film deposited on the first surface 102 of the silicon substrate 10, the greater the prestress applied to the silicon substrate 10.

[0062] After the silicon substrate 10 is placed into the furnace tube, and the heating stage is completed, a reaction gas is introduced to begin the silicon nitride deposition stage. That is, a silicon nitride thin film is deposited on the second surface 101 of the deformed silicon substrate 10 as the first thin film.

[0063] like Figure 5 As shown, in this embodiment, an LPCVD process is used to deposit a silicon nitride film as a first thin film 14 on the second surface 101 of the deformed silicon substrate 10. The reaction gas during deposition includes NH3, the process temperature is 800°C, and an excess of NH3 is introduced to make the atomic ratio of silicon to nitrogen in the formed silicon nitride film close to the ideal 3:4. That is, there is no need to change the ratio of the reaction gas during LPCVD silicon nitride deposition, thus preventing the introduction of disordered groups (such as hydrogen bonds) into the silicon nitride film, maintaining the original chemical composition of the silicon nitride film, and therefore not affecting the properties of the silicon nitride film. Furthermore, the silicon nitride first thin film 14 formed in this way will generate tensile stress (first stress).

[0064] Using the above process, when a silicon nitride film as the first thin film 14 is deposited on the second surface 101 of the deformed silicon substrate 10, a fifth silicon nitride film 15 is also deposited simultaneously on the first surface 102 of the silicon substrate 10, i.e., on the surface of the second silicon dioxide film 13 away from the silicon substrate 10. This film will also generate tensile stress, such as... Figure 5 As shown.

[0065] Step S4: By cooling, the substrate with the first thin film undergoes deformation recovery, releasing the first stress present in the first thin film. After the deposition stage is completed, the silicon substrate 10 is sent out of the furnace tube and cooled down.

[0066] During the cooling process, the silicon substrate 10 undergoes volume shrinkage. Since the coefficient of thermal expansion of the second silicon dioxide film 13 is less than that of the silicon substrate 10, the silicon substrate 10 will recover its deformation and return to a state with a smaller Bow value (substrate curvature) during cooling and shrinkage. That is, during the cooling process of the silicon substrate 10, the shrinkage deformation occurring on the second surface 101 of the silicon substrate 10 will be greater than the shrinkage deformation occurring on the first surface 102 of the silicon substrate 10.

[0067] During the above process, the first silicon nitride film 14 on the second surface 101 of the silicon substrate 10 will also shrink along with the shrinkage of the silicon substrate 10, thus releasing its tensile stress and resulting in a low-stress film. Meanwhile, the tensile stress of the fifth silicon nitride film 15 on the first surface 102 of the silicon substrate 10 will become greater, such as... Figure 6 As shown.

[0068] Therefore, the present invention utilizes the heating and cooling process of the furnace tube itself during deposition to deposit a first silicon nitride film 14 with tensile stress on the second surface 101 of the silicon substrate 10 that deforms after heating, and utilizes the deformation recovery of the silicon substrate 10 caused by cooling to cause the first silicon nitride film 14 on the second surface 101 of the silicon substrate 10 to shrink, thereby releasing the tensile stress (first stress) present in the first silicon nitride film 14.

[0069] It is worth noting that the greater the deformation caused by the prestress applied to the silicon substrate 10 before deposition, the more shrinkage space the first silicon nitride film 14 will have after stress release, that is, the greater the reduction in its tensile stress.

[0070] Step S5: Remove the second film. After cooling the silicon substrate 10 to a predetermined temperature (e.g., room temperature), a conventional substrate surface dielectric removal process (substrate back dielectric removal process) is used to remove the fifth silicon nitride film 15 and the second silicon dioxide film 13 on the first surface 102 of the silicon substrate 10. If necessary, the third silicon dioxide film 11 on the first surface 102 of the silicon substrate 10 can also be removed. This results in a structure where a low-stress first silicon nitride film 14 is deposited on the second surface 101 of the silicon substrate 10, as shown below. Figure 7 As shown.

[0071] This invention introduces a second silicon dioxide film 13 with a low coefficient of thermal expansion on the first surface 102 of a silicon substrate 10. By utilizing the heating and cooling process during furnace deposition, the silicon substrate 10 can be deformed and restored, thereby releasing the tensile stress present in the first silicon nitride film 14 deposited on the second surface 101 of the silicon substrate 10. This not only eliminates the need for other complex structures and processes, but also facilitates the subsequent removal of the second silicon dioxide film 13 formed on the first surface 102 of the silicon substrate 10.

[0072] In fact, apart from depositing a second silicon dioxide film 13 with a low coefficient of thermal expansion on the first surface 102 of the silicon substrate 10, any other method that makes the overall structure before LPCVD silicon nitride exhibit a significantly higher deformation on the second surface 101 of the silicon substrate 10 than on the first surface 102 can achieve the effect of reducing the tensile stress within the first silicon nitride film 14 on the second surface 101 after LPCVD silicon nitride. For example, the coefficient of thermal expansion of the materials in each structural layer on the substrate can decrease sequentially from the second surface to the first surface. Alternatively, an asymmetrical structure can be used, where the thickness of silicon dioxide on the first surface of the silicon substrate 10 is significantly higher than that on the second surface. Since the coefficient of thermal expansion of silicon dioxide is less than that of silicon, the overall deformation on the second surface will also be significantly higher than that on the first surface.

[0073] Furthermore, any means of introducing prestress before depositing the first silicon nitride film, which allows the substrate to be in a bent state (with tensile stress on the top surface), will help reduce the tensile stress after the first silicon nitride film is deposited on the second surface 101. For example, the above effect can be achieved by pre-depositing a film with high tensile stress on the first surface of the substrate before depositing the first silicon nitride film.

[0074] An application of the above-described method for reducing stress in high-temperature deposited thin films according to the present invention includes fabricating passive devices using the first thin film 14 after the first stress has been released. For example, one application of the above-described method for reducing stress in high-temperature deposited thin films according to the present invention involves using the first silicon nitride thin film 14 after the tensile stress has been released and employing a waveguide patterning process to fabricate a silicon nitride waveguide passive device. Through the above-described method for reducing stress in high-temperature deposited thin films according to the present invention, the first silicon nitride thin film 14 obtained on the second surface 101 of the silicon substrate 10 maintains the original chemical composition of the silicon nitride thin film since the proportion of reactant gases during LPCVD silicon nitride is not changed, thus not affecting the properties of the silicon nitride thin film. Furthermore, since the tensile stress in the first silicon nitride thin film 14 is effectively released, exhibiting the characteristics of a low-stress thin film, even when deposited to a relatively thick thickness, it will not cause cracking or peeling off from the substrate, thereby ensuring the patterning accuracy when manufacturing the corresponding silicon nitride waveguide device.

[0075] In summary, this invention, during the high-temperature thin film deposition process, first deforms the substrate through a heating process before the deposition reaction to apply prestress to the substrate before film deposition, and then deposits the required thin film (first thin film 14) on the substrate surface. Afterwards, by cooling, the substrate recovers its deformation, thus fully releasing the first stress present in the deposited thin film. This effectively solves the problem of subsequent possible film cracking and peeling off from the substrate, which makes it difficult to pattern the corresponding devices.

[0076] While embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations fall within the scope and spirit of the invention as set forth in the claims. Furthermore, the invention described herein may have other embodiments and can be implemented or carried out in various ways.

Claims

1. A method for reducing stress in high-temperature deposited thin films, characterized in that, include: In the high-temperature deposition thin film process, the substrate is first deformed by heating, and then a first thin film is deposited on the surface of the deformed substrate. Then, the substrate with the first thin film is cooled to restore its deformation and release the first stress present in the first thin film.

2. The method for reducing stress in high-temperature deposited thin films according to claim 1, characterized in that, By heating, a second stress is applied to the first surface of the substrate, causing the substrate to deform as a whole, and then the first film is deposited on the second surface of the substrate opposite to the first surface, wherein the second stress is of the same stress type as the first stress.

3. The method for reducing stress in high-temperature deposited thin films according to claim 2, characterized in that, The stress types of the first stress and the second stress include tensile stress.

4. The method for reducing stress in high-temperature deposited thin films according to claim 3, characterized in that, Before performing the high-temperature deposition thin film process, a second thin film is first formed on the first surface. The coefficient of thermal expansion of the second thin film is smaller than that of the substrate. When the high-temperature deposition thin film process is performed and the substrate is heated, tensile stress is applied to the first surface, causing the substrate to undergo deformation due to the smaller deformation on the first surface compared to the second surface. By depositing the first thin film with tensile stress on the second surface of the substrate after deformation, and by utilizing the deformation recovery of the substrate caused by cooling, the first thin film located on the second surface shrinks, thereby releasing the first stress present in the first thin film.

5. The method for reducing stress in high-temperature deposited thin films according to claim 4, characterized in that, Before the formation of the second thin film, a third thin film is formed on the first surface. The second thin film is formed on the surface of the third thin film. The coefficient of thermal expansion of the third thin film is between the coefficient of thermal expansion of the substrate and the coefficient of thermal expansion of the second thin film. The thickness of the second thin film is greater than the thickness of the third thin film, or the coefficient of thermal expansion of the third thin film is equal to the coefficient of thermal expansion of the second thin film. And / or, a fourth thin film is formed on the second surface. The first thin film is formed on the surface of the fourth thin film. The coefficient of thermal expansion of the fourth thin film is equal to the coefficient of thermal expansion of the second thin film. The thickness of the second thin film is greater than the thickness of the fourth thin film, or the coefficient of thermal expansion of the fourth thin film is greater than or equal to the coefficient of thermal expansion of the substrate.

6. The method for reducing stress in high-temperature deposited thin films according to claim 5, characterized in that, The substrate includes a silicon substrate or an SOI substrate, the second thin film includes a silicon dioxide thin film, and / or the third and / or the fourth thin film includes a silicon dioxide thin film.

7. The method for reducing stress in high-temperature deposited thin films according to claim 5, characterized in that, The thickness of the second film is 0.5~1μm.

8. The method for reducing stress in high-temperature deposited thin films according to claim 1, characterized in that, The first thin film includes a silicon nitride thin film, and the high-temperature deposition thin film process includes a furnace tube deposition thin film process, in which the silicon nitride thin film is deposited in a furnace tube using an LPCVD process, and by introducing an excess of NH3, the atomic ratio of silicon to nitrogen in the formed silicon nitride thin film is close to the ideal 3:4, and / or the process temperature for depositing the silicon nitride thin film is 700~900℃.

9. An application of the method for reducing stress in a high-temperature deposited thin film according to any one of claims 1-8, the application comprising fabricating a passive device using a first thin film after the first stress has been released.

10. The application according to claim 9, characterized in that, The passive device includes a silicon nitride waveguide.

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