Ultra-thin silicon oxynitride interface material, tunneling oxidation passivation structure, preparation method and application thereof

Abstract

The present invention provides an ultra-thin silicon oxynitride interface material, a tunneling oxidation passivation structure, and a preparation method and application thereof, wherein the ultra-thin silicon oxynitride interface material is a SiON film with a thickness of 1nm-4nm, and the percentage of N atoms in the SiON film is 1%-40%. The ultra-thin silicon oxynitride interface material of the present invention has the characteristics of high nitrogen content. Compared with silicon oxide, the diffusion rate of boron in the SiON film is low, thereby effectively reducing the destructive effect of boron on the SiON film, improving the integrity of the SiON film, and maintaining the chemical passivation effect. The SiON film with a high nitrogen concentration can significantly reduce the concentration of boron on the silicon surface, thereby reducing boron defects; in addition, the energy band structure of the SiON film is close to that of silicon nitride, and its valence band step is relatively small, which is conducive to hole transmission, improves the hole transmission efficiency and hole selectivity, thereby improving the passivation quality, and is also conducive to reducing the contact resistivity.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and in particular to an ultra-thin silicon oxynitride interface material, a tunneling oxidation passivation structure, and a preparation method and application thereof. Background Art

[0002] Tunnel Oxide Passivated Contact (TOPCon) solar cell is a new type of crystalline silicon solar cell proposed by Fraunhofer in Germany in 2013. The typical structure of its N-type cell is as follows: Figure 1 As shown in Figure 1, the core of this structure is to use an ultra-thin silicon oxide layer and a doped polysilicon stacked structure to passivate the silicon wafer surface. The passivation mechanism of the tunneling silicon oxide passivation contact structure mainly comes from two aspects: one is the chemical passivation of the interface silicon oxide layer, and the other is the field passivation of the doped atoms. Therefore, improving the integrity of the interface silicon oxide is conducive to improving the chemical passivation effect of the surface.

[0003] In the prior art, the preparation process of TOPCon cells is as follows: cleaning and texturing - diffusion of boron emitter - etching - preparation of SiO2 on the back - PECVD heavily doped polysilicon - high temperature annealing - front surface aluminum oxide, Si3N4 - screen printing. For the tunneling silicon oxide passivation contact technology, its electron collection uses n-type phosphorus-doped polysilicon film, while the hole collection uses p-type boron-doped polysilicon film. Due to the good effect of n-type passivation contact technology, it has been widely accepted as the next generation of industrial high-efficiency crystalline silicon cell technology, but n-type TOPCon cells are expensive and not conducive to large-scale production, while p-type TOPCon technology is compatible with aluminum paste materials, which is conducive to reducing costs. Therefore, it is of practical significance to develop and improve p-type TOPCon technology.

[0004] Chinese invention patent CN105742391A discloses a tunneling silicon oxygen nitrogen layer passivation contact solar cell and its preparation method. The preparation method is a plasma-assisted nitrous oxide oxidation method. The specific method is to use PECVD to oxidize the silicon surface. Since the reaction gas contains N elements, a nitrogen-containing ultra-thin silicon oxide layer, i.e., SiON film, is formed in this process. However, there are two significant problems with the silicon oxide layer directly prepared by the plasma nitrous oxide assisted oxidation method: first, the nitrogen concentration in the SiON film is low, which cannot achieve the effect of blocking boron diffusion and enrichment; second, the plasma directly acts on the surface of the silicon wafer, which will introduce significant ion bombardment damage defects. The above problems will affect the passivation effect of the silicon oxide layer on the silicon wafer. The optimal passivation effect of the p-TOPCon prepared based on this nitrogen-containing ultra-thin silicon oxide layer can only make the potential open circuit voltage reach 700mV-705mV. Summary of the invention

[0005] In view of the deficiencies of the prior art, the technical problem to be solved by the present invention is how to improve the passivation effect of TOPCon.

[0006] To solve the above problems, the first aspect of the present invention provides an ultra-thin silicon oxynitride interface material, wherein the ultra-thin silicon oxynitride interface material is a SiON film with a thickness of 1nm-4nm, and the percentage of N atoms in the SiON film is 1%-40%.

[0007] The ultra-thin silicon oxynitride interface material of the present invention has the characteristic of high nitrogen content. Compared with silicon oxide, the diffusion rate of boron in the SiON film is low, thereby effectively reducing the destructive effect of boron on the SiON film, improving the integrity of the SiON film, and maintaining the chemical passivation effect. The SiON film with a high nitrogen concentration can significantly reduce the concentration of boron on the silicon surface, thereby reducing boron defects; in addition, the energy band structure of the SiON film is close to that of silicon nitride, and its valence band step is relatively small, which is conducive to hole transmission, improves the hole transmission efficiency and hole selectivity, thereby improving the passivation quality, and is also conducive to reducing the contact resistivity.

[0008] A second aspect of the present invention provides a method for preparing the ultra-thin silicon oxynitride interface material, comprising the following steps:

[0009] S1, growing a layer of SiO2 film on a silicon wafer by using a non-ion bombardment oxidation method;

[0010] S2. The SiO2 film is subjected to surface nitridation treatment by a PECVD method in a treatment atmosphere of nitrogen-containing gas and oxygen-containing gas to generate a SiON film.

[0011] The preparation method first grows a bombardment-free silicon oxide layer on the silicon wafer, which can significantly reduce the ion bombardment damage introduced by the plasma nitridation process, thereby improving the passivation quality. This method effectively reduces the interface state defects. The interface state obtained by the conventional plasma nitrous oxide oxidation method is usually 2*10 12 eV*cm -2 When the preparation method of the present invention is used, the density of defect states can be reduced to 0.4*10 12 eV*cm -2 .

[0012] Preferably, in step S2, the nitrogen-containing gas is NH3, and the oxygen-containing gas is N2O. When NH3 and N2O are used for surface nitridation treatment, on the one hand, during the decomposition of NH3, the N concentration is high, which can significantly introduce N elements, and also generate H atoms, which will etch silicon oxide; on the other hand, the introduction of N2O can simultaneously supplement the oxygen source, maintain the thickness of the SiON film, and avoid the thickness being too low due to the etching effect of H ions.

[0013] Preferably, in step S2, the flow ratio of the nitrogen-containing gas to the oxygen-containing gas is 2:1 to 8:1.

[0014] Preferably, the non-ion bombardment oxidation method in step S1 is an ozone oxidation method or a nitric acid oxidation method.

[0015] The method of the present invention can adjust the silicon oxide thickness and the ratio of the NH3 and N2O mixed gases according to actual needs, thereby regulating the thickness and composition of the SiON film.

[0016] The third aspect of the present invention provides a tunneling oxidation passivation structure, including a silicon wafer, a passivation tunneling layer and a doped polysilicon layer, wherein the material of the passivation tunneling layer is the above-mentioned ultra-thin silicon oxynitride interface material, and the passivation tunneling layer is located between the silicon wafer and the doped polysilicon layer.

[0017] Preferably, the material of the doped polysilicon layer is a boron-doped amorphous silicon film.

[0018] The tunneling oxide passivation structure of the present invention uses an ultra-thin silicon oxynitride interface material as a passivation tunneling layer, which can reduce the destructive effect of boron on the tunneling oxide layer, improve the passivation quality, reduce the contact resistivity, and achieve excellent contact performance. The tunneling oxide passivation structure is applied to P-TOPCon, and the potential open circuit voltage can reach more than 720mV, and the contact resistivity is less than 5mΩcm 2 .

[0019] A fourth aspect of the present invention provides a method for preparing the above-mentioned tunneling oxide passivation structure, comprising the following steps:

[0020] S1, growing a layer of SiO2 film on a silicon wafer by using a non-ion bombardment oxidation method;

[0021] S2, using a PECVD method to perform surface nitridation treatment on the SiO2 film, with the treatment atmosphere being a nitrogen-containing gas and an oxygen-containing gas, to generate a SiON film;

[0022] S3, depositing a doped amorphous silicon film on the SiON film by a PECVD method;

[0023] S4. Perform annealing to obtain a tunneling oxide passivation structure.

[0024] The preparation method is simple to operate, and is compatible with existing mass production equipment technology, especially PECVD equipment. The gas consumables used are low in cost, and almost no additional consumables costs are added.

[0025] Preferably, in step S4, the annealing temperature is 820-1100°C.

[0026] Silicon oxynitride has higher thermal stability than silicon oxide and can withstand higher and faster temperature change annealing treatments. According to actual needs, the silicon oxide thickness, the mixing ratio of nitrogen-containing gas and oxygen-containing gas can be adjusted to control the thickness and composition of the SiON film, thereby matching different high-temperature annealing temperatures.

[0027] A fifth aspect of the present invention provides an application of the tunneling oxide passivation structure, wherein the tunneling oxide passivation structure is applied to an N-type or P-type tunneling oxide layer passivation contact solar cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A diagram of the structure of a solar cell with tunnel oxide passivation contact;

[0029] Figure 2 This is the microstructure of the SiON film in Example 1. DETAILED DESCRIPTION

[0030] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. It should be noted that the following embodiments are only used to illustrate the implementation method and typical parameters of the present invention, and are not used to limit the parameter range described in the present invention. Reasonable changes derived therefrom are still within the scope of protection of the claims of the present invention.

[0031] It should be noted that the endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this article.

[0032] The embodiment of the present invention provides a tunneling oxidation passivation structure, including a silicon wafer, a passivation tunneling layer and a doped polysilicon layer, wherein the material of the passivation tunneling layer is an ultra-thin silicon oxynitride interface material, and the passivation tunneling layer is located between the silicon wafer and the doped polysilicon layer. The ultra-thin silicon oxynitride interface material is a SiON film with a thickness of 1nm-4nm, and the percentage of N atoms in the SiON film is 1%-40%.

[0033] The tunneling oxide passivation structure can be applied to N-type or P-type tunneling oxide passivation contact solar cells. When applied to P-type tunneling oxide passivation contact solar cells, the material of the doped polysilicon layer is a boron-doped amorphous silicon film, and the silicon oxynitride interface material with a high nitrogen content is beneficial to improving the passivation quality of p-TOPCon. The principles include: 1) Compared with silicon oxide, the diffusion rate of boron in SiON film is low, thereby effectively reducing the destructive effect of boron on SiON film, improving the integrity of SiON film, and maintaining the chemical passivation effect; 2) SiON film with high nitrogen concentration can significantly reduce the concentration of boron on the silicon surface, thereby reducing boron defects; 3) The band structure of SiON film is close to silicon nitride, and its valence band step is relatively small, which is beneficial to hole transmission, improving hole transmission efficiency and hole selectivity, thereby improving passivation quality, and also helping to reduce contact resistivity. The potential open circuit voltage of P-type TOPCon can reach more than 720mV, and the contact resistivity is less than 5mΩcm 2 .

[0034] An embodiment of the present invention also provides a method for preparing the above tunneling oxide passivation structure, comprising the following steps:

[0035] S1, growing a layer of SiO2 film on a silicon wafer by using a non-ion bombardment oxidation method;

[0036] S2, using a PECVD method to perform surface nitridation treatment on the SiO2 film, with the treatment atmosphere being a nitrogen-containing gas and an oxygen-containing gas, to generate a SiON film;

[0037] S3, depositing a doped amorphous silicon film on the SiON film by a PECVD method;

[0038] S4. Perform annealing to obtain a tunneling oxide passivation structure.

[0039] In a specific embodiment of the present invention, the non-ion bombardment oxidation method in step S1 is an ozone oxidation method or a nitric acid oxidation method, preferably an ozone oxidation method. In step S2, the nitrogen-containing gas is NH3, the oxygen-containing gas is N2O, and the flow ratio of the nitrogen-containing gas to the oxygen-containing gas is 2:1 to 8:1. In step S3, the annealing temperature is 820-1100°C.

[0040] The present invention will be described in detail below through specific embodiments. In the following embodiments and comparative examples, all silicon wafers are N-type single crystal silicon wafers with a thickness of 160 μm, double-sided chemical polishing, and a resistivity of 0.8 Ω·cm. The passivation structure used in the following embodiments and comparative examples is a double-sided p-type tunneling silicon oxide passivation structure.

[0041] Example 1

[0042] This embodiment prepares a tunneling oxidation passivation structure, including the following steps:

[0043] (1) Cut the silicon wafer into 4 cm × 4 cm size and perform standard RCA cleaning.

[0044] (2) Place the silicon wafer in an ozone generator to grow a SiO2 film with a thickness of about 1.5 nm.

[0045] (3) The sample was placed in PECVD for treatment, using N2O and NH3 as the treatment atmosphere, with a flow ratio of N2O and NH3 of 4:1, a power of 5W, and a treatment time of 300S to generate a SiON film. The thickness of the SiON film is 1.7nm, and the microstructure is as follows Figure 2 shown.

[0046] (4) Boron-doped amorphous silicon films are deposited on both sides of the silicon wafer using PECVD.

[0047] (5) The sample is placed in a tubular annealing furnace for annealing at a temperature of 880-1000°C for 30 minutes.

[0048] Example 2

[0049] This embodiment prepares a tunneling oxidation passivation structure, including the following steps:

[0050] (1) Cut the silicon wafer into 4 cm × 4 cm size and perform standard RCA cleaning.

[0051] (2) Place the silicon wafer in an ozone generator to grow a SiO2 film with a thickness of about 1.5 nm.

[0052] (3) The sample was placed in PECVD for treatment, using N2O and NH3 as the treatment atmosphere, the flow ratio of N2O and NH3 was 2:1, the power was 5 W, the treatment time was 300 s, and a SiON film was generated.

[0053] (4) Boron-doped amorphous silicon films are deposited on both sides of the silicon wafer using PECVD.

[0054] (5) The sample is placed in a tubular annealing furnace for annealing at a temperature of 880-1000°C for 30 minutes.

[0055] Example 3

[0056] This embodiment prepares a tunneling oxidation passivation structure, including the following steps:

[0057] (1) Cut the silicon wafer into 4 cm × 4 cm size and perform standard RCA cleaning.

[0058] (2) Place the silicon wafer in an ozone generator to grow a SiO2 film with a thickness of about 1.5 nm.

[0059] (3) The sample was placed in PECVD for treatment, using N2O and NH3 as the treatment atmosphere, the flow ratio of N2O and NH3 was 8:1, the power was 5 W, the treatment time was 300 s, and a SiON film was generated.

[0060] (4) Boron-doped amorphous silicon films are deposited on both sides of the silicon wafer using PECVD.

[0061] (5) The sample is placed in a tubular annealing furnace for annealing at a temperature of 880-1000°C for 30 minutes.

[0062] Comparative Example 1

[0063] Comparative Example A tunneling oxidation passivation structure is prepared, comprising the following steps:

[0064] (1) Cut the silicon wafer into 4 cm × 4 cm size and perform standard RCA cleaning.

[0065] (2) Place the silicon wafer in nitric acid to form a SiO2 film.

[0066] (3) After the silicon wafer is cleaned and dried, a boron-doped amorphous silicon film is deposited on both sides of the silicon wafer using PECVD.

[0067] (4) The sample is placed in a tubular annealing furnace for annealing at a temperature of 880-1000°C for 30 minutes.

[0068] Comparative Example 2

[0069] Comparative Example A tunneling oxidation passivation structure is prepared, comprising the following steps:

[0070] (1) Cut the silicon wafer into 4 cm × 4 cm size and perform standard RCA cleaning.

[0071] (2) The silicon wafer was placed in PECVD for treatment, using N2O and NH3 as the treatment atmosphere, the flow ratio of N2O and NH3 was 2:1, the power was 5 W, the treatment time was 300 s, and a SiON film was generated.

[0072] (3) After the silicon wafer is cleaned and dried, a boron-doped amorphous silicon film is deposited on both sides of the silicon wafer using PECVD.

[0073] (4) The sample is placed in a tubular annealing furnace for annealing at a temperature of 880-1000°C for 30 minutes.

[0074] The components of the passivation tunneling layer in the tunneling oxidation passivation structure of the embodiment and the comparative example were analyzed by X-ray photoelectron spectroscopy. The analysis results are shown in Table 1 below.

[0075] Element Si atomic content percentage O atomic content percentage N atomic content percentage Example 1 50.74 43.59 5.67 Example 2 50.68 38.94 10.38 Example 3 49.67 47.59 2.74 Comparative Example 1 51.65 48.25 0.1 Comparative Example 2 50.31 48.93 0.76

[0076] Table 1 Contents of Si, O and N in the passivation tunneling layer

[0077] Test of Passivation Performance The passivation performance results of the tunneling oxidation passivation structure of the embodiment and the comparative example are shown in Table 2 below.

[0078] Annealing temperature Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 880℃ 717mV 713mV 710mV 678mV 612mV 920℃ 720mV 715mV 713mV 694mV 664mV 980℃ 726mV 722mV 708mV 653mV 698mV 1000℃ 696mV 687mV 623mV 612mV 662mV

[0079] Table 2 Passivation performance of tunneling oxide passivation structure

[0080] From the test results, it can be seen that the passivation performance of the tunneling oxide passivation structure prepared in Examples 1-3 is better than that of Comparative Examples 1-2. By selecting a suitable annealing temperature, the passivation effect of Examples 1-3 can make the potential open circuit voltage reach above 720mV. The back junction battery prepared by the process of Example 1 has an efficiency of 22.04%.

[0081] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A method for preparing a tunneling oxide passivation structure, characterized in that: The following steps are involved: S1, using the non-ion bombardment oxidation method to grow a layer of SiO2 film on the silicon wafer; S2. Surface nitridation treatment of the SiO2 film is performed by a PECVD method in a treatment atmosphere of nitrogen-containing gas and oxygen-containing gas to form a SiON film; S3, depositing a boron-doped amorphous silicon film on the SiON film using a PECVD method; S4. Perform annealing to obtain a tunneling oxide passivation structure.

2. The method for preparing a tunneling oxide passivation structure according to claim 1, wherein: In step S4, the annealing temperature is 820-1100°C.

3. The method for preparing a tunneling oxide passivation structure according to claim 1, wherein: In step S2, the nitrogen-containing gas is NH3, and the oxygen-containing gas is N2O.

4. The method for preparing a tunneling oxide passivation structure according to claim 1, wherein: In step S2, the flow ratio of the nitrogen-containing gas to the oxygen-containing gas is 2:1 to 8:

1.

5. The method for preparing a tunneling oxide passivation structure according to claim 1, wherein: The non-ion bombardment oxidation method in step S1 is an ozone oxidation method or a nitric acid oxidation method.

6. A tunneling oxide passivation structure, characterized in that: The tunneling oxide passivation structure is prepared by the preparation method according to any one of claims 1 to 5, wherein the passivation tunneling layer comprises a silicon wafer, a passivation tunneling layer and a doped polysilicon layer, wherein the material of the passivation tunneling layer is an ultra-thin silicon oxynitride interface material, wherein the ultra-thin silicon oxynitride interface material is a SiON film having a thickness of 1 nm to 4 nm, wherein the atomic percentage of nitrogen in the SiON film is 1% to 40%, and wherein the passivation tunneling layer is located between the silicon wafer and the doped polysilicon layer.

7. The use of the tunneling oxide passivation structure according to claim 6, characterized in that: The tunneling oxide passivation structure is applied to N-type or P-type tunneling oxide layer passivation contact solar cells.

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