Method for regulating and controlling growth uniformity of tin oxide film

Abstract

The invention discloses a method for adjusting and controlling the growth uniformity of a tin oxide film, which comprises the following steps of: placing a polished silicon wafer in a carrier boat for bearing the silicon wafer, and arranging a flow uniformizing device below the carrier boat; and after the cavity reaches a vacuum state and the temperature reaches 80-120 DEG C, sequentially introducing a tin source, introducing large-flow argon for primary purging, introducing small-flow argon for secondary purging, introducing an oxygen source, introducing large-flow argon for tertiary purging and introducing small-flow argon for quaternary purging, and repeating for 50-200 times. According to the scheme, through the Bernoulli principle, the pressure intensity of places with small flow velocity in fluid is large, the pressure intensity of places with large flow velocity is small, the movable baffle with the opening degree controlled through the pressure intensity is manufactured at the air exhaust position, airflow is redistributed, and the air uniformity is improved. And through a large and small flow superposition purging mode, it is guaranteed that gas pressure difference is not generated in the source introduction step to affect airflow flowing, the purging capacity is enhanced, and the film thickness uniformity is improved.

Description

Technical Field

[0001] This invention relates to the field of tin oxide thin film preparation, and more specifically to a method for controlling the uniformity of tin oxide thin film growth. Background Technology

[0002] As competition in the photovoltaic industry intensifies, developing new battery technologies has become a key path for companies to break through homogeneous competition. After decades of development, the photoelectric conversion efficiency of traditional crystalline silicon solar cells has reached nearly 26%, gradually approaching the theoretical limit (approximately 29.4%), with limited room for further improvement. In contrast, perovskite solar cells, with their much higher theoretical efficiency than crystalline silicon cells (single-junction perovskite cells around 33-34%, and crystalline silicon / perovskite tandem cells reaching over 40%), combined with low manufacturing costs and flexibility potential, have become a key next-generation photovoltaic technology direction for both policy and corporate focus. In the perovskite solar cell structure, tin oxide (SnO2) is considered an ideal electron transport layer material due to its high electron mobility, wide bandgap, low-temperature process compatibility, and good energy level matching with the perovskite layer. Therefore, preparing uniform, stable, and high-quality tin oxide thin films is one of the necessary conditions for achieving high-efficiency perovskite solar cells.

[0003] Currently, atomic layer deposition (ALD) technology is the primary method for preparing tin oxide thin films. This technique, through the alternating introduction of precursors and reactive gases, enables nanometer-level precision control of film thickness and excellent step coverage. However, in the ALD deposition process of tin oxide, commonly used tin sources (such as tetramethylaminotin, TDMA-Sn) have low saturated vapor pressures and poor diffusion properties, making their distribution within the process chamber difficult to achieve uniformity. This necessitates extremely high requirements for gas flow uniformity. As production scales up, the size of the process chamber increases accordingly to improve capacity, further exacerbating the non-uniformity of gas flow distribution. This makes uniformity control of tin oxide thin films particularly challenging, often resulting in uneven film thickness distribution, long process debugging cycles, and difficulty in meeting stringent technical specifications in actual production.

[0004] To control the uniformity of ALD films, existing technologies typically focus on optimizing process parameters and improving gas flow distribution. For example, patent CN112838144B proposes a method for depositing alumina films on a pyramidal textured surface using a bidirectional alternating gas flow pattern. This involves alternating between inlet-outlet and outlet gas flow patterns to improve gas distribution uniformity within a relatively long reaction chamber. While this method can improve the uniformity of film coverage on complex microstructure surfaces, its reliance on periodic gas flow direction switching increases the complexity of the process sequence. Furthermore, as the chamber size increases, the gas distribution within the chamber (at the very center) still differs significantly from that at the inlet or outlet, resulting in unresolved issues regarding film deposition uniformity. Patent CN116682894B, through a process design that introduces a low-flow-rate propellant gas after each precursor is introduced, combined with a high-flow-rate purge gas, accelerates precursor diffusion within the chamber and enhances the purging effect, thereby improving batch-to-batch uniformity of the alumina film. This method focuses on improving precursor distribution and byproduct removal through airflow dynamics. However, the parameter settings for the propellant and purge gases are mainly for the reaction system of trimethylaluminum (TMA) and water. Its applicability and optimization effect for tin source systems with poorer diffusion and different reaction characteristics are still unclear. Summary of the Invention

[0005] To address the aforementioned problems, the purpose of this invention is to provide a method for controlling the uniformity of tin oxide film growth, thereby solving the problem of poor tin oxide film deposition uniformity that still exists in the prior art when depositing tin oxide films in enlarged cavities.

[0006] To achieve the above objectives, the present invention first provides a method for controlling the uniformity of tin oxide film growth, comprising the following steps: The polished silicon wafer is placed in a carrier boat, with a flow equalization device installed below it. After the wafer is placed, a vacuum is drawn, and the cavity is heated to 80-120°C. Then, a tin source is introduced sequentially, followed by a high-flow-rate argon gas purging process, a low-flow-rate argon gas purging process, an oxygen source, a high-flow-rate argon gas purging process, and a low-flow-rate argon gas purging process. This process is repeated to obtain a silicon wafer with a uniform tin oxide film deposited on its cross-section. The flow rate of the high-flow-rate argon gas is greater than that of the tin source, the flow rate of the low-flow-rate gas is the same as that of the oxygen source, and the flow rate of the high-flow-rate gas is greater than that of the low-flow-rate gas.

[0007] In one embodiment of the present invention, during the deposition of tin oxide film, tin source, oxygen source and purging gas are introduced by means of furnace inlet and furnace tail outlet, and the flow equalization device is arranged above the furnace tail outlet.

[0008] In one embodiment of the present invention, the flow equalization device includes two sets of cross-arranged partition components; each set of partition components consists of multiple transverse partition plates and multiple longitudinal partition plates arranged cross-arranged to enclose multiple gas separation grids; the transverse partition plates of the upper set of partition components are arranged perpendicularly to the transverse partition plates of the lower set of partition components; the transverse partition plates are completely fixed aluminum plates; the longitudinal partition plates are aluminum plates with a swingable movable structure at their bottom; the gas separation grids of the upper set of partition components and the gas separation grids of the lower set of partition components are vertically aligned so that the airflow can pass through the gas separation grids of the upper set of partition components and the gas separation grids of the lower set of partition components without obstruction.

[0009] In one embodiment of the present invention, the longitudinal partition plate includes an upper fixed aluminum plate and a lower movable aluminum plate, wherein the fixed aluminum plate and the movable aluminum plate are connected by a movable bearing.

[0010] In one embodiment of the present invention, the spacing between the horizontal partition plates and the spacing between the vertical partition plates in the upper partition assembly are equal to the spacing between the corresponding partition plates in the lower partition assembly, so as to ensure that the upper and lower gas partition grids are of the same size and are aligned.

[0011] In one embodiment of the present invention, the transverse partition and the longitudinal partition are arranged perpendicularly to each other.

[0012] In one embodiment of the present invention, after the cavity is heated to 80~120°C, it needs to be kept at that temperature for 100-3000 seconds.

[0013] In one embodiment of the present invention, the tin source can be an inorganic tin source such as tin tetrachloride, or an organic tin source such as tetramethyltin, tetra(dimethylamino)tin, tetraethyltin, tetra(ethylamino)tin, and tert-butyltin oxide, etc., preferably tetra(dimethylamino)tin (TDMASn).

[0014] In one embodiment of the present invention, the tin source introduced in the present invention refers to nitrogen gas carrying the tin source, wherein the flow rate of the nitrogen gas carrying the tin source is 500-30000 sccm, and the introduction time of the nitrogen gas carrying the tin source is 0.5-10s.

[0015] In one embodiment of the present invention, the flow rate of the high-flow argon gas is 1000-50000 sccm, and the purging time is 10-40s, the purpose of which is to purge the battery cross-section and gap TDMASn.

[0016] In one embodiment of the present invention, the flow rate of the low-flow argon gas is 500-30000 sccm, and the second purging time is 10-40s. The purpose is to purge the battery cross-section and gap TDMASn, and at the same time create the same pressure as when the oxygen source is introduced, so as to prevent the pressure difference from causing uneven airflow when the source is introduced.

[0017] In one embodiment of the present invention, the oxygen source is preferably water, and the introduction of the oxygen source refers to the introduction of 500-30000 sccm of water-carrying nitrogen gas for a duration of 0.5-10 seconds.

[0018] In one embodiment of the present invention, the high-flow-rate argon gas is used for three purging cycles for 10-40 seconds, the purpose of which is to purge the battery cross-section and interstitial water.

[0019] In one embodiment of the present invention, the time for the four purges with a small flow of argon gas is 10-40 seconds. The purpose is to purge the battery cross-section and gap TDMASn, and at the same time create the same pressure as when tinning, so as to prevent the pressure difference from causing uneven airflow when the power is turned on.

[0020] In one embodiment of the present invention, a cycle is formed by introducing a tin source, purging with a large flow of argon gas once, purging with a small flow of argon gas a second time, introducing an oxygen source, purging with a large flow of argon gas a third time, and purging with a small flow of argon gas a fourth time. The tin oxide deposition requires 50-200 cycles to grow a tin oxide film of a specific thickness on the cross-section.

[0021] In one embodiment of the present invention, the thickness of the tin oxide film is 5-25 nm, and the thickness difference of the tin oxide film within the silicon wafer is less than or equal to 1.0%.

[0022] The present invention also provides a tin oxide film prepared according to the above method.

[0023] The present invention also provides the application of the above-mentioned tin oxide film in photovoltaic cells.

[0024] Beneficial effects: (1) When depositing tin oxide films in a large cavity using the conventional ALD method, after introducing the tin and oxygen sources, the large size of the ALD cavity results in a significant difference in airflow pressure between the center of the cavity and the inlet and outlet. This leads to substantial differences in the thickness of the deposited films at the inlet, outlet, and center of the cavity, resulting in poor uniformity of the deposited tin oxide film. This invention addresses this by installing a flow equalization device below the silicon wafer where the tin oxide film is to be deposited. After gas is introduced, the flow equalization device redistributes the gas according to the pressure difference, which helps improve the uniformity of the airflow distribution within the cavity, thereby increasing the uniformity of the deposited tin oxide film.

[0025] (2) The flow equalization device of the present invention is designed based on Bernoulli's principle, specifically based on the relationship between airflow and pressure in Bernoulli's principle. The flow equalization device of the present invention includes gas dividing grids separated by horizontal and vertical dividing plates. A movable structure is provided below the vertical dividing plate. When the gas flow velocity between adjacent gas dividing grids is different, according to Bernoulli's principle, the grid with faster gas flow velocity has lower pressure. The different flow velocities will create a pressure difference between the front and back of the movable aluminum sheet, causing the aluminum sheet to move towards the grid with faster flow velocity, thus obstructing the flow in the grid with faster flow velocity. At the same time, it increases the bottom space of the grid with slower flow velocity, increasing its flow velocity, and finally reaching a state of equilibrium. The present invention forms a flow equalization device by placing two sets of 90° intersecting dividing components under the silicon wafer, so that the airflow is regulated in both the horizontal and vertical directions, achieving a uniform effect across the entire surface.

[0026] (3) In addition to the flow equalization device, the present invention further improves the uniformity of tin oxide film by combining process improvement. In terms of process, the purging is carried out by superimposing large and small flow rates, which not only ensures that the gas pressure difference does not affect the airflow during the power supply step, but also enhances the purging ability and improves the uniformity of film thickness.

[0027] (4) In this invention, high molecular weight inert gas argon (39.95 g / mol) is used instead of nitrogen (28 g / mol) for purging, which improves the dragging ability of reactants and by-products, improves purging efficiency, prevents reactant residues, reduces CVD reaction, and improves film thickness uniformity. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the separating component in the flow equalization device used in this invention; Figure 2 This is a schematic diagram illustrating the control principle of the flow equalization device of the present invention; Figure 3 This is a schematic diagram showing the relative positions of the flow equalization device and the silicon wafer within the cavity of the present invention. Detailed Implementation

[0029] The present invention will be further described below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0030] The structure of the separating component in the flow equalization device of the present invention is as follows: Figure 1As shown, the partition assembly consists of multiple horizontal partition plates and multiple vertical partition plates arranged in a cross pattern to enclose and form multiple gas partition grids; the horizontal partition plates are completely fixed aluminum sheets, and the vertical partition plates include upper fixed aluminum sheets and bottom movable aluminum sheets, with the fixed aluminum sheets and movable aluminum sheets connected by movable bearings.

[0031] The flow equalization device consists of two sets of cross-arranged partition components. The gas partition grids of the upper partition component and the lower partition component are vertically aligned to allow unobstructed airflow through the gas partition grids of both components. The spacing between the horizontal and vertical partition plates in the upper partition component is equal to the spacing between the corresponding partition plates in the lower partition component, ensuring that the gas partition grids of the upper and lower components are of the same size and are aligned. The relative positions of the flow equalization device and the silicon wafer in the ALD deposition chamber are as follows: Figure 3 As shown, gas enters the cavity through the furnace inlet, flows past the vertically placed silicon wafers, passes through the flow equalization device, and finally exits from the exhaust port. The principle of the separation component in the flow equalization device to regulate gas uniformity is as follows: Figure 2 As shown, when the gas flow rates between adjacent gas-separating squares are different, according to Bernoulli's principle, the square with the faster gas flow rate has lower pressure. This difference in flow rate creates a pressure difference between the front and back of the movable aluminum sheet, causing the sheet to move towards the square with the faster flow rate, thus obstructing the flow. Simultaneously, it increases the space at the bottom of the square with the slower flow rate, increasing its velocity, eventually reaching equilibrium. The flow equalization device consists of two sets of 90° intersecting separating components, allowing for separate airflow control both laterally and longitudinally, achieving a uniform flow across the entire surface.

[0032] The present invention provides an apparatus and method for optimizing the uniformity of tin oxide, comprising the following steps: The original silicon wafer is polished and then placed in a cavity equipped with a flow equalization device for processing. The process flow is as follows: (1) Evacuation and temperature control: Evacuate the chamber and maintain the temperature at 80-120℃ for 100-3000s; (2) Tin introduction: Introduce 500-30000 sccm of nitrogen carrying TDMASn for 0.5-10 s; (3) High flow rate argon purging: Introduce 1000-50000 sccm of argon gas for 10-40 seconds to purge the cell cross-section and gap TDMASn; (4) Small flow argon purging: Introduce 500-30000 sccm of argon gas for 10-40 seconds to purge the battery cross-section and gap TDMASn. At the same time, create the same pressure as when water is introduced to prevent the pressure difference from causing uneven airflow when the power source is turned on. (5) Water flow: Introduce 500-30000 sccm of water-carrying nitrogen gas for 0.5-10 seconds; (6) High flow rate argon purging: Introduce 1000-50000 sccm of argon gas for 10-40 seconds to purge the water from the cross-section and gaps of the battery; (7) Small flow argon purging: Introduce 500-30000 sccm of argon gas for 10-40s to purge the battery cross-section and gap TDMASn. At the same time, create the same pressure as when tinning to prevent pressure difference from causing uneven airflow when energizing. The above steps (2)-(7) are cycled for 50-200 cycles to grow a tin oxide film of a specific thickness, and the film thickness is tested using a full-spectrum ellipsometry.

[0033] Example 1 The original silicon wafer is polished and then placed in a cavity equipped with a flow equalization device for processing. The process is as follows: (1) Evacuation and temperature control: Evacuate the chamber and keep it at a constant temperature of 90°C for 1800 seconds; (2) Tin introduction: Introduce 30000 sccm of nitrogen carrying TDMASn for 2 seconds; (3) High flow rate argon purging: Introduce 50,000 sccm of argon gas for 10 seconds to purge the cross-section and gap of the battery TDMASn; (4) Small flow argon purging: Introduce 30000 sccm of argon gas for 10 seconds to purge the battery cross-section and gap TDMASn. At the same time, create the same pressure as when water is introduced to prevent the pressure difference from causing uneven airflow when the power source is turned on. (5) Water flow: Introduce 30,000 sccm of water-carrying nitrogen gas for 2 seconds; (6) High flow rate argon purging: Introduce 50,000 sccm of argon gas for 10 seconds to purge the water from the cross-section and gaps of the battery; (7) Small flow argon purging: Introduce 30000 sccm of argon gas for 10s to purge the battery cross-section and gap TDMASn. At the same time, create the same pressure as when tinning to prevent pressure difference from causing uneven airflow when energizing. The above steps (2)-(7) are repeated for 100 cycles to grow a tin oxide film of a specific thickness on the cross-section. The film thickness is tested using a full-spectrum ellipsometry, and the film thickness data is shown in Table 1.

[0034] Comparative Example 1 The original silicon wafer is polished and then placed in a cavity for processing. No flow equalization device is used. The process is as follows: (1) Evacuation and temperature control: Evacuate the chamber and keep it at a constant temperature of 90°C for 1800 seconds; (2) Tin introduction: Introduce 30000 sccm of nitrogen carrying TDMASn for 2 seconds; (3) High flow rate argon purging: Introduce 50,000 sccm of argon gas for 10 seconds to purge the cross-section and gap of the battery TDMASn; (4) Small flow argon purging: Introduce 30000 sccm of argon gas for 10 seconds to purge the battery cross-section and gap TDMASn. At the same time, create the same pressure as when water is introduced to prevent the pressure difference from causing uneven airflow when the power source is turned on. (5) Water flow: Introduce 30,000 sccm of water-carrying nitrogen gas for 2 seconds; (6) High flow rate argon purging: Introduce 50,000 sccm of argon gas for 10 seconds to purge the water from the cross-section and gaps of the battery; (7) Small flow argon purging: Introduce 30000 sccm of argon gas for 10s to purge the battery cross-section and gap TDMASn. At the same time, create the same pressure as when tinning to prevent pressure difference from causing uneven airflow when energizing. The above steps (2)-(7) were repeated for 100 cycles to grow a tin oxide film of a specific thickness on the cross-section. The film thickness was tested using a full-spectrum ellipsometry, and the film thickness data are shown in Table 2.

[0035] Example 2 The original silicon wafer is polished and then placed in a cavity equipped with a flow equalization device for processing. The process is as follows: (1) Evacuation and temperature control: Evacuate the chamber and keep it at a constant temperature of 90°C for 1800 seconds; (2) Tin passage: Introduce 1000 sccm of nitrogen carrying TDMASn for 10 seconds; (3) High flow rate argon purging: Introduce 2000 sccm of argon gas for 40 s to purge the cross-section and gap of the battery TDMASn; (4) Small flow argon purging: Introduce 1000 sccm of argon gas for 40 seconds to purge the cross-section and gap of the battery TDMASn. At the same time, create the same pressure as when water is introduced to prevent the pressure difference from causing uneven airflow when the power source is turned on. (5) Water flow: Introduce 1000 sccm of water-carrying nitrogen gas for 10 seconds; (6) High flow rate argon purging: Introduce 2000 sccm of argon gas for 40 seconds to purge the water from the cross-section and gaps of the battery; (7) Small flow argon purging: Introduce 1000 sccm of argon gas for 40 seconds to purge the battery cross-section and gap TDMASn. At the same time, create the same pressure as when tinning to prevent pressure difference from causing uneven airflow when energizing. The above steps (2)-(7) were repeated for 100 cycles to grow a tin oxide film of a specific thickness on the cross-section. The film thickness was tested using a full-spectrum ellipsometry, and the film thickness data are shown in Table 3.

[0036] Comparative Example 2 The difference between Comparative Example 2 and Example 2 is that, instead of using alternating large and small flow rates of argon gas for purging, argon gas was used for a single purging.

[0037] The original silicon wafer is polished and then placed in a cavity equipped with a flow equalization device for processing. The process is as follows: (1) Evacuation and temperature control: Evacuate the chamber and keep it at a constant temperature of 90°C for 1800 seconds; (2) Tin passage: Introduce 1000 sccm of nitrogen carrying TDMASn for 10 seconds; (3) Argon purging: Introduce 1000 sccm of argon gas for 80 seconds to purge the cross-section and gap of the battery TDMASn. At the same time, create the same pressure as when water is introduced to prevent the pressure difference from causing uneven airflow when the power source is turned on. (4) Water flow: Introduce 1000 sccm of water-carrying nitrogen gas for 10 seconds; (5) Argon purging: Introduce 1000 sccm of argon gas for 80 seconds to purge the battery cross-section and gap TDMASn. At the same time, create the same pressure as when tinning to prevent uneven airflow caused by pressure difference when powering on. The above steps (2)-(5) were repeated for 100 cycles to grow a tin oxide film of a specific thickness on the cross-section. The film thickness was tested using a full-spectrum ellipsometry, and the film thickness data are shown in Table 4.

[0038] Comparative Example 3 The difference between Comparative Example 3 and Comparative Example 2 is that the flow rate is different when using argon gas for a single purging.

[0039] The original silicon wafer is polished and then placed in a cavity equipped with a flow equalization device for processing. The process is as follows: (1) Evacuation and temperature control: Evacuate the chamber and keep it at a constant temperature of 90°C for 1800 seconds; (2) Tin passage: Introduce 1000 sccm of nitrogen carrying TDMASn for 10 seconds; (3) Argon purging: Introduce 2000 sccm of argon gas for 80 seconds to purge the cross-section and gap of the battery TDMASn. At the same time, create the same pressure as when water is introduced to prevent the pressure difference from causing uneven airflow when the power is turned on. (4) Water flow: Introduce 1000 sccm of water-carrying nitrogen gas for 10 seconds; (5) Argon purging: Introduce 2000 sccm of argon gas for 80 seconds to purge the battery cross-section and gap TDMASn. At the same time, create the same pressure as when tinning to prevent uneven airflow caused by pressure difference when powering on. The above steps (2)-(5) were repeated for 100 cycles to grow a tin oxide film of a specific thickness on the cross-section. The film thickness was tested using a full-spectrum ellipsometry, and the film thickness data are shown in Table 5.

[0040] Example 3 The original silicon wafer is polished and then placed in a cavity equipped with a flow equalization device for processing. The process is as follows: (1) Evacuation and temperature control: Evacuate the chamber and keep it at a constant temperature of 90°C for 1800 seconds; (2) Tin introduction: Introduce 10000 sccm of nitrogen carrying TDMASn for 2 seconds; (3) High flow rate argon purging: Introduce 20000 sccm of argon gas for 10 s to purge the cross-section and gap of the battery TDMASn; (4) Small flow argon purging: Introduce 10000 sccm of argon gas for 10s to purge the battery cross-section and gap TDMASn. At the same time, create the same pressure as when water is introduced to prevent the pressure difference from causing uneven airflow when the power source is turned on. (5) Water flow: Introduce 10000 sccm of water-carrying nitrogen gas for 2 seconds; (6) High flow rate argon purging: Introduce 20000 sccm of argon gas for 10 seconds to purge the cross-section of the battery and the water in the gaps; (7) Small flow argon purging: Introduce 10000 sccm of argon gas for 10s to purge the battery cross-section and gap TDMASn. At the same time, create the same pressure as when tinning to prevent pressure difference from causing uneven airflow when energizing. The above steps (2)-(7) are repeated for 100 cycles to grow a tin oxide film of a specific thickness on the cross-section. The film thickness is tested using a full-spectrum ellipsometry, and the film thickness data is shown in Table 6.

[0041] Comparative Example 4 The difference between Comparative Example 4 and Example 3 is that nitrogen gas was used for purging.

[0042] The original silicon wafer is polished and then placed in a cavity equipped with a flow equalization device for processing. The process is as follows: (1) Evacuation and temperature control: Evacuate the chamber and keep it at a constant temperature of 90°C for 1800 seconds; (2) Tin introduction: Introduce 10000 sccm of nitrogen carrying TDMASn for 2 seconds; (3) High flow rate nitrogen purging: Introduce 20000 sccm of nitrogen for 10 s to purge the battery cross-section and gap TDMASn; (4) Small flow nitrogen purging: Introduce 10000 sccm of nitrogen for 10s to purge the battery cross-section and gap TDMASn. At the same time, create the same pressure as when water is introduced to prevent the pressure difference from causing uneven airflow when the power is turned on. (5) Water flow: Introduce 10000 sccm of water-carrying nitrogen gas for 2 seconds; (6) High flow rate nitrogen purging: Introduce 20,000 sccm of nitrogen for 10 seconds to purge water from the battery cross-section and gaps; (7) Small flow nitrogen purging: Introduce 10000 sccm of nitrogen for 10s to purge the battery cross-section and gap TDMASn. At the same time, create the same pressure as when tinning to prevent pressure difference from causing uneven airflow when powering on. The above steps (2)-(7) are repeated for 100 cycles to grow a tin oxide film of a specific thickness on the cross-section. The film thickness is tested using a full-spectrum ellipsometry, and the film thickness data is shown in Table 7.

[0043] Table 1. Thickness and uniformity of tin oxide films at different locations within the carrier boat and silicon wafer in Example 1.

[0044] Table 2. Thickness and uniformity of tin oxide films at different locations within the carrier boat and silicon wafer in Comparative Example 1.

[0045] Table 3. Thickness and uniformity of tin oxide films at different locations within the carrier boat and silicon wafer in Example 2.

[0046] Table 4. Thickness and uniformity of tin oxide films at different locations within the carrier boat and silicon wafer in Comparative Example 2.

[0047] Table 5. Thickness and uniformity of tin oxide films at different locations within the carrier boat and silicon wafer in Comparative Example 3.

[0048] Table 6. Thickness and uniformity of tin oxide films at different locations within the carrier boat and silicon wafer in Example 3.

[0049] Table 7. Thickness and uniformity of tin oxide films at different locations within the carrier boat and silicon wafer in Comparative Example 4.

[0050] From the experiments in Example 1 and Comparative Example 1, and the data in Tables 1 and 2, it can be seen that the film thickness uniformity deteriorated after the flow equalization device of the present invention was removed. This indicates that the flow equalization device of the present invention has a regulating effect on the gas, which can make the gas flow more uniform and improve the uniformity of tin oxide film thickness.

[0051] From the experiments in Examples 2, 2, and 3, and the data in Tables 3, 4, and 5, it can be seen that if only a high-flow-rate purging is used after introducing the tin source, the inter-wafer uniformity will differ significantly. Reducing the gas flow rate during purging will further increase the inter-wafer uniformity, but the intra-wafer and inter-wafer uniformity will still be relatively large. This invention combines high-flow-rate purging with low-flow-rate purging. The high flow rate increases the purging capacity without increasing the process time, while the low-flow-rate purging flow rate is consistent with the source-introduction step, used to balance pressure during process step switching. This prevents gas inhomogeneity caused by differences in flow rates between the purging and source-introduction steps, improves gas uniformity, and ultimately optimizes film thickness uniformity.

[0052] As can be seen from the experiments in Example 3 and Comparative Example 4, combined with the data in Tables 6 and 7, the argon gas used in this invention has a stronger purging ability than nitrogen gas, which can further optimize the film thickness uniformity.

[0053] Based on all embodiments, comparative examples, and the results obtained, this solution optimizes airflow uniformity at the hardware level by adding a flow equalization device, then uses a gas with stronger purging capacity and a high-flow-rate superimposed low-flow-rate purging, greatly enhancing the purging effect. Further optimization of the purging process was achieved, ultimately significantly improving the uniformity of tin oxide film thickness, providing a good foundation for subsequent optimization of the electron transport layer in perovskite solar cells.

[0054] Based on this result, this method can also be applied to various tubular optimization of film uniformity.

[0055] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for controlling the uniformity of tin oxide film growth, characterized in that, Includes the following steps: The polished silicon wafer is placed in a carrier boat, with a flow equalization device installed below it. After the wafer is placed, a vacuum is drawn, and the cavity is heated. Once the temperature reaches 80-120°C, a tin source is sequentially introduced, followed by a high-flow-rate argon gas purging process, a low-flow-rate argon gas purging process, an oxygen source, a high-flow-rate argon gas purging process, and a low-flow-rate argon gas purging process. This process is repeated to obtain a silicon wafer with a uniform tin oxide film deposited on its cross-section. The flow rate of the high-flow-rate argon gas is greater than the flow rate of the tin source, the flow rate of the low-flow-rate gas is the same as the flow rate of the oxygen source, and the flow rate of the high-flow-rate gas is greater than the flow rate of the low-flow-rate gas. The flow equalization device includes two sets of cross-arranged partition components. Each set of partition components consists of multiple horizontal partition plates and multiple vertical partition plates arranged in a cross pattern to form multiple gas separation grids. The horizontal partition plates of the upper set of partition components are perpendicular to the horizontal partition plates of the lower set of partition components. The horizontal partition plates are completely fixed aluminum plates. The vertical partition plates are aluminum plates with a swingable structure at their bottom. The gas separation grids of the upper set of partition components and the gas separation grids of the lower set of partition components are vertically aligned so that the airflow can pass through the gas separation grids of the upper set of partition components and the gas separation grids of the lower set of partition components without obstruction.

2. The method according to claim 1, characterized in that, The longitudinal partition plate includes an upper fixed aluminum plate and a lower movable aluminum plate, which are connected by a movable bearing.

3. The method according to claim 1, characterized in that, The tin source is selected from at least one of inorganic tin sources or organic tin sources. The inorganic tin source includes tin tetrachloride, and the organic tin source is selected from at least one of tetramethyltin, tetra(dimethylamino)tin, tetraethyltin, tetra(ethylamino)tin, and tert-butyltin oxide. The tin source is introduced by introducing nitrogen gas carrying the tin source. The flow rate of the nitrogen gas carrying the tin source is 500-30000 sccm, and the introduction time of the nitrogen gas carrying the tin source is 0.5-10s.

4. The method according to claim 1, characterized in that, The flow rate of the high-flow-rate argon gas is 1000-50000 sccm, and the purging time is 10-40 s.

5. The method according to claim 1, characterized in that, The flow rate of the low-flow argon gas is 500-30000 sccm, and the second purging time is 10-40 s.

6. The method according to claim 1, characterized in that, The oxygen source is water, and the oxygen source is introduced by introducing 500-30000 sccm of water-carrying nitrogen gas for 0.5-10 seconds.

7. The method according to claim 1, characterized in that, The high-flow-rate argon gas is used for three purging cycles for 10-40 seconds, and the low-flow-rate argon gas is used for four purging cycles for 10-40 seconds.

8. The method according to claim 1, characterized in that, A cycle consists of introducing a tin source, purging with a high flow rate of argon gas for one purging, purging with a low flow rate of argon gas for a second purging, introducing an oxygen source, purging with a high flow rate of argon gas for a third purging, and purging with a low flow rate of argon gas for a fourth purging. The tin oxide deposition process involves 50-200 cycles. The thickness of the tin oxide film is 5-25 nm, and the thickness difference of the tin oxide film within the silicon wafer is less than or equal to 1.0%.

9. The tin oxide film prepared by the method according to any one of claims 1 to 8.

10. The application of the tin oxide film according to claim 9 in photovoltaic cells.

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