Thin film deposition process for improving film explosion of back contact battery and improving efficiency

Abstract

The invention belongs to the technical field of solar cell manufacturing, and particularly relates to a thin film deposition process for improving film explosion of a back contact cell and improving efficiency. The method comprises the following steps: feeding a silicon wafer with an aluminum oxide layer into a back film PECVD (Plasma Enhanced Chemical Vapor Deposition) machine furnace tube, setting all temperature zones from a furnace mouth to a furnace tail to 400-500 DEG C, firstly depositing a silicon oxide layer, then depositing a silicon nitride layer, and carrying out other process steps according to the existing production line process. According to the method, the number of H atoms in the aluminum oxide film layer is kept at the low temperature of 400-500 DEG C, then overflow of the H atoms is blocked by means of a layer of thin silicon oxide, and therefore the passivation performance is enhanced, efficiency improvement is facilitated, and the film explosion problem can be solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of solar cell manufacturing, and particularly relates to a thin film deposition process for improving film explosion of back contact cells and improving efficiency. BACKGROUND

[0002] Currently, the BC solar cell is relatively advanced in the solar cell industry, and the structure of the BC solar cell is to first deposit an aluminum oxide film on the front and back surfaces of a wafer, and then deposit a silicon nitride film thereon to passivate the silicon surface; the aluminum oxide film of the BC cell is first deposited by using an atomic layer deposition (ALD) device, and then the silicon nitride film is deposited by using a tube PECVD machine.

[0003] Meanwhile, the problem of film explosion on the back surface of the BC cell is common, and the film explosion phenomenon is related to the aluminum oxide, but also related to the surface structure of the silicon wafer; the front surface of the BC cell is a textured structure, and the back surface is a polished structure; the phenomenon in the industry is that the polished structure is prone to film explosion, that is, the back surface of the cell wafer has the problem of film explosion; the analysis of the causes of film explosion in the industry is that there is a certain H atom in the aluminum oxide film, and after the silicon nitride film is deposited, the Si-H bond in the aluminum oxide layer is instantaneously broken under the influence of the temperature of about 800 DEG C during screen sintering, H atoms rapidly gather to form H gas, break through the silicon nitride film under the pressure difference, cause the silicon nitride film on the surface to be damaged, and the subsequent damaged bare positions are polluted without the protection of the silicon nitride layer, and finally cause the cell wafer to have obvious efficiency decay.

[0004] In order to solve the problem of film explosion, some companies will choose to heat as much as possible before depositing the silicon nitride to break the Si-H bond in the aluminum oxide, so that H escapes from the surface of the silicon wafer (H escape phenomenon occurs at about 500 DEG C) to improve the film explosion, but the escape of the surface H will affect the passivation effect. Since the H atoms in the aluminum oxide will begin to escape during the heating process, if the temperature during the deposition of the silicon nitride is controlled to make the H on the surface of the silicon wafer escape as little as possible, although the passivation effect of H can be greatly retained, the problem of film explosion will be aggravated. SUMMARY

[0005] The purpose of the present application is to solve the problem of film explosion first, and then use the low-temperature scheme to improve the efficiency, solve the problem that the back surface of the BC cell industry is difficult to implement the low-temperature (<500 DEG C) process, and provide a thin film deposition process for improving the film explosion of the back contact cell and improving the efficiency, which uses a back film PECVD machine, the process temperature is set to 400-500 DEG C, and a thin silicon oxide layer is deposited before depositing the silicon nitride.

[0006] Regarding the technical points of reducing the process temperature and depositing the silicon oxide layer first, the design idea of the present application is: reversely using high temperature (> 500 DEG C) to trigger the diffusion of hydrogen -> to the silicon-based interface -> to form hydrogen gas, reducing the escape of H by reducing the process temperature, retaining the number of H ions on the surface of the silicon wafer, and improving the passivation performance of aluminum oxide; The principle of depositing silicon oxide first is to use the bond energy difference, the bond energy of Si-O bond is about 452 KJ / mol, and the bond energy of Si-H bond is about 318 KJ / mol, so that the silicon oxide layer can lock the H atoms in the aluminum oxide layer at the same sintering temperature (about 800 DEG C), and improve the problem that the H atoms in the aluminum oxide rapidly gather to form hydrogen gas at high sintering temperature and break through the silicon nitride film to cause the film to burst.

[0007] The present application is realized by the following technical solutions:

[0008] A thin film deposition process for improving the film burst of back contact cells and improving efficiency, the silicon wafer with an aluminum oxide layer is sent into the back film PECVD machine furnace tube, a silicon oxide layer of 2nm-4nm is first deposited, which is set as deposition one, a silicon nitride layer is then deposited, which is set as deposition two and deposition three.

[0009] The specific process temperature is: all temperature zones from the furnace mouth to the furnace tail are set to 400-500 DEG C.

[0010] The specific process steps are: start, nitrogen filling, furnace door opening, boat feeding, furnace door closing, temperature rising, vacuumizing, leak detection, constant pressure one, deposition one, vacuumizing, constant pressure two, deposition two, deposition three, vacuumizing, purging, nitrogen filling, furnace door opening, boat taking, and end.

[0011] As preferred process parameters, the deposition one time is set to 30s-60s, the silane flow is set to 300sccm, the nitrous oxide flow is set to 8000sccm, the pressure is set to 200Pa, the radio frequency power is set to 20000W, and the pulse ratio is set to 2 / 60.

[0012] The deposition one setting time of 30s to obtain a 2nm thick silicon oxide layer is the most preferred, it is verified by adjusting the process parameters that the effect difference caused by 2nm, 3nm and 4nm thickness is not large, 1nm thickness exists film burst phenomenon, and 5nm thickness exists efficiency reduction trend, therefore, preparing 2nm thickness has the advantages of energy saving and time saving.

[0013] As preferred process parameters, the deposition two time is set to 135s, the silane flow is set to 2100sccm, the ammonia flow is set to 8000sccm, the pressure is set to 225Pa, the radio frequency power is set to 20000W, and the pulse ratio is set to 5 / 90.

[0014] As preferred process parameters, the time for depositing three is set to 850s, the silane flow rate is set to 900sccm, the ammonia flow rate is set to 10350sccm, the pressure is set to 225Pa, the radio frequency power is set to 24000W, and the pulse ratio is set to 5 / 60.

[0015] As preferred process parameters, the time for the constant pressure first step is set to 30s.

[0016] As preferred process parameters, the time for the constant pressure second step is set to 30s.

[0017] Advantages of the present application:

[0018] The present application maintains the number of H atoms in the aluminum oxide film layer by low temperature 400-500℃, and then blocks the overflow of H atoms by a thin silicon oxide coating, and the three-layer thin film structure of aluminum oxide-silicon oxide-silicon nitride formed by the process not only enhances the passivation performance and improves the film explosion problem. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical scheme and advantages of the present application more clear and explicit, the present application will be further described in detail below in combination with specific examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0020] In the production of BC batteries, the normal coating process is: first double-sided aluminum oxide film, then front side silicon nitride film, and then back side silicon nitride film. The present application process is applied to the PECVD machine for coating the back side silicon nitride, and is implemented by using the HPE530-10A back film equipment of Grand Laser.

[0021] The present application uses silane and dinitrogen monoxide to react to form a film, the reaction speed is fast, has no effect on the machine capacity, and only needs to add a dinitrogen monoxide pipeline and a flow meter to the back film machine; it should be noted that the low temperature scheme needs to pay attention to the temperature and time setting of the auxiliary heating pipe on the machine with auxiliary heating, and too high auxiliary heating temperature will also cause the Si-H bond to break prematurely, affecting the H passivation effect of the aluminum oxide layer.

[0022] Based on the examples in the present application, all other examples obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present application. The experimental methods in the following examples are not specified, and are usually carried out according to the conventional conditions or according to the conditions recommended by the manufacturers. Unless otherwise specified, all percentages, ratios, proportions or parts are by weight.

[0023] The reagents and raw materials used in the examples and comparative examples of the present application can be obtained through commercial channels unless otherwise specified.

[0024] The following relates to two processes, namely the process of the present application and the existing production line process, and the technical effects of the process of the present application are better than the prior art by comparison.

[0025] The inventive process is as follows:

[0026] The silicon wafer on which the aluminum oxide film is completed is filled in a graphite boat, the graphite boat is transported to the furnace tube of the back film PECVD machine table by automatic equipment, the furnace tube is loaded with the process parameters of the present application and the process is run:

[0027] A thin film deposition process for improving the film explosion of back contact cells and improving efficiency, comprising the following steps: start, nitrogen filling, furnace door opening, boat loading, furnace door closing, temperature rising, vacuumizing, leak detection, constant pressure one, deposition one, vacuumizing, constant pressure two, deposition two, deposition three, vacuumizing, purging, nitrogen filling, furnace door opening, boat unloading, and end.

[0028] The temperature of all temperature zones of the furnace tube is set to 400-500℃, specifically from the furnace mouth to the furnace tail, the temperature is set to 480, 480, 470, 470, 455, and 450.

[0029] The parameters set for the key steps in the above process are as follows:

[0030] The time of the constant pressure step is set to 30s, and the time of the deposition step is set to 30s; the flow rate of silane in the deposition step is set to 300sccm, the flow rate of nitrous oxide is set to 8000sccm, the pressure is set to 200Pa, the radio frequency power is set to 18000W, the pulse ratio is set to 2 / 60, and the actual test generates a silicon oxide thickness of about 2nm.

[0031] The time of the constant pressure step is set to 30s, and the time of the deposition step is set to 135s; the flow rate of silane in the deposition step is set to 2100sccm, the flow rate of ammonia is set to 8000sccm, the pressure is set to 225Pa, the radio frequency power is set to 20000W, and the pulse ratio is set to 5 / 90.

[0032] The time of the deposition step is set to 850s; the flow rate of silane in the deposition step is set to 900sccm, the flow rate of ammonia is set to 10350sccm, the pressure is set to 225Pa, the radio frequency power is set to 24000W, and the pulse ratio is set to 5 / 60.

[0033] In addition to the adjustment of constant pressure 1 and deposition 1 for preparing silicon oxide, the other steps are run in the conventional manner of the existing process, and after the process is completed, a silicon wafer with aluminum oxide-silicon oxide-silicon nitride three-layer film is obtained.

[0034] The optimization selection for the thickness of 2 nm of silicon oxide is mainly based on the effect difference and cost. The following examples 1, 2, 3, 4, and 5 are used to study the thickness of silicon oxide. The test method is based on the process steps in example 1. The deposition time, special gas flow, and radio frequency power are adjusted to make the thickness of the silicon oxide layer between 1-5 nm, and the effect is verified.

[0035] Example 1

[0036] After 3000 pieces of silicon wafer after the positive film are evenly distributed into two groups, one group of 1500 pieces of silicon wafer is loaded into the graphite boat, and the above-mentioned invention process is used. The graphite boat is transported to the furnace tube of the back film PECVD machine table by automatic equipment, and the deposition step time is set to 15 s, and other steps remain unchanged, and a 1 nm thick silicon oxide layer is obtained.

[0037] Then the same path, another group of 1500 pieces of silicon wafer is loaded into the graphite boat, and the graphite boat is transported to the furnace tube of the back film PECVD machine table by automatic equipment, and the deposition step time is set to 30 s, and other steps remain unchanged, and a 2 nm thick silicon oxide layer is obtained.

[0038] After the same film deposition furnace tube is completed, the printed product electrical performance data is tested by using the HALM machine, and the EL test machine is used to check the film explosion situation. The above test results form table 1, and the specific data is as follows:

[0039]

[0040] Example 2

[0041] After 3000 pieces of silicon wafer after the positive film are evenly distributed into two groups, one group of 1500 pieces of silicon wafer is loaded into the graphite boat, and the above-mentioned invention process is used. The graphite boat is transported to the furnace tube of the back film PECVD machine table by automatic equipment, and the deposition step time is set to 30 s, and other steps remain unchanged, and a 2 nm thick silicon oxide layer is obtained.

[0042] Then the same path, another group of 1500 pieces of silicon wafer is loaded into the graphite boat, and the graphite boat is transported to the furnace tube of the back film PECVD machine table by automatic equipment, and the deposition step time is set to 30 s, and other steps remain unchanged, and a 2 nm thick silicon oxide layer is obtained.

[0043] After the same film deposition furnace tube is completed, the printed product electrical performance data is tested by using the HALM machine, and the EL test machine is used to check the film explosion situation. The above test results form table 1, and the specific data is as follows:

[0044]

[0045] Example 3

[0046] Then, the same path, the other group of 1500 pieces of silicon wafers into the graphite boat, the graphite boat through the automated equipment to the back film PECVD machine furnace tube, only adjust the deposition step time set to 60s, other steps remain the same, get 4nm thickness of silicon oxide layer.

[0047] Then, the same path, the other group of 1500 pieces of silicon wafers into the graphite boat, the graphite boat through the automated equipment to the back film PECVD machine furnace tube, only adjust the deposition step time set to 60s, other steps remain the same, get 4nm thickness of silicon oxide layer.

[0048] After the same film deposition furnace tube to complete the thin film deposition, after printing, using HALM machine test product electrical performance data, using EL tester to check the film explosion, the above test results form table 3, the specific data as follows:

[0049]

[0050] Example 4

[0051] Then, the same path, the other group of 1500 pieces of silicon wafers into the graphite boat, the graphite boat through the automated equipment to the back film PECVD machine furnace tube, only adjust the deposition step time set to 60s, other steps remain the same, get 4nm thickness of silicon oxide layer.

[0052] Then, the same path, the other group of 1500 pieces of silicon wafers into the graphite boat, the graphite boat through the automated equipment to the back film PECVD machine furnace tube, only adjust the deposition step time set to 60s, other steps remain the same, get 4nm thickness of silicon oxide layer.

[0053] After the same film deposition furnace tube to complete the thin film deposition, after printing, using HALM machine test product electrical performance data, using EL tester to check the film explosion, the above test results form table 4, the specific data as follows:

[0054]

[0055] Example 4

[0056] Then, the same path, the other group of 1500 pieces of silicon wafers into the graphite boat, the graphite boat through the automated equipment to the back film PECVD machine furnace tube, only adjust the deposition step time set to 60s, other steps remain the same, get 4nm thickness of silicon oxide layer.

[0057] Then the same path, another group of 1500 silicon chips into the graphite boat, graphite boat through the automated equipment to the back film PECVD machine furnace tube, only adjust the deposition step time set to 75s, the other steps remain the same, get 5nm thickness of silicon oxide layer.

[0058] After the same film deposition furnace tube is completed, after printing, using HALM machine test product electrical performance data, using EL tester to view the membrane, the above test results form table 5, the specific data as follows:

[0059]

[0060]

[0061] According to the data in table 1~5 analysis: example 2, 3, 4 data show 2nm, 3nm, 4nm explosion film is 0, and the efficiency is close; Example 1 shows that 1nm exists explosion film phenomenon, example 5 shows that 5nm exists efficiency slightly decreased. At present, by adjusting the process parameters to verify the effect of 2nm, 3nm, 4nm thickness is not big, and preparation of 2nm thickness has the advantages of energy saving and time saving, therefore, the verification result is to select 2nm thickness of silicon oxide layer parameters.

[0062] The above examples 1~5 are according to the process of the application, using back film PECVD machine under the condition of 400~500℃ low temperature uniform material comparison verification, wherein the deposition time, the gas flow and the radio frequency power and the pressure parameters can be adjusted according to the size of the furnace tube diameter and the different hardware, the core is that the thickness of the prepared aluminum oxide is 2nm~4nm.

[0063] Comparative example 1:

[0064] The existing production line process is as follows:

[0065] The silicon wafer coated with aluminum oxide is filled in the graphite boat, and the graphite boat is transported to the furnace tube of the back film PECVD machine through the automatic equipment. The furnace tube is loaded with the process parameters of the production line and the existing process is run.

[0066] A thin film deposition process, comprising the following steps: start, fill nitrogen, open furnace door, put boat, close furnace door, heat up, pump down, leak detection, pump down, constant pressure 1, deposition 1, deposition 2, pump down, purge, fill nitrogen, open furnace door, take boat, end.

[0067] The above process temperature: from the furnace mouth to the furnace tail is set to 535, 535, 515, 515, 490, 480.

[0068] The time of the constant pressure 1 step is set to 30s, and the time of the deposition 1 step is set to 135s; the flow rate of silane of the deposition 1 step is set to 2100sccm, the flow rate of ammonia is set to 8000sccm, the pressure is set to 225Pa, the radio frequency power is set to 20000W, and the pulse ratio is set to 5 / 90.

[0069] The time of the deposition 2 step is set to 850s; the flow rate of silane of the deposition 2 step is set to 900sccm, the flow rate of ammonia is set to 10350sccm, the pressure is set to 225Pa, the radio frequency power is set to 24000W, and the pulse ratio is set to 5 / 60.

[0070] The other steps are operated in a conventional manner of the existing process, and the silicon wafer with the aluminum oxide-silicon nitride coating is obtained after the process is completed.

[0071] The following is a comparison experiment by using the product of the process and the product line process of the application:

[0072] The experimental object is the mixed silicon wafer.

[0073] The comparison experiment: experiments 1-3 are respectively verified.

[0074] Experiment 1: running the process of the application and the existing product line process once.

[0075] Experiment 2: running the process of the application and the product line process (using the temperature of the application process) once.

[0076] Experiment 3: running the process of the application and the application process (using the temperature of the product line process) once.

[0077] The same furnace tube and the same graphite boat are used to perform experiments 1, 2 and 3, and after each group of experiments is completed, the same machine is used to perform printing, and the electrical performance is tested by the HALM tester after the subsequent screen printing machine, and the number of broken membrane pieces is determined by the online EL detection.

[0078] The experimental results are as follows:

[0079] For experiment 1,

[0080] The experimental group: the new process of the application is used;

[0081] The control group: the existing product line process is used.

[0082] After the coating is completed and printing is performed, the electrical performance data is tested by the HALM machine, and the number of broken membrane pieces is determined by the online EL detection, and the data is recorded in Table 6:

[0083]

[0084] For experiment 2,

[0085] Experimental group: adopt the new process of the application;

[0086] Control group: use the existing production line process, but the temperature adopts the temperature of the application process, specifically, from the furnace mouth to the furnace tail, set to 480, 480, 470, 470, 455, 450, and there is no silicon oxide layer.

[0087] After the coating is completed, the electrical performance data is tested by using the HALM machine after printing, and the number of exploded membrane pieces is determined by online EL detection, and the data records are shown in Table 7:

[0088]

[0089] For experiment 3,

[0090] Experimental group: adopt the new process of the application;

[0091] Control group: use the application process, but the temperature adopts the temperature of the production line process, specifically, from the furnace mouth to the furnace tail, set to 535, 535, 515, 515, 490, 480.

[0092] After the coating is completed, the electrical performance data is tested by using the HALM machine after printing, and the number of exploded membrane pieces is determined by online EL detection, and the data records are shown in Table 8:

[0093]

[0094] According to the results of the exploded membrane and electrical performance data in Tables 6-8:

[0095] The existing production line process generally has a high proportion of exploded membranes (1.30% of exploded membranes); directly reducing the temperature of the production line process will cause serious exploded membranes (6.78% of exploded membranes); therefore, the comparison is obvious, and it can be seen that, on the basis of the production line process only with a silicon nitride layer, directly reducing the temperature will obviously increase the proportion of exploded membranes. However, combined with the experimental data of the three groups, the improvement of the efficiency (about 0.05%) is due to the reduction of the process temperature, and the pieces with the silicon oxide structure in the experiment have no exploded membranes. Therefore, the process of the application not only improves the efficiency, but also avoids the problem of exploded back membranes by adding a layer of silicon oxide and reducing the process temperature.

[0096] Finally, it should be noted that the above description is only a preferred embodiment of the application and is not intended to limit the application, although the application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent replacements to some technical features, and any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. A thin film deposition process for improving back contact battery film explosion and improving efficiency, using a back film PECVD machine, characterized in that: All temperature zones from the furnace mouth to the furnace tail are set to 400-500°C. The process steps include: Deposition 1: depositing a silicon oxide layer with a thickness of 2nm to 4nm; Deposition 2 and Deposition 3: depositing a silicon nitride layer.

2. A thin film deposition process for improving back contact battery film explosion and improving efficiency according to claim 1, characterized in that: In the deposition step 1, the time was set to 30s to 60s, the silane flow rate was set to 300sccm, the nitrous oxide flow rate was set to 8000sccm, the pressure was set to 200Pa, the RF power was set to 20000W, and the pulse ratio was set to 2 / 60.

3. The thin film deposition process for improving back contact battery film explosion and improving efficiency according to claim 2, characterized in that: In the second deposition step, the time was set to 135 s, the silane flow rate was set to 2100 sccm, the ammonia flow rate was set to 8000 sccm, the pressure was set to 225 Pa, the RF power was set to 20000 W, and the pulse ratio was set to 5 / 90.

4. The thin film deposition process for improving back contact battery film explosion and improving efficiency according to claim 3, characterized in that: In the three deposition steps, the time was set to 850 s, the silane flow rate was set to 900 sccm, the ammonia flow rate was set to 10350 sccm, the pressure was set to 225 Pa, the RF power was set to 24000 W, and the pulse ratio was set to 5 / 60.

5. A thin film deposition process for improving back contact battery film explosion and improving efficiency according to any one of claims 1 to 4, characterized in that: The specific steps include starting, filling with nitrogen, opening the furnace door, putting in the boat, closing the furnace door, heating, evacuating, leak detection, constant pressure one, deposition one, evacuating, constant pressure two, deposition two, deposition three, evacuating, purging, filling with nitrogen, opening the furnace door, taking out the boat, and ending.

6. The thin film deposition process for improving back contact battery film explosion and improving efficiency according to claim 5, characterized in that: The time for the constant pressure step was set to 30 s.

7. The thin film deposition process for improving back contact battery film explosion and improving efficiency according to claim 5, characterized in that: The time of the constant pressure second step was set to 30 s.

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