CN117790631A - Secondary boron expansion normal pressure annealing process and system based on TOPCON battery - Google Patents
Secondary boron expansion normal pressure annealing process and system based on TOPCON battery Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 95
- 230000008569 process Effects 0.000 title claims abstract description 94
- 238000000137 annealing Methods 0.000 title claims abstract description 54
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical group [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 title claims abstract description 44
- 229910052796 boron Inorganic materials 0.000 title claims abstract description 44
- 238000007254 oxidation reaction Methods 0.000 claims abstract description 86
- 230000003647 oxidation Effects 0.000 claims abstract description 83
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 48
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 47
- 239000010703 silicon Substances 0.000 claims abstract description 47
- 230000001590 oxidative effect Effects 0.000 claims abstract description 18
- 239000010453 quartz Substances 0.000 claims abstract description 18
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 18
- 238000009279 wet oxidation reaction Methods 0.000 claims abstract description 15
- 235000012431 wafers Nutrition 0.000 claims description 41
- 239000002253 acid Substances 0.000 claims description 28
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 28
- 229910052810 boron oxide Inorganic materials 0.000 claims description 22
- JKWMSGQKBLHBQQ-UHFFFAOYSA-N diboron trioxide Chemical compound O=BOB=O JKWMSGQKBLHBQQ-UHFFFAOYSA-N 0.000 claims description 22
- 238000004140 cleaning Methods 0.000 claims description 21
- 239000000843 powder Substances 0.000 claims description 17
- 238000010438 heat treatment Methods 0.000 claims description 13
- 238000001816 cooling Methods 0.000 claims description 9
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- 230000007547 defect Effects 0.000 abstract description 5
- 239000012528 membrane Substances 0.000 abstract 1
- 230000006872 improvement Effects 0.000 description 17
- 230000000052 comparative effect Effects 0.000 description 11
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 9
- 239000005388 borosilicate glass Substances 0.000 description 9
- 238000012360 testing method Methods 0.000 description 9
- 238000012423 maintenance Methods 0.000 description 8
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- 239000001301 oxygen Substances 0.000 description 7
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- 239000000463 material Substances 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- 238000012986 modification Methods 0.000 description 3
- 239000007800 oxidant agent Substances 0.000 description 3
- 238000001556 precipitation Methods 0.000 description 3
- AFCARXCZXQIEQB-UHFFFAOYSA-N N-[3-oxo-3-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)propyl]-2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidine-5-carboxamide Chemical compound O=C(CCNC(=O)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F)N1CC2=C(CC1)NN=N2 AFCARXCZXQIEQB-UHFFFAOYSA-N 0.000 description 2
- 229910004298 SiO 2 Inorganic materials 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
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- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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Abstract
The invention discloses a secondary boron expansion normal pressure annealing process and system based on a TOPCON battery, wherein the process comprises the following steps: controlling the internal pressure and the external pressure of the furnace tube to be consistent, and introducing N 2 Sending the silicon wafer after SE introduction into a furnace tube; raising the temperature to 800-850 ℃ and preserving the heat; then the temperature is increased to 860 ℃ to 970 ℃ and the heat is preserved; stop turning on N 2 Introducing O 2 Oxidizing; raising the temperature to 980-1050 ℃ for continuous oxidation; keep open O 2 Dry oxidation, or first pass O 2 Dry oxidation is carried out, and then O is kept on 2 Simultaneously H is introduced 2 O is subjected to wet oxidation; keep open O 2 The temperature is reduced to 800-900 ℃; the temperature is reduced to 800-840 ℃ and O is stopped 2 Re-introducing N 2 And taking out the quartz boat. The performance of the silicon wafer manufactured by the process is superior to that of the negative pressure annealing process, the oxidation efficiency is high, the oxide layer is thicker, and the defect that the negative pressure oxidation furnace tube is easy to deform and damage and separate is overcomeAnd the membrane pump is easy to be blocked.
Description
Technical Field
The invention belongs to the technical field of solar cell manufacturing, and particularly relates to a secondary boron expansion normal pressure annealing process and system based on a TOPCON cell.
Background
The battery technology is continuously improved, the latest TOPCO battery technology is also continuously developed, and along with the introduction of a Selective Emitter (SE) of the high-efficiency battery technology, the preparation process of the TOPCO battery is changed from the original high-temperature boron expansion process to the process of front boron expansion deposition boron source, laser direct doping and SE+secondary boron expansion oxidation annealing process, and the secondary boron expansion oxidation annealing is the post annealing. Although a new technology is introduced, the existing secondary boron diffusion oxidation annealing process and equipment basically extend the functions of the original boron diffusion process and equipment and have the functions of high temperature, oxidation and negative pressure. The negative pressure function has the function of uniformly distributing the boron source (pressure of 100 mbar) in the boron source deposition stage, but in the secondary boron diffusion oxidation annealing process, the pressure used for the current oxidation is 800mbar, and the requirement on the pressure is not high. The inventor of the application found in practical research that the pressure value of 800mbar is not very different from the normal pressure (1000 mbar), but the pressure value can cause some technical defects, and further cause great negative effects on actual production, including (1) the furnace tube is easily deformed and damaged under the conditions of high temperature negative pressure for a long time, which is usually high temperature close to 1050 ℃, pressure of 800mbar and oxygen; (2) At present, the post-annealing process is used for a long time, boron oxide is separated out to a certain extent, the boron source in the furnace tube is easy to be excessive after long-time use, the excessive boron source diffuses to the silicon substrate to cause process deviation, and in addition, the vacuum pump is blocked after the boron oxide powder is crystallized for a long time. (3) The post-annealing process employs oxygen for oxidation to form BSG, which has a relatively slow oxidation rate and requires a longer time or higher temperature for oxidation to reach the same thickness of BSG. Regarding the above technical problems, no effective solution has been known in the prior art.
Disclosure of Invention
The invention aims to solve the technical problem of overcoming the defects of the prior art and providing a secondary boron expansion normal pressure annealing process and system based on a TOPCON battery, wherein the oxidation efficiency is high, and the performance of the manufactured silicon wafer is better.
In order to solve the technical problems, the invention adopts the following technical scheme:
a secondary boron-expansion normal-pressure annealing process based on TOPCON batteries comprises the following steps:
(1) Feeding the boat, controlling the pressure in the furnace tube of the annealing furnace to be consistent with the external air pressure, controlling the temperature to be 700-800 ℃, and introducing N 2 Loading the silicon wafers after SE introduction into a quartz boat and feeding the silicon wafers into a furnace tube of an annealing furnace;
(2) Keeping constant temperature, keeping the pressure in the furnace tube consistent with the external air pressure, and keeping N introduced 2 Raising the temperature to 800-850 ℃ and preserving heat;
(3) Heating, keeping the pressure in the furnace tube consistent with the external air pressure, and keeping N introduced 2 Raising the temperature to 860-970 ℃;
(4) Keeping constant temperature, keeping the pressure in the furnace tube consistent with the external air pressure, and keeping N introduced 2 Preserving heat at 860-970 ℃;
(5) Oxidizing, keeping the pressure in the furnace tube consistent with the external air pressure, keeping the temperature to be 860-970 ℃, and stopping introducing N 2 Introducing O 2 Oxidizing;
(6) Heating up and oxidizing to keep the pressure in the furnace tube consistent with the external air pressure, and keeping O introduced 2 Raising the temperature to 980-1050 ℃ and continuing oxidation;
(7) Constant-temperature oxidation, keeping the pressure in the furnace tube consistent with the external air pressure, keeping the temperature between 980 ℃ and 1050 ℃, and keeping the O introduced 2 Dry oxidation, or introduction of O 2 Dry oxidation is carried out, then O is maintained 2 Simultaneously with the introduction of H 2 O is subjected to wet oxidation;
(8) Cooling and oxidizing, keeping the pressure in the furnace tube consistent with the external air pressure, and keeping the O introduced 2 Stopping the introduction of H 2 O, the temperature is reduced to 800-900 ℃;
(9) Cooling, keeping the pressure in the furnace tube consistent with the external air pressure, stopping introducing O, wherein the temperature is 800-840 DEG C 2 Re-introducing N 2 ；
(10) Discharging the boat, keeping the pressure in the furnace tube consistent with the external air pressure, keeping the temperature at 800-840 ℃, and keeping N introduced 2 Loading furnace tubeAnd taking out the quartz boat with the silicon wafer, and ending the process.
Further improvement: in the step (7), O is introduced 2 The flow of the catalyst is 10 slm-25 slm, and the constant-temperature oxidation time is 60 min-100 min.
Further improvement: in the step (7), the H is introduced 2 O is liquid water with the flow rate of 1 g/min-5 g/min.
Further improvement: in the step (7), O is firstly introduced 2 The dry oxidation is carried out for 30 min-50 min, and then O is maintained 2 Simultaneously with the introduction of H 2 The time for O to be wet oxidized is 30 min-50 min.
Further improvement: in the step (7), only O is introduced 2 When dry oxidation is carried out, the temperature is controlled to 1040-1050 ℃, and correspondingly, in the step (6), the temperature is increased to 1040-1050 ℃.
Further improvement: in the step (7), O is firstly introduced 2 Dry oxidation is carried out, then O is maintained 2 Simultaneously with the introduction of H 2 When O is subjected to wet oxidation, the temperature is controlled to be 980-1030 ℃, and correspondingly, in the step (6), the temperature is increased to 980-1030 ℃.
Further improvement: in the step (1), N is introduced 2 The flow rate of (2) is 3 slm-5 slm.
Further improvement: in the step (2), N is introduced 2 The flow of the water is 15 slm-30 slm, and the constant temperature time is 5 min-20 min.
Further improvement: in the step (3), N is introduced 2 The flow of the water is 15 slm-30 slm, and the heating time is 10 min-20 min.
Further improvement: in the step (4), N is introduced 2 The flow of the water is 5 slm-15 slm, and the constant temperature time is 5 min-10 min.
Further improvement: in the step (5), O is introduced 2 The flow of the catalyst is 15 slm-20 slm, and the oxidation time is 3 min-5 min.
Further improvement: in the step (6), O is introduced 2 The flow rate of the water is 15 sccm-20 sccm, and the heating time is 10 min-15 min.
Further improvement: in the step (8), theO 2 The flow of the water is 5 slm-20 slm, and the cooling time is 50 min-70 min.
Further improvement: in the step (9), N is introduced 2 The flow rate of (2) is 5 slm-10 slm.
Further improvement: in the step (10), N is introduced 2 The flow rate of (2) is 3 slm-5 slm.
The invention also provides a secondary boron expansion normal pressure annealing system based on the TOPCO battery, which comprises a furnace tube, a furnace door, an air inlet main tube, an exhaust tube, an acid discharge tube, a cleaning tube and a collecting box, wherein air inlets of the air inlet main tube and the exhaust tube are respectively positioned at two ends of the furnace tube, an air outlet end of the exhaust tube is communicated with the acid discharge tube, the cleaning tube and the collecting box are respectively positioned at two ends of the acid discharge tube, the cleaning tube is used for cleaning boron oxide powder in the acid discharge tube, and the collecting box is used for collecting the boron oxide powder cleaned in the acid discharge tube.
Further improvement: the air inlet main pipe is positioned at the tail end of the furnace, the inlet of the exhaust pipe is positioned at the mouth end of the furnace, the acid discharge pipe is arranged at the outer side of the tail of the furnace, the exhaust pipe extends from the mouth of the furnace to the tail of the furnace to the acid discharge pipe, and the acid discharge pipe is connected with peripheral negative pressure equipment.
Further improvement: the cleaning pipe is provided with a stop valve which is opened or closed at regular time through the controller so as to realize automatic injection of water at regular time and cleaning of the acid discharge pipe.
Further improvement: the air inlet main pipe is communicated with N 2 Air inlet, O 2 Air inlet and H 2 And an O inlet, wherein each gas enters the furnace tube through the air inlet header pipe.
Compared with the prior art, the invention has the advantages that:
(1) The invention relates to a secondary boron-expansion normal-pressure annealing process based on TOPCON batteries, which ensures that the doping performance and sheet resistance of the prepared silicon wafer meet the product indexes, and SiO of the silicon wafer 2 The thickness of the oxide layer is obviously increased, the oxidation rate is also increased, and in general, the performance of the silicon wafer manufactured by the normal pressure annealing process is better than that of the silicon wafer manufactured by the negative pressure annealing process, particularly the SiO obtained by the normal pressure annealing process has higher oxidation efficiency 2 OxidationThe layer is thicker. More importantly, one of the following: the negative pressure oxidation process is adopted, so that the defect of negative pressure oxidation in the prior art can be avoided, the temperature of 1050 ℃ and the negative pressure oxidation process of 800mbar are adopted in the prior art, the furnace tube and the quartz boat are easy to deform and damage after long-term use, if the oxidation temperature is reduced to 980 ℃, the reaction time is prolonged, the energy is not saved, the furnace tube is not protected, and the effect is not caused, and the normal pressure is mainly because the peak temperature of the oxidation stage in the secondary boron expansion annealing process is about 1050 ℃, the temperature is relatively close to the softening temperature of the furnace tube and the quartz boat, the pressure outside the furnace tube is higher than the internal pressure by the negative pressure process, the furnace tube wall is always subjected to extrusion force from outside to inside due to the existence of pressure difference, and the furnace tube is easy to deform and even crack in the extremely high temperature environment close to the softening temperature of the furnace tube material for a long time; the pressure difference between the inside and the outside of the furnace body is not existed in the normal pressure process, the furnace wall is not extruded by the external atmospheric pressure, and the influence on the furnace body is not great even if the time of the oxidation reaction needs to be prolonged. And two,: the normal pressure process does not need to use a diaphragm pump for vacuumizing, so that the process and equipment for vacuumizing are simplified, the requirement of the process on air tightness is reduced, the problem of blocking of boron oxide powder crystals can be avoided, as the post-annealing process is used for a long time, boron oxide is separated out to a certain extent, excessive boron sources in a furnace tube are easily caused, excessive boron sources are diffused to a silicon substrate, process deviation is caused, and the problems of blocking and maintenance of the pump are also caused. In order to overcome the process deviation caused by boron oxide precipitation, the invention can be provided with a pure water cleaning component for cleaning the furnace tube, but the existing negative pressure process cannot adopt water washing, the problem of blockage of the diaphragm pump can be aggravated by water washing, and the diaphragm pump and a waste discharge pipeline can only be cleaned and maintained by regular shutdown. And thirdly,: the normal pressure process can avoid the sealing problem of a vacuum system under the high temperature condition, and provides a basis for the stability of TOPCO secondary boron expansion annealing equipment.
(2) The invention provides a better scheme based on the secondary boron expansion normal pressure annealing process of TOPCO battery, which divides the constant temperature oxidation stage into O only 2 Dry oxidation stage as oxidant and simultaneous use of O 2 And H 2 Wet oxidation stage with O as oxidant and other technological conditionsOn the same premise, the process of normal pressure, dry oxidation and wet oxidation is adopted, so that the peak temperature of the oxidation process can be reduced on the premise of guaranteeing various indexes of the prepared silicon wafer, the protection of the furnace tube and the quartz boat is greatly beneficial, the service life of the furnace tube is greatly prolonged, the equipment maintenance cost is reduced, the equipment maintenance time is saved, and the productivity is further improved. Under the same technological conditions, the process of normal pressure, dry oxidation and wet oxidation of the invention can lead the oxide layer to grow faster and thicker, and can obtain SiO with better process than the process of normal pressure, dry oxidation and negative pressure 2 The thickness of the oxide layer is favorable for modifying the thickness of the process sample borosilicate glass (BSG), the annealing process in the prior art adopts oxygen to oxidize to form the BSG, and the wet oxidation formed under the high-temperature condition of pure water is combined to enable the overall oxidation rate to be higher than that of single oxygen, so that the oxidation rate can be regulated to form thicker BSG, the process is matched with the subsequent wet process cleaning regulation, the process window is wider, and the leakage risk of the battery is reduced.
(3) The secondary boron expansion normal pressure annealing system based on the TOPCON battery does not need a vacuum device, simplifies equipment, can effectively overcome the problem of boron oxide powder crystallization blockage, has a certain degree of boron oxide precipitation after long-term use of post annealing equipment in the prior art, is easy to cause excessive boron sources in a furnace tube, causes process deviation when the excessive boron sources are diffused to a silicon substrate, and can cause pump blockage, thereby increasing maintenance cost. The secondary boron expansion normal pressure annealing system provided by the invention is provided with the pure water inlet with a wet oxidation function, and can carry out the reaction while carrying out the precipitated part of boron oxide powder through waste gas with certain humidity in the oxidation process.
Drawings
FIG. 1 is a graph showing the oxidation doping profile of the silicon wafers prepared in example 1 and comparative example 1 according to the present invention.
Fig. 2 is a schematic diagram of the system configuration of embodiment 3 of the present invention.
Legend description: 1. a furnace tube; 2. a furnace door; 3. an intake manifold; 31. o (O) 2 An air inlet; 32. n (N) 2 An air inlet; 33. h 2 An O inlet; 4. an exhaust pipe; 5. an acid pipe; 6. cleaning the tube; 61. a stop valve; 7. and (5) collecting a box.
Detailed Description
The invention is described in further detail below with reference to the drawings and specific examples of the specification.
Example 1
The invention relates to a secondary boron expansion normal pressure annealing process based on TOPCON batteries, which comprises the following steps:
(1) Feeding a boat, controlling the pressure in the furnace tube to be consistent with the external atmospheric pressure, wherein the atmospheric pressure in different altitude areas is generally 750-1060 mbar, in the embodiment, the external atmospheric pressure is 1000mbar, controlling the temperature in the furnace tube to be 780 ℃, and introducing N 2 The flow of the silicon wafer is 1slm (namely 1000 sccm), and the silicon wafer after SE is introduced is loaded in a quartz boat and is sent into a furnace tube of an annealing furnace;
(2) Keeping the temperature constant, keeping the pressure in the furnace tube at 1000mbar, and introducing N 2 The flow rate of the mixture is increased to 15slm, the temperature is increased to 850 ℃, and the mixture is kept for 10min;
(3) Heating, maintaining the pressure in the furnace tube at 1000mbar, and maintaining N 2 The flow rate of (2) is 15slm, the temperature is raised to 970 ℃, and the heating time is 15min;
(4) Keeping the temperature and the pressure in the furnace tube at 1000mbar and keeping N 2 The flow rate of (2) is 15slm, the temperature is 970 ℃, and the temperature is kept for 5min;
(5) Oxidizing, controlling the pressure in the furnace tube to be 1000mbar and the temperature to be 970 ℃, and stopping introducing N 2 Introducing O with flow of 20slm 2 Oxidizing to make oxygen fully fill the furnace tube as much as possible at the stage, wherein the oxidation time is 5min;
(6) Heating up and oxidizing, keeping the pressure in the furnace tube at 1000mbar, and controlling O 2 The flow rate of (2) is 15slm, the temperature is raised to 1045 ℃, and the heating time is 12min;
(7) Constant-temperature oxidation, maintaining the pressure in the furnace tube at 1000mbar and 1045 ℃, and introducing O 2 Continuously oxidizing at a flow rate of 15slm for 75min;
(8) Cooling and oxidizing, keeping the pressure in the furnace tube at 1000mbar, and introducing O 2 Continuously oxidizing at a flow rate of 15slm, and cooling to 800 ℃ for 60min;
(9) Cooling, maintaining the pressure in the furnace tube at 1000mbar and 800 ℃, stopping introducing O 2 Introducing N 2 Is 5slm.
(10) Discharging the boat, maintaining the pressure in the furnace tube at 1000mbar and the temperature at 800 ℃, and introducing N 2 The flow of the silicon wafer is 5slm, the quartz boat with the silicon wafer in the furnace tube is taken out, and the process is finished.
Table 1 process parameters of example 1
Comparative example 1
The main steps of the secondary boron-diffusion negative pressure annealing process based on TOPCO battery are basically the same as those of the embodiment 1, except that: in the steps (5), (6), (7) and (8), the furnace tube pressure is 800mbar, and the previous stage has corresponding negative pressure pumping and leakage detecting steps.
Table 2 process parameters of comparative example 1
In order to compare the influence of the negative pressure oxidation process and the normal pressure oxidation process on the performance of the silicon wafer, the silicon wafers prepared in example 1 and comparative example 1 were subjected to SiO respectively 2 Thickness testing, sheet resistance testing and doping condition testing.
1. SiO under different pressure conditions 2 Thickness performance
The silicon wafers prepared in example 1 and comparative example 1 were selected to be respectivelySquare evenly distributed 9 test sites for testing SiO in the silicon wafers prepared in example 1 and comparative example 1 2 The results are shown in Table 3:
TABLE 3 SiO in silicon wafers prepared in example 1 and comparative example 1 2 Thickness contrast
Note that: in the table, sample 1 and sample 2 are parallel samples, sample 3 and sample 4 are parallel samples, and the test results of the two parallel samples have certain differences due to the difference of details such as the placement positions in the quartz boat.
As can be seen from table 3, as the pressure increases, the thickness of the oxide layer increases under the same oxidation conditions, thereby also indicating that the atmospheric process employed in this example is more advantageous for increasing the oxidation rate and increasing the oxidation efficiency.
2. Sheet resistance test for preparing silicon wafer under different pressure conditions
From the silicon wafers produced in example 1 and comparative example 1, 5 detection positions (distributed at four corners and at the center of a square silicon wafer) were selected, respectively, and the sheet resistances of the silicon wafers produced in example 1 and comparative example 1 were tested, and the results are shown in Table 4:
TABLE 4 sheet resistance comparison of silicon wafers prepared in example 1 and comparative example 1
Note that: the difference of the sheet resistance data of different positions of the same silicon wafer in the table belongs to the normal difference.
As can be seen from Table 4, the negative pressure oxidation and the normal pressure oxidation processes have little effect on the sheet resistance of the silicon wafer and are negligible.
3. Doping conditions of silicon wafers prepared under different pressure conditions
The doping profiles of the silicon wafers prepared in example 1 and comparative example 1 were tested, and as can be seen from fig. 1, the doping profiles of the silicon wafers prepared in the negative pressure and normal pressure processes were substantially identical.
In summary, compared with the silicon wafer prepared by the negative pressure process in the prior art, the silicon wafer prepared by the secondary boron expansion normal pressure annealing process based on the TOPCON battery has basically consistent doping performance and sheet resistance, and SiO 2 The thickness of the oxide layer is obviously increased, the oxidation rate is also improved, and in general, the performance of the product prepared by the secondary boron expansion normal pressure annealing process is superior to that of the product prepared by the negative pressure annealing process. Although the negative pressure condition in the prior art can shorten the free path of molecules in the diffusion process, the boron source diffusion and the deposition on the surface of the silicon wafer are facilitated, and the diffusion uniformity is improved; however, in the secondary boron expansion annealing, boron source deposition is completed in the prior boron expansion stage, only the high-temperature junction pushing and oxidizing are needed to generate borosilicate glass (BSG), the importance of negative pressure is weakened essentially, and the oxidation rate and the oxidation quality are increased along with the increase of oxygen partial pressure, so that the invention adopts the normal pressure process, not only does not lose various performances of the prepared silicon wafer, but also obtains higher oxidation efficiency and better SiO 2 Oxide layer thickness. More importantly, (1) the secondary boron expansion annealing process provided by the invention avoids the defect that the furnace tube and the quartz boat are easy to deform and damage due to high temperature and negative pressure in long-term use in the prior art because the pressure outside the furnace tube is higher than the pressure inside the furnace tube in the negative pressure oxidation process, the furnace tube wall is always subjected to extrusion force from outside to inside due to the existence of pressure difference, and the furnace tube wall is easy to damage due to long-term use in a high-temperature environment close to the softening temperature of the furnace tube material; (2) The normal pressure process avoids using a diaphragm pump, not only simplifies the process and equipment for pumping negative pressure, but also can avoid the problem of boron oxide powder crystallization blockage, because the post annealing process is used for a long time, boron oxide is separated out to a certain extent, excessive boron sources in a furnace tube are easy to cause, excessive boron sources are diffused to a silicon substrate, not only can cause process deviation, but also can cause pump blockage and maintenance problems. In order to overcome the process deviation caused by boron oxide precipitation, the invention can be provided with a pure water cleaning component for cleaning the furnace tube, and the existing negative pressure process is thatThe problem of blockage of the diaphragm pump is aggravated by adopting water washing, and the diaphragm pump and the waste discharge pipeline can be cleaned and maintained only by stopping the diaphragm pump periodically.
Example 2
The main steps of the secondary boron-expansion normal-pressure annealing process based on TOPCO battery of the invention are basically the same as those of the embodiment 1, except that:
the temperature of the heating oxidation in the step (6) is 1030 ℃;
the constant temperature oxidation in the step (7) is divided into two stages of dry oxidation and wet oxidation, the total time of the oxidation reaction in the whole step (7), the pressure in the reaction process and the introduction of O 2 The flow rate of (2) was the same as in example 1, except that the temperature of the oxidation reaction was 1030℃and pure water was required for wet oxidation, specifically:
(7-1) dry oxidation, maintaining the pressure in the furnace tube at 1000mbar and the temperature at 1030 ℃, introducing O 2 The flow rate of the catalyst is 15slm, and the reaction time of the dry oxidation is 35min;
(7-2) wet oxidation, maintaining the pressure in the furnace tube at 1000mbar and the temperature at 1030 ℃, introducing O 2 The flow rate of the catalyst is 15slm, liquid pure water with the flow rate of 2g/min is introduced, the pure water is vaporized under the high temperature condition, and the reaction time of wet oxidation is 40min.
Table 5 process parameters of example 2
Performance testing of the silicon wafer prepared in this example was performed in the manner of the test in example 1, including SiO of the silicon wafer 2 The thickness, sheet resistance and doping conditions are equivalent to those of the silicon wafer prepared in example 1, so that the silicon wafer prepared in the example can meet the production requirements.
The oxidation process of the embodiment adopts a process of combining dry oxidation under normal pressure and wet oxidation, and can prepare the silicon wafer with the thickness of an oxide layer, sheet resistance and doping condition meeting the requirements under the condition of the same pressure and total oxidation time. The material of the reaction furnace tube and the quartz boat for bearing the silicon wafer is quartz, although the reaction furnace tube and the quartz boat are resistant to high temperature, the quartz boat can be softened when reaching a certain temperature, the peak temperature of the existing annealing process is relatively close to the softening temperature of the furnace tube and the quartz boat, the embodiment can reduce the oxidation peak temperature by 10 ℃, the protection of the furnace tube and the quartz boat is greatly beneficial, and in the conventional high-temperature negative-pressure oxidation process, the furnace tube is simultaneously extruded from outside to inside by atmospheric pressure in the long-term high-temperature process because the pressure outside the furnace tube is larger than the internal pressure, and the furnace tube is easy to damage such as deformation and cracking. Therefore, compared with the existing technology under the negative pressure oxidation condition of 1040-1050 ℃, the normal pressure oxidation technology of 1030 ℃ in the embodiment can greatly prolong the service life of the furnace tube, reduce the equipment maintenance cost, save the equipment maintenance time and further improve the productivity. The inventor of the applicant of the present invention has found in practical research that the process of the present invention can be realized with oxidation peak temperatures as low as 980 ℃, but with prolonged reaction times and increased energy consumption.
Example 3
The invention discloses a secondary boron-expansion normal-pressure annealing system based on a TOPCon battery, which is shown in fig. 2 and comprises a furnace tube 1, a furnace door 2, an air inlet header pipe 3, an exhaust pipe 4, an acid exhaust pipe 5, a cleaning pipe 6 and a collecting box 7, wherein air inlets of the air inlet header pipe 3 and the exhaust pipe 4 are respectively positioned at two ends of the furnace tube 1, an air outlet end of the exhaust pipe 4 is communicated with the acid exhaust pipe 5, the cleaning pipe 6 and the collecting box 7 are respectively positioned at two ends of the acid exhaust pipe 5, the cleaning pipe 6 is used for cleaning boron oxide powder in the acid exhaust pipe 5, and the collecting box 7 is used for collecting the boron oxide powder washed and cleaned in the acid exhaust pipe 5.
In this embodiment, the air inlet header 3 is located at the tail end of the furnace, the inlet of the exhaust pipe 4 is located at the mouth end of the furnace, the acid discharge pipe 5 is arranged outside the tail, the exhaust pipe 4 extends from the mouth to the tail to the acid discharge pipe 5, and the acid discharge pipe 5 is connected with peripheral equipment such as a peripheral acid discharge exhaust system.
In this embodiment, the cleaning pipe 6 is provided with a stop valve 61, and the stop valve 61 is opened or closed by a controller at regular time to automatically inject water into and clean the acid discharge pipe 5 at regular time, boron oxide powder flushed from the acid discharge pipe 5 flows into the collecting box 7 along with the wastewater, and then the powder in the collecting box 7 is treated at regular time.
In this embodiment, the intake manifold 3 is connected to a first intake port 31, a second intake port 32 and a third intake port 33, and the first intake port 31 is N 2 The air inlet, the second air inlet 32 is O 2 The third inlet 33 is H 2 And an O inlet, wherein each gas enters the furnace tube through the gas inlet header pipe 3. Set up H 2 The O inlet can be used for a long time, and boron oxide powder precipitated in the furnace tube can be washed regularly (the washing of the tube wall is mainly carried out under the condition of high temperature water in the period of maintenance). At the same time H 2 O can also be used as an oxidant, and the oxidation rate is higher than that of oxygen, so that the oxidation rate can be adjusted, a function of modifying the thickness of BSG exists, and the oxidation rate is matched with a subsequent winding-removing plating process, so that a wider process window is provided, and the leakage risk of a battery is reduced.
In this embodiment, the furnace door 2 has a furnace mouth heat insulation structure, so that energy loss caused by heat exchange between excessive heat of the furnace mouth and the outside under normal pressure can be prevented.
In this embodiment, because a normal pressure process is adopted in the furnace tube 1, the air tightness requirement on the system is not high, the strict air tightness detection work in the early stage of the process is avoided, negative pressure equipment is not needed, the equipment cost is saved, the secondary boron expansion annealing process is facilitated, the oxidation efficiency is improved, more importantly, the cleaning tube 6 can be arranged to regularly wash the acid discharge tube 5, so that the acid discharge tube 5 is cleaned and dredged regularly, and the acid discharge tube 5 is prevented from being blocked by precipitated boron oxide powder after long-term use.
The tail gas exhaust of this embodiment can utilize the little negative pressure that the sour system provided of factory, can also use low-power pump or multitube single pump to satisfy the negative pressure requirement, and power equipment that provides little negative pressure is far away from the reacting furnace generally, and the boron oxide powder is enriched at sour afterbody of calandria 5 basically when washing sour calandria 5, can not lead to the power equipment jam of little negative pressure. In contrast, in the conventional reaction furnaces for the negative pressure oxidation process, the furnace tube cleaning water is generally directly pumped by a diaphragm pump for providing negative pressure to the reaction, so that the diaphragm pump is easily blocked when the boron oxide crystal powder is cleaned.
While the invention has been described with reference to preferred embodiments, it is not intended to be limiting. Many possible variations and modifications of the disclosed technology can be made by anyone skilled in the art, or equivalent embodiments with equivalent variations can be made, without departing from the scope of the invention. Therefore, any simple modification, equivalent variation and modification of the above embodiments according to the technical substance of the present invention shall fall within the scope of the technical solution of the present invention.
Claims (10)
1. A secondary boron-expansion normal-pressure annealing process based on a TOPCON battery is characterized in that: the method comprises the following steps:
(1) Feeding the boat, controlling the pressure in the furnace tube of the annealing furnace to be consistent with the external air pressure, controlling the temperature to be 700-800 ℃, and introducing N 2 Loading the silicon wafers after SE introduction into a quartz boat and feeding the silicon wafers into a furnace tube of an annealing furnace;
(2) Keeping constant temperature, keeping the pressure in the furnace tube consistent with the external air pressure, and keeping N introduced 2 Raising the temperature to 800-850 ℃ and preserving heat;
(3) Heating, keeping the pressure in the furnace tube consistent with the external air pressure, and keeping N introduced 2 Raising the temperature to 860-970 ℃;
(4) Keeping constant temperature, keeping the pressure in the furnace tube consistent with the external air pressure, and keeping N introduced 2 Preserving heat at 860-970 ℃;
(5) Oxidizing, keeping the pressure in the furnace tube consistent with the external air pressure, keeping the temperature to be 860-970 ℃, and stopping introducing N 2 Introducing O 2 Oxidizing;
(6) Heating oxidation, maintaining furnace tubeThe internal pressure is consistent with the external air pressure, and O is introduced 2 Raising the temperature to 980-1050 ℃ and continuing oxidation;
(7) Constant-temperature oxidation, keeping the pressure in the furnace tube consistent with the external air pressure, keeping the temperature between 980 ℃ and 1050 ℃, and keeping the O introduced 2 Dry oxidation, or introduction of O 2 Dry oxidation is carried out, then O is maintained 2 Simultaneously with the introduction of H 2 O is subjected to wet oxidation;
(8) Cooling and oxidizing, keeping the pressure in the furnace tube consistent with the external air pressure, and keeping the O introduced 2 Stopping the introduction of H 2 O, the temperature is reduced to 800-900 ℃;
(9) Cooling, keeping the pressure in the furnace tube consistent with the external air pressure, stopping introducing O, wherein the temperature is 800-840 DEG C 2 Re-introducing N 2 ；
(10) Discharging the boat, keeping the pressure in the furnace tube consistent with the external air pressure, keeping the temperature at 800-840 ℃, and keeping N introduced 2 And taking out the quartz boat with the silicon chips in the furnace tube, and ending the process.
2. The TOPCon cell-based secondary boron-expansion atmospheric annealing process according to claim 1, characterized in that: in the step (7), O is introduced 2 The flow of the catalyst is 10 slm-25 slm, and the constant-temperature oxidation time is 60 min-100 min.
3. The TOPCon battery-based secondary boron-expansion atmospheric annealing process according to claim 2, characterized in that: in the step (7), the H is introduced 2 O is liquid water with the flow rate of 1 g/min-5 g/min; first let in O 2 The dry oxidation is carried out for 30 min-50 min, and then O is maintained 2 Simultaneously with the introduction of H 2 The time for O to be wet oxidized is 30 min-50 min.
4. A TOPCon cell-based secondary boron-diffusion atmospheric annealing process according to claim 3, characterized by: in the step (7), only O is introduced 2 When dry oxidation is carried out, the temperature is controlled to be 1040-1050 ℃, and correspondingly, in the step (6), the temperature is increased to be 1040-1050 ℃;
in the step (7), O is firstly introduced 2 Dry oxidation is carried out, then O is maintained 2 Simultaneously with the introduction of H 2 When O is subjected to wet oxidation, the temperature is controlled to be 980-1030 ℃, and correspondingly, in the step (6), the temperature is increased to 980-1030 ℃.
5. The TOPCon cell-based secondary boron atmospheric annealing process according to any one of claims 1 to 4, characterized in that: in the step (1), N is introduced 2 The flow rate of (2) is 3 slm-5 slm.
6. The TOPCon cell-based secondary boron atmospheric annealing process according to any one of claims 1 to 4, characterized in that: in the step (2), N is introduced 2 The flow of the water is 15 slm-30 slm, and the constant temperature time is 5 min-20 min;
in the step (3), N is introduced 2 The flow of the water is 15 slm-30 slm, and the heating time is 10 min-20 min;
in the step (4), N is introduced 2 The flow of the water is 5 slm-15 slm, and the constant temperature time is 5 min-10 min.
7. The TOPCon cell-based secondary boron atmospheric annealing process according to any one of claims 1 to 4, characterized in that: in the step (5), O is introduced 2 The flow of the catalyst is 15 slm-20 slm, and the oxidation time is 3 min-5 min;
in the step (6), O is introduced 2 The flow rate of the water is 15 sccm-20 sccm, and the heating time is 10 min-15 min;
in the step (8), O is introduced 2 The flow of the water is 5 slm-20 slm, and the cooling time is 50 min-70 min.
8. The TOPCon cell-based secondary boron atmospheric annealing process according to any one of claims 1 to 4, characterized in that: in the step (9), N is introduced 2 The flow of the water is 5 slm-10 slm;
in the step (10), N is introduced 2 The flow rate of (2) is 3 slm-5 slm.
9. A secondary boron expansion normal pressure annealing system based on TOPCON battery is characterized in that: including boiler tube (1), furnace gate (2), air inlet manifold (3), blast pipe (4), sour calandria (5), wash pipe (6) and collecting box (7), the air inlet of air inlet manifold (3) and blast pipe (4) is located the both ends of boiler tube (1) respectively, the end of giving vent to anger of blast pipe (4) communicates with sour calandria (5), wash pipe (6) and collecting box (7) are located the both ends of sour calandria (5) respectively, wash pipe (6) are used for wasing the boron oxide powder in sour calandria (5), collecting box (7) are used for collecting the boron oxide powder that washs down in sour calandria (5).
10. The TOPCon cell-based secondary boron atmospheric annealing system according to claim 9, wherein: the air inlet main pipe (3) is positioned at the tail end of the furnace, the inlet of the exhaust pipe (4) is positioned at the mouth end of the furnace, the acid discharge pipe (5) is arranged at the outer side of the tail end of the furnace, the exhaust pipe (4) extends from the mouth of the furnace to the tail end of the furnace to the acid discharge pipe (5), and the acid discharge pipe (5) is connected with peripheral negative pressure equipment; a stop valve (61) is arranged on the cleaning pipe (6), and the stop valve (61) is opened or closed at regular time through a controller so as to realize automatic injection of water at regular time and cleaning of the acid discharge pipe (5); n is communicated with the air inlet header pipe (3) 2 Air inlet (31), O 2 Air inlet (32) and H 2 And an O inlet (33) for allowing each gas to enter the furnace tube through the air inlet header pipe (3).
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