A method for producing a thermal silicon oxide film

Abstract

The application belongs to the technical field of preparation of oxide film materials, and particularly relates to a preparation method of thermal silicon oxide film, which comprises the following steps: forming a polysilicon film on the surface of a substrate in an LPCVD reaction furnace, stopping the supply of silane gas, inputting nitrogen, increasing the temperature, and after the temperature and pressure are stabilized, stopping the input of nitrogen, inputting dry oxygen, and generating the thermal silicon oxide film; the thickness of the thermal silicon oxide film is effectively controlled by controlling the flow rate and time of inputting oxygen, the preparation method breaks the limitation of non-silicon substrate materials, the thermal silicon oxide film can be prepared on different substrate materials in the LPCVD reaction furnace, the thickness ratio of the silicon oxide and the polysilicon can be controlled, the preparation method has the advantages of short time, low cost and simple process, the prepared product has uniform film thickness and low surface roughness value, can meet the requirements of wafer bonding process, and does not need additional process treatment.

Description

Technical Field

[0001] This invention belongs to the technical field of oxide film material preparation, and specifically relates to a method for thermally oxidizing silicon thin films. Background Technology

[0002] With the rapid development of wireless communication technology, the market demand for radio frequency (RF) front-end devices continues to grow. Power amplifiers, duplexers, low-noise amplifiers, and filters, as core components of communication systems, are receiving increasing attention due to their material performance and structural design requirements. Heterogeneous integration of multiple materials is a crucial pathway to improve material performance and integration levels. Current technologies for preparing composite thin film materials typically involve bonding heterogeneous materials onto silicon or other substrates. Against this backdrop, polycrystalline silicon and silicon oxide thin films, due to their excellent physicochemical properties, have gradually become a research focus.

[0003] Chemical vapor deposition (CVD) is an important method for thin film material preparation. It is a method that forms a uniform thin film by reacting reactive gases on the surface of a substrate. Depending on the 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 is widely used in thin film production due to its high uniformity and high quality of deposited films under low pressure conditions. LPCVD offers advantages such as high production efficiency, stable film quality, and easily controllable thickness, and is widely used to prepare thin films such as polycrystalline silicon, amorphous silicon, and silicon nitride.

[0004] Silicon oxide thin films are excellent surface passivation films, and current methods for their preparation primarily employ thermal oxidation, chemical vapor deposition (such as PECVD), or sputtering. Thermal oxidation, due to its superior uniformity, high density, and low interface defects, significantly improves device performance and is widely used in silicon-based devices. However, thermal oxidation is often limited by process conditions and substrate material properties, making it difficult to apply to certain non-silicon substrates. To address this issue, traditional methods typically involve first growing a polycrystalline silicon thin film on the substrate using LPCVD technology, and then transferring the film to a thermal oxidation furnace to prepare a silicon oxide thin film. The heating, cooling, pressurization, and depressurization processes between the two processes in this method require a significant amount of time, increasing time costs, consuming a lot of energy, and wasting resources. Furthermore, the surface of the product is easily contaminated, affecting the quality of the oxide film. Due to the limitations of the thermal oxidation furnace itself and the process, the quality of the prepared oxide film is also poor. The surface roughness and film thickness uniformity of the wafers prepared by this traditional method are difficult to meet the requirements of the bonding process, requiring additional chemical mechanical polishing and other processes, which increases costs, reduces film thickness, and is not conducive to the subsequent preparation of composite thin film materials. Summary of the Invention

[0005] To address the existing technical problems, this invention provides a method for preparing thermally oxidized silicon thin films. This method overcomes the limitations of non-silicon substrate materials and prepares thermally oxidized silicon thin films on different substrate materials within an LPCVD reactor. The thickness ratio of silicon oxide to polycrystalline silicon can be controlled. This preparation method is time-efficient, low-cost, and simple. The prepared thermally oxidized silicon thin films have uniform thickness and low surface roughness, which can meet the requirements of wafer bonding processes without the need for additional processing.

[0006] This invention aims to provide a method for one-step growth of thermally oxidized silicon thin films on silicon-based or non-silicon-based substrates. This method integrates LPCVD and thermal oxidation processes using an LPCVD equipment, enabling continuous operation of polycrystalline silicon thin film deposition and thermally oxidized silicon thin film preparation. Traditional methods first prepare polycrystalline silicon thin films using LPCVD, and then prepare silicon oxide thin films in a thermal oxidation furnace. The equipment switching and transfer operations between these processes are time-consuming, increasing both time and cost. Furthermore, due to the limitations of the thermal oxidation furnace itself and the process, the final product often exhibits uneven film thickness and high roughness. Compared to traditional processes, this invention completes the entire process within the LPCVD reactor, directly preparing the thermally oxidized silicon thin film. This significantly shortens the time, simplifies the process, and reduces wafer contamination during equipment switching and transfer, as well as the impact of temperature and voltage fluctuations on the wafer. It overcomes the limitations of the thermal oxidation furnace, resulting in a product with uniform film thickness and low roughness, meeting the requirements for composite film preparation via bonding processes. It eliminates the need for additional CMP processes, ensuring film thickness, simplifying the process, and reducing costs. This invention achieves the preparation of thermally oxidized silicon thin films in a single process, which not only effectively reduces the process flow but also lowers the overall costs of equipment operation and material handling, thereby improving production efficiency and making it suitable for large-scale manufacturing needs. It also enhances product quality and facilitates the preparation of subsequent composite films.

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

[0008] A method for preparing a thermally oxidized silicon thin film, characterized by comprising the following steps:

[0009] (1) A polycrystalline silicon thin film is formed on the substrate surface inside the LPCVD reactor;

[0010] (2) Stop the supply of silane gas, introduce nitrogen gas, raise the temperature in the reactor to the temperature required for thermal oxidation, until the temperature and pressure stabilize, stop the supply of nitrogen gas, and then introduce dry oxygen gas to oxidize the surface of the polycrystalline silicon film and generate a thermally oxidized silicon film layer.

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

[0012] Preferably, in step (1), the substrate is a silicon-based substrate or a non-silicon-based substrate. More preferably, the substrate is one of silicon, quartz, silicon carbide, and sapphire. This invention effectively overcomes the limitations of thermal oxidation methods, which require the selection of silicon-based substrate materials and the requirement for generation in a thermal oxidation furnace. It enables the preparation of polycrystalline silicon on silicon-based or non-silicon-based substrates, and allows for the thermal oxidation process to be performed without changing equipment, resulting in high-quality thermally oxidized silicon thin films.

[0013] Preferably, in step (1), the conditions for forming the polycrystalline silicon thin film are: a temperature of 550-580℃ and a reaction pressure of 42-56Pa.

[0014] More preferably, in step (1), the conditions for forming the polycrystalline silicon thin film are as follows: the flow rate of silane gas is 300-360 sccm; before the silane gas is introduced, the flow rate of nitrogen gas is 520-600 sccm; after the temperature is raised to the required temperature, the flow rate of nitrogen gas is reduced to 180-200 sccm; and after the temperature and pressure are stabilized, the introduction of nitrogen gas is stopped.

[0015] Preferably, in step (2), the flow rate of nitrogen gas is initially 520-600 sccm, and nitrogen gas is introduced for 5-10 minutes. After the required temperature is reached, the flow rate of nitrogen gas is reduced to 180-200 sccm. After the temperature and pressure stabilize, the nitrogen gas is then introduced. The gas is first washed with a larger flow rate of nitrogen gas to effectively remove the residual gas in the furnace, avoid affecting the quality of the oxide film, and do not introduce other gases that may have an impact. Other methods of removing residual gases, such as extracting residual gases, cannot completely remove residual gases, which will affect the quality of the thermally oxidized silicon film. At the same time, this method requires high energy consumption and has a high cost, which is not conducive to industrial production.

[0016] Preferably, in step (2), the oxygen flow rate is 200-260 sccm. More preferably, in step (2), the required temperature for thermal oxidation is 950-1050℃ and the required pressure is 42-56 Pa, which effectively overcomes the limitations of thermal oxidation furnaces. Setting appropriate temperature and pressure in the LPCVD reactor is more conducive to generating thermally oxidized silicon films of better quality.

[0017] Preferably, the thermally oxidized silicon thin film has a uniform thickness and a surface roughness value of <1nm; three different thin film structures can be obtained through the preparation method: pure polycrystalline silicon thin film, polycrystalline silicon / silicon oxide bilayer thin film, and pure silicon oxide thin film.

[0018] The thermally oxidized silicon thin film prepared by the above-mentioned method is used in the preparation of composite films. The thermally oxidized silicon thin film prepared by this method has uniform film thickness and low roughness value, which can meet the bonding process requirements. It can be used to prepare composite films without the need for additional wafer processing such as CMP, which effectively ensures film thickness, reduces costs, and is conducive to the industrial production of composite films.

[0019] This invention provides a method for preparing thermally oxidized silicon thin films, which can prepare high-performance thermally oxidized silicon thin films on various substrate materials (such as silicon, quartz, silicon carbide, sapphire, etc.). This effectively overcomes the limitation of existing technologies that can only prepare thermally oxidized silicon thin films on silicon wafers in a thermal oxidation furnace through a one-step thermal oxidation process. The preparation method of this invention can prepare polycrystalline silicon thin films and thermally oxidized silicon thin films (including polycrystalline silicon / silicon oxide bilayer films and pure silicon oxide films). Moreover, the thickness ratio of the silicon oxide layer and the polycrystalline silicon layer in the film is adjustable. That is, polycrystalline silicon / silicon oxide bilayer films of different thicknesses can be obtained according to actual needs. Different film thickness ratios of polycrystalline silicon and thermally oxidized silicon films will affect the operating frequency, quality factor, broadband capacity, and other performance parameters of radio frequency front-end devices (such as surface acoustic wave filters, sensors, etc.) in the current electronic information field. Therefore, the control of the thickness ratio of polycrystalline silicon to silicon oxide is of great significance for practical applications.

[0020] This invention proposes a method for preparing thermally oxidized silicon thin films, which achieves the preparation of thermally oxidized silicon thin films in a one-step LPCVD device. The films prepared by this method have the characteristics of uniform thickness and low surface roughness. Compared with traditional processes, it significantly shortens the preparation time, simplifies the process, reduces energy consumption, lowers production costs, and produces higher-quality products that meet the requirements of bonding processes, thus facilitating the industrialization of composite thin films. In addition, this method has high controllability. By adjusting the oxygen flow rate and time, films with different polycrystalline silicon / silicon oxide film thickness ratios can be prepared. It also overcomes the technical limitation that thermally oxidized silicon thin films cannot be prepared in one step on non-silicon substrates, which is beneficial for 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. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the gas path structure of the LPCVD equipment used in this invention;

[0022] Figure 2 This is a schematic diagram of a polycrystalline silicon thin film structure;

[0023] Figure 3 This is a schematic diagram of a polycrystalline silicon / silicon oxide bilayer thin film structure;

[0024] Figure 4 This is a schematic diagram of a pure silicon oxide thin film structure;

[0025] In the diagram, 1 is the nitrogen pipeline, 2 is the silane gas pipeline, 3 is the oxygen pipeline, and 4 is the reactor. Detailed Implementation

[0026] To more clearly illustrate the overall concept of the present invention, detailed descriptions are provided below by way of examples. Many specific details are set forth in the following description to provide a thorough understanding of the invention; however, the invention may also be implemented in other ways different from those described herein, and therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0027] The gas path structure of the LPCVD equipment in this invention is as follows: Figure 1 As shown.

[0028] The method for preparing thermally oxidized silicon thin films provided by this invention can actually produce three different thin film structures: pure polycrystalline silicon thin films (such as...) Figure 2 As shown), polycrystalline silicon / silicon oxide bilayer thin films (as shown in Figure 3), pure silicon oxide thin films (as shown in Figure 4). Figure 4 As shown), the specific process includes at least the following steps:

[0029] (1) A polycrystalline silicon thin film is formed on the substrate surface inside the LPCVD reactor;

[0030] (2) Stop the supply of silane gas, introduce nitrogen gas, raise the temperature in the reactor to the temperature required for thermal oxidation, until the temperature and pressure stabilize, stop the supply of nitrogen gas, and then introduce dry oxygen gas to oxidize the surface of the polycrystalline silicon film and generate a thermally oxidized silicon film layer.

[0031] (3) By controlling the oxygen flow rate and oxygen introduction time, the thickness of the thermal oxidized silicon film can be effectively controlled; (4) After the film is generated, the heating is stopped and the oxygen valve is closed. At the same time, the nitrogen valve is opened to purge the gas, remove the unreacted reaction gas and by-product gas, and raise the pressure to the maximum pressure level. The furnace body is cooled to room temperature and transported to the outside of the furnace body by loading boat; finally, the thermal oxidized silicon film has a uniform thickness and a surface roughness value of <1nm.

[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, or sapphire. This effectively overcomes the limitation that the thermal oxidation method must select a silicon-based substrate material. Polycrystalline silicon can be prepared on silicon-based or non-silicon-based substrates. At the same time, without changing the equipment, the thermal oxidation process can be carried out to prepare a thermally oxidized silicon thin film.

[0033] In step (1), the conditions for forming the polycrystalline silicon thin film are as follows: temperature is 550-580℃, specifically 550℃, 560℃, 570℃, or 580℃; reaction pressure is 42-56Pa, specifically 42Pa, 44Pa, 45Pa, 48Pa, 52Pa, or 56Pa; and the flow rate of the silane gas is 300-360 sccm, specifically 300 sccm, 310 sccm, 325 sccm, or 330 sccm. 345 sccm, 350 sccm, 360 sccm; Before introducing silane gas, nitrogen gas is first introduced to remove impurity gases from the reactor. The initial nitrogen flow rate is 520-600 sccm. After heating to the required temperature, the nitrogen flow rate is reduced to 180-200 sccm. After the temperature and pressure stabilize, the nitrogen gas is stopped. Under certain reaction temperature and pressure, silane gas decomposes into silicon atoms and hydrogen gas. The silicon atoms are deposited on the substrate material to form a polycrystalline silicon thin film.

[0034] In step (2), the initial flow rate of nitrogen gas is 520-600 sccm, specifically 520 sccm, 530 sccm, 550 sccm, 580 sccm, or 600 sccm. Nitrogen gas is introduced for 5-10 minutes. After reaching the desired temperature, the flow rate is reduced to 180-200 sccm. Once the temperature and pressure stabilize, the reduced flow rate is further adjusted to 180 sccm, 190 sccm, 195 sccm, or 200 sccm, before stopping the nitrogen flow. Using a higher nitrogen flow rate for gas washing effectively removes residual gases from the furnace, preventing any impact on the quality of the oxide film and avoiding the introduction of other potentially harmful gases. Other methods for removing residual gases, such as evacuation, cannot completely remove them and may affect thermal oxidation. The quality of silicon thin films is improved, but the energy consumption required by this method is high and the cost is large, which is not conducive to industrial production. In step (2), the flow rate of oxygen is 200-260 sccm, specifically 200 sccm, 210 sccm, 220 sccm, 230 sccm, 250 sccm, 260 sccm. The temperature required for thermal oxidation is 950-1050℃, specifically 950℃, 965℃, 985℃, 990℃, 1000℃, 1035℃, 1050℃. The required pressure is 42-56 Pa, specifically 42 Pa, 44 Pa, 45 Pa, 48 Pa, 52 Pa, 56 Pa. This effectively breaks through the limitations of thermal oxidation furnaces. Setting appropriate temperature and pressure in the LPCVD reactor is more conducive to generating thermally oxidized silicon thin films of better quality.

[0035] In step (3), in order to obtain a pure silicon oxide film, you can choose to change the flow rate of oxygen and the time of oxygen introduction, or you can simply extend the time.

[0036] This invention can first prepare a polycrystalline silicon thin film. By controlling the flow rate and time of oxygen introduction, the thickness of the polycrystalline silicon and silicon oxide can be controlled, so that part of the polycrystalline silicon is oxidized to silicon oxide, thereby obtaining a polycrystalline silicon / silicon oxide bilayer film with a certain thickness ratio. If it is necessary to prepare a high-quality pure silicon oxide film on a substrate without a polycrystalline silicon layer, the flow rate of oxygen can be increased and the oxygen introduction time can be extended to completely convert the polycrystalline silicon film into a pure silicon oxide film.

[0037] The thermally oxidized silicon thin film prepared by the above-mentioned method is used in the preparation of composite films. The thermally oxidized silicon thin film prepared by this method has uniform film thickness and low roughness value, which can meet the bonding process requirements. It can be used to prepare composite films without the need for additional wafer processing such as CMP, which effectively ensures film thickness, reduces costs, and is conducive to the industrial production of composite films.

[0038] This invention aims to provide a method for one-step growth of thermally oxidized silicon thin films on silicon-based or non-silicon-based substrates. This method integrates LPCVD and thermal oxidation processes using an LPCVD equipment, enabling continuous operation of polycrystalline silicon thin film deposition and thermally oxidized silicon thin film preparation. Traditional methods first prepare polycrystalline silicon thin films using LPCVD, and then prepare silicon oxide thin films in a thermal oxidation furnace. The equipment switching and transfer operations between these processes are time-consuming, increasing both time and cost. Furthermore, due to limitations of the thermal oxidation furnace itself and the process, the final product often exhibits uneven film thickness and high roughness. Compared to traditional processes, this invention completes the entire process within the LPCVD reactor, directly preparing the thermally oxidized silicon thin film. This significantly shortens the time, simplifies the process, and reduces wafer contamination during equipment switching and transfer, as well as the impact of temperature and voltage fluctuations on the wafer. It overcomes the limitations of the thermal oxidation furnace, producing a product with uniform film thickness and low roughness, meeting the requirements for composite film preparation via bonding processes. It eliminates the need for additional CMP processes, ensuring film thickness, simplifying the process, and reducing costs. This invention achieves the preparation of thermally oxidized silicon thin films in a single process, which not only effectively reduces the process flow but also lowers the overall costs of equipment operation and material handling, thereby improving production efficiency and making it suitable for large-scale manufacturing needs. It also enhances product quality and facilitates the preparation of subsequent composite films.

[0039] Specific embodiments are shown below:

[0040] The LPCVD equipment in Examples 1-3 below includes a reactor 1 and three gas pipelines: nitrogen pipeline 1 (for nitrogen), silane gas pipeline 2 (for silane gas), and oxygen pipeline 3 (for oxygen).

[0041] Example 1

[0042] A method for preparing polycrystalline silicon thin films:

[0043] First, a silicon carbide substrate wafer is placed on a loading boat. Specifically, to ensure uniform airflow during polycrystalline silicon growth and to guarantee intra-wafer and inter-wafer uniformity of film thickness, a small number of identical auxiliary wafers (using silicon carbide substrate wafers) are attached to both sides of the placed silicon carbide substrate. Then, the substrate wafer and auxiliary wafers are fed together into the LPCVD reactor and removed from the loading boat. Nitrogen gas (flow rate 550 sccm) is introduced into the LPCVD reactor for 8 minutes to remove impurity gases. The furnace temperature is then raised to the silane reaction temperature of 550°C, and the nitrogen flow rate is reduced to 200 sccm. After the temperature and pressure stabilize,... Close the nitrogen valve to stop the nitrogen supply, open the silane gas valve, and introduce silane gas (SiH4) at 360 sccm. Under conditions of 550℃ and 48 Pa, a 1 μm polycrystalline silicon thin film is generated. Close the silane gas valve to stop heating and end the polycrystalline silicon thin film growth. Open the nitrogen valve to purge the gas and remove unreacted silane gas and byproduct hydrogen from the furnace chamber. The furnace pressure is then raised back to the maximum pressure level. Nitrogen supply is stopped, and the furnace is cooled to room temperature. The polycrystalline silicon thin film is then transported out of the furnace via a loading boat. This completes the preparation of the polycrystalline silicon thin film on the substrate wafer.

[0044] Example 2

[0045] A method for preparing thermally oxidized silicon thin films:

[0046] The main process includes: first, growing a polycrystalline silicon thin film on a substrate wafer using LPCVD technology; then, oxidizing the polycrystalline silicon thin film layer in an LPCVD reactor using thermal oxidation technology to obtain a thermally oxidized silicon film. This thermally oxidized silicon film is produced by a chemical reaction between the polycrystalline silicon layer and dry oxygen at high temperatures, rather than being deposited on the polycrystalline silicon film. Therefore, the thickness of the polycrystalline silicon thin film layer prepared in the first stage is the total thickness of the polycrystalline silicon / oxygen bilayer film in the final wafer. The specific operation steps are as follows:

[0047] First, a polycrystalline silicon thin film is formed on the substrate wafer, following the same steps as in Example 1. After the polycrystalline silicon growth is complete, the silane gas valve is closed, heating is stopped, and the growth of the polycrystalline silicon thin film is ended. At the same time, the nitrogen valve is opened, with a nitrogen flow rate of 550 sccm and a purging time of 10 minutes for gas purging. After removing the residual gas in the furnace, heating is started. During the heating period, nitrogen is continuously introduced to remove as much residual gas as possible from the furnace. Heating continues until the furnace temperature reaches 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 stabilized, 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. This makes the atmosphere in the furnace cavity reach the oxygen-rich atmosphere required for the 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 thin film to generate a 500 nm thermal silicon oxide thin film, thus obtaining a polycrystalline silicon / silicon oxide (thickness ratio 1:1) bilayer film.

[0048] Once the thermal silicon oxide film reaches the target thickness, the oxygen valve is closed to stop heating, and the nitrogen valve is opened (nitrogen flow rate is 550 sccm) for purging to remove unreacted reaction gases and byproduct gases. The pressure is then increased to the maximum pressure level, and the nitrogen supply is stopped. The furnace body is then cooled to room temperature, and the film is transported out of the furnace body in a loading boat. This completes the fabrication of a polycrystalline silicon / silicon oxide bilayer film on the substrate wafer.

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

[0050] Example 3

[0051] A method for preparing thermally oxidized silicon thin films:

[0052] The main process involves first growing a polycrystalline silicon thin film on a substrate wafer using LPCVD technology, and then oxidizing the polycrystalline silicon thin film layer in an LPCVD reactor using thermal oxidation technology. By controlling the oxygen flow rate and ventilation time during the thermal oxidation stage, the first polycrystalline silicon thin film is completely oxidized, thereby preparing a pure silicon oxide thin film layer without a polycrystalline silicon layer on the substrate. Therefore, the thickness of the polycrystalline silicon thin film prepared in the first stage is the thickness of the pure silicon oxide thin film.

[0053] First, a polycrystalline silicon thin film is formed on the substrate wafer, following the same steps as in Example 1. After the polycrystalline silicon growth is complete, the silane gas valve is closed, heating is stopped, and the growth of the polycrystalline silicon thin film is ended. At the same time, the nitrogen valve is opened, with a nitrogen flow rate of 550 sccm and a purging time of 10 minutes for gas purging. After removing the residual gas in the furnace, heating begins. During the heating process, nitrogen is continuously introduced to remove as much residual gas as possible from the furnace. Heating continues until the furnace temperature reaches the reaction temperature of 1000°C required for thermal oxidation. The nitrogen flow rate is then reduced to 200 sccm. After the temperature and pressure stabilize, 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 atmosphere in the furnace cavity reaches the oxygen-rich atmosphere required for the 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 thin film to form a thermally oxidized silicon thin film until the first layer of polycrystalline silicon thin film is completely oxidized, thereby obtaining a pure silicon oxide thin film layer on the substrate wafer.

[0054] Once the thermal silicon oxide film reaches the target thickness, the oxygen valve is closed to stop heating, and the nitrogen valve is opened (nitrogen flow rate is 550 sccm) for gas purging to remove unreacted reaction gases and byproduct gases. The pressure is increased to the maximum pressure level, and the nitrogen supply is stopped. The furnace body is then cooled to room temperature, and the film is transported out of the furnace body in a loading boat. Thus, a pure silicon oxide film is fabricated on the substrate wafer.

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

[0056] Through the detailed descriptions of the three implementation examples above, it can be seen that the preparation method provided by this invention can meet the growth requirements of different types of thin film structures on different substrate materials. Furthermore, by integrating the LPCVD process and thermal oxidation process into a single LPCVD device, the preparation of thermally oxidized silicon thin films can be completed in one step, significantly shortening the process time and saving production costs. It offers advantages such as high efficiency, low cost, high flexibility, and high production capacity. It should be noted that the different thin film structures shown in the three embodiments above have a progressive relationship in the preparation process. That is, a polycrystalline silicon thin film needs to be grown first, then the polycrystalline silicon thin film needs to be thermally oxidized to prepare silicon oxide to obtain a bilayer film structure, and finally, the polycrystalline silicon can be completely oxidized to obtain a pure silicon oxide thin film. However, due to the long heating, cooling, and gas rinsing times of the LPCVD equipment, only one type of thin film structure can be prepared per batch.

[0057] Example 4

[0058] The difference from Example 1 is that the selected substrate wafer and the accompanying wafer are silicon substrates, while everything else is the same as in Example 1.

[0059] Example 5

[0060] The difference between Example 2 and Example 4 is that the polycrystalline silicon prepared in Example 4 was selected, while all other aspects are the same as in Example 2.

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

[0062] Example 6

[0063] The difference between Example 3 and Example 4 is that the polycrystalline silicon prepared in Example 4 was selected, while all other aspects are the same as in Example 2.

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

[0065] Comparative Example 1

[0066] A method for preparing thermally oxidized silicon thin films:

[0067] The polycrystalline silicon thin film prepared in Example 1 was placed in a thermal oxidation furnace. It was first purged with nitrogen to remove impurities from the furnace. Then, the temperature was raised to the reaction temperature of 1000°C. After the temperature and pressure were stabilized, the nitrogen valve was closed and the oxygen valve was opened to introduce dry oxygen into the furnace. Under the conditions of 1000°C and 10 kPa, the dry oxygen reacted with the surface of the polycrystalline silicon thin film to generate a 500 nm thermal silicon oxide thin film, thus obtaining a polycrystalline silicon / silicon oxide (thickness ratio 1:1) bilayer film.

[0068] Once the thermal oxidation film reaches the target thickness, the oxygen valve is closed, heating is stopped, and the nitrogen valve is opened to introduce nitrogen for purging, removing unreacted reaction gases and byproduct gases. The pressure is restored to a high pressure level, nitrogen supply is stopped, and the thermal oxidation furnace is cooled to room temperature. The film is then transported out of the furnace. This completes the fabrication of a polycrystalline silicon / silicon oxide bilayer film on the substrate wafer.

[0069] The roughness of the thermally oxidized silicon film obtained by the above method is 5-6 nm, and the difference between the thickest and thinnest parts of the final product is 60-70 nm.

[0070] Comparative Example 1 uses a two-step method and two sets of equipment to prepare thermally oxidized silicon thin films. First, a polycrystalline silicon thin film is prepared using an LPCVD device. After preparation, the polycrystalline silicon thin film is transferred to a thermal oxidation furnace to prepare a silicon oxide thin film. The change of equipment is cumbersome, wastes manpower and resources, and also leads to heat waste, increased energy consumption, and longer time cycle. During this process, changes in temperature and pressure, as well as product contamination during the transfer, will affect the quality of the thermally oxidized silicon thin film. At the same time, the limitations of the thermal oxidation furnace itself also result in poor product quality.

[0071] Comparative Example 2

[0072] A method for preparing thermally oxidized silicon thin films:

[0073] The LPCVD equipment used below is commercially available and differs from the LPCVD equipment of this invention. This equipment includes a reactor and two gas pipelines.

[0074] First, a silicon carbide substrate wafer is placed on a loading boat. Specifically, to ensure uniform airflow during polycrystalline silicon growth and to guarantee intra-wafer and inter-wafer uniformity of film thickness, a small number of identical auxiliary wafers (using silicon carbide substrate wafers) are attached to both sides of the substrate. Then, the substrate wafer and auxiliary wafers are fed together into the LPCVD reactor and removed from the loading boat. The LPCVD reactor is connected to a vacuum pump, which removes impurities from the furnace. The vacuum pump evacuates the impurity gases from the furnace to a pressure of 1 Pa, and then silane gas (SiH4) is introduced at a flow rate of 360 sccm. A 1 μm polycrystalline silicon thin film is generated at 550°C and 48 Pa. The silane gas valve is then closed, heating is stopped, and the polycrystalline silicon thin film growth is complete.

[0075] Then, the impurity gas inside the furnace is evacuated using a vacuum pump until the pressure is 1 Pa. The silane gas pipeline is disconnected from the silane gas cylinder, and the silane gas pipeline is connected to the oxygen cylinder. The valve is opened to introduce oxygen at a flow rate of 260 sccm. The temperature is increased by continuing to heat the furnace to achieve the oxygen-rich atmosphere required for the thermal oxidation of polycrystalline silicon. At 1000℃ and 48 Pa, the dry oxygen reacts with the surface of the polycrystalline silicon film to generate a 500 nm thermal silicon oxide film, thus obtaining a polycrystalline silicon / silicon oxide (thickness ratio 1:1) bilayer film.

[0076] Once the thermal silicon oxide film reaches the target thickness, the valve is closed, the oxygen supply is stopped, heating is stopped, and the furnace body is cooled down to room temperature. The oxygen cylinder is disconnected, and air is introduced into the reactor to restore the furnace body to maximum pressure. The film is then transported out of the furnace body by a loading boat. Thus, a polycrystalline silicon / silicon oxide bilayer film is fabricated on the substrate wafer.

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

[0078] Because the residual gas in the polycrystalline silicon growth and silicon oxide preparation processes in the comparative example is removed by vacuuming, an absolute vacuum cannot be achieved. As a result, a small amount of impurity gas and silane reaction gas still exist in the reaction zone. This makes the interface between polycrystalline silicon and silicon oxide unclear, affecting subsequent applications. It also affects the roughness and uniformity of the final thermal silicon oxide film. At the same time, when using a vacuum pump to create a vacuum and introduce oxygen, it is necessary to change the equipment and gas cylinders, which makes the operation cumbersome, increases labor and time costs, and increases energy consumption.

[0079] Based on the two comparative examples and embodiments described above, the thermally oxidized silicon films prepared in Comparative Examples 1 and 2 have inferior thickness uniformity and roughness compared to the thermally oxidized silicon film prepared in Example 2. Comparative Example 1, compared to Example 2, uses a thermal oxidation furnace to prepare the thermally oxidized silicon film. This requires the polycrystalline silicon to be transferred, making the surface susceptible to contamination. Furthermore, the thermal oxidation furnace, unlike LPCVD equipment, has different oxidation conditions, resulting in significantly poorer film thickness uniformity and higher surface roughness. Comparative Example 2 uses a different LPCVD equipment than Example 2. Due to the different equipment, impurity gases are removed by evacuation, and oxygen is introduced by changing gas cylinders. Consequently, the film thickness uniformity and roughness of the final product are inferior to those of Example 2. Both Comparative Examples 1 and 2 involve cumbersome processes, increasing time costs, wasting manpower and resources, and leading to increased energy consumption, all of which are detrimental to industrial production. Compared to Comparative Examples 1 and 2, this invention simplifies the process, is easier to operate, saves production time, reduces energy consumption, effectively improves product quality, and is conducive to large-scale application.

[0080] This invention proposes a method for preparing thermally oxidized silicon thin films, which achieves the preparation of thermally oxidized silicon thin films in a one-step LPCVD device. The films prepared by this method are characterized by uniform thickness and low surface roughness. Compared with traditional processes, it significantly shortens the preparation time, simplifies the process, reduces energy consumption, lowers production costs, and produces higher-quality products that meet the requirements of bonding processes, thus facilitating the industrialization of composite films. In addition, this method offers high controllability; by adjusting the oxygen flow rate and time, films with different thickness ratios can be prepared, overcoming the technical limitation that thermally oxidized silicon thin films cannot be prepared in one step on non-silicon substrates. This is beneficial for 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 description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a thermally oxidized silicon thin film, characterized in that, Includes the following steps: (1) In the LPCVD reactor, a polycrystalline silicon thin film is formed on the substrate surface. The conditions for the formation of the polycrystalline silicon thin film are as follows: the flow rate of silane gas is 300~360 sccm; before the silane gas is introduced, nitrogen gas is introduced to remove the impurity gas in the reactor. The initial flow rate of nitrogen gas is 520~600 sccm. After the temperature is raised to the required temperature, the flow rate of nitrogen gas is reduced to 180~200 sccm. After the temperature and pressure stabilize, the nitrogen gas is stopped. (2) Stop the supply of silane gas, first introduce nitrogen gas at a flow rate of 520~600 sccm for 5-10 minutes, raise the temperature in the reactor to the temperature required for thermal oxidation, reduce the flow rate of nitrogen gas to 180~200 sccm, and after the temperature and pressure stabilize, stop the supply of nitrogen gas, then introduce dry oxygen at a flow rate of 200~260 sccm to oxidize the surface of the polycrystalline silicon film and generate a thermally oxidized silicon film layer; (3) By controlling the oxygen flow rate and oxygen introduction time, the thickness of the thermally oxidized silicon film can be effectively controlled; the thermally oxidized silicon film has a uniform thickness and a surface roughness value of <1 nm.

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

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

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

6. The method for preparing a thermally oxidized silicon thin film according to claim 1, characterized in that: Three different thin film structures can be obtained through different preparation methods: pure polycrystalline silicon thin film, polycrystalline silicon / silicon oxide bilayer thin film, and pure silicon oxide thin film.

7. The application of the thermally oxidized silicon thin film prepared by any of the methods described in claims 1-6 in the preparation of composite films.

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