Silicon wafer back sealing process

Abstract

The invention provides a silicon wafer back sealing process which comprises the following steps: depositing an LTO film on the back of a silicon wafer, the thickness of the LTO film being the initial thickness; cleaning liquid is adopted to clean the silicon wafer, the cleaning liquid is mixed liquid of hydrochloric acid, hydrofluoric acid and ultrapure water, film damage is generated in the cleaning process, and the thickness of the LTO film is the set thickness after cleaning is completed; and depositing a POLY film on the LTO film. The method has the beneficial effects that the mixed solution of hydrochloric acid, hydrofluoric acid and ultrapure water is used for cleaning the silicon wafer, boron ions and compounds thereof are effectively removed, the electrical property of the silicon wafer is ensured, the film damage of the LTO film is effectively reduced by controlling the cleaning time, and the normal use of the silicon wafer is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductors, and in particular relates to a silicon wafer backsealing process. Background Art

[0002] In the process of semiconductor silicon wafer production, backsealing usually adopts the super backsealing process (i.e., LTO+POLY). The outermost layer structure of this process is the POLY layer. If there is metal impurity contamination (especially boron ions) under the POLY layer during the deposition of the POLY film, during the epitaxial process, the metal impurities under the POLY layer will slowly diffuse from the inside of the POLY to the front edge of the silicon wafer along with the high-temperature process, resulting in abnormal SRP testing at the front edge of the silicon wafer and poor resistivity uniformity in the overall plane. Because it is currently impossible to achieve an absolutely boron-ion-free environment in the dust-free workshop at the silicon wafer processing end, usually after depositing the LTO film thickness, the silicon wafer is cleaned with the cleaning solution SC2 to remove boron ions, but the cleaning effect is not good, and boron ions cannot be effectively removed, affecting the electrical performance of the silicon wafer. Summary of the Invention

[0003] To solve the above technical problems, the present invention provides a silicon wafer backsealing process, which effectively solves the technical problem that boron ions cannot be effectively removed during the silicon wafer backsealing process and overcomes the deficiencies of the prior art.

[0004] The technical solution adopted by the present invention is: a silicon wafer backsealing process, including the following steps:

[0005] Deposit an LTO film on the back of the silicon wafer, and the thickness of the LTO film is the initial thickness;

[0006] Clean the silicon wafer with a cleaning solution, and the cleaning solution is a mixed solution of hydrochloric acid, hydrofluoric acid and ultrapure water. Film loss occurs during the cleaning process, and the thickness of the LTO film after cleaning is the set thickness;

[0007] Deposit a POLY film on the LTO film.

[0008] Further, during the cleaning process, calculate the film loss thickness according to the initial thickness and the set thickness of the LTO film, and set the cleaning duration according to the corresponding relationship between the film loss thickness and the cleaning duration.

[0009] Further, the cleaning duration is set to t, and the film loss thickness is set to d. When t>300s,

[0010] When 200s<t≤300s,

[0011] When 100s<t≤200s,

[0012] When 50 s < t ≤ 100 s,

[0013] When t ≤ 50 s,

[0014] Furthermore, the volume ratio of the hydrochloric acid, hydrofluoric acid and ultrapure water is (0.5 - 2):(0.5 - 3):(45 - 40).

[0015] Furthermore, the cleaning temperature of the cleaning solution is set to 55 - 75 °C.

[0016] Furthermore, the initial thickness of the LTO film is

[0017] Furthermore, the set thickness of the LTO film is

[0018] Furthermore, the thickness of the POLY film is

[0019] The advantages and positive effects of the present invention are as follows: Due to the adoption of the above technical solution, a mixed solution of hydrochloric acid, hydrofluoric acid and ultrapure water is used to clean the silicon wafer, effectively removing boron ions and their compounds, ensuring the electrical performance of the silicon wafer, and by controlling the cleaning duration, effectively reducing the film loss of the LTO film and ensuring the normal use of the silicon wafer. Description of the Drawings

[0020] Figure 1 is a flowchart of a silicon wafer backsealing process according to an embodiment of the present invention.

[0021] Figure 2 is a comparison diagram of the cleaning effect of a silicon wafer backsealing process according to an embodiment of the present invention and the prior art.

[0022] Figure 3 is a corresponding relationship diagram of the film loss thickness and cleaning duration of a silicon wafer backsealing process according to an embodiment of the present invention. Detailed Embodiments

[0023] An embodiment of the present invention provides a silicon wafer backsealing process, and the embodiments of the present invention will be described below with reference to the accompanying drawings.

[0024] In the description of the embodiments of the present invention, it should be understood that the orientation or positional relationship indicated by terms such as "top" and "bottom" is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention. In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "set" and "connect" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific situations.

[0025] As Figure 1 shown, an LTO film backsealing process for silicon wafers in an embodiment of the present invention includes the following steps:

[0026] S1. Deposit an LTO film on the back of the silicon wafer, and the thickness of the LTO film is the initial thickness;

[0027] Deposit an LTO film on the back of the silicon wafer by chemical vapor deposition, and the thickness of the LTO film is the initial thickness, usually set to

[0028] S2. Clean the silicon wafer with a cleaning solution, which is a mixed solution of hydrochloric acid, hydrofluoric acid and ultrapure water. Film loss occurs during the cleaning process, and the thickness of the LTO film after cleaning is the set thickness;

[0029] Specifically, the set thickness of the LTO film is

[0030] Specifically, the volume ratio of hydrochloric acid, hydrofluoric acid and ultrapure water is (0.5 - 2):(0.5 - 3):(45 - 40).

[0031] Specifically, the cleaning temperature of the cleaning solution is set to 55 - 75 °C.

[0032] In order to remove boron ions, after depositing the LTO film on the back of the silicon wafer, the silicon wafer needs to be cleaned with a cleaning solution. In the prior art, SC2 cleaning solution is usually used for cleaning, and SC2 cleaning solution is a mixed solution of hydrochloric acid, hydrogen peroxide and ultrapure water. In this technical solution, a mixed solution of hydrochloric acid, hydrofluoric acid and ultrapure water is used as the cleaning solution. Hydrofluoric acid can more effectively remove boron ions. When the concentrations and service lives of the two cleaning solutions are the same, compare the cleaning effects of the two cleaning solutions, as Figure 2 shown. In Figure 2It can be clearly seen that after cleaning with a mixed solution of hydrochloric acid, hydrofluoric acid, and ultrapure water, the content of boron ions and their compounds is significantly lower than that after cleaning with the SC2 cleaning solution. And in Figure 2 it can be seen that when cleaning with a mixed solution of hydrochloric acid, hydrofluoric acid, and ultrapure water, different cleaning durations have no obvious effect on the content of boron ions and their compounds.

[0033] Since the main component of the LTO film is silicon dioxide, hydrofluoric acid in the cleaning solution can react chemically with silicon dioxide. Therefore, film loss will occur to the LTO film during the cleaning process. The wear thickness of the LTO film will change with the cleaning duration. Therefore, by controlling the cleaning duration, the wear thickness of the LTO film is controlled within a certain range so that the final thickness of the LTO film meets the requirements of the set thickness.

[0034] After a large number of experimental verifications, the corresponding relationship between the film loss thickness d of the LTO film and the cleaning duration t after cleaning with a mixed solution of hydrochloric acid, hydrofluoric acid, and ultrapure water is as Figure 3 shown. It can be seen from the figure that:

[0035] When t > 300s,

[0036] When 200s < t ≤ 300s,

[0037] When 100s < t ≤ 200s,

[0038] When 50s < t ≤ 100s,

[0039] When t ≤ 50s,

[0040] Calculate the film loss thickness based on the initial thickness and the set thickness of the LTO film. Select an appropriate cleaning duration according to the film loss thickness and the corresponding relationship between the film loss thickness and the cleaning duration.

[0041] S3. Deposit a POLY film on the LTO film.

[0042] Deposit a POLY film on the LTO film by chemical vapor deposition. The thickness of the POLY film is usually set to

[0043] Example 1: A silicon wafer backsealing process includes the following steps:

[0044] S1. Deposit an LTO film on the back of the silicon wafer by chemical vapor deposition. The thickness of the LTO film is the initial thickness

[0045] S2. Clean the silicon wafer with a cleaning solution, which is a mixed solution of hydrochloric acid, hydrofluoric acid and ultrapure water. The ratio of hydrochloric acid, hydrofluoric acid and ultrapure water is 1:1:44, and the cleaning temperature is set at 60 °C.

[0046] After cleaning, the thickness of the LTO film is the set thickness According to the initial thickness of the LTO film and the set thickness Calculate the film loss thickness as According to the film loss thickness and the relationship diagram as Figure 3 shown, set the cleaning duration to 355 s.

[0047] S3. Deposit a POLY film on the LTO film by chemical vapor deposition. The thickness of the POLY film is set to

[0048] Example 2: A silicon wafer back-sealing process includes the following steps:

[0049] S1. Deposit an LTO film on the back of the silicon wafer by chemical vapor deposition. The thickness of the LTO film is the initial thickness

[0050] S2. Clean the silicon wafer with a cleaning solution, which is a mixed solution of hydrochloric acid, hydrofluoric acid and ultrapure water. The ratio of hydrochloric acid, hydrofluoric acid and ultrapure water is 1:1:44, and the cleaning temperature is set at 60 °C.

[0051] After cleaning, the thickness of the LTO film is the set thickness According to the initial thickness of the LTO film and the set thickness Calculate the film loss thickness as According to the film loss thickness and the relationship diagram as Figure 3 shown, set the cleaning duration to 250 s.

[0052] S3. Deposit a POLY film on the LTO film by chemical vapor deposition. The thickness of the POLY film is set to

[0053] Example 3: A silicon wafer back-sealing process includes the following steps:

[0054] S1. Deposit an LTO film on the back of the silicon wafer by chemical vapor deposition. The thickness of the LTO film is the initial thickness

[0055] S2. Clean the silicon wafer with a cleaning solution, which is a mixed solution of hydrochloric acid, hydrofluoric acid and ultrapure water. The ratio of hydrochloric acid, hydrofluoric acid and ultrapure water is 1:1:44, and the cleaning temperature is set at 60 °C.

[0056] The thickness of the LTO film after cleaning is the set thickness According to the initial thickness of the LTO film and the set thickness calculate the film loss thickness as According to the film loss thickness and as shown in Figure 3 the relationship diagram, set the cleaning duration to 145 s

[0057] S3. Deposit a POLY film on the LTO film by chemical vapor deposition, and set the thickness of the POLY film to

[0058] Example 4: A silicon wafer back-sealing process includes the following steps

[0059] S1. Deposit an LTO film on the back of the silicon wafer by chemical vapor deposition, and the thickness of the LTO film is the initial thickness

[0060] S2. Clean the silicon wafer with a cleaning solution, which is a mixed solution of hydrochloric acid, hydrofluoric acid and ultrapure water. The ratio of hydrochloric acid, hydrofluoric acid and ultrapure water is 1:1:44, and the cleaning temperature is set to 60 °C

[0061] The thickness of the LTO film after cleaning is the set thickness According to the initial thickness of the LTO film and the set thickness calculate the film loss thickness as According to the film loss thickness and as shown in Figure 3 the relationship diagram, set the cleaning duration to 60 s

[0062] S3. Deposit a POLY film on the LTO film by chemical vapor deposition, and set the thickness of the POLY film to

[0063] Example 5: A silicon wafer back-sealing process includes the following steps

[0064] S1. Deposit an LTO film on the back of the silicon wafer by chemical vapor deposition, and the thickness of the LTO film is the initial thickness

[0065] S2. Clean the silicon wafer with a cleaning solution, which is a mixed solution of hydrochloric acid, hydrofluoric acid and ultrapure water. The ratio of hydrochloric acid, hydrofluoric acid and ultrapure water is 1:1:44, and the cleaning temperature is set to 60 °C

[0066] The thickness of the LTO film after cleaning is the set thickness According to the initial thickness of the LTO film and the set thickness calculate the film loss thickness as According to the film loss thickness and as shown inFigure 3 The relational diagram shown has a cleaning duration set to 20 s.

[0067] S3. Deposit a POLY film on the LTO film by chemical vapor deposition, and set the thickness of the POLY film to

[0068] The advantages and positive effects of the present invention are:

[0069] During the backsealing process of the silicon wafer, a mixed solution of hydrochloric acid, hydrofluoric acid, and ultrapure water is used to clean the silicon wafer, effectively removing boron ions and their compounds, ensuring the electrical performance of the silicon wafer, and by controlling the cleaning duration, effectively reducing the film loss of the LTO film and ensuring the normal use of the silicon wafer.

[0070] The above has described the embodiments of the present invention in detail, but the content described is only the preferred embodiments of the present invention and cannot be considered as limiting the scope of implementation of the present invention. Any equivalent changes and improvements made according to the scope of the application of the present invention shall still fall within the scope covered by the patent of the present invention.

Claims

1. A silicon wafer back-sealing process, characterized in that: The following steps are involved: Depositing an LTO film on the back side of the silicon wafer, wherein the LTO film has an initial thickness; The silicon wafer is cleaned by using a cleaning liquid, wherein the cleaning liquid is a mixture of hydrochloric acid, hydrofluoric acid and ultrapure water, and film damage is generated during the cleaning process. After the cleaning is completed, the thickness of the LTO film is a set thickness; A POLY film is deposited on the LTO film.

2. A silicon wafer back-sealing process according to claim 1, characterized in that: During the cleaning process, the film loss thickness is calculated according to the initial thickness and the set thickness of the LTO film, and the cleaning time is set according to the corresponding relationship between the film loss thickness and the cleaning time.

3. A silicon wafer back-sealing process according to claim 2, characterized in that: The cleaning time is set to t, the film loss thickness is set to d, When t>300s, When 200s<t≤300s, When 100s<t≤200s, When 50s<t≤100s, When t≤50s, 4. A silicon wafer back-sealing process according to any one of claims 1 to 3, characterized in that: The volume ratio of the hydrochloric acid, hydrofluoric acid and ultrapure water is (0.5-2):(0.5-3):(45-40).

5. A silicon wafer back-sealing process according to any one of claims 1 to 3, characterized in that: The cleaning temperature of the cleaning solution is set to 55-75°C.

6. A silicon wafer back-sealing process according to any one of claims 1 to 3, characterized in that: The initial thickness of the LTO film is 7. A silicon wafer back-sealing process according to any one of claims 1 to 3, characterized in that: The set thickness of the LTO film is 8. A silicon wafer back-sealing process according to any one of claims 1 to 3, characterized in that: The thickness of the POLY film is

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