A boron diffusion method with high uniformity

Abstract

The present invention discloses a highly uniform boron diffusion method. By depositing BC13 under different pressure and temperature conditions, the distribution of the deposition within the tube is adjusted to achieve improved uniformity. The boron diffusion method of the present invention achieves more uniform silicon wafer square resistance in the furnace inlet and furnace tail regions, thereby improving the uniformity of the overall square resistance of the furnace tube. The method of the present invention is applicable to large-diameter and long-length furnace tubes, improving the uniformity of the intra- and inter-wafer square resistance of the silicon wafers throughout the furnace tube.

Description

Technical Field

[0001] The present invention particularly relates to a boron diffusion method with high uniformity. Background Art

[0002] In the field of solar photovoltaic cell technology, P-type PERC cell technology has become the mainstream in the market due to its mature process technology and reduced costs. Although it has a large market share and is likely to remain the mainstream cell technology for the next 1-2 years, the fact that PERC cells are increasingly approaching their theoretical limits ultimately indicates that cell technology is facing a new technological inflection point.

[0003] To further improve the efficiency of photovoltaic cells, new technology routes have been proposed and entered the experimental and even mass production stages. Topcon, IBC, and their derivative technology routes all utilize boron diffusion equipment. To reduce the investment cost of these new technologies, greater production capacity and adaptability to large silicon wafers are required, requiring the diameter and length of the furnace tubes to be further increased. This subsequently leads to a deterioration in the uniformity of sheet resistance within and between boron-expanded wafers. This is because with large diameter and length furnace tubes, it is difficult to maintain a consistent gas source atmosphere during the deposition step in all areas of the furnace tube.

[0004] The current existing boron expansion process is difficult to take into account the uniformity issues in the furnace mouth and furnace tail areas. Summary of the Invention

[0005] In view of the above situation, in order to overcome the defects of the prior art, the present invention provides a boron diffusion method with high uniformity.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A boron diffusion method with high uniformity comprises the following steps:

[0008] (1) Place the silicon wafer into a quartz boat, and push the quartz boat into the quartz tube of the diffusion furnace;

[0009] (2) Evacuate to a pressure of 20-500 mBar;

[0010] (3) Raise the temperature to 750-950°C, introduce 50-500 sccm of BC13 gas and 100-5000 sccm of O2 gas, maintain for 2-20 minutes, and perform the first deposition;

[0011] (4) Use nitrogen or oxygen to adjust the pressure to the process pressure required for the next source; continue to introduce 50-500 sccm of BC13 gas and 100-5000 sccm of O2 gas, maintain for 2-20 minutes, and perform the second deposition;

[0012] (5) Heating to 900-1050°C, introducing nitrogen, and advancing, maintaining for 0-30 minutes;

[0013] (6) Heating to 950-1100°C, introducing oxygen, and maintaining for 20-120 minutes for oxidation;

[0014] (7) When the temperature drops to 700-850°C, introduce nitrogen, back-pressure, and remove the quartz boat from the diffusion furnace quartz tube;

[0015] (8) Remove the silicon wafer from the quartz boat.

[0016] Furthermore, in step (4), nitrogen or oxygen is introduced to adjust the pressure to 20-500 mBar.

[0017] Furthermore, in step (4), nitrogen or oxygen is introduced to adjust the pressure to 50-500 mBar.

[0018] Furthermore, in step (5), 1-5 L of nitrogen is introduced.

[0019] Furthermore, in step (6), the temperature is raised to 950-1050° C., 1-50 L of oxygen is introduced, and maintained for 20-120 minutes.

[0020] Furthermore, after step (4), at least one deposition step is added. The number of deposition steps can be further increased under different pressures according to the uniformity, and the present invention does not specifically limit it.

[0021] The beneficial effects of the present invention are:

[0022] (1) The present invention adjusts the deposition distribution of BC13 throughout the tube by depositing under different pressure and temperature conditions, thereby achieving better uniformity. The boron diffusion method of the present invention makes the silicon wafer square resistance in the furnace inlet and furnace tail areas more uniform, thereby improving the uniformity of the overall square resistance of the furnace tube.

[0023] (2) The method of the present invention can be applied to furnace tubes with large diameters and long lengths, thereby improving the uniformity of the intra-wafer and inter-wafer square resistances of the silicon wafers in the entire furnace tube, thereby improving the feasibility of mass production of furnace tubes with larger diameters and longer lengths. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the boron diffusion process in Example 1.

[0025] Figure 2 This is a schematic flow chart of the boron diffusion method in Example 2.

[0026] Figure 3 Schematic diagram comparing the diffusion square resistance of silicon wafers in Examples 1-2 and Comparative Examples 1-3. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is described and illustrated below in conjunction with the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely used to explain this application and are not intended to limit this application. Based on the embodiments provided in this application, all other embodiments obtained by those of ordinary skill in the art without making any creative efforts are within the scope of protection of this application.

[0028] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it refer to independent or alternative embodiments that are mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described in this application may be combined with other embodiments unless there is a conflict.

[0029] Unless otherwise defined, the technical or scientific terms involved in this application should have the usual meaning understood by people with ordinary skills in the technical field to which this application belongs. The words "one", "a", "the" and the like involved in this application do not indicate quantity restrictions and can indicate the singular or plural. The terms "include", "comprise", "have" and any of their variations involved in this application are intended to cover non-exclusive inclusions; the words "connect", "connected", "coupled" and the like involved in this application are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. The "multiple" involved in this application means greater than or equal to two. "And / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, "A and / or B" can mean: A exists alone, A and B exist at the same time, and B exists alone. The terms "first", "second", "third" and the like involved in this application are merely to distinguish similar objects and do not represent a specific ordering of objects.

[0030] The gases and / or reagents and / or instruments used in the following examples and comparative examples can all be obtained through commercial channels.

[0031] In the following Examples 1-2 and Comparative Examples 1-2, the inner diameter of the quartz furnace tube is 430 mm, the tube length is 3550 mm, and the silicon wafer size is 210 mm * 210 mm; Comparative Example 3 adopts the method in the prior art (CN111341649); wherein, the inner diameter of the quartz furnace tube is 380 mm, the tube length is 3100 mm, and the silicon wafer size is: 166 mm * 166 mm.

[0032] Example 1

[0033] A boron diffusion method with high uniformity comprises the following steps:

[0034] (1) Place the silicon wafers to be boron diffused into a quartz boat, and push the boat into the quartz tube of a diffusion furnace at an internal temperature of 800°C. In this embodiment, each boat contains 2,000 silicon wafers.

[0035] (2) Evacuate to a pressure of 70 mBar;

[0036] (3) Raise the temperature to 830°C, introduce 200 sccm of BCl3 gas and 1000 sccm of O2 gas, maintain for 10 minutes, and perform the first deposition;

[0037] (4) Nitrogen gas was introduced to return the pressure to 100 mBar, and 200 sccm of BC13 gas and 1000 sccm of O2 gas were introduced, maintained for 5 minutes, and the second deposition was performed;

[0038] (5) Raise the temperature to 950°C, introduce 3 L of nitrogen, and maintain for 5 min;

[0039] (6) Oxidation: Heat to 1030°C, introduce 10 L of oxygen, and maintain for 30 min;

[0040] (7) Cooling and removing the boat: The temperature is lowered to 750°C, nitrogen is introduced, and back pressure is applied to remove the quartz boat from the quartz tube of the diffusion furnace;

[0041] (8) Unloading: Remove the silicon wafer from the quartz boat.

[0042] Example 2

[0043] A boron diffusion method with high uniformity comprises the following steps:

[0044] (1) Place the silicon wafers to be boron diffused into a quartz boat, and push the boat into the quartz tube of a diffusion furnace at an internal temperature of 800°C. In this embodiment, each boat contains 2,000 silicon wafers.

[0045] (2) Evacuate to a pressure of 70 mBar;

[0046] (3) Raise the temperature to 830°C, introduce 200 sccm of BCl3 gas and 1000 sccm of O2 gas, maintain for 10 minutes, and perform the first deposition;

[0047] (4) Nitrogen was introduced to return the pressure to 85 mBar, and 200 sccm of BC13 gas and 1000 sccm of O2 gas were introduced, maintained for 5 minutes, and the second deposition was performed;

[0048] (5) Nitrogen gas was introduced to return the pressure to 100 mBar, and 200 sccm of BC13 gas and 1000 sccm of O2 gas were introduced, maintained for 5 minutes, and the third deposition was performed;

[0049] (6) Raise the temperature to 950°C, introduce 3 L of nitrogen, and maintain for 5 min;

[0050] (7) Oxidation: Heat to 1030°C, introduce 10 L of oxygen, and maintain for 30 min;

[0051] (8) Cooling down and removing the boat: The temperature is reduced to 750°C, and the quartz boat is removed from the quartz tube of the diffusion furnace;

[0052] (9) Unloading: Remove the silicon wafer from the quartz boat.

[0053] Example 3

[0054] A boron diffusion method with high uniformity comprises the following steps:

[0055] (1) Place the silicon wafers to be boron diffused into a quartz boat, and push the boat into the quartz tube of a diffusion furnace at an internal temperature of 720°C. In this embodiment, each boat contains 2,000 silicon wafers.

[0056] (2) Evacuate to a pressure of 50 mBar;

[0057] (3) Raise the temperature to 810°C, introduce 250 sccm of BCl3 gas and 1500 sccm of O2 gas, maintain for 15 minutes, and perform the first deposition;

[0058] (4) Nitrogen was introduced to return the pressure to 120 mBar, and 250 sccm of BC13 gas and 1500 sccm of O2 gas were introduced, and maintained for 5 minutes for the second deposition;

[0059] (5) Raise the temperature to 950°C, introduce 4 L of nitrogen, and maintain for 5 min;

[0060] (6) Oxidation: Heat to 1050°C, introduce 15 L of oxygen, and maintain for 30 min;

[0061] (7) Cooling and removing the boat: The temperature is lowered to 750°C, nitrogen is introduced, and back pressure is applied to remove the quartz boat from the quartz tube of the diffusion furnace;

[0062] (8) Unloading: Remove the silicon wafer from the quartz boat.

[0063] Comparative Example 1

[0064] A boron diffusion method comprises the following steps:

[0065] (1) Place the silicon wafers to be boron diffused into a quartz boat, and push the boat into the quartz tube of a diffusion furnace at an internal temperature of 800°C. In this embodiment, each boat contains 2,000 silicon wafers.

[0066] (2) Evacuate to a pressure of 150 mBar;

[0067] (3) Raise the temperature to 830°C, introduce 200 sccm of BCl3 gas and 1000 sccm of O2 gas, maintain for 15 minutes, and perform deposition;

[0068] (4) Raise the temperature to 950°C, introduce 3 L of nitrogen, and maintain for 5 min;

[0069] (5) Oxidation: Heat to 1030°C, introduce 10 L of oxygen, and maintain for 30 min;

[0070] (6) Cooling down and removing the boat: The temperature is reduced to 750°C, and the quartz boat is removed from the quartz tube of the diffusion furnace;

[0071] (7) Unloading: Remove the silicon wafer from the quartz boat.

[0072] Comparative Example 2

[0073] A boron diffusion method comprises the following steps:

[0074] (1) Place the silicon wafers to be boron diffused into a quartz boat, and push the boat into the quartz tube of a diffusion furnace at an internal temperature of 800°C. In this embodiment, each boat contains 2,000 silicon wafers.

[0075] (2) Evacuate to a pressure of 70 mBar;

[0076] (3) Raise the temperature to 830°C, introduce 200 sccm of BCl3 gas and 1000 sccm of O2 gas, maintain for 15 minutes, and perform deposition;

[0077] (4) Raise the temperature to 950°C, introduce 3 L of nitrogen, and maintain for 5 min;

[0078] (5) Oxidation: Heat to 1030°C, introduce 10 L of oxygen, and maintain for 30 min;

[0079] (6) Cooling down and removing the boat: The temperature is reduced to 750°C, and the quartz boat is removed from the quartz tube of the diffusion furnace;

[0080] (7) Unloading: Remove the silicon wafer from the quartz boat.

[0081] Comparative Example 3

[0082] A boron diffusion method in the prior art includes the following steps:

[0083] (1) Place the silicon wafers to be boron diffused into a quartz boat, and push the boat into a diffusion furnace quartz tube at an internal temperature of 820°C and a pressure of 200 mbar. In this embodiment, each quartz boat contains 1,800 silicon wafers.

[0084] (2) 300 sccm of BCl3 gas and 500 sccm of O2 gas were introduced into the quartz furnace tube and maintained for 5 minutes for the first deposition;

[0085] (3) Raise the temperature to 870°C, continue to introduce 300 sccm of BCl3 gas and 500 sccm of O2 gas simultaneously, maintain for 5 minutes, and perform the second deposition;

[0086] (4) Raise the temperature to 1000°C and turn on the vacuum pump at the same time to make the furnace atmosphere at a low pressure state below 100 mbar;

[0087] (5) After the temperature stabilizes, introduce 5 L of nitrogen and maintain for 5 min;

[0088] (6) Introduce 20 L of oxygen and maintain for 20 minutes;

[0089] (7) The temperature is lowered to 750°C and the quartz boat is removed from the diffusion furnace quartz tube;

[0090] (8) Unloading: Remove the silicon wafer from the quartz boat.

[0091] Before unloading, the silicon wafers at different positions on the quartz boat in Examples 1-2 and Comparative Examples 1-3 were sampled and tested. The test results are as follows: Figure 3 As shown, through Figure 3 The data shown show that the silicon wafers produced by the diffusion method of the present invention have good uniformity and high consistency (i.e., low inconsistency) in diffusion resistance. Using the prior art method (CN111341649) and using the furnace tubes and silicon wafers of the dimensions described in Examples 1-2 for boron diffusion, the uniformity of the diffusion resistance within and between the wafers deteriorated, and was worse than that of Comparative Example 3.

[0092] Those skilled in the art should understand that the various technical features of the above-described embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the various technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0093] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art may make various modifications and improvements without departing from the scope of the present application, and such modifications and improvements are all within the scope of protection of the present application.

Claims

1. A boron diffusion method with high uniformity, characterized in that: The following steps are involved: (1) Place the silicon wafer into a quartz boat, and push the quartz boat into the quartz tube of the diffusion furnace; (2) Evacuate to a pressure of 20-500 mBar; (3) Raise the temperature to 750-950°C, introduce 50-500 sccm of BC13 gas and 100-5000 sccm of O2 gas, maintain for 2-20 minutes, and perform the first deposition; (4) Use nitrogen or oxygen to adjust the pressure and return it to the process pressure required for the next step of the source; continue to introduce 50-500 sccm of BC13 gas and 100-5000 sccm of O2 gas, maintain for 2-20 minutes, and perform the second deposition; (5) Heating to 900-1050°C, introducing nitrogen, and advancing, maintaining for 0-30 minutes; (6) Raise the temperature to 950-1100°C, introduce oxygen, and maintain for 20-120 minutes for oxidation; (7) When the temperature drops to 700-850°C, introduce nitrogen, back-pressure, and remove the quartz boat from the diffusion furnace quartz tube; (8) Remove the silicon wafer from the quartz boat.

2. The method for boron diffusion with high uniformity according to claim 1, wherein: In step (4), nitrogen or oxygen is introduced to adjust the pressure to 20-500 mBar.

3. The method for boron diffusion with high uniformity according to claim 2, wherein: In step (4), nitrogen or oxygen is introduced to adjust the pressure to 50-500 mBar.

4. The method for boron diffusion with high uniformity according to claim 2, wherein: In step (5), 1 to 5 L of nitrogen is introduced.

5. The method for boron diffusion with high uniformity according to claim 2, wherein: In step (6), the temperature is raised to 950-1100° C., 1-50 L of oxygen is introduced, and maintained for 20-120 min.

6. The method for boron diffusion with high uniformity according to claim 1, wherein: After step (4), at least one deposition step is added.

Images