Preparation method of thermal silicon oxide film

Abstract

The invention belongs to the technical field of preparation of oxide film materials, and particularly relates to a preparation method of a thermal silicon oxide film, which comprises the following steps: forming a polycrystalline silicon film on the surface of a substrate in an LPCVD (Low Pressure Chemical Vapor Deposition) reaction furnace, stopping supply of silane gas, introducing nitrogen, raising the temperature, stopping introducing nitrogen and introducing dry oxygen until the temperature and the pressure are stable, and carrying out heat treatment to obtain the thermal silicon oxide film. Generating a thermal silicon oxide film; the thickness of the thermal silicon oxide thin film is effectively controlled by controlling the flow rate of introduced oxygen and the time of introducing oxygen, the preparation method breaks through the limitation of a non-silicon-based substrate material, the thermal silicon oxide thin film is prepared on different substrate materials in an LPCVD reaction furnace, the thickness ratio of silicon oxide to polycrystalline silicon can be regulated and controlled, and the thickness of the thermal silicon oxide thin film is improved. The preparation method is short in time, low in cost and simple in process, the prepared product is uniform in film thickness and low in surface roughness value, the requirement of a wafer bonding process can be met, and additional process treatment is not needed.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of oxide film materials, and particularly relates to a method for thermally oxidizing silicon thin films. Background Art

[0002] With the rapid development of wireless communication technology, the market demand for radio frequency front-end devices continues to grow. Among them, as the core devices of communication systems, such as power amplifiers, duplexers, low-noise amplifiers, filters, etc., more attention is paid to the material performance indicators and structural design requirements. The heterogeneous integration of multiple materials is an important path to improve material performance and integration degree. In the prior art, when preparing composite thin film materials, heterogeneous materials are usually transferred to a silicon substrate or other substrates by bonding. Under this background, polysilicon and silicon oxide thin films have gradually become the research focus due to their excellent physical and chemical properties.

[0003] Chemical vapor deposition (CVD) technology is an important method for preparing thin film materials, which is a method of forming a uniform thin film by chemical reaction of reaction gases on the substrate surface. According to different reaction conditions, CVD technology can be divided into atmospheric pressure chemical vapor deposition (APCVD), low pressure chemical vapor deposition (LPCVD), and plasma enhanced chemical vapor deposition (PECVD). Among them, LPCVD technology has been widely used in thin film preparation production due to its high uniformity and high quality of depositing thin films under low pressure conditions. Using the LPCVD process has the advantages of high production efficiency, stable film quality, and easy thickness control, and is widely used for preparing polysilicon, amorphous silicon, silicon nitride and other thin films.

[0004] Silicon oxide thin film is a good surface passivation film. Existing thin film preparation mostly adopts thermal oxidation method, chemical vapor deposition method (such as PECVD) or sputtering method. The thermal oxidation method can significantly improve device performance because of the good uniformity, high density and few interface defects of the generated thin film, and is widely used in silicon-based devices. However, the thermal oxidation method is usually limited by process conditions and the properties of substrate materials, and it is difficult to be applied to some non-silicon-based substrate materials. To solve this problem, the traditional method usually first grows a polysilicon thin film on the substrate material by LPCVD technology, and then transfers it to a thermal oxidation furnace to prepare a silicon oxide thin film. In this method, the processes of heating, cooling, pressurizing, depressurizing, and equipment conversion between the two processes require a lot of time, increasing the time cost, high energy consumption, and also causing waste of resources. Moreover, the surface of the product is easily contaminated, affecting the quality of the oxide film. And due to the limitations of the thermal oxidation furnace itself and the process, the quality of the prepared oxide film is also poor. The parameters such as surface roughness and film thickness uniformity of the wafers prepared by this traditional method are difficult to meet the requirements of the bonding process, and additional processes such as chemical mechanical polishing are required, increasing the cost and also reducing the film thickness, which is not conducive to the subsequent preparation of composite thin film materials. Summary of the Invention

[0005] To solve the existing technical problems, the present invention provides a method for preparing a thermal silicon oxide film. This preparation method breaks through the limitations of non-silicon-based substrate materials. In an LPCVD reactor, a thermal silicon oxide film can be prepared on different substrate materials, and the thickness ratio of silicon oxide to polysilicon can be regulated. This preparation method requires a short time, low cost, and simple process. The prepared thermal silicon oxide film has a uniform film thickness and a low surface roughness value, can meet the requirements of the wafer bonding process, and does not require additional process treatment.

[0006] The present invention aims to provide a method for realizing the growth of a thermal silicon oxide film in one step on a silicon-based or non-silicon-based substrate material. This method integrates the LPCVD process and the thermal oxidation process using an LPCVD device to achieve continuous operation of polysilicon film deposition and thermal silicon oxide film preparation. In the traditional method, a polysilicon film is first prepared by the LPCVD process, and then a silicon oxide film is prepared in a thermal oxidation furnace. The equipment switching and transfer operations during the process take a long time, increasing the time and cost consumption. Moreover, due to the limitations of the thermal oxidation furnace itself and the process, the finally prepared product has an uneven film thickness and a high roughness value. Compared with the traditional process, the present invention completes the entire process flow in an LPCVD reactor, directly prepares a thermal silicon oxide film, greatly shortens the time, simplifies the process flow, reduces the contamination of the wafer during the equipment switching and transfer process, as well as the influence of temperature rise and fall, pressure rise and fall, etc. on the wafer, breaks through the limitations of the thermal oxidation furnace, and the prepared product has a uniform film thickness and a low roughness value, can meet the requirements of the bonding process for preparing a composite film, no longer requires additional processes such as CMP, ensures the film thickness, simplifies the process, and reduces the cost. By realizing the preparation of a thermal silicon oxide film in one process, the present invention not only effectively reduces the process flow, but also reduces the comprehensive cost of equipment operation and material handling, thereby improving production efficiency and meeting the requirements of large-scale manufacturing, improving the quality of the product, and being beneficial to the preparation of the subsequent composite film.

[0007] The technical solution of the present invention is as follows:

[0008] A method for preparing a thermal silicon oxide film, characterized by comprising the following steps:

[0009] (1) Form a polysilicon film on the surface of a substrate in an LPCVD reactor;

[0010] (2) Stop supplying silane gas, introduce nitrogen, raise the temperature in the reactor to the temperature required for thermal oxidation until the temperature and pressure are stable, then stop introducing nitrogen, and then introduce dry oxygen to oxidize the surface of the polysilicon film to form a thermal silicon oxide film layer;

[0011] (3) By controlling the flow rate and duration of oxygen introduction, the thickness of the thermal silicon oxide film can be effectively controlled.

[0012] Preferably, in step (1), the substrate is a silicon-based substrate or a non-silicon-based substrate. Further preferably, the substrate is one of silicon, quartz, silicon carbide, and sapphire. The present invention effectively breaks through the limitations that the thermal oxidation method must select a silicon-based substrate material and must be generated in a thermal oxidation furnace, and can realize the preparation of polysilicon on a silicon-based or non-silicon-based substrate. At the same time, without replacing the equipment, the thermal oxidation process can be carried out to prepare a thermal silicon oxide film with better quality.

[0013] Preferably, in step (1), the conditions for forming the polysilicon film are: the temperature is 550 - 580 °C, and the reaction pressure is 42 - 56 Pa.

[0014] Further preferably, in step (1), the conditions for forming the polysilicon film are: the flow rate of silane gas introduced is 300 - 360 sccm; before introducing the silane gas, the flow rate of nitrogen gas introduced first is 520 - 600 sccm, and after heating to the required temperature, the flow rate of nitrogen gas drops to 180 - 200 sccm. After the temperature and pressure are stable, the introduction of nitrogen gas is stopped.

[0015] Preferably, in step (2), the flow rate of nitrogen gas introduced first is 520 - 600 sccm. Nitrogen gas is introduced for 5 - 10 minutes first. After reaching the required temperature, the flow rate of nitrogen gas drops to 180 - 200 sccm. After the temperature and pressure are stable, the introduction of nitrogen gas is stopped. By introducing a larger flow rate of nitrogen gas for scrubbing first, the residual gas in the furnace can be effectively removed, avoiding affecting the quality of the oxide film, and no other gases that will have an impact are introduced. Using other methods to remove residual gases, such as pumping out the residual gas, this method cannot completely pump out the residual gas, which will affect the quality of the thermal silicon oxide film. At the same time, this method requires high energy consumption and high cost, which is not conducive to industrial production.

[0016] Preferably, in step (2), the flow rate of oxygen introduced is 200 - 260 sccm. Further preferably, in step (2), the temperature required for thermal oxidation is 950 - 1050 °C, and the required pressure is 42 - 56 Pa, effectively breaking through the limitations of the thermal oxidation furnace. By setting appropriate temperature and pressure in the LPCVD reaction furnace, it is more conducive to generating a thermal silicon oxide film with better quality.

[0017] Preferably, the film thickness of the thermal silicon oxide film is uniform, and the surface roughness value < 1 nm; three different film structures can be obtained through the preparation method: pure polysilicon film, polysilicon / silicon oxide bilayer film, and pure silicon oxide film.

[0018] Application of the thermally oxidized silicon thin film prepared by the above method for preparing a thermally oxidized silicon thin film in the preparation of a composite thin film. The thermally oxidized silicon thin film prepared by the method for preparing a thermally oxidized silicon thin film has uniform film thickness and low roughness value, can meet the requirements of the bonding process, is used to prepare a composite thin film, does not require additional processes such as CMP to process the wafer, effectively guarantees the film thickness, reduces the cost, and is conducive to the industrial production of the composite thin film.

[0019] The method for preparing a thermally oxidized silicon thin film provided by the present invention can prepare high-performance thermally oxidized silicon thin films on various substrate materials (such as silicon, quartz, silicon carbide, sapphire, etc.), effectively breaking through the limitation in the prior art that thermally oxidized silicon thin films can only be prepared on silicon wafers in a thermal oxidation furnace by a one-step thermal oxidation technology; the preparation method of the present invention can prepare polycrystalline silicon thin films and thermally oxidized silicon thin films (including polycrystalline silicon / silicon oxide double-layer thin films and pure silicon oxide thin films), and the thickness ratio of the silicon oxide layer and the polycrystalline silicon layer in the thin film can be adjusted, that is, different polycrystalline silicon / silicon oxide double-layer thin films with different thicknesses can be obtained according to actual needs. Polycrystalline silicon and thermally oxidized silicon thin films with different film thickness ratios will affect performance parameters such as the operating frequency, quality factor, and broadband capacity of radio frequency front-end devices (such as surface acoustic wave filters, sensors, etc.) in the current electronic information field. Therefore, the regulation of the thickness ratio of polycrystalline silicon to silicon oxide is of great significance for practical applications.

[0020] The method for preparing a thermally oxidized silicon thin film proposed by the present invention realizes the preparation of a thermally oxidized silicon thin film in one step in an LPCVD device. The thin film prepared by this method has the characteristics of uniform thickness and small surface roughness. Compared with the traditional process, the preparation time is significantly shortened, the process is simplified, the energy consumption is reduced, the production cost is reduced, the quality of the prepared product is better, and it can meet the requirements of the bonding process, which is conducive to the industrial production of the composite thin film; in addition, this method has high controllability. By adjusting the flow rate and time of oxygen, thin films with different polycrystalline silicon / silicon oxide film thickness ratios can be prepared, and it also breaks through the technical limitation that thermally oxidized silicon thin films cannot be prepared in one step on non-silicon-based substrates, which is conducive to the preparation of composite thin film materials and provides a new technical path for the high-performance and large-scale manufacturing of radio frequency front-end devices. Description of the Drawings

[0021] Figure 1 Schematic diagram of the gas path structure of the LPCVD device used in the present invention;

[0022] Figure 2 Schematic diagram of the polycrystalline silicon thin film structure;

[0023] Figure 3 Schematic diagram of the polycrystalline silicon / silicon oxide double-layer thin film structure;

[0024] Figure 4 Schematic diagram of the pure silicon oxide thin film structure;

[0025] In the figure, 1 is a nitrogen gas pipeline, 2 is a silane gas pipeline, 3 is an oxygen gas pipeline, and 4 is a reaction furnace. Specific embodiments

[0026] To more clearly illustrate the overall concept of the present invention, the following will be described in detail by way of examples. In the following description, many specific details are set forth in order to fully understand the present invention. However, the present invention can also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0027] The gas path structure of the LPCVD device in the present invention is as Figure 1 shown.

[0028] A method for preparing a thermal oxide silicon thin film provided by the present invention can actually prepare three different thin film structures: a pure polysilicon thin film (as Figure 2 shown), a polysilicon / silicon oxide double-layer thin film (as shown in 3), and a pure silicon oxide thin film (as Figure 4 shown). The specific process at least includes the following steps:

[0029] (1) Form a polysilicon thin film on the surface of the substrate in the LPCVD reaction furnace;

[0030] (2) Stop supplying silane gas, introduce nitrogen gas, raise the temperature in the reaction furnace to the temperature required for thermal oxidation until the temperature and pressure are stable, then stop introducing nitrogen gas, and then introduce dry oxygen to oxidize the surface of the polysilicon thin film to generate a thermal oxide silicon thin film layer;

[0031] (3) Effectively control the thickness of the thermal oxide silicon thin film by controlling the oxygen flow rate and the oxygen introduction time; (4) After the thin film is formed, stop heating and raising the temperature, then close the oxygen valve, and at the same time open the nitrogen valve for gas washing to remove the unreacted reaction gas and by-product gas, raise the pressure to the large pressure level, cool the furnace body to room temperature, and transport it to outside the furnace by the loading boat in pieces; finally, a thermal oxide silicon thin film with uniform film thickness and surface roughness value < 1 nm is obtained.

[0032] In step (1), the substrate is a silicon-based substrate or a non-silicon-based substrate. Specifically, the substrate is one of silicon, quartz, silicon carbide, and sapphire, effectively breaking through the limitation that the thermal oxidation method must select a silicon-based substrate material. Polysilicon can be prepared on a silicon-based or non-silicon-based substrate, and at the same time, without replacing the equipment, a thermal oxidation process can be carried out to prepare a thermal oxide silicon thin film.

[0033] In step (1), the conditions for forming the polysilicon thin film are as follows: the temperature is 550 - 580 °C, specifically, 550 °C, 560 °C, 570 °C, or 580 °C can be selected; the reaction pressure is 42 - 56 Pa, specifically, 42 Pa, 44 Pa, 45 Pa, 48 Pa, 52 Pa, or 56 Pa can be selected; the flow rate of the silane gas introduced is 300 - 360 sccm, specifically, 300 sccm, 310 sccm, 325 sccm, 330 sccm, 345 sccm, 350 sccm, or 360 sccm can be selected; before introducing the silane gas, nitrogen is first introduced to remove the impurity gas in the reaction furnace. The flow rate of the nitrogen introduced first is 520 - 600 sccm. After the temperature is raised to the required temperature, the flow rate of nitrogen is reduced to 180 - 200 sccm. After the temperature and pressure are stabilized, the introduction of nitrogen is stopped; at a certain reaction temperature and pressure, the silane gas decomposes into silicon atoms and hydrogen, and the silicon atoms are deposited on the substrate material to form a polysilicon thin film.

[0034] In step (2), the flow rate of the nitrogen introduced first is 520 - 600 sccm, specifically, 520 sccm, 530 sccm, 550 sccm, 580 sccm, or 600 sccm can be selected. Nitrogen is introduced for 5 - 10 minutes first. After reaching the required temperature, the flow rate of nitrogen is reduced to 180 - 200 sccm. After the temperature and pressure are stabilized, specifically, the flow rates of nitrogen after reduction are 180 sccm, 190 sccm, 195 sccm, or 200 sccm, and then the introduction of nitrogen is stopped; by introducing a large flow rate of nitrogen for gas washing, the residual gas in the furnace can be effectively removed, avoiding affecting the quality of the oxide film, and no other gases that will cause impacts are introduced; if other methods for removing residual gases are used, such as pumping out the residual gas, this method cannot completely pump out the residual gas, which will affect the quality of the thermal oxidation silicon thin film. At the same time, this method requires high energy consumption and high cost, which is not conducive to industrial production; in step (2), the flow rate of the oxygen introduced is 200 - 260 sccm, specifically, 200 sccm, 210 sccm, 220 sccm, 230 sccm, 250 sccm, or 260 sccm can be selected. The temperature required for thermal oxidation is 950 - 1050 °C, specifically, 950 °C, 965 °C, 985 °C, 990 °C, 1000 °C, 1035 °C, or 1050 °C can be selected. The required pressure is 42 - 56 Pa, specifically, 42 Pa, 44 Pa, 45 Pa, 48 Pa, 52 Pa, or 56 Pa can be selected, effectively breaking through the limitations of the thermal oxidation furnace. By setting appropriate temperature and pressure in the LPCVD reaction furnace, it is more conducive to generating a thermal oxidation silicon thin film with better quality.

[0035] In step (3), in order to obtain a pure oxide silicon thin film, the flow rate of the oxygen introduced and the time of introducing the oxygen can be changed, or only the time can be extended.

[0036] The present invention can first prepare a polysilicon thin film. By controlling the flow rate and time of oxygen introduced, the thicknesses of the polysilicon and silicon oxide are controlled, so that part of the polysilicon is oxidized to silicon oxide, and then a polysilicon / silicon oxide double-layer thin film with a certain thickness ratio is obtained. If a high-quality pure silicon oxide thin film without a polysilicon layer needs to be prepared on a substrate, the polysilicon thin film can be completely converted into a pure silicon oxide thin film by increasing the flow rate of oxygen and prolonging the time of oxygen introduction.

[0037] The application of the thermally oxidized silicon thin film prepared by the above method for preparing a thermally oxidized silicon thin film in the preparation of a composite thin film. The thermally oxidized silicon thin film prepared by the method for preparing a thermally oxidized silicon thin film has a uniform film thickness and a low roughness value, can meet the requirements of the bonding process, and is used to prepare a composite thin film. It does not require additional processes such as CMP to process the wafer, effectively guarantees the film thickness, reduces the cost, and is conducive to the industrial production of the composite thin film.

[0038] The present invention aims to provide a method for realizing the growth of a thermally oxidized silicon thin film in one step on a silicon-based or non-silicon-based substrate material. This method integrates the LPCVD process and the thermal oxidation process using an LPCVD device to realize the continuous operation of the deposition of a polysilicon thin film and the preparation of a thermally oxidized silicon thin film. In the traditional method, a polysilicon thin film is first prepared by the LPCVD process, and then a silicon oxide thin film is prepared in a thermal oxidation furnace. The equipment switching and transfer operations during the process take a long time, increasing the time and cost consumption. Moreover, due to the limitations of the thermal oxidation furnace itself and the process, the finally prepared product has an uneven film thickness and a high roughness value. Compared with the traditional process, the present invention completes the entire process flow in the LPCVD reaction furnace and directly prepares a thermally oxidized silicon thin film, greatly shortening the time, simplifying the process flow, reducing the contamination of the wafer during the equipment switching and transfer process, as well as the influence of temperature rise and fall, pressure rise and fall, etc. on the wafer, breaking through the limitations of the thermal oxidation furnace. The prepared product has a uniform film thickness and a low roughness value, can meet the requirements of the bonding process for preparing a composite thin film, no longer requires additional processes such as CMP, ensures the film thickness, simplifies the process, and reduces the cost. By realizing the preparation of a thermally oxidized silicon thin film in one process, the present invention not only effectively reduces the process flow, but also reduces the comprehensive cost of equipment operation and material handling, thereby improving the production efficiency and meeting the requirements of large-scale manufacturing, improving the quality of the product, and being conducive to the preparation of the subsequent composite thin film.

[0039] The specific embodiments are as follows:

[0040] The LPCVD device in the following Examples 1-3 includes a reaction furnace 1 and three gas pipelines, namely a nitrogen gas pipeline 1 (for introducing nitrogen gas), a silane gas pipeline 2 (for introducing silane gas), and an oxygen gas pipeline 3 (for introducing oxygen gas).

[0041] Example 1

[0042] A method for preparing a polysilicon thin film:

[0043] First, place the silicon carbide substrate wafer on the loading boat. Specifically, to make the gas flow uniform during the growth of polysilicon and ensure the in - wafer and between - wafer uniformity of the grown film thickness, a small amount of the same number of dummy wafers (using silicon carbide substrate wafers is sufficient) are attached to both sides of the placed silicon carbide substrate material. Then, send the substrate wafer and the dummy wafers into the LPCVD reactor together and withdraw the loading boat. Introduce nitrogen gas (flow rate 550 sccm) into the LPCVD reactor for 8 minutes to remove impurity gases. Raise the temperature in the furnace to the silane reaction temperature of 550 °C, and reduce the nitrogen gas flow rate to 200 sccm. After the temperature and pressure are stabilized, close the nitrogen gas valve to stop introducing nitrogen gas, open the silane gas valve, and introduce silane gas (SiH4) at 360 sccm. Under the conditions of 550 °C and 48 Pa, a 1 - μm polysilicon thin film is formed. Close the silane gas valve, stop heating and temperature rising, and end the growth of the polysilicon thin film. Open the nitrogen gas valve for purging to remove the unreacted silane gas and by - product hydrogen gas in the furnace cavity. When the pressure in the furnace returns to the large - pressure level, stop introducing nitrogen gas, cool the furnace body to restore the furnace body temperature to room temperature, and send the wafer with the grown polysilicon thin film out of the furnace through the loading boat. Thus, the polysilicon thin film on the substrate wafer is prepared.

[0044] Example 2

[0045] A method for preparing a thermal oxide silicon thin film:

[0046] The main process includes: first, grow and prepare a polysilicon thin film on the substrate wafer by LPCVD technology, and then oxidize the polysilicon thin film layer in the LPCVD reactor by thermal oxidation technology to obtain an oxygen - thermal oxide silicon thin film. That is, the thermal oxide silicon thin film is obtained by a chemical reaction of the polysilicon layer with dry oxygen under high - temperature conditions, rather than being deposited on the polysilicon thin film. Therefore, the thickness of the polysilicon thin film layer prepared in the first stage is the total thickness of the polysilicon / oxide double - layer thin film in the wafer. The specific operation steps are as follows:

[0047] First, a polycrystalline silicon film is generated on a substrate wafer, and the steps are the same as those in Example 1. After the growth of polycrystalline silicon is completed, the silane gas valve is closed, the heating and temperature rise is stopped, and the growth of the polycrystalline silicon film is terminated. At the same time, the nitrogen valve is opened, the nitrogen flow rate is 550 sccm, and the introduction time is 10 min. Gas washing is performed. After the residual gas in the furnace is removed, heating and temperature rise are started. During the heating period, nitrogen is continuously introduced to remove the residual gas in the furnace body as much as possible. The heating and temperature rise are continued to increase the temperature in the furnace to 1000° C., a reaction temperature required for thermal oxidation, and the nitrogen flow rate is reduced to 200 sccm. After the temperature and pressure are maintained stable, the nitrogen valve is closed, and the oxygen valve is opened to introduce dry oxygen into the furnace at a flow rate of 260 sccm, so that the cavity atmosphere in the furnace reaches the oxygen-rich atmosphere required for thermal oxidation of polycrystalline silicon. Under the conditions of 1000° C. and 48 Pa, the dry oxygen reacts with the surface of the polycrystalline silicon film to generate a 500 nm thermal oxide silicon film, i.e., a polycrystalline silicon / silicon oxide (thickness ratio 1:1) double-layer film is obtained;

[0048] When the thickness of the thermal silicon oxide film reaches the target thickness, the oxygen valve is closed, heating is stopped, the nitrogen valve is opened (nitrogen flow rate is 550sccm) for gas washing to remove unreacted reaction gases and by-product gases, the pressure rises to the maximum pressure level, the nitrogen gas is stopped from being introduced, the furnace body is cooled down to restore the furnace temperature to room temperature, and the film is transported out of the furnace body by loading boats. At this point, a polycrystalline silicon / silicon oxide double-layer film is prepared on the substrate wafer.

[0049] The roughness of the thermally oxidized silicon film obtained by the above method is less than 1 nm, and the difference between the thickness of the thickest part and the thickness of the thinnest part of the obtained product is 10-20 nm.

[0050] Example 3

[0051] A method for preparing a thermal silicon oxide film:

[0052] The main process includes first growing a polycrystalline silicon film on a substrate wafer through LPCVD technology, and then oxidizing the polycrystalline silicon film layer through thermal oxidation technology in a LPCVD reactor. By controlling the oxygen flow rate and ventilation time in the thermal oxidation stage, the first layer of polycrystalline silicon film is completely oxidized, thereby preparing a pure silicon oxide film layer on the substrate that does not contain a polycrystalline silicon layer. Therefore, the thickness of the polycrystalline silicon film prepared in the first stage is the thickness of the pure silicon oxide film in the form of a sheet.

[0053] First, a polycrystalline silicon film is grown on a substrate wafer, and the steps are the same as those in Example 1. After the growth of polycrystalline silicon is completed, the silane gas valve is closed, the heating and temperature rise is stopped, and the growth of the polycrystalline silicon film is terminated. At the same time, the nitrogen valve is opened, the nitrogen flow rate is 550 sccm, and the introduction time is 10 minutes. Gas washing is performed. After the residual gas in the furnace is removed, heating and temperature rise is started. During the heating period, nitrogen is continuously introduced to remove the residual gas in the furnace body as much as possible. The heating and temperature rise is continued to increase the temperature in the furnace to the reaction temperature of 1000° C. required for thermal oxidation. The nitrogen flow rate is reduced to 200 sccm. After the temperature and pressure are maintained stable, the nitrogen valve is closed, the oxygen valve is opened, and dry oxygen is introduced into the furnace at a flow rate of 260 sccm, so that the cavity atmosphere in the furnace reaches the oxygen-rich atmosphere required for thermal oxidation of polycrystalline silicon. Under the conditions of 1000° C. and 48 Pa, the dry oxygen reacts with the surface of the polycrystalline silicon film to generate a thermally oxidized silicon film, until the first layer of the polycrystalline silicon film is completely oxidized, thereby preparing a pure silicon oxide film layer on the substrate wafer.

[0054] When the thickness of the thermal silicon oxide film reaches the target thickness, the oxygen valve is closed, heating is stopped, the nitrogen valve is opened (nitrogen flow rate is 550sccm) for gas washing to remove unreacted reaction gas and by-product gas, the pressure rises to the maximum pressure level, the nitrogen supply is stopped, the furnace body is cooled down to restore the furnace temperature to room temperature, and the film is transported out of the furnace body by loading boat, so that a pure silicon oxide film is obtained on the substrate wafer.

[0055] The roughness of the pure silicon oxide film obtained by the above method is less than 1 nm, and the difference between the thickness of the thickest part and the thickness of the thinnest part of the obtained product is 10-20 nm.

[0056] Through the detailed description of the above three implementation cases, it can be known that the preparation method provided by the present invention can meet the growth requirements of different types of thin film structures on different substrate materials, and the LPCVD process and the thermal oxidation process are integrated in the LPCVD device, which can complete the preparation of thermally oxidized silicon thin films in one step, greatly shortening the process time and saving production costs. It has the advantages of high efficiency, low cost, high flexibility and high production capacity. It should be noted that the different thin film structures shown in the above three embodiments have a progressive relationship in the preparation process, that is, it is necessary to grow a polysilicon thin film first, and then thermally oxidize the polysilicon thin film to prepare silicon oxide to obtain a double-layer film structure, and finally the polysilicon can be completely oxidized to prepare a pure silicon oxide film. However, due to the long temperature rise and fall and gas washing time of the LPCVD equipment, one thin film structure is prepared in each batch.

[0057] Example 4

[0058] The difference from Example 1 is that the selected substrate wafer and companion wafer are silicon substrates, and the rest are the same as Example 1.

[0059] Example 5

[0060] Different from Example 2, the polysilicon prepared in Example 4 was selected, and the others were the same as those in Example 2.

[0061] The roughness of the thermally oxidized silicon film obtained by the above method was <1 nm, and the difference between the film thickness at the thickest part and the thinnest part of the obtained product was 10 - 20 nm.

[0062] Example 6

[0063] Different from Example 3, the polysilicon prepared in Example 4 was selected, and the others were the same as those in Example 2.

[0064] The roughness of the thermally oxidized silicon film obtained by the above method was <1 nm, and the difference between the film thickness at the thickest part and the thinnest part of the obtained product was 10 - 20 nm.

[0065] Comparative Example 1

[0066] A method for preparing a thermally oxidized silicon film:

[0067] Place the polysilicon film prepared in Example 1 in a thermal oxidation furnace. First, purge with nitrogen to remove the impurity gases in the furnace. Then, raise the temperature to the reaction temperature of 1000 °C. After the temperature and pressure are stabilized, close the nitrogen valve and open the oxygen valve to introduce dry oxygen into the furnace. At 1000 °C and 10 kPa, an oxidation reaction occurs between the dry oxygen and the surface of the polysilicon film to form a 500 - nm thermally oxidized silicon film, thus obtaining a polysilicon / silicon oxide (thickness ratio 1:1) double - layer film;

[0068] When the thickness of the thermally oxidized silicon film reaches the target thickness, close the oxygen valve, stop heating, open the nitrogen valve to introduce nitrogen for purging, remove the unreacted reaction gases and by - product gases, restore the pressure to the large - pressure level, stop introducing nitrogen, cool down the thermal oxidation furnace to restore the furnace body temperature to room temperature, and transport the wafer to outside the furnace. Thus, a polysilicon / silicon oxide double - layer film is fabricated on the substrate wafer.

[0069] The roughness of the thermally oxidized silicon film obtained by the above method was 5 - 6 nm, and the difference between the film thickness at the thickest part and the thinnest part of the finally obtained product was 60 - 70 nm.

[0070] In Comparative Example 1, a thermal silicon oxide film was prepared by a two-step method using two sets of equipment. First, a polysilicon film was prepared using an LPCVD equipment, and then after the preparation was completed, the polysilicon film was transferred to a thermal oxidation furnace equipment to prepare a silicon oxide film. The replacement of the two sets of equipment was rather cumbersome, wasting manpower and material resources, and also resulting in heat waste, increased energy consumption, and increased time cycle. During this process, changes in temperature and pressure, as well as product contamination during the transfer, would all affect the quality of the thermal silicon oxide film. At the same time, the limitations of the thermal oxidation furnace equipment itself also made the quality of the prepared product poor.

[0071] Comparative Example 2

[0072] A method for preparing a thermal silicon oxide film:

[0073] The LPCVD equipment used below was obtained commercially. This equipment is different from the LPCVD equipment of the present invention and includes a reaction furnace and two gas pipelines.

[0074] First, place the silicon carbide substrate wafer on the loading boat. Specifically, in order to make the gas flow uniform during the growth of polysilicon and ensure the in-wafer and between-wafer uniformity of the grown film thickness, a small amount of the same number of dummy wafers (using silicon carbide substrate wafers) are attached to both sides of the placed substrate material. Then, send the substrate wafer and the dummy wafers into the LPCVD reaction furnace together and withdraw the loading boat. The LPCVD reaction furnace is connected to a vacuum pump, and the impurities in the furnace are removed using the vacuum pump. The vacuum pump pumps out the impurity gas in the furnace body until the pressure reaches 1 Pa, and then silane gas (SiH4) is introduced with a flow rate of 360 sccm. At 550 °C and 48 Pa, a 1-μm polysilicon film is formed. Close the silane gas valve, stop heating and temperature rising, and end the growth of the polysilicon film.

[0075] Then, use the vacuum pump to pump out the impurity gas in the furnace body until the pressure reaches 1 Pa. Disconnect the silane gas pipeline from the silane gas cylinder, connect the silane gas pipeline to an oxygen cylinder, open the valve to introduce oxygen with a flow rate of 260 sccm, and continue heating and temperature rising to make the chamber atmosphere in the furnace body reach the oxygen-rich atmosphere required for the thermal oxidation of polysilicon. At 1000 °C and 48 Pa, the dry oxygen reacts with the surface of the polysilicon film to form a 500-nm thermal silicon oxide film, that is, a polysilicon / silicon oxide (thickness ratio 1:1) double-layer film is obtained.

[0076] When the thickness of the thermal silicon oxide film reaches the target thickness, close the valve, stop supplying oxygen, stop heating, cool down the furnace body to restore the furnace body temperature to room temperature, disconnect the oxygen cylinder, introduce air into the reaction furnace to make the pressure in the furnace body return to normal pressure, and transport the wafers out of the furnace through the loading boat. Thus, a polysilicon / silicon oxide double-layer film is prepared on the substrate wafer.

[0077] The roughness of the thermally oxidized silicon thin film obtained by the above method is 2-3 nm, and the difference between the film thickness at the thickest part and the thinnest part of the product is 30-40 nm.

[0078] Since in the comparative example, a vacuum pumping method is used to remove residual gases between the two processes of polysilicon growth and silicon oxide preparation, the problem is that an absolute vacuum state cannot be achieved, so that there are still a small amount of impurity gases and silane reaction gases in the reaction zone, which will make the interface between polysilicon and silicon oxide unclear, affecting subsequent applications, and also affecting the roughness and film thickness uniformity of the final thermally oxidized silicon thin film; at the same time, when using a vacuum pump to pump vacuum and introducing oxygen, it is necessary to replace the device and gas cylinder, which will cause cumbersome operations, increase labor costs and time costs, and increase energy consumption.

[0079] Based on the above two comparative examples and the embodiment, the thermally oxidized silicon thin films prepared in Comparative Examples 1 and 2 have worse film thickness uniformity and roughness than the thermally oxidized silicon thin film prepared in Embodiment 2; compared with Embodiment 2, Comparative Example 1 uses a thermal oxidation furnace to prepare the thermally oxidized silicon thin film, and the polysilicon needs to be transferred, and the surface is easily contaminated. And affected by changes in temperature, pressure, etc., since the thermal oxidation furnace equipment is different from the LPCVD equipment, the set oxidation conditions are different, and the uniformity of the film thickness of the finally prepared thin film is significantly worse, and the surface roughness of the thermally oxidized silicon thin film is higher; compared with Embodiment 2, Comparative Example 2 uses different LPCVD equipment. Due to the difference in equipment, a gas extraction method is used to remove impurity gases, and the gas cylinder is replaced to pass oxygen in the middle. Finally, the film thickness uniformity and roughness of the obtained product are not as good as those in Embodiment 2; whether it is Comparative Example 1 or Comparative Example 2, the operation of the process is more cumbersome, increasing the time cost, wasting manpower and material resources, and also causing an increase in energy consumption, which is not conducive to industrial production. Compared with Comparative Examples 1 and 2, the present invention simplifies the process, is easier to operate, saves production, reduces energy consumption, effectively improves the product quality, and is conducive to large-scale popularization and application.

[0080] A method for preparing a thermally oxidized silicon thin film proposed by the present invention realizes the preparation of the thermally oxidized silicon thin film in one step in an LPCVD device. The thin film prepared by this method has the characteristics of uniform thickness and small surface roughness. Compared with the traditional process, the preparation time is significantly shortened, the process is simplified, the energy consumption is reduced, the production cost is reduced, the quality of the prepared product is better, and it can meet the requirements of the bonding process, which is conducive to the industrial production of composite thin films; in addition, this method has high controllability. By adjusting the flow rate and time of oxygen, thin films with different film thickness ratios can be prepared, breaking through the technical limitation that thermally oxidized silicon thin films cannot be prepared in one step on non-silicon-based substrates, which is conducive to the preparation of composite materials and provides a new technical path for the high-performance and large-scale manufacturing of radio frequency front-end devices.

[0081] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a thermally oxidized silicon film, characterized in that: The following steps are involved: (1) In the LPCVD reactor, a polysilicon film is formed on the surface of the substrate; (2) stopping the supply of silane gas and introducing nitrogen gas to raise the temperature in the reaction furnace to the temperature required for thermal oxidation. After the temperature and pressure are stable, stopping the introduction of nitrogen gas and introducing dry oxygen gas to oxidize the surface of the polysilicon film to form a thermally oxidized silicon film layer. (3) The thickness of the thermal silicon oxide film can be effectively controlled by controlling the oxygen flow rate and oxygen injection time.

2. The method for preparing a thermally oxidized silicon film according to claim 1, characterized in that: In step (1), the substrate is a silicon-based substrate or a non-silicon-based substrate.

3. The method for preparing a thermally oxidized silicon film according to claim 2, characterized in that: In step (1), the substrate is one of silicon, quartz, silicon carbide, and sapphire.

4. The method for preparing a thermally oxidized silicon film according to claim 1, characterized in that: In step (1), the conditions for forming the polysilicon thin film are: temperature of 550-580°C and reaction pressure of 42-56Pa.

5. The method for preparing a thermally oxidized silicon film according to claim 1, characterized in that: In step (1), the conditions for forming the polysilicon film are as follows: the flow rate of the silane gas is 300 to 360 sccm; before the silane gas is introduced, nitrogen is introduced to remove the impurity gas in the reaction furnace, and the flow rate of the nitrogen is initially 520 to 600 sccm. After the temperature is raised to the required temperature, the flow rate of the nitrogen is reduced to 180 to 200 sccm. After the temperature and pressure are stabilized, the introduction of nitrogen is stopped.

6. The method for preparing a thermally oxidized silicon film according to claim 1, characterized in that: In step (2), the nitrogen gas is first introduced at a flow rate of 520 to 600 sccm for 5 to 10 minutes, and the temperature is raised to reach the desired temperature. The nitrogen gas flow rate is then reduced to 180 to 200 sccm, and the nitrogen gas is stopped after the temperature and pressure are stabilized.

7. The method for preparing a thermally oxidized silicon film according to claim 1, characterized in that: In step (2), the flow rate of oxygen gas is 200 to 260 sccm.

8. The method for preparing a thermally oxidized silicon film according to claim 1, characterized in that: In step (2), the temperature required for thermal oxidation is 950-1050°C and the pressure required is 42-56Pa.

9. The method for preparing a thermally oxidized silicon film according to claim 1, characterized in that: The thermal silicon oxide film has a uniform film thickness and a surface roughness value of less than 1 nm. The preparation method can obtain three different film structures: a pure polysilicon film, a polysilicon / silicon oxide double-layer film, and a pure silicon oxide film.

10. Use of the thermal silicon oxide film prepared by the method for preparing a thermal silicon oxide film according to any one of claims 1 to 9 in preparing a composite film.

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