Heat treatment process

Abstract

The heat treatment process comprises the following steps: putting a product to be treated into a furnace tube, and vacuumizing; the furnace tube is heated, the temperature of the furnace tube is increased to the intermediate temperature and kept constant, the time-temperature curve of the furnace tube in the constant temperature stage is a temperature rise platform, and the temperature rise platform means that the temperature approaches to the intermediate temperature along with time increase; the furnace tube is continuously heated, the temperature of the furnace tube is increased to the target temperature and kept constant, and reaction gas is introduced in the temperature increasing process and the constant temperature keeping process; and keeping the target temperature of the furnace tube, and continuously introducing the reaction gas. At least one intermediate temperature is set for constant temperature, so that each area of the furnace tube has more balanced temperature, then the furnace tube is heated to enable the furnace tube to rise from the intermediate temperature to the target temperature, and during the period, reaction gas is introduced into the furnace tube to enable the reaction gas to enter the furnace tube. The to-be-treated products in all the areas of the furnace tube have the consistent temperature, and the temperature rise balance of all the areas of the furnace tube can be achieved, so that the uniformity of a generated film layer is improved.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic material manufacturing and processing, and more specifically, to a heat treatment process. Background Art

[0002] Semiconductor or photovoltaic materials are widely used in electronics, new energy and other industries. Semiconductor and photovoltaic materials usually need to undergo certain chemical treatments before they can be applied to products. Chemical vapor deposition (CVD) technology has been widely used in semiconductor or photovoltaic material processing. Common CVD technologies include plasma enhanced chemical vapor deposition (PECVD), low pressure chemical vapor deposition (LPCVD), atmospheric pressure chemical vapor deposition (APCVD), etc. Among them, APCVD and LPCVD are often used in low pressure processes or atmospheric pressure processes to prepare oxide layers and amorphous silicon layers in semiconductor processes. The manufacturing process is usually to send the material to be processed into a reactor and perform a thermal reaction under certain temperature and pressure conditions to achieve it.

[0003] In the traditional LPCVD process for preparing an oxide layer on the surface of a silicon wafer to be processed, the oxide layer is grown by heating the reactor tube to the reaction temperature and then introducing oxygen. However, since the actual temperature of the reactor tube is not uniform from the tube mouth to the tail, the film thickness uniformity of the oxide layer in different areas of the reactor tube is quite different, which indirectly affects the film quality and electrical performance parameters of the surface of the material to be processed. Summary of the invention

[0004] In view of this, the present application provides a heat treatment process, comprising: S1: Place the product to be processed into the furnace tube and evacuate it; S2: heating the furnace tube to raise the temperature of the furnace tube to an intermediate temperature and keep the temperature constant. During the constant temperature stage, the time-temperature curve of the furnace tube is a temperature rise platform, and the temperature rise platform means that the temperature approaches the intermediate temperature as time increases; S3: continuing to heat the furnace tube, so that the furnace tube is heated from the intermediate temperature to the target temperature and maintained at a constant temperature, and the reaction gas is introduced during the heating and temperature maintaining process; and S4: maintaining the target temperature of the furnace tube and continuing to introduce the reaction gas.

[0005] The heat treatment process of the present application is carried out in a furnace tube. By setting at least one intermediate temperature for constant temperature, each area of ​​the furnace tube has a more balanced temperature. The furnace tube is then heated to increase the temperature of the furnace tube from the intermediate temperature toward the target temperature. During this period, a reaction gas is introduced into the furnace tube. When the reaction gas enters the furnace tube, the product to be treated in each area of ​​the furnace tube has a consistent temperature, which can achieve balanced temperature rise in each area of ​​the furnace tube, thereby improving the uniformity of the generated film layer (such as an oxide layer) and achieving higher product efficiency.

[0006] Furthermore, S2 includes: setting at least two gradually increasing intermediate temperatures for the furnace tube in sequence and maintaining a constant temperature when the temperature is raised to each of the intermediate temperatures.

[0007] Further, S2 includes: heating the furnace tube so that the temperature of the furnace tube reaches a first intermediate temperature and maintaining a constant temperature, wherein the time-temperature curve of the furnace tube is a first temperature rise platform during the constant temperature stage, and the first temperature rise platform refers to the temperature approaching the first intermediate temperature as time increases; The furnace tube is continued to be heated so that the temperature of the furnace tube reaches a second intermediate temperature and is kept constant at a constant temperature. During the constant temperature stage, the time-temperature curve of the furnace tube is a second temperature rising platform. The second temperature rising platform means that the temperature approaches the second intermediate temperature as time increases. The second intermediate temperature is greater than the first intermediate temperature and less than the target temperature.

[0008] Furthermore, the difference between the second intermediate temperature and the first intermediate temperature is less than or equal to 20 degrees Celsius.

[0009] Furthermore, S2 also includes: continuing to heat the furnace tube so that the temperature of the furnace tube reaches a third intermediate temperature and maintaining a constant temperature, wherein the time-temperature curve of the furnace tube is a third temperature rising platform during the constant temperature stage, wherein the third temperature rising platform refers to the temperature approaching the third intermediate temperature as time increases, and the third intermediate temperature is greater than the second intermediate temperature and less than the target temperature.

[0010] Furthermore, S2 also includes: continuing to heat the furnace tube so that the temperature of the furnace tube reaches a fourth intermediate temperature and maintaining a constant temperature, wherein the time-temperature curve of the furnace tube is a fourth temperature rising platform during the constant temperature stage, wherein the fourth temperature rising platform refers to the temperature approaching the fourth intermediate temperature as time increases, and the fourth intermediate temperature is greater than the third intermediate temperature and less than the target temperature.

[0011] Furthermore, the heat treatment process is a low-pressure chemical vapor deposition process.

[0012] Furthermore, the product to be processed is a silicon wafer, and the reaction gas introduced in S3 and S4 is oxygen.

[0013] Furthermore, the flow rate of the reaction gas introduced in S3 is smaller than the flow rate of the reaction gas introduced in S4.

[0014] Furthermore, the flow rate of the reaction gas introduced in S3 is less than 5000 sccm, and the flow rate of the reaction gas introduced in S4 is greater than or equal to 20000 sccm. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a flow chart of the heat treatment process of an embodiment of the present application.

[0016] Figure 2 A schematic diagram of a furnace tube used in the heat treatment process of an embodiment of the present application.

[0017] Figure 3 FIG. 1 is a time-temperature curve diagram of a heat treatment process according to an embodiment of the present application.

[0018] Figure 4 This is a time-temperature curve diagram of a heat treatment process according to another embodiment of the present application.

[0019] Description of main component symbols: Furnace tube 10 , furnace mouth 11 , furnace tail 13 , temperature zone 12 , silicon wafer carrier 20 . DETAILED DESCRIPTION

[0020] The traditional process of using LPCVD to oxidize the surface of silicon wafers includes the following steps: placing the silicon wafer into a process furnace tube → evacuating to <10mTor → heating to the target temperature and maintaining the temperature → maintaining the target temperature and introducing oxygen to a normal pressure state → oxidizing the tube under normal pressure to grow an oxide layer.

[0021] However, this process has the following defects: (1) After vacuuming, the temperature of the silicon wafer rises from low temperature to the target temperature in a discrete manner, especially for horizontal furnace tube equipment. The heat exchange at the furnace mouth is large, and the rapid flow of gas during vacuuming causes heat loss, resulting in uneven actual heat distribution at the furnace mouth, furnace center and furnace tail, which in turn leads to large differences between different batches of products. (2) Oxygen is usually introduced in a high temperature environment of 590℃~620℃. The density and uniformity of the oxide layer are affected by the low temperature heating stage, resulting in large differences in the uniformity of the oxide layer thickness, which affects the passivation voltage and conversion efficiency of the battery product.

[0022] The present application provides a heat treatment process, which is carried out in a furnace tube, and can achieve balanced temperature rise in various areas of the furnace tube, thereby improving the uniformity of the film layer (such as an oxide layer) generated on the product to be processed, and achieving higher product efficiency. The product to be processed can be a silicon wafer for a solar cell, a wafer for a chip, etc. The furnace tube is a quartz furnace tube, which is made of high-purity quartz, can withstand high temperatures and remain chemically inert. A heating coil is arranged around the furnace tube, usually composed of a resistance wire, for heating the inside of the furnace tube. The furnace tube includes a relative furnace mouth and a furnace tail. The furnace mouth is provided with a flange for connecting the furnace tube to the gas line and ensuring the sealing and stability of the connection. The gas line enters the furnace tube from the outside of the furnace tube via the flange. The furnace tube is also provided with an exhaust port for discharging the exhaust gas inside the furnace tube to the outside of the furnace tube.

[0023] See also Figure 1 The heat treatment process of the present application includes the following steps S1 to S4. In the embodiment of the present application, the heat treatment process is described as an LPCVD process, but it is not limited to this, and can also be other processes that require heat treatment, such as a boron diffusion process and a phosphorus diffusion process.

[0024] S1: Place the product to be processed into the furnace tube and evacuate it.

[0025] In the present application embodiment, Figure 2 As shown, the inner cavity of the furnace tube 10 extends from the furnace mouth 11 to the furnace tail 13. The product to be processed enters the furnace tube 10 along the furnace mouth 11. The furnace tube 10 is divided into a plurality of temperature zones 12 in the extending direction from the furnace mouth 11 to the furnace tail 13. Each temperature zone 12 is provided with an independent temperature sensor (not shown) to monitor the temperature of the temperature zone. The temperature control of the heating and cooling of the furnace tube can be achieved by setting a temperature control program.

[0026] In the embodiment of the present application, the product to be processed is a silicon wafer. The silicon wafer is placed on a silicon wafer carrier 20. The silicon wafer carrier 20 carries a plurality of silicon wafers, and the silicon wafers on the silicon wafer carrier 20 are arranged in multiple layers in the longitudinal direction. The silicon wafer carrier 20 carrying a plurality of silicon wafers is pushed from the furnace port 11 into the furnace tube 10, and this step can be called boat entry.

[0027] The furnace tube has an initial temperature (standby temperature) inside, which is usually higher than the room temperature. When the furnace tube is opened and the boat is put into the process, the temperature of each temperature zone of the furnace tube will drop rapidly. At this time, the thermal field outputs power to make up for the temperature loss; when the vacuum is evacuated, the heat in the furnace tube will be drawn away, resulting in heat loss inside the furnace tube, and the temperature of each temperature zone of the furnace tube will also drop.

[0028] S2: Heat the furnace tube to raise the temperature of the furnace tube to the middle temperature and keep the temperature constant.

[0029] The function of step S2 is to make each temperature zone of the furnace tube in a more uniform heat state (unify the actual temperature of multiple temperature zones) by setting an intermediate temperature lower than the target temperature before reaching the target temperature, so as to prepare for the subsequent introduction of the reaction gas, and ensure that when the reaction gas is introduced, the temperature of each temperature zone of the furnace tube is consistent, that is, the temperature of the silicon wafers in each temperature zone of the furnace tube is consistent, so as to reduce the temperature difference between the silicon wafers. In the embodiment of the present application, the temperature of each temperature zone of the furnace tube is consistent, which means that the temperature difference of each temperature zone is less than or equal to 5°C.

[0030] Usually, the difference between the target temperature and the intermediate temperature is controlled within 150° C. In some embodiments, taking the target temperature as 600° C. as an example, the intermediate temperature can be set to 470° C.

[0031] In the actual heating process of the furnace tube, the temperature will not reach the preset temperature and will remain unchanged. It may exceed the preset temperature or fail to reach the preset temperature. Therefore, constant temperature is required to stabilize the temperature at the preset temperature.

[0032] Figure 3 The time-temperature relationship curve of each temperature zone of the furnace tube in the heat treatment process of an embodiment is shown, wherein the horizontal axis represents time and the vertical axis represents the temperature of the furnace tube. Generally, in the conventional heat treatment heating process, the temperature rises with time until the target temperature is reached, and the overall curve is a slanted line with a slope, until the target temperature is reached and the temperature is constant, and the curve is a horizontal line parallel to the horizontal axis.

[0033] Figure 3 The multiple curves are time-temperature curves of different batches of products in the same temperature zone of the same furnace tube. In this application, the temperature is kept constant after reaching the intermediate temperature in step S2. Figure 3 The time-temperature curve in the experiment shows a temperature rise platform. Figure 3 That is, before reaching the target temperature, the time-temperature curve of the furnace tube presents a temperature rise platform, which means that as time goes by, the temperature of the furnace tube approaches the middle temperature. Figure 3 As shown, the temperatures of products from different batches all stabilize and approach the middle temperature of the heating platform for a certain period of time, and then continue to heat up to the target temperature.

[0034] It is understandable that the longer the time for maintaining a constant temperature at the intermediate temperature (the time corresponding to the temperature rise platform), the more uniform the heat of each temperature zone of the corresponding furnace tube, but too long a constant temperature time will correspondingly lead to a longer heat treatment process time, which is not conducive to shortening the processing cycle and reducing production costs. In some embodiments, the time for maintaining a constant temperature at the intermediate temperature can be 1-5 minutes, for example, 3 minutes.

[0035] In some other embodiments, S2 includes sequentially setting at least two intermediate temperatures for the furnace tube and maintaining a constant temperature when the temperature is raised to each intermediate temperature. By sequentially setting at least two intermediate temperatures, the last intermediate temperature needs a shorter time to stabilize, so that the temperature consistency of the furnace tube before the temperature is raised from the last intermediate temperature to the target temperature is good.

[0036] Please refer to Figure 4 , taking setting two intermediate temperatures as an example, S2 includes: The furnace tube is heated so that the temperature of the furnace tube reaches a first intermediate temperature and is kept at a constant temperature, wherein the time-temperature curve of the furnace tube in the constant temperature stage presents a first temperature rise platform, wherein the first temperature rise platform means that as time increases, the temperatures of various temperature zones of the furnace tube approach the first intermediate temperature; The furnace tube is continued to be heated until the temperature of the furnace tube reaches the second intermediate temperature and is kept at a constant temperature. The time-temperature curve of the furnace tube in the constant temperature stage presents a second temperature rising platform. The second temperature rising platform means that as time goes by, the temperatures of various temperature zones of the furnace tube approach the second intermediate temperature. The second intermediate temperature is greater than the first intermediate temperature and less than the target temperature. Figure 4 In the figure, the two dotted boxes indicate the first heating platform and the second heating platform respectively.

[0037] Before rising to the target temperature, a first intermediate temperature and a second intermediate temperature are set. The temperatures of various temperature zones of the furnace tube are roughly balanced by maintaining the first intermediate temperature constant, and the temperatures of various temperature zones of the furnace tube are finely balanced by maintaining the second intermediate temperature constant.

[0038] In some embodiments, the difference between the second intermediate temperature and the first intermediate temperature is less than or equal to 20°C, for example, the difference is 15°C, 10°C, 8°C, or 5°C. The difference between two adjacent intermediate temperatures can be set as required. By setting an appropriate difference between two adjacent intermediate temperatures, the temperatures of each temperature zone of the furnace tube can be made more consistent. If the difference between two adjacent intermediate temperatures is set too large, it is difficult to accurately control the temperatures of each temperature zone of the furnace tube to be consistent.

[0039] Taking setting three intermediate temperatures as an example, S2 includes: The furnace tube is heated so that the temperature of the furnace tube reaches a first intermediate temperature and is kept at a constant temperature. The time-temperature curve of the furnace tube in the constant temperature stage presents a first temperature rise platform. The first temperature rise platform means that as time increases, the temperature of each temperature zone of the furnace tube approaches the first intermediate temperature. The furnace tube is continued to be heated until the temperature of the furnace tube reaches the second intermediate temperature and is kept constant temperature. The time-temperature curve of the furnace tube in the constant temperature stage presents a second temperature rise platform. The second temperature rise platform means that as time increases, the temperature of each temperature zone of the furnace tube approaches the second intermediate temperature, and the second intermediate temperature is greater than the first intermediate temperature and less than the target temperature. The furnace tube is continued to be heated until the temperature of the furnace tube reaches the third intermediate temperature and is kept at a constant temperature. The time-temperature curve of the furnace tube in the constant temperature stage presents a third temperature rising platform. The third temperature platform means that as time goes by, the temperatures of various temperature zones of the furnace tube approach the third intermediate temperature, and the third intermediate temperature is greater than the second intermediate temperature and less than the target temperature.

[0040] In some embodiments, the difference between the third intermediate temperature and the second intermediate temperature is less than or equal to 20°C, for example, the difference is 15°C, 10°C, 8°C, or 5°C.

[0041] Taking setting four intermediate temperatures as an example, S2 includes: The furnace tube is heated so that the temperature of the furnace tube reaches a first intermediate temperature and is kept at a constant temperature. The time-temperature curve of the furnace tube in the constant temperature stage presents a first temperature rise platform. The first temperature rise platform means that as time increases, the temperature of each temperature zone of the furnace tube approaches the first intermediate temperature. The furnace tube is continued to be heated until the temperature of the furnace tube reaches the second intermediate temperature and is kept constant temperature. The time-temperature curve of the furnace tube in the constant temperature stage presents a second temperature rise platform. The second temperature rise platform means that as time increases, the temperature of each temperature zone of the furnace tube approaches the second intermediate temperature, and the second intermediate temperature is greater than the first intermediate temperature and less than the target temperature. The furnace tube is continued to be heated until the temperature of the furnace tube reaches the third intermediate temperature and is kept at a constant temperature. The time-temperature curve of the furnace tube in the constant temperature stage presents a third temperature rising platform. The third temperature platform means that as time increases, the temperatures of various temperature zones of the furnace tube approach the third intermediate temperature, and the third intermediate temperature is greater than the second intermediate temperature and less than the target temperature. The furnace tube is continued to be heated until the temperature of the furnace tube reaches the fourth intermediate temperature and is kept constant at a constant temperature. The time-temperature curve of the furnace tube in the constant temperature stage presents a fourth temperature rising platform. The fourth temperature platform means that as time goes by, the temperatures of various temperature zones of the furnace tube approach the fourth intermediate temperature, and the fourth intermediate temperature is greater than the third intermediate temperature and less than the target temperature.

[0042] In some embodiments, the difference between the fourth intermediate temperature and the third intermediate temperature is less than or equal to 20°C, for example, the difference is 15°C, 10°C, 8°C, or 5°C.

[0043] It is understandable that the more intermediate temperatures are set, the more uniform the heat of each temperature zone of the corresponding furnace tube (the temperature of each temperature zone is more consistent), but it will lead to a longer heat treatment process, which is not conducive to shortening the processing cycle and reducing production costs. Therefore, considering the heating effect and heating time and other factors, 1-4 intermediate temperatures can usually be set.

[0044] This application can significantly improve the temperature rise convergence of the tubular equipment by setting an intermediate temperature lower than the target temperature, and effectively improve the temperature uniformity of the furnace tube in the process. The product to be processed is heated more evenly in the tubular equipment, and the uniformity of the film layer is significantly improved, which improves the cell passivation effect in photovoltaic products.

[0045] S3: Continue to heat the furnace tube, so that the temperature of the furnace tube reaches the target temperature and maintains a constant temperature, and introduce the reaction gas during the heating and temperature maintaining process.

[0046] In some embodiments, the reaction gas introduced in S3 is oxygen. When the temperature is raised from the last intermediate temperature to the target temperature, the reaction gas, such as oxygen, is introduced into the furnace tube, so that the temperature of the silicon wafers located in each temperature zone of the furnace tube is consistent when the reaction gas is introduced, thereby ensuring the uniformity of the silicon oxide layer generated on the surface of the silicon wafer. That is, the heat treatment process of the present application can ensure that the products to be processed placed in each area of ​​the furnace tube have the same temperature when the reaction gas is introduced.

[0047] In some other embodiments, for the boron diffusion process, the reaction gas is a boron-containing source gas; for the phosphorus diffusion process, the reaction gas is a phosphorus-containing source gas.

[0048] S4: Maintain the target temperature of the furnace tube and continue to introduce the reaction gas.

[0049] In some embodiments, the reaction gas introduced in S4 is oxygen. The introduction of oxygen returns the gas pressure in the furnace tube to a normal pressure state, entering a normal pressure oxidation state. The target temperature and the state of introducing oxygen are maintained, so that the desired film layer continues to grow to a desired thickness.

[0050] The flow rate of the reaction gas introduced in S3 is less than the flow rate of the reaction gas introduced in S4. The flow rate of the reaction gas introduced in S3 is less than 5000 sccm, and the flow rate of the reaction gas introduced in S4 is greater than or equal to 20000 sccm.

[0051] Provided below are the thermal treatment processes of the present application and existing thermal treatment processes used to perform LPCVD processes to generate a tunneling oxide layer (silicon oxide layer) on a silicon wafer.

[0052] The existing LPCVD process is as follows: a silicon wafer carrier loaded with silicon wafers is pushed into a furnace tube for evacuation; the furnace tube is heated to a target temperature of 600°C and kept at a constant temperature, and oxygen is introduced into the furnace tube; the target temperature of the furnace tube is maintained and oxygen is continued to be introduced.

[0053] The LPCVD process of the present application: push the silicon wafer carrier loaded with silicon wafers into the furnace tube (the same furnace tube as the existing LPCVD process) and evacuate; heat the furnace tube to make the temperature of the furnace tube reach the intermediate temperature of 400°C, and keep the temperature constant for 3 minutes; continue to heat the furnace tube to make the furnace tube reach the target temperature of 600°C and keep the temperature constant, and introduce oxygen during the heating and temperature-constant processes; maintain the target temperature of the furnace tube and continue to introduce oxygen. Except for the differences in the above-mentioned process steps, the other parameters of the LPCVD process of the present application are the same, such as the oxygen flow rate.

[0054] Table 1 shows the test results of the thickness of the tunnel oxide layer obtained by the existing LPCVD process, and Table 2 shows the test results of the thickness of the tunnel oxide layer obtained by the LPCVD process of the present application. The areas B1-B10 are arranged in sequence from the furnace mouth to the furnace tail of the furnace tube. Four areas B1, B4, B7, and B10 were selected for sampling of silicon wafers, and silicon wafer samples located at the top, middle, and bottom in the longitudinal direction were selected in each area. The thickness of each silicon wafer was tested at five positions, namely the positions of the four corners and the center position.

[0055] Table 1 Table 2 It can be seen from the test results in Table 1 and Table 2 that the uniformity of the thickness of the tunnel oxide layer obtained by the LPCVD process of the present application is significantly higher than the uniformity of the thickness of the tunnel oxide layer obtained by the existing LPCVD process.

[0056] The heat treatment process of the present application is carried out in a furnace tube. By setting at least one intermediate temperature for constant temperature, each area of ​​the furnace tube has a more balanced temperature. The furnace tube is then heated to increase the temperature of the furnace tube from the intermediate temperature toward the target temperature. During this period, a reaction gas is introduced into the furnace tube. When the reaction gas enters the furnace tube, the product to be treated in each area of ​​the furnace tube has a consistent temperature, which can achieve balanced temperature rise in each area of ​​the furnace tube, thereby improving the uniformity of the generated film layer (such as an oxide layer) and achieving higher product efficiency.

[0057] The above implementation modes are only used to illustrate the technical solutions of the present application and are not intended to limit the present application. Although the present application has been described in detail with reference to the above preferred implementation modes, a person skilled in the art should understand that the technical solutions of the present application may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A heat treatment process, characterized in that: include: S1: Place the product to be processed into the furnace tube and evacuate it; S2: heating the furnace tube to raise the temperature of the furnace tube to an intermediate temperature and keep the temperature constant. During the constant temperature stage, the time-temperature curve of the furnace tube is a temperature rise platform, and the temperature rise platform means that the temperature approaches the intermediate temperature as time increases; S3: continuing to heat the furnace tube, so that the furnace tube is heated from the intermediate temperature to the target temperature and maintained at a constant temperature, and the reaction gas is introduced during the heating and temperature maintaining process; and S4: maintaining the target temperature of the furnace tube and continuing to introduce the reaction gas.

2. The heat treatment process according to claim 1, characterized in that: S2 includes: At least two gradually increasing intermediate temperatures are sequentially set for the furnace tube and the temperature is kept constant when the temperature is raised to each of the intermediate temperatures.

3. The heat treatment process according to claim 2, characterized in that: S2 includes: The furnace tube is heated so that the temperature of the furnace tube reaches a first intermediate temperature and is kept at a constant temperature. During the constant temperature stage, the time-temperature curve of the furnace tube is a first temperature rise platform, and the first temperature rise platform means that the temperature approaches the first intermediate temperature as time increases; The furnace tube is continued to be heated so that the temperature of the furnace tube reaches a second intermediate temperature and is kept constant at a constant temperature. During the constant temperature stage, the time-temperature curve of the furnace tube is a second temperature rising platform. The second temperature rising platform means that the temperature approaches the second intermediate temperature as time increases. The second intermediate temperature is greater than the first intermediate temperature and less than the target temperature.

4. The heat treatment process according to claim 3, characterized in that: A difference between the second intermediate temperature and the first intermediate temperature is less than or equal to 20 degrees Celsius.

5. The heat treatment process according to claim 3, characterized in that: S2 also includes: continuing to heat the furnace tube so that the temperature of the furnace tube reaches a third intermediate temperature and is kept at a constant temperature. During the constant temperature stage, the time-temperature curve of the furnace tube is a third temperature rise platform. The third temperature rise platform means that the temperature approaches the third intermediate temperature as time increases. The third intermediate temperature is greater than the second intermediate temperature and less than the target temperature.

6. The heat treatment process according to claim 5, characterized in that: S2 also includes: continuing to heat the furnace tube so that the temperature of the furnace tube reaches a fourth intermediate temperature and is kept at a constant temperature, wherein the time-temperature curve of the furnace tube is a fourth temperature rise platform during the constant temperature stage, wherein the fourth temperature rise platform refers to the temperature approaching the fourth intermediate temperature as time increases, and the fourth intermediate temperature is greater than the third intermediate temperature and less than the target temperature.

7. The heat treatment process according to claim 1, characterized in that: The heat treatment process is a low pressure chemical vapor deposition process.

8. The heat treatment process according to claim 7, characterized in that: The product to be processed is a silicon wafer, and the reaction gas introduced in S3 and S4 is oxygen.

9. The heat treatment process according to claim 7, characterized in that: The flow rate of the reaction gas introduced in S3 is smaller than the flow rate of the reaction gas introduced in S4.

10. The heat treatment process according to claim 7, characterized in that: The flow rate of the reaction gas introduced in S3 is less than 5000 sccm, and the flow rate of the reaction gas introduced in S4 is greater than or equal to 20000 sccm.

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