A thin film deposition method based on PECVD and a thin film deposition method for solar cells

Abstract

The present invention discloses a thin film deposition method based on PECVD and a thin film deposition method for solar cells. According to the thin film deposition method based on PECVD of the present invention, a thin film is deposited on the surface of a substrate, comprising the following steps: placing the substrate in a coating chamber; evacuating the coating chamber; introducing a process gas into the coating chamber; and causing a radio frequency power supply to output alternately at different pulse ratios; wherein the pulse ratios include at least a first pulse ratio and a second pulse ratio, the second pulse ratio being greater than the first pulse ratio, and the radio frequency power supply outputting alternately at the first pulse ratio and the second pulse ratio. The thin film deposition method based on PECVD of the present invention can, to a certain extent, achieve both uniform film thickness and shorten process time.

Description

Technical Field

[0001] The present invention relates to the technical field of PECVD process technology, and in particular to a thin film deposition method based on PECVD and a thin film deposition method for solar cells. Background Art

[0002] Thin films deposited based on the PECVD method (Plasma Enhanced Chemical Vapor Deposition) have excellent electrical properties and good substrate adhesion, and are widely used in fields such as ultra-large-scale integrated circuits, optoelectronic devices, and MEMS.

[0003] For example, RF-PECVD (radio frequency-enhanced plasma chemical vapor deposition) is widely used in the deposition of doped silicon-based thin films in solar cells. During this deposition process, different reactant gases are introduced depending on the desired film composition. Under the glow discharge action of an RF power source, the power is regularly output according to the set pulse on / off ratio, ionizing the mixed gas to form a plasma, which deposits the desired film on the silicon wafer.

[0004] During the deposition step, assuming other process parameters remain unchanged, the smaller the RF power supply's pulse on-off ratio, the slower the deposition rate and the more uniform the deposited film. The larger the RF power supply's pulse on-off ratio, the faster the deposition rate and the more uneven the deposited film. Therefore, in order to obtain a suitable thin film in the shortest possible deposition time, it is necessary to select an appropriate pulse on-off ratio range. However, despite this, with the increasing demand for cost reduction and process time reduction, even with optimized process parameters, it is difficult to achieve both film thickness uniformity and process time. Summary of the Invention

[0005] To address this issue, the present invention proposes a thin film deposition method based on PECVD, which can achieve both uniform film thickness and shortened process time to a certain extent. Furthermore, the present invention also proposes a thin film deposition method for solar cells.

[0006] According to the first aspect of the present invention, a PECVD-based thin film deposition method deposits a coating on the surface of a substrate, comprising the following steps: placing the substrate in a coating chamber; evacuating the coating chamber; introducing process gas into the coating chamber; and causing a radio frequency power supply to output alternately at different pulse ratios; wherein the pulse ratios include at least a first pulse ratio and a second pulse ratio, the second pulse ratio being greater than the first pulse ratio, and the radio frequency power supply outputs alternately at the first pulse ratio and the second pulse ratio.

[0007] The thin film deposition method based on PECVD according to the first aspect of the present invention can achieve both uniformity of film thickness and shortened process time to a certain extent.

[0008] In some embodiments, the first pulse ratio ranges from 1:25 to 1:15, and the second pulse ratio ranges from 1:12.5 to 1:7.5.

[0009] In some embodiments, multiple layers of thin films are deposited on the same surface of the substrate; when depositing each layer of thin film, the RF power supply is output alternately at the first pulse ratio and the second pulse ratio.

[0010] In some embodiments, when depositing different thin films, among the pulse ratios output by the RF power supply, at least the first pulse ratio has a different magnitude.

[0011] According to the second aspect of the thin film deposition method for a solar cell of the present invention, a thin film is deposited on the surface of a solar cell serving as a substrate using any of the above-mentioned PECVD-based thin film deposition methods.

[0012] The thin film deposition method for a solar cell according to the second aspect of the present invention can achieve both uniformity in film thickness and shortened process time to a certain extent.

[0013] In some embodiments, a silicon nitride film and a silicon oxynitride film are deposited on the surface of the solar cell, wherein, when depositing the silicon nitride film, the first pulse ratio is in a range of greater than 1:17 and less than 1:15, and the second pulse ratio is in a range of greater than 1:12.5 and less than 1:7.5; when depositing the silicon oxynitride film, the first pulse ratio is in a range of greater than 1:25 and less than 1:15, and the second pulse ratio is in a range of greater than 1:12.5 and less than 1:7.5.

[0014] In some embodiments, the silicon nitride film is a graded film, and when the graded layers of the silicon nitride film are sequentially deposited from the inside to the outside, at least the first pulse ratio becomes larger sequentially.

[0015] In some embodiments, the silicon nitride film has at least a first layer, a second layer and a third layer from the inside to the outside; wherein, when depositing the first layer, 2160 sccm of silane and 9350 sccm of ammonia are introduced as process gases, the first pulse ratio is 1:17, and the second pulse ratio is 1:8.5; when depositing the second layer, 1465 sccm of silane and 10780 sccm of ammonia are introduced as process gases, the first pulse ratio is 1:16, and the second pulse ratio is 1:8; when depositing the third layer, 1275 sccm of silane and 11250 sccm of ammonia are introduced as process gases, the first pulse ratio is 1:15, and the second pulse ratio is 1:7.5.

[0016] In some embodiments, the silicon oxynitride film is a gradient film, and when the gradient layers of the silicon oxynitride film are sequentially deposited from the inside out, the first pulse ratio of each layer is the same and the second pulse ratio of each layer is the same.

[0017] In some embodiments, before the step of alternately outputting the RF power supply at different pulse ratios, the method further includes: heating the coating chamber to a preset temperature according to different positions along the axial direction of the coating chamber. DETAILED DESCRIPTION

[0018] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0019] In the following examples, the process methods without specific conditions are generally carried out in accordance with conventional conditions in the art or the conditions recommended by the manufacturer; the raw materials used, unless otherwise specified, are all raw materials available from commercial channels such as conventional markets.

[0020] According to the first embodiment, a PECVD-based thin film deposition method is used to deposit a coating on the surface of a substrate. The method includes the following steps:

[0021] S101: placing the substrate in a coating chamber.

[0022] S102: vacuuming the coating chamber.

[0023] S103: Introduce process gas into the coating chamber.

[0024] S104: Alternately outputting the RF power supply at different pulse ratios. The pulse ratios include at least a first pulse ratio and a second pulse ratio, wherein the second pulse ratio is greater than the first pulse ratio. The RF power supply alternately outputs the first pulse ratio and the second pulse ratio.

[0025] According to the thin film deposition method based on PECVD of this embodiment, it is possible to achieve both uniformity of film thickness and shorten process time to a certain extent.

[0026] The PECVD method of this embodiment is, for example, based on a capacitively coupled plasma device. During the deposition step, assuming other process parameters remain constant, a smaller RF power supply pulse on / off ratio results in a slower deposition rate and a more uniform deposited film layer. A larger RF power supply pulse on / off ratio results in a faster deposition rate and a more uneven deposited film layer. Conventional techniques typically select a pulse ratio range that balances film thickness uniformity and process time. For example, a pulse ratio range of 1:16 to 1:12 is considered sufficient to achieve both film thickness uniformity and process time reduction. However, this process time may sometimes still not meet the required requirements.

[0027] In this embodiment, by making the RF power supply output alternately with different pulse ratios, that is, changing the RF power supply glow discharge from a fixed-period pulse on-off ratio output to a pulse ratio output alternating between long and short periods, it is possible to increase the deposition rate and reduce the deposition time to a certain extent without changing the process parameters and maintaining the deposition effect.

[0028] Examples of the substrate include sheets such as silicon wafers for solar cells, and sheets such as silicon wafers and glass for semiconductor devices.

[0029] When a single, fixed pulse ratio is selected, the pulse ratio of the RF power supply is preferably in the range of 1:16 or more and 1:12 or less. When the pulse ratio is less than 1:16, the deposition time may be too long, resulting in increased production costs. When the pulse ratio is greater than 1:12.5, dust will be generated, and this dust will adhere to the surface of the substrate, thereby affecting the deposition quality. For example, based on the current PECVD process with large production capacity and graphite boat loading, in order to shorten the deposition time, the RF power supply power is set to a higher level. Under this condition, when the pulse ratio is greater than 1:12, the deposition rate will become very fast, the uniformity and density of the deposited film thickness will deteriorate, and the quality of the deposited film will be difficult to meet the process effect requirements.

[0030] However, in the case where the RF power supply is output alternately with different pulse ratios as in the present embodiment, the range of the pulse ratio of the RF power supply is preferably greater than 1:25 and less than 1:7.5. Specifically, the range of the first pulse ratio can be greater than 1:25 and less than 1:15, and the range of the second pulse ratio is greater than 1:12.5 and less than 1:7.5. As the range of the first pulse ratio, selecting greater than 1:25 and less than 1:15 can improve the uniformity and density of the deposited film layer. As the range of the second pulse ratio, selecting greater than 1:12.5 and less than 1:7.5 can improve the deposition rate. By selecting two pulse ratios for alternate output, it is possible to compensate to a certain extent for the problem of increased production costs due to too low a pulse ratio or affecting deposition quality due to too high a pulse ratio in the case of a single, fixed pulse ratio, and to a certain extent achieve both uniformity of film thickness and shortened process time.

[0031] Furthermore, although an example has been given in which the pulse ratio has two different pulse ratios, namely the first pulse ratio and the second pulse ratio, the present invention is not limited thereto, and the pulse ratio may have three or more different pulse ratios.

[0032] In some embodiments, multiple thin films may be deposited on the same surface of a substrate. During the deposition of each thin film layer, the RF power supply is alternately output at a first pulse ratio and a second pulse ratio. For example, taking the film layers on the surface of a solar cell as an example, the n-side (or p-side) of the solar cell may include a silicon nitride film, a silicon oxynitride film, and a silicon oxide film. During the deposition of these different thin films, the RF power supply can be alternately output at the first pulse ratio and the second pulse ratio, thereby achieving a certain degree of uniformity in film thickness and shortening process time.

[0033] Furthermore, when depositing different thin films, the pulse ratios output by the RF power supply, at least the first pulse ratio, may vary. For example, because different thin films require different process gas compositions or concentrations, or to ensure that the final film quality meets requirements, the first pulse ratio may be appropriately adjusted for different film types to ensure that the deposited film thickness, refractive index, uniformity, and density meet overall requirements.

[0034] As a specific embodiment, the PECVD-based thin film deposition method of the first embodiment can be used to deposit thin films on solar cells. That is, according to the second embodiment, the thin film deposition method for solar cells can use any of the above-mentioned PECVD-based thin film deposition methods to deposit a thin film on the surface of a solar cell serving as a substrate.

[0035] The thin film deposition method for solar cells using the above-mentioned PECVD-based thin film deposition method can achieve both uniformity in film thickness and shortened process time to a certain extent.

[0036] In some embodiments, the PECVD-based thin film deposition method can be used to deposit a silicon nitride film and a silicon oxynitride film on the surface of a solar cell. Preferably, when depositing a silicon nitride film, the first pulse ratio is in the range of 1:17 or more and 1:15 or less, and the second pulse ratio is in the range of 1:12.5 or more and 1:7.5 or less. In addition, when depositing a specific layer of silicon nitride film, it is preferred that the pulse-off time of the second pulse ratio is 50% of the pulse-off time of the first pulse ratio. When depositing a silicon oxynitride film, the first pulse ratio is in the range of 1:25 or more and 1:15 or less, and the second pulse ratio is in the range of 1:12.5 or more and 1:7.5 or less. In addition, when depositing a specific layer of silicon oxynitride film, it is preferred that the pulse-off time of the second pulse ratio is 75% of the pulse-off time of the first pulse ratio.

[0037] Furthermore, in some embodiments, the silicon nitride film is a graded film. As the graded layers of silicon nitride film are deposited from the inside out, at least the first pulse ratio increases sequentially. Due to the passivation requirements for the process film layers, the refractive index distribution of the film layers gradually changes from high to low refractive index. The first film layer must be deposited with relatively high uniformity and density (a high refractive index film layer), and the thickness of the deposited film increases sequentially from high to low refractive index films. Therefore, deposition is performed by gradually increasing the pulse ratio toward the lower refractive index, ensuring a passivation effect with uniformity and density while minimizing deposition time.

[0038] Furthermore, as described above, when the silicon oxynitride film is a graded film, when the graded layers of silicon oxynitride film are deposited sequentially from the inside out, the first pulse ratio for each layer is the same, and the second pulse ratio for each layer is the same. The special gases required for the silicon oxynitride reaction are silane, nitrous oxide, and ammonia. The addition of nitrous oxide makes the reaction process very intense and the deposition rate very fast, resulting in poor uniformity and density of the deposited silicon oxynitride film and difficulty in control. Therefore, the reaction rate is reduced, and the pulse on / off ratio is decreased to improve uniformity and density. Furthermore, due to the extremely fast reaction rate of nitrous oxide when added, silicon can be oxidized even in the absence of a glow (no power supply). Furthermore, even with two different substances, the same pulse ratio can result in different reaction rates. Therefore, when nitrous oxide is introduced, the first pulse ratio for each layer can be the same, and the second pulse ratio for each layer can also be the same.

[0039] In addition, as described above, before the step of causing the RF power supply to output alternately at different pulse ratios, it also includes: within the coating chamber, heating to a preset temperature according to different positions along the axial direction of the coating chamber. For example, the temperature decreases successively from the furnace mouth to the furnace tail of the coating chamber. For example, 6 temperature zones can be divided in sequence from the furnace mouth to the furnace tail of the coating chamber, and temperature zones 1-6 are heated to 545°C, 540°C, 535°C, 535°C, 530°C and 525°C respectively and kept at a constant temperature. Therefore, referring to the embodiment and the comparative example, it can be seen that the thickness of the thin film deposition at each position of the furnace mouth, the furnace and the furnace tail can be made roughly the same. In addition, it should be noted that the constant temperature interval can allow a certain range of floating, for example, a floating of ±10°C can be allowed.

[0040] The thin film deposition method for a solar cell according to this embodiment is described below with reference to specific examples.

[0041] [Example 1]

[0042] On a horizontal PECVD system, a silicon nitride film, a silicon oxynitride film, and a silicon oxide film are sequentially deposited on the surface of the solar cell. The silicon nitride film is a graded film, with a first, second, and third layer from the inside out. The silicon oxynitride film is also a graded film, with a first and second layer from the inside out. The silicon oxide film is a single layer.

[0043] Solar cells are placed on graphite boats, with multiple solar cells placed on one graphite boat. The graphite boats are then transported into the furnace (coating chamber) of the PECVD equipment using a known boat pusher.

[0044] Specifically, the thin film deposition is completed according to the following steps.

[0045] S200: boat loading step, the graphite boat carrying the solar cells is grabbed from the docking station by the manipulator of the boat pushing device and placed on the boat pushing paddle.

[0046] S201: Boat entry step, the graphite boat is sent into the furnace (i.e., the coating chamber) of the PECVD equipment through the paddle, and the furnace door is closed.

[0047] Furthermore, after the furnace door is closed, the interior is divided into six temperature zones from the furnace entrance to the furnace tail, each with a preset temperature. For example, temperature zones 1-6 from the furnace entrance to the furnace tail are set to 545°C, 540°C, 535°C, 535°C, 530°C, and 525°C, respectively. Because the plasma concentration is higher at the furnace tail than at the furnace entrance, the preset temperature at the furnace tail is slightly lower than that at the furnace entrance, thereby improving the uniformity of the coating thickness of the solar cells at various locations within the furnace.

[0048] In order to make the constant temperature in the following constant temperature step faster, the nitrogen gas in the furnace is set to 10,000 sccm and the pressure in the furnace is set to 10,000 mtorr.

[0049] S202: Constant temperature step, constant temperature in the furnace from normal pressure to set temperature.

[0050] Specifically, the nitrogen in the furnace is set to 0 sccm, the pressure in the furnace is set to 10,000 mtorr, the auxiliary heating is turned on (the temperature is set to 550°C), and the temperature zones 1-6 are heated to 545°C, 540°C, 535°C, 535°C, 530°C and 525°C respectively and kept constant.

[0051] S203: The first vacuuming step is to open the main vacuum valve to evacuate the furnace to a vacuum bottom pressure state.

[0052] S204: Leak detection step, close the main pumping valve and check whether the pressure in the furnace recovers from the bottom pressure at a normal rate (leak rate standard <120mtorr / min)

[0053] S205: The second vacuuming step is to open the main vacuum valve to reduce the pressure in the furnace to the vacuum bottom pressure state. The furnace nitrogen is set to 0 sccm and the pressure in the furnace is set to 0 mtorr.

[0054] S206: Constant pressure step, open the main pumping valve, and in addition, introduce the process gas required for depositing the silicon nitride film into the furnace, keep the pressure constant to the pressure required for the deposition step, and provide the atmosphere field required for the deposition step.

[0055] In the constant pressure step, the temperature zones 1-6 in the furnace are set to 545°C, 540°C, 535°C, 535°C, 530°C, and 525°C respectively, the silane in the furnace is 2160sccm, the ammonia is set to 9350sccm, the nitrous oxide is set to 0sccm, and the pressure in the furnace is 1500mtorr.

[0056] S207: A first deposition step is to turn on the RF power supply to glow-ionize the mixed gas, wherein the RF power supply is alternately output at a pulse ratio of 1:17 (first pulse ratio) and a pulse ratio of 1:8.5 (second pulse ratio), thereby depositing a first layer of silicon nitride film.

[0057] In the first deposition step, the temperature zones 1-6 in the furnace are set to 545°C, 540°C, 535°C, 535°C, 530°C, and 525°C respectively, the silane in the furnace is 2160sccm, the ammonia is 9350sccm, the nitrous oxide is 0sccm, the pressure in the furnace is 1500mtorr, the power is 25.5KW, the pulse on setting of the first pulse ratio is 5ms, the pulse off setting is 85ms, the pulse on setting of the second pulse ratio is 5ms, and the pulse off setting is 42.5ms.

[0058] S208: In the second deposition step, the main pumping valve is opened. Furthermore, the process gas required for depositing the silicon nitride film is introduced into the furnace, maintained at a constant pressure required for the deposition step, and the required atmosphere field is provided. The RF power supply is turned on to glow-ionize the mixed gas. The RF power supply is alternately output at a pulse ratio of 1:16 (a first pulse ratio) and a pulse ratio of 1:8 (a second pulse ratio), thereby depositing the second layer of the silicon nitride film.

[0059] In the second deposition step, the temperature zones 1-6 in the furnace are set to 545°C, 540°C, 535°C, 535°C, 530°C, and 525°C respectively, the silane in the furnace is 1465sccm, the ammonia is set to 10780sccm, the nitrous oxide is set to 0sccm, the pressure in the furnace is 1550mtorr, the power is 27KW, the pulse on setting of the first pulse ratio is 5ms, and the pulse off setting is 80ms; the pulse on setting of the second pulse ratio is 5ms, and the pulse off setting is 40ms.

[0060] S209: In the third deposition step, the main pumping valve is opened. Furthermore, the process gas required for depositing the silicon nitride film is introduced into the furnace, maintained at a constant pressure required for the deposition step, and the required atmosphere field is provided. The RF power supply is turned on to glow-ionize the mixed gas. The RF power supply is alternately output at a pulse ratio of 1:15 (a first pulse ratio) and a pulse ratio of 1:7.5 (a second pulse ratio), thereby depositing the third layer of the silicon nitride film.

[0061] In the third deposition step, the temperature zones 1-6 in the furnace are set to 545°C, 540°C, 535°C, 535°C, 530°C, and 525°C respectively, the silane in the furnace is 1275sccm, the ammonia is set to 11250sccm, the nitrous oxide is set to 0sccm, the pressure in the furnace is 1550mtorr, the power is 27KW, the pulse on setting of the first pulse ratio is 5ms, and the pulse off setting is 75ms; the pulse on setting of the second pulse ratio is 5ms, and the pulse off setting is 37.5ms.

[0062] S210: A fourth deposition step is to turn on the RF power supply to glow-ionize the mixed gas, wherein the RF power supply is alternately output at a pulse ratio of 1:25 (first pulse ratio) and a pulse ratio of 1:12.5 (second pulse ratio), thereby depositing a first layer of the silicon oxynitride film.

[0063] In the fourth deposition step, the temperature zones 1-6 in the furnace are set to 545°C, 540°C, 535°C, 535°C, 530°C, and 525°C respectively, the silane in the furnace is 1075sccm, the ammonia is 4705sccm, and the nitrous oxide is 6720sccm. The pressure in the furnace is 1450mtorr, the power is 25.5KW, the pulse on setting of the first pulse ratio is 5ms, and the pulse off setting is 125ms. The pulse on setting of the second pulse ratio is 5ms, and the pulse off setting is 62.5ms.

[0064] S211: In the fifth deposition step, the main pumping valve is opened. Furthermore, the process gas required for depositing the silicon oxynitride film is introduced into the furnace, maintained at a constant pressure required for the deposition step, and the required atmosphere is provided. The RF power supply is turned on to glow-ionize the mixed gas. The RF power supply is alternately output at a pulse ratio of 1:25 (first pulse ratio) and a pulse ratio of 1:12.5 (second pulse ratio), thereby depositing the second layer of the silicon oxynitride film.

[0065] In the fifth deposition step, the temperature zones 1-6 in the furnace are set to 545°C, 540°C, 535°C, 535°C, 530°C, and 525°C respectively, the silane in the furnace is 810sccm, the ammonia is 3675sccm, and the nitrous oxide is 8080sccm. The pressure in the furnace is 1450mtorr, the power is 25.5KW, the pulse on setting of the first pulse ratio is 5ms, and the pulse off setting is 125ms; the pulse on setting of the second pulse ratio is 5ms, and the pulse off setting is 62.5ms.

[0066] S212: a sixth deposition step, turning on the RF power supply to glow-ionize the mixed gas, wherein the RF power supply is alternately output at a pulse ratio of 1:25 (first pulse ratio) and a pulse ratio of 1:12.5 (second pulse ratio), thereby depositing a first layer of the silicon oxide film.

[0067] In the sixth deposition step, the temperature zones 1-6 in the furnace are set to 545°C, 540°C, 535°C, 535°C, 530°C, and 525°C respectively, the silane in the furnace is 900sccm, the ammonia is 0sccm, the nitrous oxide is 11660sccm, the pressure in the furnace is 1400mtorr, the power is 22.5KW, the pulse on setting of the first pulse ratio is 5ms, the pulse off setting is 125ms, the pulse on setting of the second pulse ratio is 5ms, and the pulse off setting is 62.5ms.

[0068] In addition, after the deposition of the surface film layer is completed, the following steps are performed, for example.

[0069] S213: The third vacuuming step is to open the main vacuum valve to pump the pressure in the furnace after deposition to the vacuum bottom pressure state.

[0070] In the third vacuum step, the temperature zones 1-6 in the furnace were set to 545°C, 540°C, 535°C, 535°C, 530°C, and 525°C, respectively. All gases in the furnace were 0 sccm, and the pressure in the furnace was set to 0 mtorr.

[0071] S214: Cleaning step, open the main pumping valve, and introduce nitrogen gas to purge the furnace tube under vacuum bottom pressure.

[0072] During the cleaning step, the temperature zones 1-6 in the furnace were set to 545°C, 540°C, 535°C, 535°C, 530°C, and 525°C, respectively; the nitrogen in the furnace was set to 20,000 sccm; and the pressure in the furnace was set to 0 mtorr.

[0073] S215: The fourth vacuuming step is to open the main vacuum valve to pump the pressure in the cleaned furnace to the vacuum bottom pressure state.

[0074] In the fourth vacuum step, the temperature zones 1-6 in the furnace were set to 545°C, 540°C, 535°C, 535°C, 530°C, and 525°C, respectively. All gases in the furnace were 0 sccm, and the pressure in the furnace was set to 0 mtorr.

[0075] S216: Back pressure step, close the main pumping valve, and introduce nitrogen gas under vacuum bottom pressure to raise the pressure to normal pressure.

[0076] In the back pressure step, the temperature zones 1-6 in the furnace were set to 545°C, 540°C, 535°C, 535°C, 530°C, and 525°C, respectively; the nitrogen in the furnace was set to 50,000 sccm; and the pressure in the furnace was set to 10,000 mtorr.

[0077] S217: Boat unloading step, transferring the graphite boat from the heating furnace to the boat pusher. The manipulator of the boat pusher device grabs the graphite boat from the boat pusher and places it on the docking station.

[0078] Thus, the silicon nitride film, the silicon oxynitride film and the silicon oxide film are sequentially deposited on the surface of the solar cell. In addition, for the specific process parameter settings of Example 1, refer to Table 1.

[0079] [Table 1]

[0080]

[0081] [Example 2]

[0082] In addition, in Example 2, a thin film of substantially the same thickness is deposited in substantially the same steps as in Example 1. The difference lies in the magnitude of the second pulse ratio, namely:

[0083] In S207: a first deposition step, the RF power supply is alternately output at a pulse ratio of 1:17 (a first pulse ratio) and a pulse ratio of 1:12.75 (a second pulse ratio), thereby depositing a first layer of silicon nitride film. The first pulse ratio has a pulse on setting of 5 ms and a pulse off setting of 85 ms, while the second pulse ratio has a pulse on setting of 5 ms and a pulse off setting of 63.75 ms.

[0084] In step S208: a second deposition step, the RF power supply is alternately output at a pulse ratio of 1:16 (a first pulse ratio) and a pulse ratio of 1:12 (a second pulse ratio), thereby depositing a second layer of the silicon nitride film. The first pulse ratio has a pulse on setting of 5 ms and a pulse off setting of 80 ms, while the second pulse ratio has a pulse on setting of 5 ms and a pulse off setting of 60 ms.

[0085] In step S209: the third deposition step, the RF power supply is alternately output at a pulse ratio of 1:15 (first pulse ratio) and a pulse ratio of 1:11.25 (second pulse ratio), thereby depositing a third layer of silicon nitride film. The first pulse ratio has a pulse on setting of 5 ms and a pulse off setting of 75 ms, while the second pulse ratio has a pulse on setting of 5 ms and a pulse off setting of 56.25 ms.

[0086] In S210: a fourth deposition step, the RF power supply is turned on to glow-ionize the mixed gas, wherein the RF power supply is alternately output at a pulse ratio of 1:25 (first pulse ratio) and a pulse ratio of 1:18.75 (second pulse ratio), thereby depositing a first layer of the silicon oxynitride film.

[0087] In the fourth deposition step, the temperature zones 1-6 in the furnace are set to 545°C, 540°C, 535°C, 535°C, 530°C, and 525°C respectively, the silane in the furnace is 1075sccm, the ammonia is 4705sccm, and the nitrous oxide is 6720sccm. The pressure in the furnace is 1450mtorr, the power is 25.5KW, the pulse on setting of the first pulse ratio is 5ms, and the pulse off setting is 125ms. The pulse on setting of the second pulse ratio is 5ms, and the pulse off setting is 93.75ms.

[0088] In step S211: the fifth deposition step, the main pump valve is opened. Furthermore, the process gas required for depositing the silicon oxynitride film is introduced into the furnace, maintained at a constant pressure required for the deposition step, and the required atmosphere is provided. The RF power supply is turned on to glow-ionize the mixed gas. The RF power supply is alternately output at a pulse ratio of 1:25 (a first pulse ratio) and a pulse ratio of 1:18.75 (a second pulse ratio), thereby depositing the second layer of the silicon oxynitride film.

[0089] In the fifth deposition step, the temperature zones 1-6 in the furnace are set to 545°C, 540°C, 535°C, 535°C, 530°C, and 525°C respectively, the silane in the furnace is 810sccm, the ammonia is 3675sccm, and the nitrous oxide is 8080sccm. The pressure in the furnace is 1450mtorr, the power is 25.5KW, the pulse on setting of the first pulse ratio is 5ms, and the pulse off setting is 125ms; the pulse on setting of the second pulse ratio is 5ms, and the pulse off setting is 93.75ms.

[0090] In S212: a sixth deposition step, the RF power supply is turned on to glow-ionize the mixed gas, wherein the RF power supply is alternately output at a pulse ratio of 1:25 (first pulse ratio) and a pulse ratio of 1:18.75 (second pulse ratio), thereby depositing a first layer of the silicon oxide film.

[0091] In the sixth deposition step, the temperature zones 1-6 in the furnace are set to 545°C, 540°C, 535°C, 535°C, 530°C, and 525°C respectively, the silane in the furnace is 900sccm, the ammonia is 0sccm, the nitrous oxide is 11660sccm, the pressure in the furnace is 1400mtorr, the power is 22.5KW, the pulse on setting of the first pulse ratio is 5ms, the pulse off setting is 125ms, the pulse on setting of the second pulse ratio is 5ms, and the pulse off setting is 93.75ms.

[0092] Thus, the silicon nitride film, the silicon oxynitride film and the silicon oxide film are sequentially deposited on the surface of the solar cell. In addition, for the specific process parameter settings of Example 2, refer to Table 2.

[0093] [Table 2]

[0094]

[0095] In addition, for comparison, this embodiment also provides a comparative example of a method for performing thin film deposition on a solar cell using a fixed pulse ratio in a known method.

[0096] [Comparative Example]

[0097] In the comparative example, a film of substantially the same thickness was deposited by substantially the same steps as in Examples 1 and 2. Furthermore, in the comparative example, substantially the same steps as in Examples 1 and 2 were performed. The difference was the pulse ratio of the RF power source, i.e.,

[0098] In step S207: a first deposition step, the RF power source is output at a pulse ratio of 1:17, thereby depositing a first layer of the silicon nitride film. The pulse ratio is set to 5 ms for pulse on and 85 ms for pulse off.

[0099] In step S208: a second deposition step, the RF power source is output at a pulse ratio of 1:16 to deposit a second layer of the silicon nitride film. The pulse ratio is set to 5 ms for pulse on and 80 ms for pulse off.

[0100] In step S209: the third deposition step, the RF power source is output at a pulse ratio of 1:15, thereby depositing the third layer of the silicon nitride film. The pulse ratio is set to 5 ms for pulse on and 75 ms for pulse off.

[0101] In step S210: the fourth deposition step, the RF power supply is output at a pulse ratio of 1:25 to deposit the first layer of the silicon oxynitride film. The pulse ratio is set to pulse on at 5 ms and pulse off at 1250 ms.

[0102] In step S211: the fifth deposition step, the RF power source is output at a pulse ratio of 1:25 to deposit the second layer of the silicon oxynitride film. The pulse ratio is set to pulse on at 5 ms and pulse off at 1250 ms.

[0103] In step S212: the sixth deposition step, the RF power source is output at a pulse ratio of 1:25 to deposit a silicon oxide film, wherein the pulse on setting is 5 ms and the pulse off setting is 1250 ms.

[0104] Thus, the silicon nitride film, the silicon oxynitride film and the silicon oxide film are sequentially deposited on the surface of the solar cell. In addition, for the specific process parameter settings of the comparative example, refer to Table 3.

[0105] [Table 3]

[0106]

[0107] The film thicknesses produced by the various examples and comparative examples are shown in Tables 4 to 6. It should be noted that Tables 4 to 6 respectively represent the total film thickness, i.e., Table 4 represents the film thickness after a silicon nitride film, a silicon oxynitride film, and a silicon oxide film are sequentially deposited on the surface of the solar cell. Table 5 represents the film thickness after a silicon nitride film, a silicon oxynitride film, and a silicon oxide film are sequentially deposited on the surface of the solar cell. Table 6 represents the film thickness after a silicon nitride film, a silicon oxynitride film, and a silicon oxide film are sequentially deposited on the surface of the solar cell.

[0108] [Table 4]

[0109]

[0110] [Table 5]

[0111]

[0112] [Table 6]

[0113]

[0114] Tables 4 to 6 show that the average film thickness deposited in Example 1 was 76.45 nm, the average refractive index was 2.11, the inter-slice U% was 3.80%, and the inter-slice refractive index was 1.26%. Furthermore, the deposition time required in Example 1 was 680 seconds, and the total process time required was 1696 seconds.

[0115] The average film thickness, average refractive index, and refractive index between slices of the deposited film in Example 2 were 75.08 nm, 2.12, 3.76% U% between slices, and 1.05% refractive index between slices, respectively. Furthermore, the deposition time required in Example 2 was 792 seconds, and the total process time required was 1807 seconds.

[0116] The average film thickness deposited in the comparative example was 76.29 nm, the average refractive index was 2.12, the U% between film thickness slices was 3.58%, and the refractive index between slices was 0.93%. In addition, the deposition time required for the comparative example was 905 seconds, and the total process time required was 1920 seconds.

[0117] It can be seen that when depositing approximately the same film thickness, Example 1 requires 225 seconds less than the comparative example, and Example 2 requires 113 seconds less than the comparative example. In Example 1, among the pulse ratios of the RF power supply alternately output, the pulse-off time of the second pulse ratio is 50% of the pulse-off time of the first pulse ratio. In Example 2, among the pulse ratios of the RF power supply alternately output, the pulse-off time of the second pulse ratio is 75% of the pulse-off time of the first pulse ratio. Since the second pulse ratio of Example 1 is greater than the second pulse ratio of Example 2, according to the above description, that is, the larger the pulse on-off ratio of the RF power supply, the faster the deposition rate, it is also shown that: the deposition time of Example 1 is less than the deposition time of Example 2 and less than the deposition time of the comparative example.

[0118] In addition, in Example 1, taking the position in the furnace as an example, the intra-chip range of one outer side of the solar cell is 1.82nm, the intra-chip range in the middle is 4.65nm, and the intra-chip range of the other outer side is 1.74nm. In Example 2, the intra-chip ranges of the same position of the solar cell are 2.53nm, 4.18nm and 4.62nm respectively. In the comparative example, the intra-chip ranges of the same position of the solar cell are 1.43nm, 4.38nm and 1.46nm respectively. According to industry requirements, for the production process of solar cells, the intra-chip range of film thickness is controlled within 10nm, which can meet the requirements of industrialization. It can be seen that the uniformity of the deposited film thickness of Example 1, Example 2 and the comparative example is within the allowable range.

[0119] It can be seen from this that in this embodiment, by making the RF power supply output alternately with different pulse ratios, that is, changing the RF power supply glow discharge from a fixed-period pulse on-off ratio output to a pulse ratio output alternating between long and short periods, it is possible to increase the deposition rate and reduce the deposition time to a certain extent without changing the process parameters and maintaining the deposition effect.

[0120] Furthermore, as described above, when the silicon nitride film is a graded film, the silicon nitride film comprises, from the inside out, a first layer, a second layer, and a third layer. When depositing the first layer, 2160 sccm of silane and 9350 sccm of ammonia are introduced as process gases, with a first pulse ratio of 1:17 and a second pulse ratio of 1:8.5. When depositing the second layer, 1465 sccm of silane and 10780 sccm of ammonia are introduced as process gases, with a first pulse ratio of 1:16 and a second pulse ratio of 1:8. When depositing the third layer, 1275 sccm of silane and 11250 sccm of ammonia are introduced as process gases, with a first pulse ratio of 1:15 and a second pulse ratio of 1:7.5. Due to the requirements for the passivation performance of the process film layer, the refractive index distribution of the film layer is deposited gradually from high refractive index to low refractive index. The first layer of thin film needs to have relatively high deposition uniformity and density (it is a high refractive index film layer), and the deposition thickness of the high refractive index film to the low refractive index film increases successively. Therefore, the deposition is carried out by gradually increasing the pulse ratio to the low refractive index, which ensures the passivation effect of the film uniformity and density, and ensures that the deposition time is as short as possible.

[0121] Furthermore, although the above description uses the thin film deposition method for solar cells as an example, the method is not limited thereto. The substrate on which the thin film needs to be deposited may also be a sheet of material such as a silicon wafer for semiconductor devices or glass.

[0122] Furthermore, although the above description describes sequential deposition of a silicon nitride film, a silicon oxynitride film, and a silicon oxide film on the surface of a solar cell, the silicon nitride film is a graded film, having, from the inside out, a first layer, a second layer, and a third layer. The silicon oxynitride film is a graded film, having, from the inside out, a first layer and a second layer. The silicon oxide film is a single-layer film. However, this is not limiting, and the type of thin film used in the solar cell can be appropriately varied depending on the desired optical performance and cell performance.

[0123] Although examples of the present embodiment have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and intent of the present embodiment, and the scope of the present embodiment is defined by the claims and their equivalents.

Claims

1. A thin film deposition method based on PECVD, which deposits a film on the surface of a substrate, characterized in that: The steps include: placing the substrate in a coating chamber; vacuuming the coating chamber; introducing process gas into the coating chamber; The radio frequency power supply is output alternately with different pulse ratios; The pulse ratios include at least a first pulse ratio and a second pulse ratio, the second pulse ratio is greater than the first pulse ratio, and the RF power source is output alternately at the first pulse ratio and the second pulse ratio; The range of the first pulse ratio is greater than or equal to 1:25 and less than or equal to 1:15, and the range of the second pulse ratio is greater than or equal to 1:12.5 and less than or equal to 1:7.

5.

2. The thin film deposition method based on PECVD according to claim 1, characterized in that: Multiple layers of thin films are deposited on the same surface of the substrate; When depositing each thin film layer, the radio frequency power source is output alternately at the first pulse ratio and the second pulse ratio.

3. A thin film deposition method for a solar cell, characterized in that: A thin film is deposited on the surface of a solar cell serving as a substrate using the PECVD-based thin film deposition method according to claim 1 or 2.

4. The thin film deposition method for solar cells according to claim 3, characterized in that: A silicon nitride film and a silicon oxynitride film are deposited on the surface of the solar cell, wherein: When depositing the silicon nitride film, the first pulse ratio is in a range of 1:17 to 1:15, and the second pulse ratio is in a range of 1:12.5 to 1:7.

5. When depositing the silicon oxynitride film, the first pulse ratio is in a range of 1:25 to 1:15, and the second pulse ratio is in a range of 1:12.5 to 1:7.

5.

5. The thin film deposition method for solar cells according to claim 4, characterized in that: The silicon nitride film is a gradient film. When the gradient layers of the silicon nitride film are sequentially deposited from the inside to the outside, at least the first pulse ratio becomes larger sequentially.

6. The thin film deposition method for solar cells according to claim 5, characterized in that: The silicon nitride film comprises at least a first layer, a second layer and a third layer from the inside out; wherein, When depositing the first layer, 2160 sccm of silane and 9350 sccm of ammonia were introduced as process gases, the first pulse ratio was 1:17, and the second pulse ratio was 1:8.5; When depositing the second layer, 1465 sccm of silane and 10780 sccm of ammonia were introduced as process gases, the first pulse ratio was 1:16, and the second pulse ratio was 1:8; When depositing the third layer, 1275 sccm of silane and 11250 sccm of ammonia were introduced as process gases, the first pulse ratio was 1:15, and the second pulse ratio was 1:7.

5.

7. The thin film deposition method for solar cells according to claim 4, characterized in that: The process gases of the silicon oxynitride film are silane, ammonia and nitrous oxide. The silicon oxynitride film is a gradient film. When the gradient layers of the silicon oxynitride film are deposited sequentially from the inside to the outside, the first pulse ratio of each layer is the same and the second pulse ratio of each layer is the same.

8. The thin film deposition method for solar cells according to claim 3, characterized in that: Before the step of causing the radio frequency power source to output alternately at different pulse ratios, the method further comprises: Inside the coating chamber, the temperature is increased to a preset temperature according to different positions of the coating chamber along the axial direction.

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