RU2614080C1 - Silicon wafer surface passivation by magnetron sputtering - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: silicon wafers surface passivation includes cleaning of crystalline silicon wafers, silicon sputtering using a magnetron with a silicon target. Silicon target sputtering is performed in argon (Ar) medium with addition of hydrogen (H₂) or in argon (Ar) medium with addition of organosilicon compounds, or in argon (Ar) medium with addition of hydrogen (H₂) and organosilicon compounds to obtain the passivation layer of hydrogenated amorphous silicon of high quality, to passivate the wafer surface and reduce the surface recombination velocity of charge carriers. At least one chemical reactant selected from the group consisting of silane (SiH₄), Si₂H₆, Si₂H_4, SiF_4, Si₂F₆ and other silicon-containing compounds is used as the organosilicon compound.

EFFECT: invention allows to reduce defects and surface recombination of charge carriers, to increase charge carriers lifetime, to improve quality, technology and safety of the passivation process.

2 cl, 1 dwg

Description

FIELD OF THE INVENTION

The invention relates to passivation of the surface of silicon wafers (mono-or polycrystalline) (options) to increase the lifetime of charge carriers in the production of solar modules using a magnetron with an argon atmosphere with the addition of hydrogen and organosilicon compounds.

State of the art

Currently, the method of plasma-chemical vapor deposition is used to passivate the surface of silicon wafers in the production of solar modules based on heterojunction (HJT technology). This method involves the deposition of a film of amorphous hydrogenated silicon by decomposition of silane diluted with hydrogen in a high-frequency glow discharge plasma. The features of the process and reactor design exclude the possibility of using a conveyor line and require flipping the plates to passivate each side. These restrictions slow down the production process and necessitate the use of additional equipment, such as flip plates.

A known method of producing a photovoltaic cell with the application of a passivation layer by the PECVD process (see [1] US patent No. 5935344, IPC H01L 31/04, published 10.08.1999), however, the disadvantage of this application is the low productivity and the need to flip the plates for applying passivation coatings on each side, and in the case of large reactors, the use of additional devices, such as substrate holders, is necessary.

Known methods for the formation and preparation of silicon thin-film modules of a solar cell (see [2] RF patent No. 2454751, IPC H01L 31/042, publ. 27.06.2012; [3] RF patent No. 2435874, IPC H01L 31/18, publ. 10.12 .2011), including the use of a torch with a high-frequency inductively coupled plasma with an induction coil; the introduction of a plasma gas selected from the group consisting of helium, neon, argon, hydrogen and mixtures thereof; in said burner with a high-frequency inductively coupled plasma to form a plasma inside said coil, injection of a chemical reagent, for example consisting of SiCl ₄ , SiH ₄ , SiHCl ₃ and SiF ₄ compounds containing silicon, into said burner; and depositing a thin film layer on the surface of the silicon substrate using a burner. Inductively coupled plasma provides pin- and nip-type layers.

The disadvantages of the known solutions compared with the claimed is the use of inductively coupled plasma, which does not allow to obtain a passivating layer of amorphous hydrogenated silicon. At the same time, atmospheric pressure is used, which may make it difficult to obtain passivating layers. When using a burner, it means the presence of a torch (its temperature will be above 200 ° C), which will lead to the creation of defects on the surface of the plate.

SUMMARY OF THE INVENTION

The technical task is to obtain a passivating layer in the form of amorphous hydrogenated silicon (a-Si: H).

The technical result is to reduce defects and surface recombination of the charge carrier, increase the lifetime of the charge carriers, increase the quality, manufacturability and safety of the passivation process.

To solve the problem and achieve the stated result, it is proposed to passivate the surface of silicon wafers, including cleaning crystalline silicon wafers, sputtering silicon with a magnetron with a silicon target, while the process of sputtering the silicon target is performed in an argon atmosphere (Ar) with the addition of hydrogen (H ₂ ), or an atmosphere of argon (Ar) with the addition of organosilicon compounds, or in an atmosphere of argon (Ar) with the addition of hydrogen (H ₂ ) and organosilicon compounds, to obtain a passivating layer of amorphous hydrogenated silicon of high quality for passivation of the wafer surface and a reduced rate of surface recombination of charge carriers. At least one chemical reagent selected from the group consisting of silane (SiH ₄ ), Si ₂ H ₆ , Si ₂ H ₄ , SiF ₄ , Si ₂ F ₆ and other compounds containing silicon is used as the organosilicon compound.

The material obtained by magnetron sputtering of a silicon target with the introduction of hydrogen or organosilicon compounds is hydrogenated amorphous silicon (a-Si: H), which is a passivating layer.

Brief Description of the Drawings

FIG. 1 - Structure using the method of magnetron sputtering to passivate the surface of crystalline silicon with amorphous hydrogenated silicon.

The positions indicated in figure 1:

1 - a plate of crystalline silicon;

2 - passivation layer made by magnetron sputtering of a silicon target in an argon atmosphere with the addition of hydrogen and (or) silane or other organosilicon compounds;

3 - p-layer;

4 - n-layer;

5 - current collector layers.

The implementation of the invention

The usual way to passivate silicon wafers during the production of solar modules is the PECVD method. In the PECVD process, highly saturated hydrogen layers grow, which reduces the number of defects in the resulting layers. The decrease in the number of defects occurs due to the passivation of dangling silicon bonds (which form the defects) by hydrogen atoms. The reduction of defects reduces the surface recombination of charge carriers, which makes it possible to use the material for passivation of silicon wafers. During passivation, hydrogen atoms are attached to dangling silicon surface bonds (in a silicon wafer). As a result, the surface recombination of charge carriers decreases. To stabilize the effect from above, a layer of amorphous hydrogenated silicon (a-Si: H) is deposited on passivated bonds. When using a magnetron with an inert atmosphere (argon atmosphere), passivation of bonds does not occur, since the atmosphere does not contain hydrogen. Also, the resulting layer of amorphous silicon (a-Si) is very defective and not saturated with hydrogen, which also does not give the effect of passivation. However, the addition of hydrogen and (or) an organosilicon compound, for example, silane, to the atmosphere, as in the claimed solution, allows solving this problem, i.e. passivation of connections begins to occur.

According to the first option, when hydrogen is introduced only, the reaction of hydrogen and silicon in the magnetron plasma takes place, as well as the decomposition and ionization of hydrogen molecules and atoms. The resulting radicals and ions passivate the surface of silicon wafers, and the formed layers of amorphous hydrogenated silicon (a-Si: H) are of sufficient quality to obtain the desired surface passivation effect. This modification of the technology makes it possible to use the method of magnetron sputtering of a silicon target to obtain passivation of the surface of a silicon wafer in the production of heterostructured solar cells. The use of magnetron sputtering technology can increase the production rate of these solar modules through the use of a conveyor line and (or) double-sided magnetrons. The latter eliminates the need for additional procedures and additional equipment (flip plate) in the production of solar modules based on heterojunction.

According to the second option, in the case of the introduction of organosilicon compounds, such as silane, its decomposition and the formation of hydrogen and silicon radicals with hydrogen occur. In this embodiment, when using hydrogen-containing silicon compounds in the atmosphere of a magnetron, hydrogen may not be used (a causal relationship between the features of the second embodiment and the technical result is similar to the first embodiment).

According to the third option, with the introduction of hydrogen and organosilicon compounds, decomposition of organosilicon compounds occurs with the formation of hydrogen ions and organosilicon compounds, as well as radicals of organosilicon compounds. As a result of this, as well as the presence of hydrogen in the atmosphere, the amorphous silicon films obtained as a result of the process are saturated with hydrogen (a causal relationship between the features of the third embodiment and the technical result is similar to the first embodiment).

First, preparatory processes are performed, including cleaning the crystalline silicon wafers, locking and loading the wafers into a magnetron.

Passivation is carried out using a magnetron with a silicon target (magnetron deposition of layers, including passivating), and the process of sputtering a silicon target is carried out in an atmosphere of argon (Ar) and hydrogen (H ₂ ). It is also possible to add silane (SiH ₄ ) or other organosilicon compounds to the atmosphere, for example, Si ₂ H ₆ , Si ₂ H ₄ , SiF ₄ , Si ₂ F ₆ , etc. In the case of using hydrogen-containing silicon compounds in the atmosphere, hydrogen can not apply. This technical solution allows to obtain a passivating layer of hydrogenated amorphous silicon (a-Si: H).

This process makes it possible to effectively use the magnetron sputtering process to passivate the surface of silicon wafers. Passivation of silicon wafers is necessary in the production of solar modules based on single-crystal or polycrystalline silicon, to increase the lifetime of charge carriers.

The use of a magnetron at this stage of production of solar modules allows the use of a conveyor. This technology also allows the use of double-sided magnetrons, which eliminates the need for flipping silicon wafers, which is necessary when using the PECVD process. These features allow you to increase the productivity of the process and make it more technological and safe.

The passivation process consists of the following operations:

1. Preparation of the plate, including cleaning;

2. Locking of the plate before passivation and loading into the magnetron;

3. Magnetron deposition of hydrogenated amorphous silicon layers;

4. Locking and unloading from a magnetron.

In the case of using a one-sided magnetron, the plate is turned over and steps 2-4 are repeated.

The steps involved in preparing plates for passivation and subsequent processing may vary.

Example

1. Removing organic contaminants from the surface of the wafers by washing the wafers (mono) or polycrystalline silicon. The plates can be washed in a weak solution of hydrofluoric (HF) and nitric (HNO ₃ ) acids at a temperature of 70 ° C for 1-5 minutes. After that, washing is carried out in deionized water.

2. Removing the damaged layer (the layer that occurs during the cutting of plates from the ingot). Removing the damaged layer can be done by exposure to a solution of caustic potassium (KOH) at a temperature of 70 ° C. After that, the plates are cleaned by using a master key in deionized water.

3. Texturing the plates. By anisotropic etching, a texture is formed on the surface of the wafer that allows you to change the optical design of the photoconverter in order to increase the final characteristics, such as current. A 15-30% potassium hydroxide (KOH) solution with the addition of a texturing additive is used as an etchant. As an additive, isopropyl alcohol (CH ₃ CH (OH) CH ₃ ), a texturizing additive of industrial production, or any other texturing additive designed to improve the quality of the texture can be used. After that, washing is carried out in deionized water.

4. Exposure in a 5% solution of hydrofluoric acid for 60 seconds, to saturate the surface with hydrogen and remove residual contaminants and rinse in deionized water. This stage is necessary to improve the quality of passivation of the surface of silicon wafers. In this case, the interval between this step and the application of the passivating layer should not exceed 1 hour, since in the case of a significant excess of this time, the quality of surface passivation decreases.

5. Drying the plate (removing liquid from the surface).

6. Application of passivating layers by magnetron sputtering.

7. Formation of the structure (deposition of n- and p-layers).

8. Application of slip layers.

If the atmosphere of the magnetron does not contain silane, hydrogen or other organosilicon compounds containing hydrogen, passivation cannot be carried out using a magnetron.

When applying the proposed technical solution (introducing silane, hydrogen or another organosilicon compound into the atmosphere of argon) with the help of a magnetron, it is possible to obtain layers of amorphous silicon, which is necessary for passivation of quality. The use of a magnetron allows the use of a conveyor and, in the case of a double-sided magnetron, to eliminate the need for plate overturn. The downsizing is also a consequence of the use of magnetrons instead of PECVD reactors (when using a PECVD reactor, it is impossible to use a conveyor and the plates must be turned over in the process (since PECVD reactors are designed in such a way that the substrate plates should be located on one of the electrodes)).

Claims (2)

1. Passivation of the surface of silicon wafers, including cleaning crystalline silicon wafers, sputtering silicon magnetron with a silicon target, characterized in that the process of sputtering the silicon target is performed in an argon atmosphere (Ar) with the addition of hydrogen (H ₂ ), or in an argon atmosphere (Ar) with the addition of organosilicon compounds, or argon (Ar) with the addition of hydrogen (H ₂₎ and organosilicon compounds, to obtain the passivation layer of hydrogenated amorphous silicon of high quality, to passivate and the wafer surface and reducing the surface recombination velocity of charge carriers. 2. Passivation according to claim 1, characterized in that at least one chemical reagent selected from the group consisting of silane (SiH ₄ ), Si ₂ H ₆ , Si ₂ H ₄ , SiF ₄ , Si is used as an organosilicon compound. ₂ F ₆ and other compounds containing silicon.

Images