A method for improving batch-to-batch uniformity of pn junction depth and its application

Abstract

The present invention relates to the technical field of TOPCon battery preparation, and discloses a method for improving the batch-to-batch uniformity of p-n junction depth. The present invention optimizes the boron diffusion process. First, the present invention sets the air inlet and the air outlet of the boron diffusion furnace at both ends of the furnace, which is a prerequisite for the boron diffusion gas to uniformly pass through all silicon wafers; then, a diffusion plate is set at the air inlet end of the boat support near the air inlet, and when the air is inlet, the gas is directly pulsed to the diffusion plate, so that the gas can be diffused in the diffusion furnace, so that the gas can uniformly pass through all silicon wafers; and a balance plate is set at the air outlet end of the boat support near the air outlet to prevent eddy currents from being generated in the furnace during air extraction, and to ensure that the mouth extraction speed is close to the tail, thereby improving the uniformity of boron diffusion.

Description

Technical Field

[0001] The present invention relates to the technical field of TOPCon battery preparation, and in particular to a method for improving batch-to-batch uniformity of pn junction depth and its application. Background Art

[0002] Solar cells are electrical devices that convert light energy directly into electrical energy through the photovoltaic effect. TOPCon cells are crystalline silicon solar cells with tunnel oxide passivation contacts based on the principle of selective carriers. Their conversion efficiency has overwhelmingly replaced PERC cells and has recently become a hot topic in the battery industry.

[0003] The general process flow of TOPCon cells includes the following steps: texturing, diffusion, SE laser, etching, annealing, back coating, front coating, back film laser grooving, screen printing, sintering, etc. Among them, diffusion is mainly to form a pn junction with a certain depth by boron diffusion on an N-type silicon wafer. At present, most of the research on pn junctions focuses on the doping concentration and junction depth of the emitter. For example, the research mainly focuses on how to optimize the doping concentration and junction depth of the emitter to improve the electrical performance parameters of the battery. From the perspective of passivation, the smaller the doping concentration and junction depth of the emitter, the smaller the Auger recombination and radiation recombination, so that the solar cell can have a higher open circuit voltage. From the perspective of electrode contact, the higher the doping concentration and depth of the emitter, the smaller the contact resistivity between the emitter and the electrode.

[0004] For example, the Chinese patent application publication number CN113809201A discloses a boron diffusion method and solar cell, which reduces the contact resistivity and carrier recombination by doping different concentrations of boron at different depths of the pn junction, thereby improving the conversion efficiency of the solar cell. However, with the continuous advancement of the research and development of high-efficiency solar cells, it is indispensable to study from different research directions to continuously improve the conversion efficiency of solar cells.

[0005] In the prior art, boron diffusion is mostly carried out using a low-pressure boron diffusion furnace. Whether it is boron doping of the target concentration or the target depth, it depends on the boron diffusion process itself in the low-pressure boron diffusion furnace. Based on previous research, the parameters of the boron diffusion process itself are studied to obtain a pn junction of the target concentration and target depth, such as optimizing the boron diffusion process and obtaining a pn junction with higher uniformity, so as to further improve the electrical performance of the TOPCon battery. This is of great significance to the development of the TOPCon battery field. Summary of the invention

[0006] In order to improve the electrical performance of TOPCon cells, the present invention provides a method and application for improving the batch-to-batch uniformity of pn junction depth. The present invention sets the air inlet and air outlet of the boron diffusion furnace at both ends of the furnace as a prerequisite for the boron diffusion gas to uniformly pass through all silicon wafers; then sets a diffusion plate at the air inlet end of the boat support near the air inlet, and directly pulses gas to the diffusion plate during air intake, so that the gas can be diffused in the diffusion furnace, so that the gas can uniformly pass through all silicon wafers; and sets a balance plate at the air outlet end of the boat support near the air outlet to prevent eddy currents from being generated in the furnace during air extraction, and ensure that the extraction speed at the mouth is close to that at the tail, thereby improving the uniformity of boron diffusion.

[0007] The specific technical scheme of the present invention is:

[0008] In a first aspect, the present invention provides a method for improving batch-to-batch uniformity of pn junction depth, comprising the following steps:

[0009] Step S1: providing a low-pressure boron diffusion furnace, which includes:

[0010] An air inlet, provided at the end of the diffusion furnace, for introducing gas into the diffusion furnace;

[0011] A gas outlet is provided at the other end of the diffusion furnace and is used as an outlet for the gas in the diffusion furnace;

[0012] Several boat trays for loading silicon wafers;

[0013] A diffusion plate is disposed at the air inlet end of the boat support near the air inlet, and the air inlet pulses gas to the diffusion plate to diffuse the gas in the diffusion furnace;

[0014] A balance plate, arranged at the gas outlet end of the boat support near the gas outlet, for making the gas flow through the boat support at a uniform flow rate;

[0015] Step S2: placing an N-type silicon substrate in the boat holder;

[0016] Step S3: The temperature in the diffusion furnace is adjusted to 850-1200°C and the pressure is adjusted to 150-700 mtorr, and a boron source and an oxygen source are introduced into the diffusion furnace through the air inlet to diffuse boron, so that a boron-doped layer is formed on the surface of the silicon substrate to obtain a pn junction.

[0017] In order to improve the electrical performance of TOPCon cells, the prior art usually studies and improves the doping concentration of boron diffusion, but there is little research on how to improve the uniformity of boron diffusion. In order to further improve the electrical performance of TOPCon cells, the present invention reduces the contact resistivity of the cell and reduces carrier recombination by improving the uniformity of the pn junction depth, thereby improving the conversion efficiency of the cell.

[0018] To this end, the present invention optimizes the boron diffusion process and provides a method for improving the batch-to-batch uniformity of the pn junction depth. First, the present invention sets the air inlet and the air outlet of the boron diffusion furnace at both ends of the furnace as a prerequisite for the boron diffusion gas to uniformly pass through all silicon wafers; then, a diffusion plate is set at the air inlet end of the boat support near the air inlet, and when the air is inlet, the gas is directly pulsed to the diffusion plate, so that the gas can be diffused in the diffusion furnace, so that the gas can uniformly pass through all silicon wafers; and a balance plate is set at the air outlet end of the boat support near the air outlet to prevent eddy currents from being generated in the furnace during air extraction, and to ensure that the pumping speed at the mouth is close to that at the tail, thereby improving the uniformity of boron diffusion.

[0019] As a preferred embodiment of the above technical solution, in step S1, the air inlet is arranged in front of the diffusion plate, and the horizontal distance between the air inlet and the diffusion plate is 150-200 mm.

[0020] The air inlet is set in front of the diffusion plate, and the horizontal distance between the air inlet and the diffusion plate is 150~200mm. When the air is inlet, the air inlet can directly pulse gas to the diffusion plate, and the gas can be diffused in the diffusion furnace after being reflected by the diffusion plate. The repeated diffusion of air intake is conducive to improving the uniformity of gas passing through all silicon wafers, thereby improving the uniformity of the pn junction depth within the wafer and within the batch. It is appropriate to set the horizontal distance between the air inlet and the diffusion plate to 150~200mm. If the distance is set too large, the diffusion effect is not good, and the boron diffusion uniformity is not good; if the distance is set too small, it is easy to cause the pn junction depth uniformity of the silicon wafer at the front end of the boat support close to the air inlet to be poor, and the pn junction depth of the silicon wafer at the front end is greatly different from the pn junction depth of the rear end. Among them, the "front" and "rear" described in the present invention are based on the gas flow direction, the gas flow in side is the front, and the gas out side is the rear.

[0021] As a preferred embodiment of the above technical solution, in step S2, the N-type silicon substrate is placed at least 60 mm away from the diffusion plate.

[0022] The function of the diffusion plate is to diffuse the boron diffusion gas in the diffusion furnace. During the process, the N-type silicon substrate should be placed at a certain distance from the diffusion plate, at least 60mm. After one side of the diffusion plate reflects the diffused gas, if the N-type silicon substrate is placed at a distance too small from the other side of the diffusion plate, such as direct contact, the gas is not diffused evenly to the N-type silicon substrates, so the uniformity within the wafer is poor, and it will cause the silicon wafer at the front end of the boat support near the air inlet to have a large difference in the pn junction depth with the rear end, resulting in poor uniformity within the batch.

[0023] Further preferably, the N-type silicon substrate is placed at least 60 mm away from the balance board.

[0024] The function of the balance plate is to prevent eddy currents from being generated in the diffusion furnace during vacuuming, and to ensure that the vacuuming speed at the mouth is close to that at the tail. The N-type silicon substrate is placed at least 60 mm away from the balance plate, which has a better effect and the obtained pn junction depth has good uniformity within the wafer and within the batch.

[0025] As a preferred embodiment of the above technical solution, the length of the boat support is 100~150cm.

[0026] As a preferred embodiment of the above technical solution, the interval between two adjacent boat supports is 120~160mm.

[0027] In order to increase the production capacity, the boron diffusion furnace is usually longer, so the boat support is also longer, but the longer boat support will cause uneven airflow in the second half of the boat support, so the uniformity of the silicon wafer in the second half of the boat support is poor. In order to further improve the uniformity of the pn junction depth, the present invention sets a plurality of boat supports, and the length of a single boat support is 100-150cm, and the interval between two adjacent boat supports is set to 120-160mm, so that the gas can be evenly diffused and flow through the silicon wafer in the boat support near the gas outlet of the diffusion furnace.

[0028] As a preferred embodiment of the above technical solution, the flow rate of the boron source is 15-30 L / h, and the flow rate of the oxygen source is 40-60 L / h.

[0029] The present invention needs to control the introduction speed of the boron source and the oxygen source within a certain range. If the gas introduction flow rate is too high, it is not conducive to gas diffusion and intake; if the gas introduction flow rate is too low, it is not conducive to the adhesion of the boron source and the oxygen source on the surface of the silicon wafer, and the boron diffusion will also be uneven.

[0030] As a preferred embodiment of the above technical solution, the boron source is boron chloride and the oxygen source is oxygen.

[0031] As a preferred embodiment of the above technical solution, in step S3, a propulsion gas is introduced into the diffusion furnace at the same time to promote the diffusion of the boron source and the oxygen source in the diffusion furnace.

[0032] As a preferred embodiment of the above technical solution, the introduction time of the boron source and the oxygen source is adjusted so that the depth of the pn junction is 0.7-1.0 μm.

[0033] In a second aspect, the present invention provides a TOPCon cell, the pn junction of which is prepared by the above method.

[0034] Compared with the prior art, the present invention has the following technical effects:

[0035] (1) The present invention optimizes the boron diffusion process. First, the present invention sets the air inlet and the air outlet of the boron diffusion furnace at both ends of the furnace, which is a prerequisite for the boron diffusion gas to uniformly pass through all silicon wafers; then, a diffusion plate is set at the air inlet end of the boat support near the air inlet, and when the air is taken in, the gas is directly pulsed to the diffusion plate so that the gas can be diffused in the diffusion furnace and pass through all silicon wafers evenly; and a balance plate is set at the air outlet end of the boat support near the air outlet to prevent vortexes from being generated in the furnace during exhaust, thereby ensuring that the exhaust speed at the mouth is close to that at the tail, thereby improving the uniformity of boron diffusion.

[0036] (2) The present invention provides a setting method for the diffusion plate, where the air inlet is set right in front of the diffusion plate, and the horizontal distance between the air inlet and the diffusion plate is 150~200mm, so that when the air is taken in, the gas can be diffused in the diffusion furnace after being reflected by the diffusion plate. The repeated diffusion of the air intake is beneficial to improving the uniformity of the gas passing through all silicon wafers, thereby improving the uniformity of the pn junction depth within the wafer and within the batch.

[0037] (3) In order to solve the problem that the pn junction depth of the silicon wafer in the second half of the boat support is poorly uniform, the present invention provides multiple boat supports, and the length of a single boat support is set to 100-150 cm, and the interval between two adjacent boat supports is set to 120-160 mm, so that the gas can be evenly diffused and flow through the silicon wafer in the boat support near the gas outlet end of the diffusion furnace. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Shown is a structural schematic diagram of a low-pressure boron diffusion furnace provided by the present invention;

[0039] Figure 2 Display as Figure 1 Schematic diagram of the structure of the middle boat support;

[0040] Figure 3 Schematic diagram showing the test locations for pn junction depth.

[0041] The accompanying drawings are marked as: 1. boron diffusion furnace, 2. air inlet, 3. air outlet, 4. boat support, 5. diffusion plate, 6. balance plate. DETAILED DESCRIPTION

[0042] The present invention will be further described below in conjunction with embodiments. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention involved in the following description are generally only embodiments of a part of the present invention, rather than all embodiments. Therefore, based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work should belong to the scope of protection of the present invention.

[0043] The present invention mainly optimizes the boron diffusion process, and other TOPCon battery preparation processes can be achieved by existing technologies. The "front" and "rear" mentioned in the present invention are based on the gas flow direction, with the gas flowing in as the front and the gas flowing out as the rear.

[0044] Example 1

[0045] This embodiment provides a method for improving the batch-to-batch uniformity of pn junction depth, comprising the following steps:

[0046] Step S1:

[0047] A low pressure boron diffusion furnace 1 is provided, such as Figure 1-2 As shown, it includes:

[0048] An air inlet 2 is provided at the end of the boron diffusion furnace 1 and is used to introduce gas into the diffusion furnace;

[0049] The gas outlet 3 is provided at the other end of the boron diffusion furnace 1 and is used as an outlet for the gas in the diffusion furnace;

[0050] A plurality of boat supports 4 for loading silicon wafers, the length of a single boat support 4 is 120 cm, and the interval between two adjacent boat supports 4 is 144 mm; two boat supports 4 are provided in this embodiment;

[0051] The diffusion plate 5 is arranged at the air inlet end of the boat support 4 near the air inlet 2, and the air inlet 2 pulses gas to the diffusion plate 5 to diffuse the gas in the diffusion furnace; wherein the air inlet 2 is arranged directly in front of the diffusion plate 5, and the horizontal distance between the air inlet 2 and the diffusion plate 5 is 160 mm; wherein the diffusion plate 5 is a solid plate and is arranged in double layers;

[0052] The balance plate 6 is arranged at the gas outlet end of the boat support 4 near the gas outlet 3, so that the gas flows through the boat support 4 at a uniform flow rate; wherein the gas outlet 3 is located behind the balance plate 6, and the horizontal distance between the gas outlet 3 and the diffusion plate 5 is 160 mm;

[0053] Step S2:

[0054] The silicon wafer placement area of ​​the boat support 4 is filled with N-type silicon substrates; Figure 1 As shown, in the boat support 4 provided in step S1, area A and area B are the placement areas of the N-type silicon substrate. With the air inlet end as the front and the air outlet end as the back, the distance between the silicon substrate placed in the front and the diffusion plate 5 is 60 mm, that is, the N-type silicon substrate is placed at least 60 mm away from the diffusion plate 5. At the same time, with the air inlet end as the front and the air outlet end as the back, the distance between the silicon substrate placed in the back and the balance plate 6 is 60 mm, that is, the N-type silicon substrate is placed at least 60 mm away from the balance plate 6.

[0055] Step S3:

[0056] The temperature in the diffusion furnace is adjusted to 950°C and the pressure is adjusted to 400 mtorr. Then, the flow rate of boron chloride is set to 20 L / h, and the flow rate of oxygen is set to 48 L / h. At the same time, boron chloride and oxygen are introduced into the diffusion furnace through the air inlet 2 to diffuse boron for 15 minutes, so that a boron doping layer is formed on the surface of the silicon substrate, thereby obtaining a pn junction. In this step, while the boron source and oxygen source are introduced, a propulsion gas is introduced into the diffusion furnace to promote the diffusion of the boron source and the oxygen source in the diffusion furnace.

[0057] Example 2

[0058] This embodiment provides a method for improving batch-to-batch uniformity of pn junction depth.

[0059] The main difference between this embodiment and embodiment 1 is that in step S1 of this embodiment, the air inlet is arranged directly in front of the diffuser plate, and the horizontal distance between the air inlet and the diffuser plate is 150 mm.

[0060] Example 3

[0061] This embodiment provides a method for improving batch-to-batch uniformity of pn junction depth.

[0062] The main difference between this embodiment and embodiment 1 is that in step S1 of this embodiment, the air inlet is arranged right in front of the diffuser plate, and the horizontal distance between the air inlet and the diffuser plate is 200 mm.

[0063] Example 4

[0064] This embodiment provides a method for improving batch-to-batch uniformity of pn junction depth.

[0065] The main difference between this embodiment and Embodiment 1 is that the length of a single boat support is 100 cm.

[0066] Example 5

[0067] This embodiment provides a method for improving batch-to-batch uniformity of pn junction depth.

[0068] The main difference between this embodiment and Embodiment 1 is that the length of a single boat support is 150 cm.

[0069] Example 6

[0070] This embodiment provides a method for improving batch-to-batch uniformity of pn junction depth.

[0071] The main difference between this embodiment and embodiment 1 is that the air inlet end is at the front and the air outlet end is at the back, and the distance between the silicon substrate placed at the front and the diffusion plate is 70 mm.

[0072] Example 7

[0073] This embodiment provides a method for improving batch-to-batch uniformity of pn junction depth.

[0074] The main difference between this embodiment and the first embodiment is that the air inlet end is at the front and the air outlet end is at the back, and the distance between the silicon substrate placed at the rear and the balance board is 70 mm.

[0075] Example 8

[0076] This embodiment provides a method for improving batch-to-batch uniformity of pn junction depth.

[0077] The main differences between this embodiment and embodiment 1 are that the temperature in the boron diffusion furnace is adjusted to 850° C., the pressure is adjusted to 150 mtorr, the inlet flow rate of boron chloride is adjusted to 15 L / h, and the inlet flow rate of oxygen is adjusted to 40 L / h.

[0078] Example 9

[0079] This embodiment provides a method for improving batch-to-batch uniformity of pn junction depth.

[0080] The main difference between this embodiment and embodiment 1 is that the temperature in the boron diffusion furnace is adjusted to 1050° C., the pressure is adjusted to 650 mtorr, the inlet flow rate of boron chloride is adjusted to 30 L / h, and the inlet flow rate of oxygen is adjusted to 60 L / h.

[0081] Comparative Example 1

[0082] This comparative example provides a boron diffusion method.

[0083] The main difference between this comparative example and Example 1 is that in step S1, the air inlet is arranged right in front of the diffuser plate, and the horizontal distance between the air inlet and the diffuser plate is 130 mm.

[0084] Comparative Example 2

[0085] This comparative example provides a boron diffusion method.

[0086] The main difference between this comparative example and Example 1 is that in step S1, the air inlet is arranged directly in front of the diffuser plate, and the horizontal distance between the air inlet and the diffuser plate is 220 mm.

[0087] Comparative Example 3

[0088] This comparative example provides a boron diffusion method.

[0089] The main difference between this comparative example and Example 1 is that the length of a single boat support is 160 cm.

[0090] Comparative Example 4

[0091] This comparative example provides a boron diffusion method.

[0092] The main difference between this comparative example and Example 1 is that the air inlet end is at the front and the air outlet end is at the back, and the distance between the silicon substrate placed at the front and the diffusion plate is 50 mm.

[0093] Comparative Example 5

[0094] This comparative example provides a boron diffusion method.

[0095] The main difference between this comparative example and Example 1 is that the air inlet end is at the front and the air outlet end is at the back, and the distance between the silicon substrate placed at the rear and the balance board is 50 mm.

[0096] Comparative Example 6

[0097] This comparative example provides a boron diffusion method.

[0098] The main difference between this comparative example and Example 1 is that the flow rate of boron chloride is 10 L / h.

[0099] Comparative Example 7

[0100] This comparative example provides a boron diffusion method.

[0101] The main difference between this comparative example and Example 1 is that the flow rate of boron chloride is 35 L / h.

[0102] Comparative Example 8

[0103] This comparative example provides a boron diffusion method.

[0104] The main difference between this comparative example and Example 1 is that the oxygen inlet flow rate is 30 L / h.

[0105] Comparative Example 9

[0106] This comparative example provides a boron diffusion method.

[0107] The main difference between this comparative example and Example 1 is that the oxygen inlet flow rate is 70 L / h.

[0108] Comparative Example 10

[0109] This comparative example provides a boron diffusion method.

[0110] The main difference between this comparative example and Example 1 is that an additional air inlet is provided, and the additional air inlet is arranged on the side wall of the diffusion furnace and is equidistant from the two ends of the diffusion furnace.

[0111] Performance Testing

[0112] The uniformity of the pn junction depth on the front side of the TOPCon cell silicon wafers prepared in Examples 1 to 9 and Comparative Examples 1 to 10 was tested respectively. The test method was as follows: a silicon wafer in the middle of each temperature zone in the boat support was taken as a test wafer (i.e., 3 wafers were taken from each boat support, the silicon wafers numbered 1 to 3 were selected from region A in sequence along the gas flow direction, and the silicon wafers numbered 4 to 6 were selected from region B in sequence along the gas flow direction). The depth of boron diffusion at point 1, point 2, point 3, point 4, and point 5 was tested with an ECV tester, and the uniformity of the boron diffusion depth was calculated. The positions of point 1, point 2, point 3, point 4, and point 5 are shown in Figure 1. Figure 3 As shown, the uniformity calculation formula is as follows:

[0113] In-chip uniformity = [(maximum value - minimum value of in-chip film thickness) / (2×average value of in-chip film thickness)]×100%;

[0114] Intra-batch uniformity = [(maximum value - minimum value of average film thickness of each silicon wafer) / (2×average film thickness)]×100%.

[0115] The test results are shown in Tables 1 to 4.

[0116] Table 1

[0117]

[0118] Table 2

[0119]

[0120] Table 3

[0121]

[0122] Table 4

[0123]

[0124] From Table 1 to Table 4, we can see that:

[0125] (1) From the data of Examples 1 to 9, it can be seen that the present invention sets the air inlet and the air outlet of the boron diffusion furnace at both ends of the furnace; then sets a diffusion plate at the air inlet end of the boat support near the air inlet, and directly pulses the gas to the diffusion plate during air intake, so that the gas can be diffused in the diffusion furnace and pass through all silicon wafers evenly; and sets a balance plate at the air outlet end of the boat support near the air outlet to prevent eddy currents from being generated in the furnace during air extraction, thereby ensuring that the extraction speed at the mouth is close to that at the tail, thereby performing a boron diffusion process, and the prepared silicon wafers have good pn junction depth uniformity, especially batch-to-batch uniformity. The batch-to-batch uniformity of the present invention can reach 2.02% (Example 6).

[0126] (2) From the comparative analysis of Comparative Examples 1 and 2 and Example 1, it can be seen that the horizontal distances between the air inlet and the diffusion plate of Comparative Examples 1 and 2 are 130 mm and 220 mm respectively, and the batch-to-batch uniformity of the pn junction depth is poor. The reason is that if the distance is set too large, the diffusion effect is not good and the boron diffusion uniformity is not good; if the distance is set too small, it is easy to cause the pn junction depth uniformity of the silicon wafer at the front end of the boat support close to the air inlet to be poor, and the pn junction depth of the silicon wafer at the front end is greatly different from the pn junction depth of the rear end, which leads to poor batch-to-batch uniformity.

[0127] (3) From the comparative analysis of Comparative Example 3 and Example 1, it can be seen that the length of a single boat support of Comparative Example 3 is 160 cm, and its batch-to-batch uniformity is greatly reduced. The uniformity of the silicon wafer numbered 3 is significantly reduced, and the silicon wafer is located at the gas outlet of the boat support. It can be seen that if the boat support is long, it is not easy for the gas to diffuse evenly through the rear half of the boat support, which will lead to poor batch-to-batch uniformity. For this reason, the present invention sets a plurality of boat supports, and the length of a single boat support is 100-150 cm, and the interval between two adjacent boat supports is set to 120-160 mm, so that the gas can be evenly diffused through the silicon wafer in the boat support located near the gas outlet of the diffusion furnace, thereby further improving the uniformity of the pn junction depth.

[0128] (4) From the comparative analysis of Comparative Example 4 and Example 1, it can be seen that during the process, the N-type silicon substrate should be placed at a certain distance from the diffuser plate, at least 60 mm. The principle is that after one side of the diffuser plate reflects the diffused gas, if the N-type silicon substrate is placed at a distance too small from the other side of the diffuser plate, the gas is not diffused uniformly to the places where the N-type silicon substrates are placed, so the uniformity within the wafer is poor and the uniformity within the batch is poor.

[0129] (5) The comparison and analysis between Comparative Example 5 and Example 1 demonstrates the important role of the balance plate in the method of the present invention. The function of the balance plate is to prevent eddy currents from being generated in the diffusion furnace during vacuuming, and to ensure that the vacuuming speed at the mouth is close to that at the tail. The N-type silicon substrate is placed at least 60 mm away from the balance plate, which has a better effect and the uniformity of the pn junction depth within the wafer and within the batch is good.

[0130] (6) By comparing comparative examples 6 to 9 with example 1, it can be seen that the present invention needs to control the introduction speed of the boron source and the oxygen source within a certain range. The reason is that if the gas introduction flow rate is too high, it is not conducive to gas diffusion and inlet, and the pn junction depth uniformity is poor; if the gas introduction flow rate is too low, it is not conducive to the attachment of the boron source and the oxygen source on the silicon wafer surface, and the boron diffusion will also be uneven.

[0131] (7) Comparison between Comparative Example 10 and Example 1 shows that Comparative Example 10 increases the intake of the middle section of the boron diffusion furnace, and the batch-to-batch uniformity of the pn junction depth obtained is greatly reduced. The reason is that the side intake will form eddies, which is not conducive to the uniform distribution of gas in the furnace, and the batch-to-batch uniformity of the pn junction depth is poor.

[0132] The raw materials and equipment used in the present invention, unless otherwise specified, are all commonly used raw materials and equipment in the art; the methods used in the present invention, unless otherwise specified, are all conventional methods in the art.

[0133] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for improving the batch-to-batch uniformity of pn junction depth, characterized in that: The following steps are involved: Step S1: providing a low-pressure boron diffusion furnace (1), which comprises: An air inlet (2) is provided at an end of the boron diffusion furnace (1) and is used to introduce gas into the diffusion furnace; A gas outlet (3) is provided at the other end of the boron diffusion furnace (1) and serves as an outlet for gas in the diffusion furnace; A plurality of boat supports (4) for loading silicon wafers; A diffusion plate (5) is arranged at the air inlet end of the boat support (4) near the air inlet (2), and the air inlet (2) pulses gas toward the diffusion plate (5) to diffuse the gas in the diffusion furnace; A balance plate (6) is arranged at the gas outlet end of the boat support (4) near the gas outlet (3) and is used to allow the gas to flow through the boat support (4) at a uniform flow rate; Step S2: placing an N-type silicon substrate in the boat support (4); Step S3: adjusting the temperature in the boron diffusion furnace to 850-1200° C. and the pressure to 150-700 mtorr, introducing a boron source and an oxygen source into the diffusion furnace through the air inlet (2) to diffuse boron, so as to form a boron doped layer on the surface of the silicon substrate to obtain a pn junction; wherein: In step S1, the air inlet is arranged in front of the diffuser plate, and the horizontal distance between the air inlet and the diffuser plate is 150-200 mm; In step S2, the N-type silicon substrate is placed at least 60 mm away from the diffusion plate; In step S2, the N-type silicon substrate is placed at least 60 mm away from the balance board; The length of the boat support is 100-150 cm, and the interval between two adjacent boat supports is 120-160 mm; The flow rate of the boron source is 15~30L / h, and the flow rate of the oxygen source is 40~60L / h.

2. A method for improving batch-to-batch uniformity of pn junction depth according to claim 1, characterized in that: The boron source is boron chloride, and the oxygen source is oxygen.

3. A method for improving batch-to-batch uniformity of pn junction depth according to claim 1, characterized in that: In step S3, a propulsion gas is introduced into the diffusion furnace at the same time.

4. A method for improving batch-to-batch uniformity of pn junction depth according to claim 1, characterized in that: The introduction time of the boron source and the oxygen source is adjusted so that the depth of the pn junction is 0.7~1.0μm.

5. A TOPCon battery, characterized in that: The pn junction is prepared by the method as described in any one of claims 1 to 4.

Images