Circulating low-pressure defluorination method for recovering first-round efficiency of graphite boat

Abstract

The invention provides a circulating low-pressure defluorination method for recovering the efficiency of a first round of a graphite boat, which comprises the following steps: introducing inert gas into a cavity to purge the surface of the graphite boat, vacuumizing and maintaining the pressure, introducing the inert gas again to purge, circulating for at least two rounds, and discharging from the boat. According to the circulating low-pressure defluorination method, washing and drying are not needed, efficient defluorination is achieved, meanwhile, the time cost is reduced, use of special gas is reduced, the production cost is saved, and large-scale application and popularization are facilitated.

Description

Technical Field

[0001] The invention belongs to the technical field of battery manufacturing, and relates to a method for recovering the first-round efficiency of a graphite boat, and in particular to a cyclic low-pressure defluorination method for recovering the first-round efficiency of a graphite boat. Background Art

[0002] At present, in the manufacturing process of TOPCon cells, PECVD equipment is usually used to deposit tunnel oxide layers and phosphorus-doped polysilicon layers, and graphite boats are used as carriers. In the actual production process, the film is not only deposited on the surface of the silicon wafer, but also on the surface of the graphite boat carrier, and gradually thickens with the increase in the number of depositions. Since the use of PECVD for thin film deposition involves electrode discharge, these thin films deposited on the surface of the carrier will affect the electric field between the boat blades, thereby causing abnormal discharge phenomena such as short circuit and high frequency, which seriously affects the film deposition quality of the battery cell.

[0003] In order to solve the above problems, technicians usually use dry etching to remove the thin film on the surface of the graphite boat after a certain period of use. However, the surface of the graphite boat after dry cleaning will adsorb fluorine, which needs to be removed by water washing later. This is because: (1) If it is not washed and dried, the surface of the graphite boat contains fluorine and absorbs fluorine, and the efficiency of the first round after going online is low (mainly reflected in the low fill factor FF and open circuit voltage Uoc); (2) If it is not washed and dried, it will take multiple rounds of processes for the electrical performance of the battery cell to gradually recover, which consumes a lot of special gases and time, and significantly increases production costs. However, if the defluorination process is washed and dried, it will also significantly increase the time cost, and there is still much room for improvement.

[0004] It can be seen that how to provide a defluorination method for restoring the first-round efficiency of a graphite boat, while achieving efficient defluorination and reducing time costs, reducing the use of special gases, and saving production costs has become an urgent problem that technical personnel in this field need to solve. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a cyclic low-pressure defluorination method for restoring the first-round efficiency of a graphite boat, which does not require water washing and drying. While achieving efficient defluorination, it reduces time costs, reduces the use of special gases, saves production costs, and is conducive to large-scale promotion and application.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] The present invention provides a cyclic low-pressure defluorination method for recovering the first-round efficiency of a graphite boat. The cyclic low-pressure defluorination method comprises: introducing an inert gas into a cavity to purge the surface of the graphite boat, evacuating and maintaining the pressure, and then introducing the inert gas again to purge the surface of the graphite boat, and then exiting the boat after at least two cycles.

[0008] The defluorination method provided by the present invention does not require water washing and drying, and can achieve efficient defluorination only through cyclic low-pressure purge, thereby restoring the first-round efficiency of the graphite boat, improving the filling factor and open-circuit voltage, while reducing time costs, reducing the use of special gases, and saving production costs.

[0009] In addition, since the cyclic low-pressure defluorination method provided by the present invention does not require water washing, the graphite boat is avoided from being soaked in water, thereby significantly extending the service life of the graphite boat, which is conducive to large-scale promotion and application.

[0010] Preferably, the cyclic low-pressure defluorination method is carried out inside a dryer after the graphite boat is dry-cleaned and before it exits the boat.

[0011] Preferably, the temperature in the cavity is 200-600°C, for example, it can be 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C or 600°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0012] Preferably, the pressure in the cavity is 500-2000mtorr, for example, it may be 500mtorr, 600mtorr, 700mtorr, 800mtorr, 900mtorr, 1000mtorr, 1100mtorr, 1200mtorr, 1300mtorr, 1400mtorr, 1500mtorr, 1600mtorr, 1700mtorr, 1800mtorr, 1900mtorr or 2000mtorr, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0013] Preferably, the inert gas includes any one of N2, Ar or He or a combination of at least two of them. Typical but non-limiting combinations include a combination of N2 and Ar, a combination of Ar and He, a combination of N2 and He, or a combination of N2, Ar and He.

[0014] Preferably, the inert gas flow rate is 1000-10000sccm, for example, it can be 1000sccm, 2000sccm, 3000sccm, 4000sccm, 5000sccm, 6000sccm, 7000sccm, 8000sccm, 9000sccm or 10000sccm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0015] In the present invention, the inert gas flow rate needs to be limited within a reasonable range. When the flow rate is less than 1000 sccm, the dilution effect is poor, which may cause fluoride or volatile byproducts to be unable to be quickly discharged from the cavity, increasing the possibility of reattachment; when the flow rate is greater than 10000 sccm, the gas in the cavity is updated too quickly, and the contact time with the residual fluoride is insufficient, the dilution effect will be affected, and an excessively large flow rate may easily cause airflow disturbances in the reaction chamber, resulting in uneven distribution of gas in the cavity, and ultimately insufficient removal of fluoride in local areas.

[0016] Preferably, the purging time is 10-600s, for example, it can be 10s, 50s, 100s, 150s, 200s, 250s, 300s, 350s, 400s, 450s, 500s, 550s or 600s, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0017] Preferably, the target pressure of vacuum extraction is ≤200mtorr, for example, it can be 20mtorr, 40mtorr, 60mtorr, 80mtorr, 100mtorr, 120mtorr, 140mtorr, 160mtorr, 180mtorr or 200mtorr, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] In the present invention, the target pressure of the vacuum pumping needs to be limited to below 200 mtorr, because low vacuum degree is conducive to the full diffusion of volatile fluorides, so that they can be smoothly desorbed from the surface of the graphite boat.

[0019] Preferably, the holding time is 5-20 min, for example, it can be 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min or 20 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] Preferably, the number of cycles is 2-20 rounds, for example, it can be 2 rounds, 3 rounds, 4 rounds, 5 rounds, 6 rounds, 7 rounds, 8 rounds, 9 rounds, 10 rounds, 11 rounds, 12 rounds, 13 rounds, 14 rounds, 15 rounds, 16 rounds, 17 rounds, 18 rounds, 19 rounds or 20 rounds, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] As a preferred technical solution of the present invention, the cyclic low-pressure defluorination method is carried out inside the dry machine after the graphite boat is dry-cleaned and before it is taken out of the boat, specifically comprising: introducing an inert gas with a flow rate of 1000-10000sccm into a cavity with a temperature of 200-600°C and a pressure of 500-2000mtorr to purge the surface of the graphite boat for 10-600s, evacuating to below 200mtorr and maintaining the pressure for 5-20min, and then re-introducing an inert gas with a flow rate of 1000-10000sccm to purge for 10-600s, and then taking the boat out after 2-20 cycles.

[0022] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The defluorination method provided by the present invention does not require water washing and drying, and can achieve efficient defluorination only through cyclic low-pressure purge, thereby restoring the first-round efficiency of the graphite boat, improving the filling factor and open-circuit voltage, and at the same time reducing time costs, reducing the use of special gases, and saving production costs.

[0025] (2) Since the cyclic low-pressure defluorination method provided by the present invention does not require water washing, the graphite boat is avoided from being soaked in water, thereby significantly extending the service life of the graphite boat, which is conducive to large-scale promotion and application. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0027] Example 1

[0028] This embodiment provides a cyclic low-pressure defluorination method, which specifically includes the following steps:

[0029] (1) After the graphite boat is dry cleaned, the temperature in the chamber is controlled to be 400°C, the pressure is controlled to be 1200 mtorr, and the flow rate of N2 is set to 5000 sccm;

[0030] (2) Open the air inlet valve and purge the surface of the graphite boat for 300 seconds;

[0031] (3) Close the air inlet valve, evacuate the chamber to 150 mtorr, and maintain the evacuation for 10 min;

[0032] (4) Open the gas inlet valve, re-introduce N2 into the chamber at a flow rate of 5000 sccm, and control the pressure in the chamber to 1200 mtorr;

[0033] (5) After purging the graphite boat surface for 300 seconds, close the air inlet valve, evacuate the chamber to 150 mtorr again, and maintain the evacuation for 10 minutes;

[0034] (6) Repeat steps (4)-(5) for a total of 10 rounds to release the boat.

[0035] Example 2

[0036] This embodiment provides a cyclic low-pressure defluorination method, which specifically includes the following steps:

[0037] (1) After the graphite boat is dry-cleaned, the temperature in the chamber is controlled to be 200°C, the pressure to be 500 mtorr, and the Ar flow rate to be set to 1000 sccm;

[0038] (2) Open the air inlet valve and purge the surface of the graphite boat for 600 seconds;

[0039] (3) Close the air inlet valve, evacuate the chamber to 200 mtorr, and maintain the evacuation for 20 min;

[0040] (4) Open the gas inlet valve, introduce Ar into the chamber again at a flow rate of 1000 sccm, and control the pressure in the chamber to 500 mtorr;

[0041] (5) After purging the graphite boat surface for 600 seconds, close the air inlet valve, evacuate the chamber to 200 mtorr again, and maintain the evacuation for 20 minutes;

[0042] (6) Repeat steps (4)-(5) 20 times in total and the boat will be launched from the air.

[0043] Example 3

[0044] This embodiment provides a cyclic low-pressure defluorination method, which specifically includes the following steps:

[0045] (1) After the graphite boat is dry-cleaned, the temperature in the chamber is controlled to be 600°C, the pressure is controlled to be 2000 mtorr, and the He flow rate is set to be 10000 sccm;

[0046] (2) Open the air inlet valve and purge the surface of the graphite boat for 10 seconds;

[0047] (3) Close the air inlet valve, evacuate the chamber to 100 mtorr, and maintain the evacuation for 5 min;

[0048] (4) Open the gas inlet valve and introduce He into the chamber again at a flow rate of 10,000 sccm, and control the pressure in the chamber to 2,000 mtorr;

[0049] (5) After purging the graphite boat surface for 10 seconds, close the air inlet valve, evacuate the chamber to 100 mtorr again, and maintain evacuation for 5 minutes;

[0050] (6) Repeat steps (4)-(5) for a total of 2 rounds to get out of the boat.

[0051] Example 4

[0052] This embodiment provides a cyclic low-pressure defluorination method. Except that the N2 flow rate in step (1) and step (4) is changed to 500 sccm, the remaining steps and conditions are the same as those in embodiment 1 and are not described in detail here.

[0053] Example 5

[0054] This embodiment provides a cyclic low-pressure defluorination method. Except that the N2 flow rate in step (1) and step (4) is changed to 15000 sccm, the remaining steps and conditions are the same as those in embodiment 1 and are not described in detail here.

[0055] Example 6

[0056] This embodiment provides a cyclic low-pressure defluorination method. Except that the target pressure of the vacuum pumping in step (3) and step (5) is changed to 250 mtorr, the remaining steps and conditions are the same as those in embodiment 1 and are not described in detail here.

[0057] Comparative Example 1

[0058] This comparative example provides a water washing defluorination method, which specifically comprises the following steps:

[0059] (1) Immerse the dry-cleaned graphite boat in a high-purity water tank;

[0060] (2) Use bubbling and ultrasonic assisted cleaning, and high-purity water cleaning for 2 hours;

[0061] (3) After cleaning, dry in a drying oven at 200°C for 2 hours.

[0062] Performance Testing

[0063] The conversion efficiency Eta, open circuit voltage Uoc and fill factor FF of the cells obtained by the defluorination method described in Examples 1-6 and Comparative Example 1 were tested. The test results of the cells obtained in Example 1 were used as standard values. The corresponding differences of the remaining examples and comparative examples are shown in Table 1 below.

[0064] Table 1

[0065] Battery Cell ΔEta ΔUoc ΔFF Example 1 0 0 0 Example 2 -0.008％ 0 -0.011 Example 3 -0.006％ -0.001 0.008 Example 4 -0.024％ -0.001 -0.036 Example 5 0.012％ 0 0.012 Example 6 -0.013％ 0 -0.006 Comparative Example 1 -0.078％ -0.001 -0.189

[0066] In the above table, ΔEta≤0.01% can be regarded as the conversion efficiency being flat.

[0067] It can be seen that the defluorination method provided by the present invention does not require water washing and drying, and can achieve efficient defluorination only through cyclic low-pressure purge, thereby restoring the first-round efficiency of the graphite boat, improving the filling factor and open-circuit voltage, and at the same time reducing time costs, reducing the use of special gases, and saving production costs.

[0068] In addition, since the cyclic low-pressure defluorination method provided by the present invention does not require water washing, the graphite boat is avoided from being soaked in water, thereby significantly extending the service life of the graphite boat, which is conducive to large-scale promotion and application.

[0069] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A cyclic low-pressure defluorination method for recovering the first-round efficiency of a graphite boat, characterized in that: The cyclic low-pressure defluorination method comprises: introducing an inert gas into a cavity to purge the surface of a graphite boat, evacuating and maintaining the pressure, and then introducing an inert gas again to purge the surface, and then exiting the boat after at least two cycles.

2. The cyclic low-pressure defluorination method according to claim 1, characterized in that: The cyclic low-pressure defluorination method is carried out inside a dry process machine after the graphite boat is dry-cleaned and before the boat is taken out of the boat.

3. The cyclic low-pressure defluorination method according to claim 1 or 2, characterized in that: The temperature in the cavity is 200-600°C.

4. The cyclic low-pressure defluorination method according to any one of claims 1 to 3, characterized in that: The pressure in the cavity is 500-2000 mtorr.

5. The cyclic low-pressure defluorination method according to any one of claims 1 to 4, characterized in that: The inert gas includes any one of N2, Ar or He, or a combination of at least two of them.

6. The cyclic low-pressure defluorination method according to any one of claims 1 to 5, characterized in that: The inert gas has an inlet flow rate of 1000-10000 sccm.

7. The cyclic low-pressure defluorination method according to any one of claims 1 to 6, characterized in that: The purging time is 10-600s.

8. The cyclic low-pressure defluorination method according to any one of claims 1 to 7, characterized in that: The target pressure of the vacuum pumping is ≤200 mtorr, and the pressure holding time is 5-20 minutes.

9. The cyclic low-pressure defluorination method according to any one of claims 1 to 8, characterized in that: The number of cycles is 2-20 rounds.

10. The cyclic low-pressure defluorination method according to any one of claims 1 to 9, characterized in that: The cyclic low-pressure defluorination method is carried out inside a dry machine after the graphite boat is dry-cleaned and before the boat is taken out of the boat, and specifically comprises: introducing an inert gas with a flow rate of 1000-10000sccm into a cavity with a temperature of 200-600°C and a pressure of 500-2000mtorr to purge the surface of the graphite boat for 10-600s, evacuating to below 200mtorr and maintaining the pressure for 5-20min, and then introducing an inert gas with a flow rate of 1000-10000sccm to purge for 10-600s again, and taking the boat out after 2-20 cycles.