Film explosion elimination method based on ALD deposition aluminum oxide film

Abstract

The invention belongs to the technical field of solar cells, and particularly relates to an aluminum oxide film explosion elimination method based on ALD deposition, which comprises the following steps: S1, introducing ozone to pre-treat the surface of a silicon wafer, changing the surface state of the silicon wafer, and reducing H atoms on the surface; s2, depositing a thin film based on an ALD mode, loading the silicon wafer into a furnace chamber, vacuumizing and heating, alternately introducing TMA and water vapor, and growing an aluminum oxide thin film on the surface of the silicon wafer; according to the pretreatment scheme, relatively low interface state density can be ensured, firstly, nitrogen is used as carrier gas to carry water vapor into a reaction chamber, and the nitrogen is introduced to purge residual water vapor in the reaction chamber; then ozone is introduced, then nitrogen is introduced to purge residual ozone in the reaction chamber, the surface state of the silicon wafer is changed, H atoms on the surface are reduced, and the phenomenon of membrane explosion is eliminated under the condition that excellent passivation performance is guaranteed; eL gray edges are completely eliminated, and the conversion efficiency of the cell is improved by 0.03% absolute value.

Description

Technical Field

[0001] The invention belongs to the technical field of solar cells, in particular to a method for eliminating film explosion based on ALD deposition of aluminum oxide thin films. Background Art

[0002] In the crystalline silicon solar cell process, ALD is commonly used to prepare aluminum oxide passivation film. Aluminum oxide film is deposited by ALD, usually using TMA as a precursor and ozone or water as an oxidant. Ozone-based aluminum oxide film has a higher surface negative charge density and better field passivation effect; water-based aluminum oxide film has a lower surface state density and exhibits a better passivation effect than ozone. Therefore, ozone-based aluminum oxide film is replaced by water, but water-based aluminum oxide film still has various performance anomalies in practical applications, the most typical of which is film explosion.

[0003] A Chinese patent with publication number CN114420790A discloses a method for preparing a laminated aluminum oxide film based on an ALD process, comprising the following steps: feeding a growth substrate into a cavity, and then using TMA and O3, TMA and H2O as growth sources, and growing a laminated aluminum oxide film on the surface of the growth substrate in an alternating pulse manner; by adopting an ALD process, in which O3 or H2O is used as a precursor source, respectively, compared with a single-layer aluminum oxide film, the interface state density of aluminum oxide is greatly reduced, and the fixed negative charge density of aluminum oxide after annealing is increased, thereby improving its chemical passivation and field passivation effects, so that it can meet the passivation requirements of some high-efficiency silicon material solar cells. After applying it to the solar cell structure, it can effectively improve the battery conversion efficiency.

[0004] In the current prior art, by adopting a stacked film structure, TMA uses O3 and H2O as growth sources respectively. However, the aluminum oxide film generated by the reaction of TMA and O3 may have different chemical compositions and microstructures, which are different from the aluminum oxide film generated by the reaction of TMA and H20. If the interfaces are not smooth enough, the interface state density will increase, which will in turn lead to an increase in the recombination rate of carriers at the interface, thereby reducing the passivation effect. In addition, in the subsequent reaction of TMA and H2O, high-temperature sintering is required to cause the H atoms in the aluminum oxide film to escape quickly, resulting in film explosion, which will cause the passivation failure in local areas.

[0005] To this end, the present invention provides a method for eliminating film explosion based on ALD deposition of aluminum oxide thin films. Summary of the invention

[0006] In order to make up for the deficiencies of the prior art, at least one technical problem raised in the background technology is solved.

[0007] The technical solution adopted by the present invention to solve the technical problem is: a method for eliminating film explosion based on ALD deposition of aluminum oxide film described in the present invention comprises the following steps: S1: pre-treat the surface of the silicon wafer by introducing ozone to change the surface state of the silicon wafer and reduce the surface H atoms; S2: Thin film deposition based on ALD method. After the silicon wafer is loaded into the furnace chamber, it is evacuated and heated. Then, TMA and water vapor are alternately introduced to grow an aluminum oxide film on the surface of the silicon wafer.

[0008] Preferably, the method for pretreating the surface of the silicon wafer in S1 is: A1: Use nitrogen as carrier gas to carry water vapor into the reaction chamber, the carrier gas flow rate is 2-10slm, and the introduction time is 3-10s; A2: introducing nitrogen to purge the residual water vapor in the reaction chamber; A3: ozone is introduced, the ozone flow rate is 3-10slm, and the introduction time is 3-10s; A4: introducing nitrogen to purge the residual ozone in the reaction chamber; A5: Repeat the sequence of A1-A4 for multiple times, the number of times is 1-10 times.

[0009] Preferably, in A2, the purge nitrogen flow rate is 4-20slm, and the purge time is 8-20s.

[0010] Preferably, in A4, nitrogen is introduced during ozone purging, the purging time is 6-20s, and the nitrogen flow rate is 4-20slm.

[0011] Preferably, in S2, vacuuming and heating are performed, wherein the cavity pressure is evacuated to below 10 Pa, and the temperature of the silicon wafer is heated to 100-200°C.

[0012] Preferably, the method for depositing a thin film by ALD in S2 is: B1: Use nitrogen as carrier gas to carry TMA vapor into the reaction chamber; B2: nitrogen is introduced to purge the residual TMA in the reaction chamber; B3: Use nitrogen as carrier gas to carry water vapor into the reaction chamber; B4: introducing nitrogen to purge the residual water vapor in the reaction chamber; B5: Repeat B1-B4 until the aluminum oxide film of the desired thickness is obtained.

[0013] Preferably, in B1, the source bottle temperature of TMA is 40-50° C., the carrier gas flow rate is 2-10 slm, and the introduction time is 3-10 s.

[0014] Preferably, in B2, the purge nitrogen flow rate is 4-20slm, and the purge time is 5-15s.

[0015] Preferably, in B3, the temperature of the water source bottle is 35-50° C., the carrier gas flow rate is 2-10 slm, and the introduction time is 3-10 s.

[0016] Preferably, in B4, the purge nitrogen flow rate is 4-20slm, and the purge time is 8-20s.

[0017] The beneficial effects of the present invention are as follows: 1. The method for eliminating film explosion based on ALD deposition of aluminum oxide film described in the present invention can ensure a low interface state density through a pretreatment scheme. First, nitrogen is used as a carrier gas to carry water vapor into the reaction chamber, and nitrogen is introduced to purge the residual water vapor in the reaction chamber; then ozone is introduced, and then nitrogen is introduced to purge the residual ozone in the reaction chamber, thereby changing the surface state of the silicon wafer, reducing the surface H atoms, and ensuring excellent passivation performance, while eliminating the film explosion phenomenon and EL gray edge defects; the EL gray edge is completely eliminated, and the battery conversion efficiency is improved by an absolute value of 0.03%.

[0018] 2. The present invention discloses a method for eliminating film explosion based on ALD deposition of aluminum oxide film, wherein the aluminum oxide film is deposited by ALD, and nitrogen is used as a carrier gas to carry TMA vapor into a reaction chamber; nitrogen is introduced to purge residual TMA in the reaction chamber; nitrogen is then used as a carrier gas to carry water vapor into the reaction chamber; nitrogen is introduced to purge residual water vapor in the reaction chamber; and the operation is repeated in sequence to obtain an aluminum oxide film of desired thickness. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be further described below in conjunction with the accompanying drawings.

[0020] Figure 1 It is a flow chart of the method for eliminating film explosion based on ALD deposition of aluminum oxide film in the present invention; Figure 2 It is a flow chart of the method for pretreating the surface of a silicon wafer in the present invention; Figure 3 is a flow chart of a method for depositing a thin film based on the ALD method in the present invention; Figure 4 It is a schematic diagram of the explosion of the aluminum oxide film in the present invention. DETAILED DESCRIPTION

[0021] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0022] like Figure 1As shown, a method for eliminating film explosion based on ALD deposition of aluminum oxide film according to an embodiment of the present invention comprises the following steps: S1: pre-treat the surface of the silicon wafer by introducing ozone to change the surface state of the silicon wafer and reduce the surface H atoms; S2: Thin film deposition based on ALD method. After the silicon wafer is loaded into the furnace chamber, it is evacuated and heated. Then, TMA and water vapor are alternately introduced to grow an aluminum oxide film on the surface of the silicon wafer.

[0023] In the prior art, a growth substrate is sent into a cavity, and then TMA and O3, TMA and H2O are used as growth sources, and an alternating pulse method is used to grow a laminated aluminum oxide film layer on the surface of the growth substrate. After the aluminum oxide film is deposited, the following processes are performed: First, SiNx is deposited on the front and back of the battery using PECVD; second, metal electrodes are printed by screen printing, and high-temperature sintering is used to make the electrode material and the silicon wafer form a good ohmic contact. However, the high-temperature sintering process will cause the H atoms in the aluminum oxide film to escape quickly, and the most important factor leading to film explosion is the H atoms on the aluminum oxide film and the surface of the silicon wafer. The aluminum oxide film has a blocking effect on the escape of H atoms, so the rapid escape of H atoms at the interface will cause film explosion, which is manifested as a gray edge in the EL test. The film explosion causes the passivation failure in the local area, resulting in dark EL. Poor EL gray edges such as Figure 4 As shown, the proportion is 1% to 2%. Although the EL gray edge ratio will be reduced by adjusting the carrier gas flow rate of water vapor, it cannot be completely eliminated; The present invention pre-treats the surface of the silicon wafer by introducing ozone before alternately introducing TMA and water vapor, thereby changing the surface state of the silicon wafer and reducing the surface H atoms. The pre-treatment scheme can ensure a lower interface state density and reduce the content of interface H, thereby ensuring excellent passivation performance and eliminating the film bursting phenomenon and EL gray edge defects. In practical applications, the EL gray edge is completely eliminated, and the battery conversion efficiency is improved by an absolute value of 0.03%. Embodiment 1

[0024] like Figure 2 and Figure 3 As shown, the method for pre-treating the surface of the silicon wafer in S1 is: A1: Nitrogen is used as carrier gas to carry water vapor into the reaction chamber, the carrier gas flow rate is 2slm, and the introduction time is 3s; A2: introducing nitrogen to purge the residual water vapor in the reaction chamber; A3: ozone is introduced, the ozone flow rate is 3slm, and the introduction time is 3s; A4: Introduce nitrogen to purge the residual ozone in the reaction chamber.

[0025] In A2, the purge nitrogen flow rate is 4 slm and the purge time is 8 s.

[0026] In A4, nitrogen was introduced during ozone purging, the purging time was 6 s, and the nitrogen flow rate was 4 slm.

[0027] In S2, vacuuming and heating are performed, wherein the cavity pressure is evacuated to below 10 Pa, and the silicon wafer temperature is heated to 100°C.

[0028] The method for depositing a thin film by ALD in S2: B1: Use nitrogen as carrier gas to carry TMA vapor into the reaction chamber; B2: nitrogen is introduced to purge the residual TMA in the reaction chamber; B3: Use nitrogen as carrier gas to carry water vapor into the reaction chamber; B4: introducing nitrogen to purge the residual water vapor in the reaction chamber; B5: Repeat B1-B4 until the aluminum oxide film of the desired thickness is obtained.

[0029] In B1, the source bottle temperature of TMA is 40° C., the carrier gas flow rate is 2 slm, and the introduction time is 3 s.

[0030] In B2, the purge nitrogen flow rate is 4 slm and the purge time is 5 s.

[0031] In B3, the temperature of the water source bottle is 35° C., the carrier gas flow rate is 2 slm, and the introduction time is 3 s.

[0032] In B4, the purge nitrogen flow rate is 4 slm and the purge time is 8 s. Embodiment 2

[0033] like Figure 2 and Figure 3 As shown, the method for pre-treating the surface of the silicon wafer in S1 is: A1: Use nitrogen as carrier gas to carry water vapor into the reaction chamber. The carrier gas flow rate is 6slm and the introduction time is 6.5s. A2: introducing nitrogen to purge the residual water vapor in the reaction chamber; A3: ozone is introduced, the ozone flow rate is 6.5slm, and the introduction time is 6.5s; A4: introducing nitrogen to purge the residual ozone in the reaction chamber; A5: Repeat the sequence of A1-A4 for 5 times.

[0034] In A2, the purge nitrogen flow rate is 12 slm and the purge time is 14 s.

[0035] In A4, nitrogen was introduced during ozone purging, the purging time was 13 s, and the nitrogen flow rate was 12 slm.

[0036] In S2, vacuuming and heating are performed, wherein the cavity pressure is evacuated to below 10 Pa, and the temperature of the silicon wafer is heated to 150°C.

[0037] The method for depositing a thin film by ALD in S2: B1: Use nitrogen as carrier gas to carry TMA vapor into the reaction chamber; B2: nitrogen is introduced to purge the residual TMA in the reaction chamber; B3: Use nitrogen as carrier gas to carry water vapor into the reaction chamber; B4: introducing nitrogen to purge the residual water vapor in the reaction chamber; B5: Repeat B1-B4 until the aluminum oxide film of the desired thickness is obtained.

[0038] In B1, the source bottle temperature of TMA is 45° C., the carrier gas flow rate is 6 slm, and the introduction time is 6.5 s.

[0039] In B2, the purge nitrogen flow rate is 12 slm and the purge time is 10 s.

[0040] In B3, the temperature of the water source bottle is 43° C., the carrier gas flow rate is 6 slm, and the introduction time is 6.5 s.

[0041] In B4, the purge nitrogen flow rate is 12 slm and the purge time is 14 s. Embodiment 3

[0042] like Figure 2 and Figure 3 As shown, the method for pre-treating the surface of the silicon wafer in S1 is: A1: Use nitrogen as carrier gas to carry water vapor into the reaction chamber. The carrier gas flow rate is 10slm and the introduction time is 10s. A2: introducing nitrogen to purge the residual water vapor in the reaction chamber; A3: ozone is introduced, the ozone flow rate is 10slm, and the introduction time is 10s; A4: introducing nitrogen to purge the residual ozone in the reaction chamber; A5: Repeat the sequence of A1-A4 for 10 times.

[0043] In A2, the purge nitrogen flow rate is 20 slm and the purge time is 20 s.

[0044] In A4, nitrogen was introduced during ozone purging, the purging time was 20 s, and the nitrogen flow rate was 20 slm.

[0045] In S2, vacuuming and heating are performed, wherein the cavity pressure is evacuated to below 10 Pa, and the temperature of the silicon wafer is heated to 200°C.

[0046] The method for depositing a thin film by ALD in S2: B1: Use nitrogen as carrier gas to carry TMA vapor into the reaction chamber; B2: nitrogen is introduced to purge the residual TMA in the reaction chamber; B3: Use nitrogen as carrier gas to carry water vapor into the reaction chamber; B4: introducing nitrogen to purge the residual water vapor in the reaction chamber; B5: Repeat B1-B4 until the aluminum oxide film of the desired thickness is obtained.

[0047] In B1, the source bottle temperature of TMA is 50° C., the carrier gas flow rate is 10 slm, and the introduction time is 10 s.

[0048] In B2, the purge nitrogen flow rate is 20 slm and the purge time is 15 s.

[0049] In B3, the temperature of the water source bottle is 50° C., the carrier gas flow rate is 10 slm, and the introduction time is 10 s.

[0050] In B4, the purge nitrogen flow rate is 20 slm and the purge time is 20 s.

[0051] When the film explosion method provided by the present invention is used, ozone is first introduced to pre-treat the surface of the silicon wafer, and the ozone pre-treatment steps are as follows: A1: Nitrogen is used as a carrier gas to carry water vapor into the reaction chamber, the carrier gas flow rate is 6slm, and the introduction time is 6.5s; A2: nitrogen is introduced to purge the residual water vapor in the reaction chamber. The purge nitrogen flow rate is usually 12 slm and the purge time is 14 s. A3: ozone is introduced, the ozone flow rate is 6.5slm, and the introduction time is 6.5s; A4: nitrogen was introduced to purge the residual ozone in the reaction chamber. During ozone purge, nitrogen was introduced for purge, the purge time was 13 s, and the nitrogen flow rate was 12 slm.

[0052] The process can be repeated multiple times in the order of steps 1, 2, 3, and 4 to ensure that the surface of the silicon wafer is fully treated. The number of times of the process is usually 5 times.

[0053] Then, after the silicon wafer is loaded into the furnace chamber, it is evacuated and heated, and then TMA and water vapor are alternately introduced. The specific steps are as follows: B1: Nitrogen is used as carrier gas to carry TMA vapor into the reaction chamber. The temperature of the TMA source bottle is usually 45°C, the carrier gas flow rate is 6slm, and the introduction time is 6.5s. B2: nitrogen is introduced to purge the residual TMA in the chamber. The purge nitrogen flow rate is usually 12 slm and the purge time is 10 s. B3: Use nitrogen as carrier gas to carry water vapor into the reaction chamber. The temperature of the water source bottle is usually 43°C, the carrier gas flow rate is 6slm, and the introduction time is 6.5s. B4: nitrogen is introduced to purge the residual water vapor in the chamber. The purge nitrogen flow rate is usually 12slm and the purge time is 14s. Steps 1, 2, 3, and 4 are cycled in sequence, and the number of cycles is adjusted according to the film thickness required by the process, and finally an aluminum oxide film of the required thickness is obtained.

[0054] By pretreating the silicon wafer surface by alternately introducing water vapor and ozone during the pretreatment process, the interface state can be kept at a low level, the passivation performance can be maintained, or even slightly improved.

[0055] After the silicon wafer is loaded into the furnace chamber, it is vacuumed and heated. Usually, the furnace chamber pressure is pumped to below 10 Pa, the silicon wafer temperature is heated to 100-200°C, and the silicon wafer is cleaned to ensure that the surface of the silicon wafer is clean and free of oil, dust and other impurities.

[0056] Working principle: ozone is introduced to pre-treat the surface of the silicon wafer. First, nitrogen is used as a carrier gas to carry water vapor into the reaction chamber, and nitrogen is introduced to purge the residual water vapor in the reaction chamber; then ozone is introduced, and then nitrogen is introduced to purge the residual ozone in the reaction chamber to change the surface state of the silicon wafer and reduce the surface H atoms; then TMA and water vapor are introduced alternately to grow an aluminum oxide film on the surface of the silicon wafer. First, nitrogen is used as a carrier gas to carry TMA vapor into the reaction chamber; nitrogen is introduced to purge the residual TMA in the reaction chamber; then nitrogen is used as a carrier gas to carry water vapor into the reaction chamber; nitrogen is introduced to purge the residual water vapor in the reaction chamber; the operation is repeated in sequence, and the number of cycles is adjusted according to the film thickness required by the process. The pretreatment scheme can ensure a lower interface state density and reduce the content of interface H, ensuring excellent passivation performance, eliminating the film explosion phenomenon and EL gray edge defects; in actual applications, the EL gray edge is completely eliminated, and the battery conversion efficiency is improved by 0.03% absolute value.

[0057] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for eliminating film explosion based on ALD deposited aluminum oxide film, characterized in that: The following steps are involved: S1: pre-treat the surface of the silicon wafer by introducing ozone to change the surface state of the silicon wafer and reduce the surface H atoms; S2: Thin film deposition based on ALD method. After the silicon wafer is loaded into the furnace chamber, it is evacuated and heated. Then, TMA and water vapor are alternately introduced to grow an aluminum oxide film on the surface of the silicon wafer.

2. The method for eliminating film explosion based on ALD deposition of aluminum oxide film according to claim 1, characterized in that: The method for pre-treating the surface of the silicon wafer in S1 is: A1: Use nitrogen as carrier gas to carry water vapor into the reaction chamber, the carrier gas flow rate is 2-10slm, and the introduction time is 3-10s; A2: introducing nitrogen to purge the residual water vapor in the reaction chamber; A3: ozone is introduced, the ozone flow rate is 3-10slm, and the introduction time is 3-10s; A4: introducing nitrogen to purge the residual ozone in the reaction chamber; A5: Repeat the sequence of A1-A4 for multiple times, the number of times is 1-10 times.

3. The method for eliminating film explosion based on ALD deposition of aluminum oxide film according to claim 2, characterized in that: In A2, the purge nitrogen flow rate is 4-20slm, and the purge time is 8-20s.

4. The method for eliminating film explosion based on ALD deposition of aluminum oxide film according to claim 2, characterized in that: In A4, nitrogen is introduced during ozone purging, the purging time is 6-20s, and the nitrogen flow rate is 4-20slm.

5. The method for eliminating film explosion based on ALD deposition of aluminum oxide film according to claim 1, characterized in that: In S2, vacuuming and heating are performed, wherein the cavity pressure is evacuated to below 10Pa, and the temperature of the silicon wafer is heated to 100-200°C.

6. The method for eliminating film explosion based on ALD deposition of aluminum oxide film according to claim 1, characterized in that: The method for depositing a thin film by ALD in S2: B1: Use nitrogen as carrier gas to carry TMA vapor into the reaction chamber; B2: nitrogen is introduced to purge the residual TMA in the reaction chamber; B3: Use nitrogen as carrier gas to carry water vapor into the reaction chamber; B4: introducing nitrogen to purge the residual water vapor in the reaction chamber; B5: Repeat B1-B4 until the aluminum oxide film of the desired thickness is obtained.

7. The method for eliminating film explosion based on ALD deposition of aluminum oxide film according to claim 6, characterized in that: In B1, the temperature of the TMA source bottle is 40-50° C., the carrier gas flow rate is 2-10 slm, and the introduction time is 3-10 s.

8. The method for eliminating film explosion based on ALD deposition of aluminum oxide film according to claim 6, characterized in that: In B2, the purge nitrogen flow rate is 4-20slm, and the purge time is 5-15s.

9. The method for eliminating film explosion based on ALD deposition of aluminum oxide film according to claim 6, characterized in that: In B3, the temperature of the water source bottle is 35-50° C., the carrier gas flow rate is 2-10 slm, and the introduction time is 3-10 s.

10. The method for eliminating film explosion based on ALD deposition of aluminum oxide film according to claim 6, characterized in that: In B4, the purge nitrogen flow rate is 4-20slm, and the purge time is 8-20s.

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