Thin film deposition method

Abstract

According to the thin film deposition method provided by the invention, the annealing treatment at 650 DEG C is performed on the first thin film deposited on the surface of the wafer boat and the surface of the furnace tube each time at the preset temperature, so that the stress of the first thin film on the surface of the wafer boat and the surface of the furnace tube tends to 0, and the stress accumulation can be effectively eliminated. Depositing and annealing are repeated until the films on the surface of the wafer boat and the surface of the furnace tube are deposited to a first preset thickness, a second film is deposited on the first film on the surface of the wafer boat and the surface of the furnace tube which are deposited to the first preset thickness, the stress of the second film is opposite to that of the first film, and the effect of neutralizing the stress is achieved; and the second thin film is polycrystalline silicon with higher roughness, so that the adhesive force of thin film deposition on the surface of a subsequent wafer boat and the surface of a furnace tube is improved. The principle is simple, the thin film stress on the surface of the wafer boat and the surface of the furnace tube obtained through repeated operation is reduced, the adhesive force is improved, and the expected maintenance frequency is reduced.

Description

Technical Field

[0001] The present application relates to semiconductor technology, and in particular to a method for thin film deposition. Background Art

[0002] Thin film deposition is a critical process in integrated circuits, but it often results in low-quality or even scrapped final products due to the defect of peeling of the deposited silicon film. Thin film deposition usually adopts the furnace tube LPCVD process. While depositing on the wafer surface, the thin film deposition process also deposits on the wafer boat surface and the furnace tube surface. With the change of wafer batches, the thickness of the film on the wafer boat surface and the furnace tube surface accumulates, and the adhesion of the film on the wafer boat surface and the furnace tube surface becomes poor. The film deposited by stress release peels off and may fall on the wafer surface during the production process, thereby affecting the wafer product. At present, the most direct and effective way to solve the problem of product impact caused by film shedding is to remove the film on the wafer boat surface and the furnace tube surface through expected maintenance, but frequent expected maintenance will greatly increase costs, which violates the principle of increasing costs and increasing efficiency.

[0003] Application Contents

[0004] Therefore, in order to overcome the above-mentioned shortcomings of the prior art, the present application designs a method for thin film deposition to solve the problem that the film adhesion on the surface of the wafer boat and the surface of the furnace tube is poor, resulting in the film falling off, thereby requiring frequent expected maintenance.

[0005] In order to achieve the above objectives, this application provides the following technical solutions:

[0006] A method for thin film deposition, comprising:

[0007] Step 1, performing thin film deposition on the wafers on the wafer boat in the furnace tube under a predetermined temperature range to obtain a first thin film by depositing the thin film to a first predetermined thickness, wherein the predetermined temperature range is 550° C. to 610° C.;

[0008] Step 2, annealing the first film on the surface of the furnace tube and the surface of the wafer boat at 650° C.;

[0009] Step 3, repeating the above steps until the cumulative thickness of the first film deposited on the furnace tube surface and the wafer boat surface reaches a second predetermined thickness value;

[0010] Step 4, depositing a second film on the first film on the surface of the furnace tube and the surface of the wafer boat, wherein the stress of the second film is opposite to that of the first film;

[0011] Step 5, repeating steps 1 to 4 until it is determined that the cumulative deposition thickness of the first film and the second film on the surface of the furnace tube and the surface of the wafer boat reaches a third predetermined thickness value, thereby obtaining a wafer boat and a furnace tube with attached films.

[0012] Specifically, the predetermined temperature for performing thin film deposition on the wafers on the wafer boat in the furnace tube is 550° C. to 580° C.

[0013] Specifically, the second thin film is deposited at a temperature of 600°C to 610°C.

[0014] Specifically, when the predetermined temperature for thin film deposition on the wafers on the wafer boat in the furnace tube is 590°C to 610°C, the second thin film deposition temperature is 620°C to 640°C.

[0015] Specifically, the first film on the surface of the furnace tube and the surface of the wafer boat is annealed at 650°C, the temperature of the furnace tube is first raised to 650°C when the furnace tube is in an empty state, and the first film on the surface of the furnace tube and the surface of the wafer boat is annealed in a nitrogen atmosphere, the annealing time is greater than one hour, and after the annealing is completed, the temperature drops to the temperature when the furnace tube is in an empty state.

[0016] Specifically, the first predetermined thickness is 8000A, 10000A or 12000A.

[0017] Specifically, the second predetermined thickness is 5 um to 7.5 um.

[0018] Specifically, the third predetermined thickness is 30um to 40um.

[0019] Specifically, before step 1, nitrogen is filled into the furnace tube until the air in the furnace tube is exhausted, and the thin film deposition is started.

[0020] Specifically, when the first film is deposited, the pressure in the furnace tube is 600 mTorr, and the reaction gas flow rate is 0.98 slm; when the second film is deposited, the pressure in the furnace tube is 300 mTorr, and the reaction gas flow rate is 0.09 slm.

[0021] Compared with the prior art, the advantages of the present application are: the present application performs an annealing treatment at 650°C on the first film deposited on the surface of the wafer boat and the surface of the furnace tube at a predetermined temperature each time, so that the stress of the first film on the surface of the wafer boat and the surface of the furnace tube tends to 0, which can effectively eliminate stress accumulation. Repeated deposition and annealing treatment until the film on the surface of the wafer boat and the surface of the furnace tube is deposited to the first predetermined thickness, and the first film deposited on the surface of the wafer boat and the surface of the furnace tube to the first predetermined thickness is deposited with a second film. The stress of the second film is opposite to that of the first film, so as to achieve the effect of neutralizing the stress, and the second film is polysilicon with a greater roughness, which improves the adhesion of the subsequent film deposition on the surface of the wafer boat and the surface of the furnace tube. The film stress on the surface of the wafer boat and the surface of the furnace tube obtained by repeated operation is reduced, the adhesion is increased, and the frequency of expected maintenance is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 is a flow chart of a thin film deposition method in an embodiment of the present application;

[0024] Figure 2 is a graph showing the relationship between silicon structure and deposition temperature in an embodiment of the present application;

[0025] Figure 3 is a comparison chart of the lifting and shedding frequency of a mixed film of amorphous silicon and polycrystalline silicon and the lifting and shedding frequency of a polycrystalline silicon film in the embodiment of the present application;

[0026] Figure 4 is a graph showing the relationship between stress and annealing temperature of a thin film deposited at a temperature of 550° C. to 610° C. in an embodiment of the present application;

[0027] Figure 5 is a graph showing the relationship between stress and annealing temperature of a film deposited at a temperature of 620° C. to 640° C. in an embodiment of the present application;

[0028] Figure 6 is a graph showing the relationship between film stress and a predetermined deposition temperature in an embodiment of the present application;

[0029] Figure 7 is a graph showing the relationship between the cumulative thickness of the first film and the number of films lifted and fallen off in the embodiment of the present application;

[0030] Figure 8 This is a comparison diagram of the lifting and falling of a thin film before and after the implementation of a thin film deposition method in an embodiment of the present application. DETAILED DESCRIPTION

[0031] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0032] The following describes the implementation methods of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific implementation methods, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, in the absence of conflict, the following embodiments and the features in the embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work belong to the scope of protection of the present application.

[0033] It should be noted that various aspects of the embodiments within the scope of protection of the present application are described below. It should be apparent that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is merely illustrative. Based on the present application, it should be understood by those skilled in the art that an aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number and aspect described herein can be used to implement the device and / or practice the method. In addition, other structures and / or functionalities other than one or more of the aspects described herein can be used to implement this device and / or practice this method.

[0034] It should also be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present application. The drawings only show components related to the present application rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0035] Additionally, in the following description, specific details are provided to facilitate a thorough understanding of the examples. However, it will be understood by those skilled in the art that the aspects described may be practiced without these specific details.

[0036] The present application provides a method for thin film deposition, such as Figure 1 As shown, the following steps are included:

[0037] Step 1: Perform thin film deposition on the wafers on the wafer boat in the furnace tube within a predetermined temperature range to obtain a first thin film having a first predetermined thickness. The predetermined temperature range is 550° C. to 610° C.

[0038] The temperature range greater than 550°C is divided into three ranges: 550°C to 580°C, 590°C to 610°C and not less than 620°C. The predetermined temperature range of 550°C to 610°C is divided into two ranges: 550°C to 580°C and 590°C to 610°C. Select one of the two temperature ranges and start the thin film deposition operation on the wafers on the wafer boat in the furnace tube. Figure 2 As shown in the figure, when the temperature is less than 550℃, the film is amorphous silicon, and the disordered arrangement of silicon atoms causes the surface roughness to be less than 1nm rms; when the temperature is greater than 605℃, the film is polycrystalline silicon, and its grains are ordered in the short range and not in the long range, which causes the surface to be rougher, with a roughness greater than or equal to 1nm rms; when the temperature is between 550 and 605℃, the film is a mixture of amorphous silicon and polycrystalline silicon, and the roughness is between the two. Figure 3 As shown in the figure, the greater the roughness of the film, the better the adhesion, and the lower the probability of the film lifting and peeling. In contrast, the probability of lifting and peeling of the amorphous and polycrystalline mixed doped film deposited at 550℃ to 580℃ is higher, and the probability of lifting and peeling of the non-doped film at 620℃ is lower.

[0039] While thin film is being deposited on the wafer, thin film will also be deposited on the furnace tube surface and the wafer boat surface, and it is consistent with the thin film deposited on the wafer. A first predetermined thickness is set. When the thickness of the thin film deposited on the wafer reaches the first predetermined thickness, the thin film on the furnace tube surface and the wafer boat surface is called the first thin film. The wafer with the first thin film attached enters the next process. After the thin film on the furnace tube surface and the wafer boat surface is subsequently processed, the wafer on the wafer boat in the furnace tube is exchanged for the next batch of wafers for deposition of the first thin film. The first thin film on the furnace tube surface and the wafer boat surface is accumulated on the original basis.

[0040] Step 2: annealing the first film on the surface of the furnace tube and the surface of the wafer boat at 650°C.

[0041] The first film deposited on the furnace tube surface and the wafer boat surface is annealed at 650°C to change the stress of the first film deposited on the furnace tube surface and the wafer boat surface at 550°C-580°C to 0, effectively eliminating stress accumulation.

[0042] like Figure 4 As shown in Figure 2, the negative stress film deposited at 550℃ and 580℃ will experience a stress mutation at 600℃~800℃, from negative stress to positive stress. And at around 650℃, the stress tends to 0. Figure 4 as well as Figure 5As shown in the figure, no matter at what temperature the film is deposited, no matter whether the stress of the film is positive or negative, the stress tends to 0 when annealed at a temperature greater than 1000°C. However, conventional film growth machines do not support high temperatures greater than 1000°C to anneal the accumulated films on the furnace tube and the wafer boat. Therefore, annealing the first film at a high temperature greater than 1000°C is excluded, and a temperature of 650°C is selected to anneal the first film on the surface of the furnace tube and the surface of the wafer boat.

[0043] Step 3, repeat the above steps until the accumulated thickness of the first film deposited on the furnace tube surface and the wafer boat surface reaches a second predetermined thickness value.

[0044] During the film accumulation process, different cumulative thicknesses may cause the film to lift and fall off, but the overall situation roughly conforms to the normal distribution. When the accumulated deposition thickness of the first film reaches the second predetermined thickness value, its adhesion decreases and the frequency of film lifting and falling off increases. Therefore, when the accumulated thickness of the first film on the furnace tube surface and the wafer boat surface reaches the second predetermined thickness, the deposition of the first film is no longer continued to avoid the frequency of film lifting and falling off being at a high value.

[0045] Step 4, depositing a second thin film, wherein the stress of the second thin film is opposite to that of the first thin film;

[0046] When the first film is deposited to the peak section where it is lifted and peeled off, that is, when the deposited thickness of the first film reaches a second predetermined thickness value, a reverse stress film is deposited on the accumulated first film, that is, a second film is deposited. The second film neutralizes the stress of the first film, and the second film is a polysilicon film. A layer of polysilicon with a greater roughness is deposited on the surface to improve the adhesion of subsequent film deposition.

[0047] Step 5, repeat the above steps until it is determined that the cumulative thickness of the first film and the second film deposited on the furnace tube surface and the wafer boat surface reaches a third predetermined thickness value, thereby obtaining a high-adhesion film.

[0048] After the second film deposition is completed, the repeated deposition annealing of the first film and the reverse stress deposition of the second film in steps 1 to 4 are performed. By repeating the operation, a film of ideal thickness can be obtained. After the repeated operation, the total film thickness reaches the set third predetermined thickness value, and finally a crystal boat and a furnace tube with an attached film are obtained.

[0049] In the above method, each time the first film deposited on the surface of the wafer boat and the surface of the furnace tube is subjected to an annealing treatment at 650°C at a predetermined temperature, the stress of the first film on the surface of the wafer boat and the surface of the furnace tube is approached to 0, which can effectively eliminate stress accumulation. The deposition and annealing treatment are repeated until the film on the surface of the wafer boat and the surface of the furnace tube is deposited to a first predetermined thickness, and a second film is deposited on the first film on the surface of the wafer boat and the surface of the furnace tube that is deposited to the first predetermined thickness. The stress of the second film is opposite to that of the first film, which achieves the effect of neutralizing the stress, and the second film is polysilicon with a greater roughness, which improves the adhesion of the subsequent film deposition on the surface of the wafer boat and the surface of the furnace tube. The film stress on the surface of the wafer boat and the surface of the furnace tube obtained by repeating this operation is reduced, the adhesion is increased, and the frequency of expected maintenance is reduced.

[0050] In one embodiment, the temperature for thin film deposition on the wafers on the wafer boat in the furnace tube is 550° C. to 580° C. Figure 2 It can be seen that the film deposited at a temperature of 550℃ to 580℃ is a mixture of amorphous silicon and polycrystalline silicon. The roughness is between amorphous silicon and polycrystalline silicon, and the adhesion is also between amorphous silicon and polycrystalline silicon. Figure 4 It can be seen that when a film with a deposition stress of 550℃ to 580℃ is annealed at 650℃, the stress of the film obtained by annealing tends to 0. When the temperature of the film deposition is 550℃ to 580℃, the annealing operation at 650℃ has the most obvious effect of eliminating its stress and making its stress tend to 0.

[0051] In one embodiment, the temperature of the second film deposition is 605°C. Figure 6 It can be seen that the stress of the first film deposited at a temperature of 550°C to 580°C is a negative stress of (-250)MPa to (-150)MPa. The stress of the second film deposited at a temperature of 605°C is 250MPa. The stress of the second film is opposite to that of the first film, and the stresses of the two are neutralized, so that the total stress tends to 0, and its adhesion is improved. The second film deposited at a temperature of 605°C is polycrystalline silicon, which is rough and has a large surface, which improves its adhesion during the subsequent film deposition process.

[0052] In one embodiment, when the first film deposition temperature is 590°C to 610°C, the second film deposition temperature is 620°C. Figure 6It can be seen that the stress of the film deposited at a temperature of 590℃~610℃ is 100MPa~250MPa, and the stress of the film deposited at a temperature of 615~620℃ is (-250)MPa~(-100)MPa. The stress of the second film is opposite to the stress of the first film. The stresses of the two are neutralized, so that the total stress tends to 0, and its adhesion is improved. The second film deposited at a temperature of 615~620℃ is polycrystalline silicon, which is rough and improves its adhesion during the subsequent film deposition process. When the deposition temperature of the first film is not less than 620℃, the deposition temperature of the second film is 605℃, which is a positive stress film. By Figure 6 It can be seen that the stress of the film deposited at a temperature greater than or equal to 620°C is (-250)MPa, and the stress of the film deposited at a temperature of 605°C is 250MPa. The stress of the second film is opposite to that of the first film, and the stresses of the two films are neutralized, so that the total stress tends to 0, and its adhesion is improved. The second film deposited at a temperature of 605°C is polysilicon, which is rough and has a large surface, which improves its adhesion in the subsequent film deposition process.

[0053] In one embodiment, in step 2, the first film on the surface of the furnace tube and the surface of the wafer boat is annealed at 650°C. The annealing process is to first increase the temperature of the furnace tube when it is in an empty state to 650°C, and anneal the first film in a nitrogen atmosphere. The annealing time is greater than one hour. After the annealing is completed, the temperature drops to the temperature when the furnace tube is in an empty state. At this time, the wafer boat can carry the next batch of wafers into the furnace tube for thin film deposition operations.

[0054] In one embodiment, the first predetermined thickness is 8000A, 10000A or 12000A.

[0055] In one embodiment, the second predetermined thickness is 5um to 7.5um. On a conventional silicon carbide crystal boat and furnace tube wall, for the deposited thin film, an expected maintenance is usually performed when the film thickness accumulates to 20um. In the process of the film thickness accumulating to 20um, different cumulative thicknesses may cause film lifting, peeling and flaking. The number of film lifting, peeling and flaking is roughly normally distributed, indicating that film lifting, peeling and flaking are random and inevitable. The deposition of the reverse stress film is performed before the high-incidence interval of film lifting, peeling and flaking, and the first film cumulative thickness before the high-incidence interval of film lifting and peeling is set as the second predetermined thickness. When the first film cumulative thickness reaches the set second predetermined thickness, the deposition of the second film is immediately implemented to avoid entering the high-incidence interval of film lifting, peeling and flaking, thereby reducing the risk of film lifting, peeling and flaking.

[0056] In one embodiment, the third predetermined thickness is 30 um to 40 um. When the total thickness of the thin film deposited on the furnace tube surface and the wafer boat surface is 40 um, the thin film deposition operation is terminated and the expected maintenance is performed.

[0057] In one embodiment, nitrogen is filled into the furnace tube for thin film deposition before steps 1 to 5 are performed, and when the air in the furnace tube is exhausted, steps 1 to 5 are performed to achieve thin film deposition. The advantage of filling the furnace tube with nitrogen to exhaust the air is that the furnace tube can be cleaned in advance before thin film deposition.

[0058] In one embodiment, when the first film is deposited, the pressure in the furnace tube is 600 mTorr and the reaction gas flow rate is 0.98 slm; when the second film is deposited, the pressure in the furnace tube is 300 mTorr and the reaction gas flow rate is 0.09 slm.

[0059] Example 1

[0060] A thin film deposition method, ultimately obtaining a thin film attached to a crystal boat and a furnace tube with high adhesion.

[0061] First, fill the furnace tube with nitrogen to exhaust the air in the furnace tube to ensure that the gas in the furnace tube is clean. Then proceed with the following steps in sequence:

[0062] Step 1: Start thin film deposition on the wafers on the wafer boat in the furnace tube at a temperature of 550°C to 580°C. At this time, the pressure in the furnace tube is 600mTorr, and the reaction gas flow rate of thin film deposition is 0.98slm. Figure 2 As shown, the film is a mixture of amorphous silicon and polycrystalline silicon, and its roughness is between that of amorphous silicon and polycrystalline silicon. Each time, a thickness of 10000A is deposited, and the film with a thickness of 10000A deposited at one time is the first film; the wafer with the first film attached is taken out of the furnace tube and enters the next process.

[0063] Step 2: anneal the first film on the surface of the furnace tube and the surface of the wafer boat at 650°C. First, raise the temperature of the furnace tube to 650°C when it is in an empty state, and anneal the first film in a nitrogen atmosphere for more than one hour. After the annealing, the temperature drops to the temperature when the furnace tube is in an empty state. Figure 4 As shown, the first film is annealed at 650° C., so that the stress of the first film approaches 0, effectively eliminating stress accumulation.

[0064] Step 3: Repeat the above steps until the cumulative thickness of the first film deposited on the furnace tube surface and the wafer boat surface reaches 7 um. Figure 7 As shown, the film accumulation of 7.5um to 15um is a high-incidence range for film lifting and peeling. When the film accumulation is greater than 7um, the stress accumulates, the adhesion decreases, and the probability of film lifting and peeling becomes significantly higher. Therefore, when the first film deposition thickness on the furnace tube surface and the wafer boat surface accumulates to 7um, the deposition of the first film on the wafer surface on the wafer boat in the furnace tube is temporarily stopped.

[0065] Step 4: Deposit a second thin film on the first thin film accumulated on the surface of the furnace tube and the surface of the wafer boat. The second thin film is deposited at 605°C. At this time, the pressure in the furnace tube is 300mTorr, and the reaction gas flow rate of the thin film deposition is 0.09slm. Figure 6 As shown in the figure, the stress of the first film deposited at a temperature of 550°C to 580°C is a negative stress of (-250)MPa to (-150)MPa, and the stress of the second film deposited at 605°C is a positive stress of 250MPa. The stress of the second film is opposite to that of the first film, and the stresses of the two films are neutralized, so that the total stress tends to 0, and its adhesion is improved. The second film deposited at a temperature of 605°C is polysilicon, which is rough and has a large surface, which improves its adhesion in the subsequent film deposition process.

[0066] Step 5, repeat the above steps until it is determined that the cumulative thickness of the first film and the second film deposited on the furnace tube surface and the wafer boat surface reaches 30 um, thereby obtaining the furnace tube surface and the wafer boat surface with attached films.

[0067] The film deposited by steps 1 to 5 has a significant improvement on the problem of film lifting and falling off. Figure 8 As shown, starting from May, the deposition method of step 1 to step 5 was carried out, and the frequency of film lifting and falling off was reduced from 10% when the deposition method of this embodiment was not carried out to less than 1%, and the film lifting and falling off was significantly improved. The furnace tube and the silicon carbide crystal boat do not need to be frequently expected maintenance, and the interval of expected maintenance is extended from the original expected maintenance of 20um film deposition to the expected maintenance of 30um film deposition, and the deposition thickness of the film is increased by 50%.

[0068] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed in the present application should be included in the protection scope of the present application.

Claims

1. A method for thin film deposition, characterized in that: include: Step 1, performing thin film deposition on the wafer on the wafer boat in the furnace tube under a predetermined temperature range to obtain a first thin film by depositing the thin film to a first predetermined thickness, wherein the predetermined temperature range is 550° C. to 610° C.; Step 2, annealing the first film on the surface of the furnace tube and the surface of the wafer boat at 650° C.; Step 3, repeating the above steps until the accumulated thickness of the first film deposited on the furnace tube surface and the wafer boat surface reaches a second predetermined thickness value; Step 4, depositing a second film on the first film on the surface of the furnace tube and the surface of the wafer boat, wherein the stress of the second film is opposite to that of the first film; Step 5, repeating steps 1 to 4 until it is determined that the cumulative deposition thickness of the first film and the second film on the surface of the furnace tube and the surface of the wafer boat reaches a third predetermined thickness value, thereby obtaining a wafer boat and a furnace tube with attached films.

2. The method according to claim 1, characterized in that The predetermined temperature for performing thin film deposition on the wafers on the wafer boat in the furnace tube is 550° C. to 580° C.

3. The method according to claim 2, characterized in that The second thin film is deposited at a temperature of 600°C to 610°C.

4. The method according to claim 1, characterized in that: When the predetermined temperature for thin film deposition on the wafers on the wafer boat in the furnace tube is 590°C to 610°C, the second thin film deposition temperature is 620°C to 640°C.

5. The method according to claim 1, characterized in that The first film on the surface of the furnace tube and the surface of the wafer boat is annealed at 650°C. The temperature of the furnace tube is first raised to 650°C when the furnace tube is in an empty state. The first film on the surface of the furnace tube and the surface of the wafer boat is annealed in a nitrogen atmosphere. The annealing time is greater than one hour. After the annealing is completed, the temperature drops to the temperature when the furnace tube is in an empty state.

6. The method according to claim 1, characterized in that The first predetermined thickness is 8000A, 10000A or 12000A.

7. The method according to claim 1, characterized in that The second predetermined thickness is 5 um to 7.5 um.

8. The method according to claim 1, characterized in that The third predetermined thickness is 30 um to 40 um.

9. The method according to claim 1, characterized in that: Before step 1, nitrogen is filled into the furnace tube until the air in the furnace tube is exhausted, and the thin film deposition is started.

10. The method according to claim 1, characterized in that When the first film is deposited, the pressure in the furnace tube is 600 mTorr and the reaction gas flow rate is 0.98 slm; when the second film is deposited, the pressure in the furnace tube is 300 mTorr and the reaction gas flow rate is 0.09 slm.

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