CN111564528A - Preparation process of polycrystalline silicon multi-grain film - Google Patents

Abstract

The invention provides a preparation process of a polycrystalline silicon multi-grain film, which comprises the following steps: (1) preparation of SiO on a monocrystalline silicon substrate₂An isolation layer; (2) corroding the SiO2 isolation layer by adopting a photoetching mask method to expose the monocrystalline silicon substrate, wherein the exposed monocrystalline silicon substrate is a nucleation area to obtain a non-uniform nucleation substrate; (3) and (3) epitaxially growing a polycrystalline silicon film on the uneven nucleation substrate prepared in the step (2) by adopting an atmospheric pressure chemical vapor deposition method. The invention prepares SiO on a monocrystalline silicon substrate₂An isolation layer; etching SiO by photoetching mask method₂Exposing the monocrystalline silicon to prepare an uneven nucleation substrate, and epitaxially growing a polycrystalline silicon film by normal-pressure chemical vapor deposition to prepare a large-grain polycrystalline silicon film; the preparation method can prepare high-quality large-grain polycrystalline silicon at high speedThe film is formed, so that the performance of the polycrystalline silicon thin film battery is improved, and the industrial application of the polycrystalline silicon thin film battery is promoted.

Description

A kind of preparation technology of polycrystalline silicon polycrystalline grain thin film

technical field

The invention belongs to the technical field of material preparation, and particularly relates to a preparation process of a polycrystalline silicon polycrystalline thin film.

Background technique

Polycrystalline silicon thin film solar cells have the advantages of both crystalline silicon solar cells (high efficiency, long life, stable performance, rich and non-toxic materials, etc.) and thin film solar cells (low material consumption and low cost), and have become a research hotspot in the field of solar energy internationally. The photoelectric conversion efficiency of polycrystalline silicon thin film solar cells prepared by Japan's Mitsubishi Corporation on quartz (SiO ₂ ) substrates reaches 16.5%, and the conversion efficiency of polycrystalline silicon thin film solar cells prepared by German Fraunhofer Institute on graphite and silicon carbide (SiC) substrates They are 11% and 9.3% respectively, and the conversion efficiency of polysilicon thin film solar cells prepared by the porous silicon separation technology of SONY Company in Japan reaches 12.5%. However, due to the limitations of process technology and processing equipment, there are still many problems in the industrialization of polycrystalline silicon thin film batteries that need to be solved urgently. Enlarging the grain size to increase the carrier mobility is one of the important process measures to improve the efficiency of polycrystalline silicon thin film solar cells.

At present, there are many techniques for preparing polysilicon thin films, which can be divided into high temperature method and low temperature method, or direct method or indirect method. Among them, the methods for directly depositing polysilicon films at high temperature include atmospheric pressure chemical vapor deposition (APCVD) and rapid thermal chemical vapor deposition (RTCVD). The temperature of high-temperature deposition is generally 800 to 1200 ° C. The polysilicon film grown in this temperature range has large grain size, good film quality, and high film growth rate; The grain size obtained by depositing the polysilicon thin film on the top is usually small, and if the grain size in the polysilicon thin film is too small, it will aggravate the recombination of grain boundaries, thereby reducing the performance of the polysilicon thin film solar cell.

In the actual industry, recrystallization technology is often used to increase the grain size to improve the crystalline quality and electrical properties of the film. Zone melting recrystallization (ZMR) and large area crystallization (LAR) are recrystallization techniques commonly used in high temperature methods. The crystal grains are grown by melting and recrystallizing the polycrystalline silicon layer at a high temperature. The combination of rapid thermal chemical vapor deposition and zone melting recrystallization can produce thin-film cells with an efficiency of more than 10% on cheap and high temperature resistant substrates. However, the zone melting and recrystallization process is complicated and the cost is too high, making it difficult to realize industrialization. .

The indirect method is generally to convert the pre-deposited amorphous silicon film into polysilicon through a certain process technology, mainly including solid phase crystallization (SPC), metal induced lateral crystallization (MILC), microwave crystallization and excimer laser crystallization (ELC). )Wait.

The solid-phase crystallization method is to first deposit an amorphous silicon film on a substrate, and then thermally anneal it to crystallize the amorphous silicon to obtain polycrystalline silicon. The main feature is that the temperature at which amorphous silicon crystallizes is lower than the temperature at which it crystallizes after melting. The grain size of the prepared polysilicon film is related to the annealing temperature and the initial structure of the amorphous silicon film. Compared with polysilicon deposited directly by CVD, the grain size of polysilicon obtained by solid-phase crystallization is larger. When the technology is annealed at a lower temperature (such as limited by the glass substrate at about 600°C), the time can be as long as ten hours.

Through the research and analysis of the current similar products, it can be seen that polycrystalline silicon thin film solar cells have always been the research hotspot in the photovoltaic industry. Using appropriate process methods to prepare large grain polycrystalline silicon thin films on heterogeneous substrates will effectively improve the Efficiency and cost reduction in polysilicon thin-film solar cells. Using the idea of inhomogeneous nucleation to prepare the seed layer and epitaxial growth is an effective way to obtain large-grain polysilicon thin films. The present invention hopes to realize the growth of large-grain polysilicon thin films through the idea of non-uniform nucleation combined with epitaxial growth. The nucleation region is selected by photolithography, and then epitaxially grown by APCVD to obtain a large-grain polysilicon film.

SUMMARY OF THE INVENTION

The invention provides a preparation process of a polycrystalline silicon polycrystalline thin film, the preparation method can prepare a high quality and large grain polycrystalline silicon thin film at a high speed, thereby improving the performance of the polycrystalline silicon thin film battery and promoting the industrial application of the polycrystalline silicon thin film battery.

To achieve the above objects, the present invention adopts the following technical solutions.

A preparation process of a polycrystalline silicon polycrystalline film, comprising the following steps:

(1) _SiO2 isolation layer is prepared on a single crystal silicon substrate;

(2) The _SiO2 isolation layer is etched by a photolithography mask method to expose the single crystal silicon substrate, wherein the exposed single crystal silicon substrate is a nucleation area, and the distance between adjacent nucleation areas is 6~ 35μm to obtain an uneven nucleation substrate;

(3) A polycrystalline silicon thin film is epitaxially grown on the non-uniform nucleation substrate obtained in step (2) by using an atmospheric pressure chemical vapor deposition method.

Further, the step (1) is specifically as follows: using a wet thermal oxidation preparation method to grow a SiO ₂ layer with a thickness of 150-300 nm on a single crystal silicon substrate, wherein the preparation temperature in the wet thermal oxidation preparation method is 1000 ~1200°C.

Further, the specific process of the step ( ₂ ) is: coating photoresist on the isolation SiO layer obtained in step (1), then adding a mask on it, and then using an ultraviolet exposure machine to expose the photoresist Carry out exposure treatment, and then use the wet etching method to etch the developed part of the photoresist, and remove the _SiO2 layer until the single crystal silicon substrate is exposed.

Further, in the process of etching the developing part of the photoresist by the wet etching method, the etching solution used is a mixed solution of HF and H ₄ F, and the volume ratio of HF and H ₄ F is (1～3):( 5 to 7).

Further, the deposition conditions of the atmospheric pressure chemical vapor deposition method in the step (3) are as follows: under normal pressure, SiHC ₁₃ is used as the deposition source, H ₂ is the carrier gas, the deposition temperature is 1000-1500° C., and the average deposition rate is is 0.5-2 μm/min, and the gas flow rate of SiHC ₁₃ is 5-10 g/min, and the gas flow rate of H ₂ is 10-15 slm.

Further, the thickness of the polysilicon film deposited in the step (3) is 20-50 μm.

A polycrystalline silicon polycrystalline grain thin film is a polycrystalline silicon polycrystalline grain thin film prepared by the above-mentioned preparation process of the polycrystalline silicon polycrystalline grain thin film.

The beneficial effects of the present invention are as follows: the present invention prepares the _SiO2 isolation layer on the single crystal silicon substrate; then the _SiO2 layer is etched by the photolithography mask method to expose the single crystal silicon, so as to prepare the uneven nucleation substrate, Then, the polycrystalline silicon thin film is epitaxially grown by atmospheric pressure chemical vapor deposition (APCVD) to prepare the polycrystalline silicon thin film with large crystal grains; the preparation method of the invention can prepare high-quality polycrystalline silicon thin film with large crystal grains at high speed, thereby improving the performance of the polycrystalline silicon thin film battery, Promote the industrial application of polysilicon thin film batteries.

Description of drawings

Fig. 1 is the process flow diagram of preparation process described in the present invention;

Fig. 2 is the surface topography diagram of the polycrystalline silicon thin film made in Example 1;

Fig. 3 is the surface topography diagram of the polycrystalline silicon thin film made in Example 2;

Fig. 4 is the surface topography diagram of the polysilicon film prepared in Example 3;

Fig. 5 is the surface topography of the polycrystalline silicon thin film prepared by Comparative Example 1;

FIG. 6 is a surface topography diagram of a polycrystalline over-thin film prepared in Comparative Example 2. FIG.

Detailed ways

Example 1

Referring to FIG. 1, a preparation process of a polycrystalline silicon polycrystalline film, comprising the following steps:

(1) Prepare a _SiO2 isolation layer on a polished single crystal silicon substrate with N-type (100) crystal orientation, specifically: using a wet thermal oxidation preparation method to grow a _SiO2 layer with a thickness of 200 nm on the single crystal silicon substrate , wherein the preparation temperature in the wet thermal oxidation preparation method is 1050 °C;

( ₂ ) The SiO isolation layer is etched by a photolithography mask method to expose the single crystal silicon substrate, wherein the exposed single crystal silicon substrate is a nucleation region, and the distance between adjacent nucleation regions is 10 μm, To obtain a non-uniform nucleation substrate, coat photoresist on the isolation SiO ₂ layer obtained in step (1), then add a mask on it, and then use an ultraviolet exposure machine to expose the photoresist, and then use The wet etching method is used to etch the photoresist developed part, and the _SiO2 layer is removed until the single crystal silicon substrate is exposed;

Wherein, in the process of etching the developed part of the photoresist by the wet etching method, the etching solution used is a mixed solution of HF and H ₄ F, and the volume ratio of HF and H ₄ F is 1:6.

(3) A polycrystalline silicon film is epitaxially grown on the uneven nucleation substrate obtained in step (2) by a normal pressure chemical vapor deposition method, and the thickness of the deposited polycrystalline silicon film is 35 μm. The EPIKVAR-121M epitaxy furnace of the institute is equipped with a graphite base and adopts electromagnetic induction heating; among them, the deposition conditions of the atmospheric pressure chemical vapor deposition method are: under normal pressure, SiHC ₁₃ is used as the deposition source, and H ₂ is used as the carrier gas , the deposition temperature was 1200 °C, the average deposition rate was 1 μm/min, and the gas flow rate of SiHC ₁₃ was 8 g/min, and the gas flow rate of H ₂ was 12.0 slm.

Example 2

In the preparation process described in this example, only the distance between adjacent nucleation regions is different from Example 1. The distance between adjacent nucleation regions in this example is 30 μm, and the rest of the process steps are exactly the same as Example 1.

Example 3

In the preparation process described in this example, only the spacing between adjacent nucleation regions is different from Example 1. The spacing between adjacent nucleation regions in this example is 35 μm, and the rest of the process steps are exactly the same as Example 1.

Comparative Example 1

In the preparation process described in this comparative example, only the spacing between adjacent nucleation regions is different from Example 1. The spacing between adjacent nucleation regions in this comparative example is 5 μm, and the rest of the process steps are exactly the same as in Example 1.

Comparative Example 2

In the preparation process described in this comparative example, only the spacing between adjacent nucleation regions is different from Example 1. The spacing between adjacent nucleation regions in this comparative example is 40 μm, and the rest of the process steps are exactly the same as Example 1.

When the spacing between adjacent nucleation regions is 5 μm, only grid-like patterns can be seen on the surface of the epitaxial silicon film, see Figure 5; when the spacing between adjacent nucleation regions increases to 10 μm and 30 μm , the surface of the epitaxial silicon film is shown as a positive pyramid array, see Figure 2 and Figure 3; but when the distance between the nucleation regions reaches 35 μm, see Figure 4, holes appear at the connection points of the four pyramids; then continue to increase the distance between the nucleation regions When the distance between them reaches 40 μm, the surface morphology of the substrate begins to become disordered, and irregular polysilicon grains begin to grow from the junction of the pyramids, and the pyramids deform or even disappear, see Figure 6.

Claims (7)

1. a preparation technology of polycrystalline silicon polycrystalline film, is characterized in that, comprises the following steps: (1) _SiO2 isolation layer is prepared on a single crystal silicon substrate; (2) The _SiO2 isolation layer is etched by a photolithography mask method to expose the single crystal silicon substrate, wherein the exposed single crystal silicon substrate is a nucleation area, and the distance between adjacent nucleation areas is 6~ 35μm to obtain an uneven nucleation substrate; (3) A polycrystalline silicon thin film is epitaxially grown on the non-uniform nucleation substrate obtained in step (2) by using an atmospheric pressure chemical vapor deposition method. 2 . The preparation process of the polycrystalline silicon polycrystalline thin film according to claim 1 , wherein the step (1) is specifically as follows: using a wet thermal oxidation preparation method to grow on a monocrystalline silicon substrate with a thickness of 150～150 . 300nm _SiO2 layer, wherein the preparation temperature in the wet thermal oxidation preparation method is 1000-1200°C. 3. The preparation process of the polysilicon polycrystalline film according to claim 1, wherein the specific process of the step ( ₂ ) is: coating photolithography on the isolation SiO layer obtained in the step (1) Then add a mask on it, and then use an ultraviolet exposure machine to expose the photoresist, and then use a wet etching method to etch the developed part of the photoresist to remove the _SiO2 layer until the monocrystalline silicon substrate is exposed. until. 4. the preparation technology of polysilicon polycrystalline grain thin film according to claim 3, is characterized in that, in the process that adopts wet etching method to carry out etching to photoresist developing part, used etching solution is the mixing of HF and H ₄ F solution, and the volume ratio of HF to H ₄ F is (1~3):(5~7). 5. the preparation technology of polycrystalline silicon polycrystalline grain thin film according to claim 1, is characterized in that, in described step (3), the deposition condition of normal pressure chemical vapor deposition method is: under normal pressure, adopt SiHC ₁₃ for deposition source, _H2 is the carrier gas, the deposition temperature is 1000-1500 °C, the average deposition rate is 0.5-2 μm/min, and the gas flow rate of SiHC ₁₃ is 5-10 g/min, and the gas flow rate of _H2 is 10-15 slm. 6 . The preparation process of the polycrystalline silicon polycrystalline film according to claim 1 , wherein the thickness of the polycrystalline silicon film deposited in the step (3) is 20-50 μm. 7 . 7 . A polycrystalline silicon polycrystalline film, characterized in that the polycrystalline silicon polycrystalline film is prepared by the preparation process of the polycrystalline silicon polycrystalline film according to claims 1 to 6 . 8 .

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