Method for improving thin film thickness of new boat support silicon wafer in LPCVD (Low Pressure Chemical Vapor Deposition) process
By performing a saturation treatment on the newly launched quartz boat tray and adjusting the LPCVD process according to the number of compensations and time, the problem of thin silicon wafer film caused by the new boat tray was solved, production efficiency was improved and capacity loss was reduced.
Patent Information
- Application Number
- CN202511006139.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-21
- Publication Date
- 2025-10-28
AI Technical Summary
In the LPCVD process, the newly introduced quartz boat support results in a thinner silicon wafer film, and existing technology requires five rounds of saturation treatment, which affects production capacity.
The newly launched quartz boat is subjected to a saturation treatment. The compensation time for each LPCVD process is adjusted by calculating the number of compensations and the time, so that the silicon wafer film thickness reaches the normal range. As the number of compensations increases, the compensation time decreases step by step to ensure that the film thickness of the new boat is within the specified range after one round of saturation.
The number of saturation treatment rounds for new boats was reduced, thereby reducing production losses, improving production efficiency, ensuring that the silicon wafer film thickness was within the specified range, saving the time of 4 saturation boat rounds, and reducing production capacity loss by 10,000 pcs.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of semiconductor technology, specifically relating to a method for improving the thinness of the silicon wafer film in the LPCVD process. Background Technology
[0002] Quartz boats, used as carriers for silicon wafers, are made of pure quartz crystal and possess extremely high water and corrosion resistance. They are commonly used in critical processes such as oxidation diffusion and LPCVD. Currently, in diffusion and LPCVD equipment production, quartz boats are typically placed inside quartz boat holders. The LPCVD process uses a large boat holder with 10 small quartz boats to load silicon wafers. After deposition, the silicon wafers are removed from the quartz boats, and new wafers are inserted for the next batch of deposition. Therefore, quartz boats are reused during the production process.
[0003] During the polycrystalline silicon deposition process, polycrystalline silicon films inevitably deposit onto the wafer carrier. As the process time and number of cycles increase, the thickness of the polycrystalline silicon film on the wafer carrier becomes thicker and thicker. After more than 2 months of use, arc-shaped dirt will form EL defects, requiring regular cleaning. After cleaning, the film thickness in the first 10 cycles after the wafer carrier is saturated is relatively low at 120~130nm, mainly due to insufficient saturation of the wafer carrier. The normal LP film thickness is 160±10nm.
[0004] Therefore, the boat support after cleaning needs to be saturated because in the normal process, the reactants need to be thermally decomposed into silane to deposit a 160nm thick phosphorus-doped microcrystalline amorphous mixed Si film on the oxide layer surface. However, after cleaning, both the silicon carbide boat and the quartz boat that load the silicon wafer will adsorb Si atoms and compete with the silicon wafer for silane, which makes the LP film thickness of the silicon wafer in the normal process too thin.
[0005] 1) Silicon carbide: Driven by thermal energy, silane molecules undergo catalytic dissociation on the activated SiC surface, and the generated active silicon species form Si-Si covalent bonds with the surface Si atoms, which is an irreversible chemical adsorption process.
[0006] 2) Quartz: High temperature-driven dehydration → active sites (Si-O-Si bonds / electron-deficient Si⁺) are generated on the surface → silanes dissociate and form covalent bonds (Si-O-Si or Si-Si bonds). This is a chemical adsorption process that is highly dependent on the surface hydroxyl groups and the dehydration state.
[0007] Current technology requires five saturation cycles to ensure the LP film thickness on silicon wafers reaches the specified range before they can be used for wafer loading after cleaning. However, one saturation cycle of the saturation process takes 133 minutes, so five saturation cycles would take 11 hours. Fully saturating a set of cleaned saturation saturation simplifies the production capacity by an estimated 13,750 pieces. Summary of the Invention
[0008] The purpose of this invention is to provide a method to improve the thinness of the silicon wafer film in the LPCVD process, thereby solving the above-mentioned technical problems existing in the prior art.
[0009] Therefore, the technical solution provided by the present invention is as follows:
[0010] A method for improving the thinness of the silicon wafer film on the new ark in the LPCVD process includes the following steps:
[0011] Step 1) Perform a saturation test on the newly launched boat support system;
[0012] Step 2) Set the number of LPCVD process compensations to n times. Calculate the compensation time for each LPCVD process based on the number of LPCVD process compensations and the compensation value. Then, obtain the total deposition time for each LPCVD process based on the compensation time.
[0013] Step 3) Load the silicon wafer and perform normal LPCVD process for cell production. Deposit according to the total deposition time of each LPCVD process to ensure that the silicon wafer film thickness of each LPCVD process is within the normal range.
[0014] Step 4) After the newly launched boat support reaches saturation, the LPCVD process is carried out according to the normal deposition time.
[0015] In step 3), 1-2 times before reaching the set number of compensation times n in the LPCVD process, the number of compensation times n is adjusted according to the silicon wafer film thickness to keep the silicon wafer film thickness within the normal range.
[0016] If the silicon wafer film thickness is too thin, increase the number of compensation cycles; if the silicon wafer film thickness is too thick, decrease the number of compensation cycles.
[0017] In step 2), the compensation time for each LPCVD process decreases with the number of compensations.
[0018] The compensation time in step 2) is calculated using the following formula:
[0019] Compensation time = (a*n*n) - (t0*n) + Compensation value
[0020] In the formula, a is the compensation coefficient, which is determined based on the center value of the film thickness on the production line and the film thickness of the first boat on the new boat carrier; n is the number of compensations; and t0 is the deposition time required to increase the film thickness by 1 nm.
[0021] The number of compensation cycles for different production lines is determined based on the silicon wafer film thickness control range; when the center value of the film thickness on the production line changes, the compensation value is adjusted to ensure that the silicon wafer film thickness is normal.
[0022] The compensation coefficient 'a' is calculated using the following formula:
[0023] a = (Center value of film thickness in production line - Film thickness of the first boat on the new boat) / Deposition step time;
[0024] The deposition step time is 1520±40s.
[0025] The number of compensation times n is 10 ± 2.
[0026] The deposition time t0 required to increase the film thickness by 1 nm is 10.5 ± 4 s.
[0027] The beneficial effects of this invention are as follows:
[0028] The method provided by this invention for improving the thinness of silicon wafer film on new LPCVD wafers in the LPCVD process involves saturating the new LPCVD wafer once, and then increasing the compensation time for normal LPCVD production on top of the deposition step time. This ensures that the LP film thickness deposited on the silicon wafer in each compensation step reaches the normal range, and after a certain number of compensation steps, the new LPCVD wafer is saturated, ensuring that the silicon wafer film thickness produced in subsequent LPCVD processes remains constant within the specified range.
[0029] As the number of compensation cycles increases, the compensation time decreases progressively, ensuring that after only one saturation cycle for a newly launched boat, the film thickness for each wafer production run is within the specified range. This saves the time of four saturation cycles and reduces production capacity loss by 10,000 pcs.
[0030] This invention solves the problem of thin LP film thickness in the first 10 rounds of LPCVD cell production after the first saturation round of the new boat. Compared with the existing 5-round saturation boat method, the advantages are that it can reduce the capacity loss of the LPCVD process. The method is scalable and can be fully covered by the LPCVD process production line. The method is operable, and production line personnel can change the compensation value and compensation number in the algorithm at any time according to the change of the LP film thickness control range. Detailed Implementation
[0031] The following specific embodiments illustrate the implementation of the invention. Those skilled in the art can easily understand other advantages and effects of the invention from the content disclosed in this specification.
[0032] Exemplary embodiments of the invention are now described; however, the invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully communicate the scope of the invention to those skilled in the art. The terminology used to refer to exemplary embodiments is not intended to limit the invention.
[0033] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.
[0034] Example 1
[0035] To address the issue of insufficient film thickness in the first 10 cycles of LPCVD solar cells after the newly cleaned wafer carrier has been fully saturated during the initial cleaning process, this invention provides a method for improving the thin film thickness of silicon wafers in the new wafer carrier during the LPCVD process, comprising the following steps:
[0036] Step 1) Perform a saturation test on the newly launched boat support system;
[0037] Step 2) Set the number of LPCVD process compensations to n times. Calculate the compensation time for each LPCVD process based on the number of LPCVD process compensations and the compensation value. Then, obtain the total deposition time for each LPCVD process based on the compensation time.
[0038] Step 3) Load the silicon wafer and perform normal LPCVD process for cell production. Deposit according to the total deposition time of each LPCVD process to ensure that the silicon wafer film thickness of each LPCVD process is within the normal range.
[0039] Step 4) After the newly launched boat support reaches saturation, the LPCVD process is carried out according to the normal deposition time.
[0040] The method provided by this invention for improving the thinness of silicon wafer film on new LPCVD wafers in the LPCVD process involves saturating the new LPCVD wafer once, and then increasing the compensation time for normal LPCVD production on top of the deposition step time. This ensures that the LP film thickness deposited on the silicon wafer in each compensation step reaches the normal range, and after a certain number of compensation steps, the new LPCVD wafer is saturated, ensuring that the silicon wafer film thickness produced in subsequent LPCVD processes remains constant within the specified range.
[0041] Example 2
[0042] Based on Example 1, this example provides a method to improve the thinness of the silicon wafer film in the LPCVD process. In step 3), 1-2 times before reaching the set number of compensation times n in the LPCVD process, the number of compensation times n is adjusted according to the silicon wafer film thickness so that the silicon wafer film thickness is within the normal range.
[0043] If the silicon wafer film thickness is too thin, increase the number of compensation cycles; if the silicon wafer film thickness is too thick, decrease the number of compensation cycles.
[0044] The number of compensation cycles refers to the number of times the deposition time needs to be compensated after the boat has been saturated once during the normal production of solar cells by loading silicon wafers. It is also the lifespan of the boat when it is newly put into operation on the machine. (Production line personnel can update this number at any time according to changes in the LP film thickness control range, or they can change the lifespan of the boat on the machine to flexibly adjust the number of compensation cycles.)
[0045] Example 3
[0046] Based on Example 1, this example provides a method to improve the thinness of the silicon wafer film in the LPCVD process. In step 2), the compensation time corresponding to each LPCVD process decreases with the number of compensations.
[0047] Each LPCVD process saturates the boat support for one cycle. Because a compensation time is added to the deposition step time (normal formulation time), the total deposition time is longer than a normal deposition process, resulting in a larger deposition volume. Therefore, the compensation time decreases with each subsequent compensation cycle; that is, the compensation time decreases progressively with each compensation cycle. Furthermore, the LP film thickness obtained from each LPCVD process meets the normal LP film thickness range (160±10nm).
[0048] As the number of compensation cycles increases, the compensation time decreases progressively, ensuring that after only one saturation cycle for a newly launched boat, the film thickness for each wafer production run is within the specified range. This saves the time of four saturation cycles and reduces production capacity loss by 10,000 pcs.
[0049] Example 4
[0050] Based on Example 1, this example provides a method to improve the thinness of the silicon wafer film in the LPCVD process. The compensation time in step 2) is calculated using the following formula:
[0051] Compensation time = (a*n*n) - (t0*n) + Compensation value
[0052] In the formula, a is the compensation coefficient, which is determined based on the center value of the film thickness on the production line and the film thickness of the first boat on the new boat carrier; n is the number of compensations; and t0 is the deposition time required to increase the film thickness by 1 nm.
[0053] Furthermore, the compensation coefficient 'a' is calculated using the following formula:
[0054] a = (Center value of film thickness on production line - Film thickness of the first vessel on the Xinzhoutuo production line) / Deposition step time
[0055] The deposition step time is 1520±40s.
[0056] The deposition time t0 required to increase the film thickness by 1 nm is 10.5 ± 4 s.
[0057] The number of compensation cycles for different production lines is determined based on the silicon wafer film thickness control range; when the center value of the film thickness on the production line changes, the compensation value is adjusted to ensure that the silicon wafer film thickness is normal.
[0058] Example 5
[0059] Based on Example 4, this example provides a method to improve the thinness of the silicon wafer film in the LPCVD process, with the compensation number n being 10±2 times.
[0060] This invention can solve the problem of thin LP film thickness in the first 10 rounds of LPCVD production after the first saturation round of the new boat. Compared with the existing technology of 5 rounds of saturation boat, the advantage is that it can reduce the capacity loss of the LPCVD process. The method is scalable and can be fully covered by the LPCVD process production line. The method is operable, and the production line personnel can change the compensation value and compensation number in the algorithm at any time according to the change of the LP film thickness control range.
[0061] Example 6
[0062] To further illustrate the effects of the present invention, this embodiment uses a production line as an example to provide a detailed description of the invention. The center value of the film thickness on this production line is 160±10 nm.
[0063] The steps to improve the thin film thickness on silicon wafers in the LPCVD process are as follows:
[0064] Step 1) Perform one round of saturation on the newly launched boat support; one round of saturation boat process takes 133 minutes; after one round of saturation on the newly launched boat support, the first boat film thickness on the new boat support is 125±10nm;
[0065] Step 2) Set the number of LPCVD process compensations to n times. Calculate the compensation time for each LPCVD process based on the number of LPCVD process compensations and the compensation value. Then, obtain the total deposition time for each LPCVD process based on the compensation time.
[0066] In this embodiment, the number of LPCVD process compensations is set to 10.
[0067] Compensation time = (a*n*n) - (t0*n) + Compensation value (1)
[0068] a = (Center value of film thickness in production line - Film thickness of the first ship on the new shipboard) / Deposition step time = [160±10nm (Center value of film thickness in production line) - 125±10nm (Film thickness of the first ship on the new shipboard)] / 1520±40s (Deposition step time) = 0.022
[0069] t0 is the deposition time required to increase the film thickness by 1 nm. 10.5 ± 4 s is taken as the middle value, i.e., t0 = 10.5.
[0070] Then the compensation time / s = (0.022 * number of times * number of times) - (10.5 * number of times) + compensation value (2)
[0071] The compensation value is 196. According to equation (2), the compensation time for 10 times and the total deposition time are shown in Table 1.
[0072] Table 1 Compensation time and total deposition time
[0073]
[0074] In Table 1, total deposition time / s = formulation time / s + compensation time / s
[0075] Time difference per second = Total deposition time of a certain round / second - Total deposition time of the previous round / second
[0076] Formulation time / s: The deposition time set in the process formulation for normal production of solar cells;
[0077] Compensation times: After the boat is saturated for one cycle after cleaning, the number of times the deposition time needs to be compensated for during the normal production of solar cells by loading silicon wafers is also the lifespan of the boat when it is newly put into operation on the machine (so that production line personnel can update it at any time according to changes in the LP film thickness control range, or the lifespan of the boat can be changed on the machine to flexibly adjust the number of compensation times).
[0078] Step 3) Load the silicon wafer and perform normal LPCVD process for cell production. Deposit according to the total deposition time of each LPCVD process to ensure that the silicon wafer film thickness of each LPCVD process is within the normal range.
[0079] The compensation was performed 10 times, and the film thickness data corresponding to each LPCVD process is shown in Table 2. Among them, the production line personnel only sampled the film thickness of the 1st / 3rd / 5th / 7th / 10th boats, and the average film thickness was the average of the 5 boats.
[0080] Table 2. Film thickness data after 10 compensation cycles
[0081]
[0082] Step 4) After the newly launched boat support reaches saturation, the LPCVD process is carried out according to the normal deposition time.
[0083] As shown in Table 2, in all 10 compensation processes, increasing the deposition time allowed the LP film thickness of the solar cells to be maintained within the normal range (160±10nm). From the 11th process onwards, deposition time compensation was no longer performed, and deposition was carried out according to the deposition time set in the normal production solar cell process formula (i.e., the formula time of 1490s in Table 1). At this point, the LP film thickness of all solar cells mounted on the boat met the requirements, which indirectly indicated that the boat was saturated, and subsequent LPCVD production could proceed according to the deposition time set in the normal production solar cell process formula.
[0084] This invention enables newly launched boats to achieve the required film thickness for the first 10 rounds of normal process after only one saturation round, saving the time of 4 rounds of boat saturation and reducing production capacity loss by 10,000 pcs.
[0085] The compensation number n in this invention is 10 ± 2 times. Comparative experiments were conducted on the same production line with 13 and 7 compensation cycles respectively, and the results are shown in Tables 3 and 4.
[0086] Table 3. Film thickness data after 13 compensation cycles
[0087]
[0088] As shown in Table 3, during the compensation rounds 1-11, the film thickness of the solar cells produced by each LPCVD process corresponding to the compensation deposition met production requirements. When compensation reached the 12th round, the film thickness of the solar cells in the 1st, 7th, and 10th boats exceeded the normal film thickness range (160±10nm), indicating that further compensation deposition when the boats were already saturated resulted in excessively long deposition times and excessively thick film thicknesses. In the 12th compensation round, the film thickness of the 1st, 3rd, 5th, 7th, and 10th boats all exceeded the normal film thickness range and could not meet production requirements.
[0089] Table 4. Film thickness data after 7 compensation cycles
[0090]
[0091] As shown in Table 3, during the compensation rounds 1-7, the film thickness of the solar cells produced by each compensated deposition LPCVD process met production requirements. After 7 rounds of compensation, the film thickness of the solar cells produced in the first uncompensated LPCVD process (i.e., deposition time of 1490s) was less than 150nm. Although the film thickness of the solar cells produced in the second uncompensated LPCVD process met the requirements, the film thickness of the solar cells produced in the third uncompensated LPCVD process was still too thin. This indicates that when the number of compensation rounds was insufficient, the solar cell did not reach saturation, resulting in a thinner film thickness in the uncompensated LPCVD process, which also failed to meet production requirements.
[0092] Therefore, it can be seen that when the number of compensations exceeds 10±2 times, the LP film thickness cannot meet the production line requirements.
[0093] In summary, as the number of compensation cycles increases, the compensation time decreases progressively, ensuring that after the newly launched boat only needs to be saturated for one cycle, the film thickness in the first 10 rounds of wafer loading is within the specified range. After the 11th cycle, the deposition time returns to the normal process deposition time of 1490s, and the deposition step time is no longer compensated. At this point, the boat has adsorbed enough silane, and the film thickness of the solar cells produced by subsequent loading of silicon wafers can be kept constant within the specified range, meeting the production line requirements.
[0094] The examples above are merely illustrative of the invention and do not constitute a limitation on the scope of protection of the invention. Any design that is the same as or similar to the invention falls within the scope of protection of the invention.
Claims
1. A method for improving the thinness of the silicon wafer film on the new boat during the LPCVD process, characterized in that: Includes the following steps: Step 1) Perform a saturation test on the newly launched boat support system; Step 2) Set the number of LPCVD process compensations to n times. Calculate the compensation time for each LPCVD process based on the number of LPCVD process compensations and the compensation value. Then, obtain the total deposition time for each LPCVD process based on the compensation time. Step 3) Load the silicon wafer and perform normal LPCVD process for cell production. Deposit according to the total deposition time of each LPCVD process to ensure that the silicon wafer film thickness of each LPCVD process is within the normal range. Step 4) After the newly launched boat support reaches saturation, the LPCVD process is carried out according to the normal deposition time.
2. The method for improving the thin film thickness of silicon wafers on a new boat during the LPCVD process according to claim 1, characterized in that: In step 3), 1-2 times before reaching the set number of compensation times n in the LPCVD process, the number of compensation times n is adjusted according to the silicon wafer film thickness to keep the silicon wafer film thickness within the normal range. If the silicon wafer film thickness is too thin, increase the number of compensation cycles; if the silicon wafer film thickness is too thick, decrease the number of compensation cycles.
3. The method for improving the thin film thickness of silicon wafers on a new boat during the LPCVD process according to claim 1, characterized in that: In step 2), the compensation time for each LPCVD process decreases with the number of compensations.
4. The method for improving the thin film thickness of silicon wafers on a new boat during the LPCVD process according to claim 1, characterized in that: The compensation time in step 2) is calculated using the following formula: Compensation time = (a*n*n) - (t0*n) + Compensation value In the formula, a is the compensation coefficient, which is determined based on the center value of the film thickness on the production line and the film thickness of the first boat on the new boat carrier; n is the number of compensations; and t0 is the deposition time required to increase the film thickness by 1 nm.
5. The method for improving the thin film thickness of silicon wafers on a new boat during the LPCVD process according to claim 4, characterized in that: The number of compensation cycles for different production lines is determined based on the silicon wafer film thickness control range; when the center value of the film thickness on the production line changes, the compensation value is adjusted to ensure that the silicon wafer film thickness is normal.
6. The method for improving the thin film thickness of silicon wafers on a new boat during the LPCVD process according to claim 4, characterized in that: The compensation coefficient 'a' is calculated using the following formula: a = (Center value of film thickness in production line - Film thickness of the first boat on the new boat) / Deposition step time; The deposition step time is 1520±40s.
7. The method for improving the thin film thickness of silicon wafers on a new boat in the LPCVD process according to claim 4, characterized in that: The number of compensation times, n, is 10 ± 2.
8. A method for improving the thin film thickness of silicon wafers on a new boat during the LPCVD process according to claim 4, characterized in that: The deposition time t0 required to increase the film thickness by 1 nm is 10.5 ± 4 s.