A method for thin film deposition

Abstract

This application provides a thin film deposition method. Each time a first thin film is deposited on the surface of a crystal boat and a furnace tube at a predetermined temperature, it is annealed at 650°C to reduce the stress of the first thin film on the crystal boat and furnace tube surfaces to near zero, effectively eliminating stress accumulation. This deposition and annealing process is repeated until the thin film on the crystal boat and furnace tube surfaces reaches a first predetermined thickness. Then, a second thin film is deposited on the first thin film at the first predetermined thickness. The second thin film has the opposite stress to the first thin film, achieving stress neutralization. Furthermore, this second thin film is made of polycrystalline silicon with a higher roughness, improving the adhesion of subsequent thin film depositions on the crystal boat and furnace tube surfaces. The principle of this application is simple. Repeated operation reduces the stress and increases the adhesion of the thin film on the crystal boat and furnace tube surfaces, reducing the frequency of expected maintenance.

Description

Technical Field

[0001] This application relates to semiconductor processes, specifically to a method for thin film deposition. Background Technology

[0002] Thin film deposition, a crucial step in integrated circuit manufacturing, often suffers from defects such as silicon film peeling, leading to low-yield or even scrapped products. Thin film deposition typically employs furnace-tube LPCVD (Liquid Crystallization) technology. During deposition, films are deposited on the wafer surface, as well as on the wafer boat and furnace tube surfaces. With each batch of wafers, the accumulated film thickness on these surfaces weakens, causing stress release and film peeling. This film may fall onto the wafer surface during production, affecting the final product. Currently, the most direct and effective solution to product defects caused by film peeling is to remove the film from the wafer boat and furnace tube surfaces through pre-installed maintenance. However, frequent pre-installed maintenance significantly increases costs, contradicting the principle of cost-effectiveness.

[0003] Application content

[0004] Therefore, in order to overcome the shortcomings of the prior art, this application designs a thin film deposition method to solve the problem of poor film adhesion on the surface of the crystal boat and the surface of the furnace tube, which leads to film detachment and thus requires frequent maintenance.

[0005] To achieve the above objectives, this application provides the following technical solution:

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

[0007] Step 1: Deposit a thin film on a wafer on a crystal boat inside a furnace tube at a predetermined temperature range to obtain a first thin film with a first predetermined thickness. The predetermined temperature range is 550°C to 610°C.

[0008] Step 2: Anneal the first film on the surface of the furnace tube and the surface of the crystal boat at 650°C;

[0009] Step 3: Repeat the above steps until the cumulative thickness of the first thin film deposited on the surface of the furnace tube and the surface of the crystal boat reaches the second predetermined thickness value.

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

[0011] Step 5: Repeat steps 1 to 4 until the cumulative thickness of the first and second films deposited on the surface of the furnace tube and the surface of the crystal boat reaches a third predetermined thickness value, thereby obtaining a crystal boat and furnace tube with the films attached.

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

[0013] Specifically, the temperature for the second thin film deposition is 600°C to 610°C.

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

[0015] Specifically, the first thin film on the surface of the furnace tube and the surface of the crystal boat is annealed at 650°C. First, the temperature of the furnace tube in an empty state is raised to 650°C, and the first thin film on the surface of the furnace tube and the surface of the crystal boat is annealed in a nitrogen atmosphere. The annealing time is more than one hour, and after the annealing is completed, the temperature is reduced 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 5µm to 7.5µm.

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

[0019] Specifically, before step 1, nitrogen gas is introduced into the furnace tube until the air inside the furnace tube is purged, and the thin film deposition begins.

[0020] Specifically, during the deposition of the first thin film, the pressure inside the furnace tube is 600 mTorr and the reaction gas flow rate is 0.98 slm; during the deposition of the second thin film, the pressure inside the furnace tube is 300 mTorr and the reaction gas flow rate is 0.09 slm.

[0021] Compared with existing technologies, the advantages of this application are as follows: This application performs an annealing treatment at 650°C on each first film deposited on the surface of the crystal boat and furnace tube at a predetermined temperature, causing the stress of the first film on the crystal boat and furnace tube surfaces to approach zero, effectively eliminating stress accumulation. Repeated deposition and annealing are performed until the film on the crystal boat and furnace tube surfaces reaches a first predetermined thickness. Then, a second film is deposited on the first film at the first predetermined thickness. The second film has opposite stress to the first film, achieving stress neutralization. Furthermore, this second film is made of polycrystalline silicon with a higher roughness, improving the adhesion of subsequent film deposition on the crystal boat and furnace tube surfaces. Repeating this operation results in reduced film stress and increased adhesion on the crystal boat and furnace tube surfaces, reducing the frequency of expected maintenance. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a flowchart of a thin film deposition method according to an embodiment of this application;

[0024] Figure 2 This is a graph showing the relationship between silicon structure and deposition temperature in the embodiments of this application;

[0025] Figure 3 This is a comparison diagram of the lifting and shedding frequency of the mixed-state thin film of amorphous silicon and polycrystalline silicon and the lifting and shedding frequency of the polycrystalline silicon thin film in the embodiments of this application.

[0026] Figure 4 This is a graph showing the relationship between stress and annealing temperature for thin films deposited at temperatures between 550°C and 610°C in embodiments of this application.

[0027] Figure 5 This is a graph showing the relationship between stress and annealing temperature for thin films deposited at temperatures between 620°C and 640°C in the embodiments of this application.

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

[0029] Figure 7 This is a graph showing the relationship between the cumulative thickness of the first film and the number of films lifted and detached in an embodiment of this application;

[0030] Figure 8 This is a comparison diagram showing the film lifting and peeling off before and after implementing a thin film deposition method in an embodiment of this application. Detailed Implementation

[0031] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0032] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0033] It should be noted that the following description covers various aspects of embodiments within the scope of protection of this application. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this application, those skilled in the art will understand that one 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 aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0034] It should also be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this application. The drawings only show the components related to this application and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

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

[0036] This application provides a method for thin film deposition, such as... Figure 1 As shown, it includes the following steps:

[0037] Step 1: Deposit a thin film on the wafer on the crystal boat in the furnace tube at a predetermined temperature range to obtain a first thin film with a first predetermined thickness. The predetermined temperature range is 550℃~610℃.

[0038] The temperature range above 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 further divided into two ranges: 550°C to 580°C and 590°C to 610°C. Select one of these two temperature ranges to begin the thin film deposition operation on the wafer on the boat inside the furnace tube. For example... Figure 2 As shown, at temperatures below 550℃, the film is amorphous silicon, and the disordered arrangement of silicon atoms results in a surface roughness of less than 1 nm rms. At temperatures above 605℃, the film is polycrystalline silicon, where the short-range order of the grains and the long-range indifference lead to a rougher surface with a roughness greater than or equal to 1 nm rms. Between 550℃ and 605℃, the film is a mixture of amorphous and polycrystalline silicon, with a roughness intermediate between the two. Figure 3 As shown, the greater the roughness of the film, the better the adhesion and the lower the probability of the film being lifted off and peeled off. In comparison, the probability of lifting off and peeling off amorphous polycrystalline mixed-state doped films deposited at temperatures of 550℃ to 580℃ is relatively high, while the probability of lifting off and peeling off undoped films deposited at 620℃ is relatively low.

[0039] During thin film deposition on the wafer, thin films are also deposited on the surface of the furnace tube and the wafer boat, and these films are identical to those deposited on the wafer. A first predetermined thickness is set. When the thickness of the film deposited on the wafer reaches the first predetermined thickness, the 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 proceeds to the next process. After subsequent processing of the films on the furnace tube surface and the wafer boat surface, the wafers on the wafer boat inside the furnace tube are replaced with the next batch of wafers for the deposition of the first thin film. The first thin films on the furnace tube surface and the wafer boat surface accumulate on top of the previous ones.

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

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

[0042] like Figure 4 As shown, negative stress films deposited at 550℃ and 580℃ undergo a stress abrupt change from negative stress to positive stress at temperatures between 600℃ and 800℃. Furthermore, the stress tends to zero near 650℃. Figure 4 as well as Figure 5As shown, regardless of the temperature at which the film is deposited, and regardless of the sign of the stress, the stress tends to zero when annealed at temperatures above 1000°C. However, conventional thin film growth equipment does not support annealing at temperatures above 1000°C on the furnace tube and the crystal boat. Therefore, annealing the first film at temperatures above 1000°C was excluded, and instead, a temperature of 650°C was chosen to anneal the first film on the surface of the furnace tube and the crystal boat.

[0043] Step 3: Repeat the above steps until the cumulative thickness of the first thin film deposited on the surface of the furnace tube and the surface of the crystal boat reaches the second predetermined thickness value.

[0044] During the film deposition process, film peeling and detachment can occur at different deposition thicknesses, but the overall distribution roughly follows a normal distribution. When the cumulative deposition thickness of the first film reaches a second predetermined thickness value, its adhesion decreases, and the frequency of film peeling and detachment increases. Therefore, when the cumulative thickness of the first film on the furnace tube surface and the crystal boat surface reaches the second predetermined thickness, the deposition of the first film is stopped to avoid the high frequency of film peeling and detachment.

[0045] Step 4: Deposit a second thin film with opposite stress to the first thin film;

[0046] When the first film is deposited to the peak region where it is lifted and detached, that is, when the cumulative thickness of the first film reaches the 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 polycrystalline silicon film, with a layer of polycrystalline silicon with greater roughness deposited on the surface to improve the adhesion of subsequent film deposition.

[0047] Step 5: Repeat the above steps until the cumulative thickness of the first and second films deposited on the surface of the furnace tube and the surface of the crystal boat reaches the third predetermined thickness value, thus obtaining a high-adhesion film.

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

[0049] The above method involves annealing the first thin film deposited on the surface of the crystal boat and furnace tube at a predetermined temperature at a 650°C after each deposition. This reduces the stress of the first thin film on the crystal boat and furnace tube surfaces to near zero, effectively eliminating stress accumulation. This deposition and annealing process is repeated until the thin film on the crystal boat and furnace tube surfaces reaches a first predetermined thickness. Then, a second thin film is deposited on the first thin film at this thickness. The second thin film has the opposite stress to the first film, achieving stress neutralization. Furthermore, this second thin film is made of polycrystalline silicon with a higher roughness, improving the adhesion of subsequent thin film depositions on the crystal boat and furnace tube surfaces. Repeating this process results in reduced film stress and increased adhesion on the crystal boat and furnace tube surfaces, reducing the frequency of expected maintenance.

[0050] In one embodiment, the temperature for thin film deposition on the wafer on the boat inside the furnace tube is 550°C to 580°C. Figure 2 It can be seen that the film deposited at temperatures between 550℃ and 580℃ is a mixture of amorphous silicon and polycrystalline silicon. Its roughness and adhesion are both intermediate between those of amorphous and polycrystalline silicon. Figure 4 It is known that when a film with a deposition stress of 550℃ to 580℃ is annealed at 650℃, the stress of the annealed film tends to be zero. When the film deposition temperature is 550℃ to 580℃, the annealing operation at 650℃ has the most significant effect on stress elimination, making the stress tend to be zero.

[0051] In one embodiment, the temperature for depositing the second thin film is 605°C. Figure 6 It can be seen that the stress of the first film deposited at a temperature of 550℃~580℃ is a negative stress of (-250)MPa~(-150)MPa. The stress of the second film deposited at a temperature of 605℃ is 250MPa. The stress of the second film is opposite to that of the first film, and the two stresses neutralize each other, causing the total stress to approach 0, thus improving its adhesion. Furthermore, the second film deposited at 605℃ is polycrystalline silicon, which has a large roughness, further enhancing its adhesion in subsequent film deposition processes.

[0052] In one embodiment, when the first thin film deposition temperature is 590°C to 610°C, the second thin film deposition temperature is 620°C. Figure 6It is known that the stress of the film deposited at temperatures of 590℃~610℃ is 100MPa~250MPa, and the stress of the film deposited at temperatures of 615~620℃ is (-250)MPa~(-100)MPa. The stress of the second film is opposite to that of the first film, and the two stresses neutralize each other, causing the total stress to tend towards 0, thus improving its adhesion. Furthermore, the second film deposited at 615~620℃ is polycrystalline silicon, which has a large roughness, further enhancing its adhesion during subsequent film deposition. When the first film is deposited at a temperature not less than 620℃, the second film is a positive stress film deposited at 605℃. Figure 6 It can be seen that the stress of the film deposited at a temperature greater than or equal to 620℃ is (-250) MPa, and the stress of the film deposited at 605℃ is 250 MPa. The stress of the second film is opposite to that of the first film, and the two stresses neutralize each other, causing the total stress to approach 0, thus improving its adhesion. Furthermore, the second film deposited at 605℃ is polycrystalline silicon, which has a large roughness, further enhancing its adhesion during subsequent film deposition processes.

[0053] In one embodiment, in step 2, the first thin film on the surface of the furnace tube and the surface of the crystal boat is annealed at 650°C. The annealing process involves first raising the temperature of the furnace tube when it is empty to 650°C, annealing the first thin film in a nitrogen atmosphere, and annealing for more than one hour. After annealing, the temperature is lowered to the temperature when the furnace tube is empty. At this time, the crystal boat can carry the next batch of wafers into the furnace tube for thin film deposition.

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

[0055] In one embodiment, the second predetermined thickness is 5µm to 7.5µm. On conventional silicon carbide boats and furnace tube walls, for deposited films, a scheduled maintenance is usually performed when the cumulative film thickness reaches 20µm. During the process of accumulating the film thickness to 20µm, different cumulative thicknesses may result in film lifting, detachment, and peeling. The number of film lifting, detachment, and peeling is roughly normally distributed, indicating that film lifting, detachment, and peeling are random and unavoidable. Reverse stress film deposition is performed before the high incidence range of film lifting, detachment, and peeling. The first cumulative film thickness before the high incidence range of film lifting, detachment, and peeling is set as the second predetermined thickness. When the first cumulative film thickness reaches the set second predetermined thickness, the deposition of the second film is immediately performed to avoid entering the high incidence range of film lifting, detachment, and peeling, thereby reducing the risk of film lifting, detachment, and peeling.

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

[0057] In one embodiment, steps 1 to 5 involve purging the furnace tube containing the deposited thin film with nitrogen before proceeding. Once the air in the furnace tube is purged, steps 1 to 5 are then performed to deposit the thin film. The advantage of purging the furnace tube with nitrogen is that it allows for pre-deposition cleaning of the furnace tube before film deposition.

[0058] In one embodiment, during the deposition of the first thin film, the pressure inside the furnace tube is 600 mTorr and the reaction gas flow rate is 0.98 slm; during the deposition of the second thin film, the pressure inside 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 that ultimately yields a thin film boat with high adhesion and a furnace tube.

[0061] First, purge the furnace tubes with nitrogen to remove any air and ensure a clean gas supply. Then proceed with the following steps:

[0062] Step 1: Thin film deposition is performed on the wafer on the crystal boat inside the furnace tube at a temperature of 550℃~580℃. At this time, the pressure inside the furnace tube is 600 mTorr, and the reaction gas flow rate for thin film deposition is 0.98 slm. Figure 2 As shown, the thin film is a mixture of amorphous silicon and polycrystalline silicon, with a roughness between that of amorphous silicon and polycrystalline silicon. A thickness of 10,000 Å is deposited each time; this 10,000 Å thick film is the first thin film. The wafer with the first thin film attached is removed from the furnace tube and proceeds to the next process.

[0063] Step 2: Anneal the first thin film on the surface of the furnace tube and the crystal boat at 650°C. First, raise the temperature of the furnace tube (when empty) to 650°C, and anneal the first thin film under a nitrogen atmosphere for more than one hour. After annealing, reduce the temperature to the temperature when the furnace tube is empty. Figure 4 As shown, the first film is annealed at 650°C to reduce the stress of the first film to 0, effectively eliminating stress accumulation.

[0064] Step 3: Repeat the above steps until the cumulative thickness of the first thin film deposited on the furnace tube surface and the crystal boat surface reaches 7 μm. Figure 7 As shown, the cumulative thickness of the thin film between 7.5 μm and 15 μm falls within the high-risk range for film lift-off and peeling. After the cumulative thickness exceeds 7 μm, stress accumulates and adhesion decreases, significantly increasing the probability of film lift-off and peeling. Therefore, when the cumulative thickness of the first thin film on the furnace tube surface and the wafer boat surface reaches 7 μm, the deposition of the first thin film on the wafer surface on the wafer boat inside the furnace tube is temporarily stopped.

[0065] Step 4: Deposit a second thin film on the first thin film accumulated on the furnace tube surface and the crystal boat surface. The second thin film is deposited at 605°C; at this time, the pressure inside the furnace tube is 300 mTorr, and the reaction gas flow rate for film deposition is 0.09 slm. Figure 6 As shown, the first film deposited at a temperature of 550℃~580℃ has a negative stress of (-250) MPa~(-150) MPa, while the second film deposited at 605℃ has a positive stress of 250 MPa. The stresses of the second film and the first film are opposite, and the stresses of the two films neutralize each other, causing the total stress to approach 0, thus improving its adhesion. Furthermore, the second film deposited at 605℃ is polycrystalline silicon, which has a large roughness, further enhancing its adhesion during subsequent film deposition processes.

[0066] Step 5: Repeat the above steps until the cumulative thickness of the first and second films deposited on the furnace tube surface and the crystal boat surface reaches 30 μm, thus obtaining the furnace tube surface and the crystal boat surface with the attached films.

[0067] The films deposited in steps 1 to 5 show a significant improvement in addressing the problem of film lifting and detachment, such as... Figure 8 As shown, starting in May, the deposition method of steps 1 to 5 was implemented. The frequency of film lift-off decreased from a high of 10% before the deposition method of this embodiment was implemented to less than 1%, showing a significant improvement in film lift-off. The furnace tube and silicon carbide boat also no longer require frequent scheduled maintenance. The interval between scheduled maintenance sessions was extended from once every 20µm of film deposition to once every 30µm of film deposition, resulting in a 50% increase in film deposition thickness.

[0068] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

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

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

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

4. The method according to claim 1, characterized in that, When the predetermined temperature for thin film deposition on the wafer in the furnace tube on the wafer boat is 590°C to 610°C, the second thin film is deposited at a temperature of 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 crystal boat is annealed at 650°C. First, the temperature of the furnace tube in an empty state is raised to 650°C, and the first film on the surface of the furnace tube and the surface of the crystal boat is annealed in a nitrogen atmosphere for more than one hour. After the annealing is completed, the temperature is reduced to the temperature of the furnace tube 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 5um to 7.5um.

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

9. The method according to claim 1, characterized in that, Before step 1, nitrogen gas is introduced into the furnace tube until the air inside the furnace tube is purged, and the thin film deposition begins.

10. The method according to claim 1, characterized in that, During the deposition of the first thin film, the pressure inside the furnace tube was 600 mTorr and the reaction gas flow rate was 0.98 slm; during the deposition of the second thin film, the pressure inside the furnace tube was 300 mTorr and the reaction gas flow rate was 0.09 slm.

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