JPH10261812A - Manufacture of p-n junction silicon substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the cost of a solar battery by manufacturing a p-n junction silicon substrate using no graphite substrate through a simple process and increasing the yield of silicon. SOLUTION: An SiO2 film 13 is formed by melt-spraying by applying an Si3 N4 mold release agent 12 to a graphite base 11 and spraying a plasma jet 4 containing SiO2 powder 3 prepared by supplying SiO2 powder 3 to a plasma gas 2 flowing through a plasma torch 1 upon the vase 11. After the SiO2 film 13 is preheated to about 1,300 deg.C, silicon 14 containing 0.1 ppmw B is sprayed on the heated film 13, and then, silicon containing P is sprayed for forming an n-layer. Thereafter, a p-n junction silicon substrate is obtained by removing the graphite base 11 by utilizing the mold release agent 12 and the SiO2 film 13 with a hydrofluoric acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel method for manufacturing a pn junction silicon substrate for a solar cell.

[0002]

2. Description of the Related Art A solar cell is a solid-state device that directly converts light energy of the sun into electric energy, and its basic structure is constituted by a semiconductor pn junction. Conventionally, a pn junction silicon substrate for a solar cell has been manufactured in the next step. First, high-purity silicon doped with 0.1 ppm of B is cast, then the surface of the ingot is peeled, and a wafer size is cut out, followed by slicing to a substrate thickness (450 μm). Next, in order to remove the cutting stress at the time of slicing, surface etching is performed to a plate thickness of 350 μm.
Then, the substrate is exposed to a POCl ₃ atmosphere furnace at 900 ° C. for 15 minutes to perform P diffusion with a thickness of 0.3 μm to manufacture a pn junction silicon substrate.

As described in the Japan Society for the Promotion of Science, “Amorphous Nano Materials 147th Committee: The 47th Research Material” (March 23, 1995), a silicon sprayed film is manufactured and then plasma CVD is performed. A pn junction substrate is manufactured by depositing high-concentration n-type sintered silicon.

[0004]

The conventional method of manufacturing a pn junction silicon substrate has many steps, and the Si yield is 60% or less due to slice loss, and the yield is as low as 54% or less when including the surface etching loss. Had become.
In addition, since the above-mentioned substrate of the Japan Society for the Promotion of Science uses a carbon substrate, the structure (excessive B doping of silicon, formation of a comb-shaped electrode structure, etc.) on the back surface which has been conventionally performed for high efficiency is used. It could not be performed, and the power loss from the electrode was large.

An object of the present invention is to provide a method for manufacturing a pn junction silicon substrate for a solar cell which has solved the above-mentioned conventional disadvantages.

[0006]

Means for Solving the Problems The present invention has been made to achieve the above object, and its technical means is to apply a release agent made of Si ₃ N ₄ on a graphite base, After spraying 200 to 400 μm of SiO ₂ powder onto the surface, a silicon substrate containing 0.05 to 0.2 ppmw of B is sprayed to produce a silicon substrate having a thickness of 200 to 350 μm.
Further, from above, a silicon powder containing 0.15 to 0.5 ppmw of P was sprayed with a thickness of 1 to 1.5 μm, the substrate was gradually cooled and annealed, and the graphite base was removed from the obtained substrate. This is a method for manufacturing a pn junction silicon substrate, characterized by removing the SiO ₂ film with hydrofluoric acid.

The release agent made of Si ₃ N ₄ makes the SiO ₂ film easily peel off from the graphite base. Since the silicon film with the graphite base attached cannot be processed to improve the conversion efficiency such as BSF or comb-shaped electrode structure on the back surface (silicon) of the solar cell when processed into a solar cell, it is released. The graphite base can be removed by the agent. The SiO ₂ film is sprayed to prevent contamination from Si ₃ N _{4 and} to form a smooth silicon spray film.
It was set to a film thickness of ｍ400 μm.

[0008] B is 0.05 to 0.2 pp on a silicon substrate.
The reason why the mw-containing silicon powder is sprayed is to form a p-type silicon layer on the silicon substrate. Most suitable values are between 0.1 and 0.15 ppmw. The reason for setting the thickness of the silicon substrate to 200 μm or more is that if the thickness is less than 200 μm, the strength may be insufficient.
The reason for limiting to the following is that if the thickness is larger than this, the photoelectric conversion efficiency of the final product is reduced.

The n-type silicon layer has a P of 0.15 to 0.5 p.
pmw, most preferably 0.2 to 0.3 ppmw, is sprayed with a plasma torch different from that for forming the silicon substrate. The thickness of the n-layer is 1 to 1.
The substrate has a thickness of 5 μm, most preferably 1 to 1.2 μm, and has an appropriate conversion efficiency. The control of the film thickness is performed by the supply speed of the P-containing SiO ₂ powder as the spray material and the spray time.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment will be described. FIG. 1 is an explanatory diagram of an embodiment of the present invention.
is there. Si as a release material on the graphite base 11_Three N_Four From
Mold release agent 12 is applied, and SiO_Two A film 13 is formed. Step
SiO in plasma gas 2 flowing in plasma torch 1 _Two 
Powder 3 is supplied together with a carrier gas, and plasma jet is applied.
4 and injected. This SiO_Two The membrane 13 is
It is formed by thermal spraying of Razuma Jet. About 300μm thickness
SiO_Two The film 13 is preheated to about 1300 ° C.
The silicon 14 containing 0.1 ppmw of B is sprayed.
Then, P-containing silicon for forming the n-layer is sprayed and gradually sprayed.
After cooling, remove the graphite base and release agent, and
Ri SiO _Two Remove the membrane.

FIG. 2 is a process flow chart for carrying out the method of the present invention. (A) Si as a release material on a 10 cm square graphite base 21
A mold release agent 22 containing ₃ N ₄ as a main component is applied, dried sufficiently, and then placed in a furnace 8 replaced with an Ar atmosphere. (B) The graphite base 21 is preheated to about 1300 ° C. by the heater 5 from above and below the base 21.

(C) The SiO ₂ powder 3 is supplied together with a carrier gas into the plasma gas flowing through the plasma torch,
While being mixed and injected into the plasma jet 4, it is sprayed while being scanned on the release agent 22 to form the SiO ₂ film 23. The supply rate of the SiO ₂ powder 3 is 10 g / min,
The deposition rate of the O ₂ film 23 is about 7.5 μ on average over the entire base.
m / sec, the film formation time is 40 seconds, and the film thickness is about 300 μm.
m (SiO ₂ film 23).

[0013] (d) ~ (e) the SiO ₂ film 23 of 300μm was formed on a graphite base 21 while heated to about 1300 ° C., the silicon 3 the SiO ₂ to 0.1ppmw containing B thereon Thermal spraying is performed on the film 23 to form a silicon sprayed film 24 having a thickness of 300 μm. The silicon 3 used is a crushed product of B-added CZ silicon having a resistivity of about 1.5 Ωcm,
The particle size is 5-20 μm, and the feed rate to the torch is 10
g / min, the deposition rate of the silicon sprayed film 24 is about 6.5.
μm / sec, and the deposition time was 45 sec.

(F) The above-mentioned substrate is held at about 900 ° C., and silicon 3 containing 0.2 ppmw of P is sprayed on the B-containing silicon sprayed film 24 to form a 1.5 μm-thick silicon sprayed film 25. I do. The P-containing silicon used is a crushed product of P-added CZ silicon having a resistivity of about 0.5 Ωcm and a particle size of 5
20 μm, the supply speed to the torch is 5.8 g / min, and the deposition rate of the silicon sprayed film 25 is about 0.75 μm / sec.
c, The film formation time was 2 seconds.

(G) After the spraying, the sprayed films 23 and 24 are
The temperature is held at 00 ° C. for about 15 minutes to change the sprayed film 25 to the sprayed film 24.
After diffusing P into (h), it is transferred to the position of the cooling device 6 and gradually cooled. (I) After slow cooling, the base 21 taken out of the furnace 8 is separated on the surface of the release agent 22 by natural cooling.

(J) The silicon substrate 26 before pickling, which has been separated from the graphite base after slow cooling, has its SiO ₂ layer removed by hydrofluoric acid (HF) in the pickling tank 7, and the silicon substrate after pickling has been removed. Then, it is sent to the next neutralization / washing step 31. As a result of manufacturing a solar cell using the pn junction silicon substrate obtained in this example, a conversion efficiency of 12.2% was obtained. In the embodiment, the thickness of the sprayed film, the supply speed of the powder, and the film forming time are limited, but the present invention is not limited to these.

[0017]

According to the present invention, a pn junction silicon substrate without a graphite base can be manufactured by a simple process, and the silicon yield is less than 60% in the prior art.
It can be easily raised to about 0%, greatly contributing to cost reduction of solar cells.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an embodiment.

FIG. 2 is a process chart of an example.

[Explanation of symbols]

1 the plasma torch 2 plasma gas 3 silicon powder or SiO ₂ powder 4 plasma jet 5 heater 6 cooler 7 San'araiso 8 Ar atmosphere furnace 11 graphite base 12 releasing agent 13 SiO ₂ sprayed film 14 silicon sprayed film 21 graphite base 22 Release agent 23 SiO ₂ film 24 B sprayed silicon film 25 B sprayed silicon film 26 Silicon substrate during pickling 27 Silicon substrate after pickling 31 Neutralization and cleaning process

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Masamichi Abe 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Prefecture Inside the Chiba Works of Steel Corporation (72) Inventor Yasuhiko Sakaguchi 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki (72) Inventor Yoshihide Kato 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Corporation Chiba Works

Claims (1)

[Claims] 1. A mold release agent made of Si ₃ N ₄ is applied on a graphite base, and a silicon powder containing 0.05 to 0.2 ppmw of B is sprayed on the upper surface of the mold release agent to have a thickness of 200 to 350 μm.
Of silicon substrate, and P
Silicon powder containing 0.5 ppmw having a thickness of 1 to 1.5
A method for manufacturing a pn junction silicon substrate, which comprises: spraying μm, gradually cooling and annealing the substrate, and removing the SiO ₂ film of the obtained substrate with hydrofluoric acid.