JP2639591B2 - Dopant film and impurity diffusion method using the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a dopant film used for a solid diffusion method and a diffusion method using the same.

[Conventional technology]

It is well known that, in the manufacture of an individual semiconductor element, p-type or n-type conductivity type impurity regions are formed in a semiconductor substrate by various diffusion methods. As the diffusion method, a gas diffusion method, a solid diffusion method, a coating diffusion method, and the like are performed. In particular, since the dispersion of impurities diffused into the semiconductor substrate adversely affects the characteristics of the semiconductor element,
As a diffusion method, a doped oxide method, which is one of solid-state diffusion methods with less variation in impurity diffusion concentration, is often used. This method uses CVD of oxides containing various impurities.
In this method, impurities are diffused into a semiconductor substrate by a thermal diffusion process by growing them on a semiconductor substrate by a technique and using these doped oxides as impurity diffusion source layers.

Although this method has little variation in impurities diffused in the semiconductor substrate, it has a disadvantage that an expensive CVD apparatus is required, productivity is poor, and it is not suitable for mass production.

As another method, a coating liquid for forming a silica-based film containing impurities is used, applied to a semiconductor substrate and dried to form an impurity diffusion source layer, and thermally diffused in the same manner as described above. There is also a coating diffusion method in which an impurity region is formed in a semiconductor substrate by using a method. However, this method has an advantage that an impurity region can be formed by a relatively simple operation without using an expensive device. Diffusion is not always easy.

Furthermore, as an improvement of the above-mentioned drawbacks of the diffusion method,
A diffusion method using a dopant film composed of an organic binder, an inorganic binder, and impurities is also known.
This is a method in which impurities are diffused into a semiconductor substrate by heating to a deposition temperature while a dopant film is sandwiched between two semiconductor substrates. By alternately connecting the film and the semiconductor substrate, there is an advantage that productivity is high because impurity diffusion processing is performed simultaneously on many semiconductor substrates by one thermal diffusion processing.

As such a dopant film, for example, an impurity compound selected from phosphorus pentoxide, arsenic, antimony, iron, cobalt, boron nitride, boric acid, indium, methyl borate and gallium, and cyanoethylated cellulose, methyl cellulose, and polyvinyl alcohol , A dopant film consisting of a homogeneous mixture with a volatile organic binder selected from the group consisting of starch and polyvinyl butyral is known (US Pat. No. 3,971,870).
Specification). This dopant film has a drawback that it is difficult to produce a uniform film in quality, and as a result, the impurity diffusion tends to vary, and the U.S. patent specification uses alumina powder as an inorganic binder. However, there is a disadvantage that alumina powder does not mix uniformly with the disclosed organic binder, and a dopant film composed of alumina powder, an organic binder and a phosphorus compound (NH ₄ H ₂ PO ₄ ) has a disadvantage. , AlPO ₄ is formed during the thermal diffusion process, remains as a precipitate on the surface of the semiconductor substrate, causes poor adhesion when forming a metal electrode, and causes a variation in impurity diffusion concentration. Not a film.

Further, as an improvement over the disadvantages of the above dopant film, an organic binder made of a vinyl-based synthetic resin, R
_4- nSi (OH) _n , Al (OR) ₃ , Ti (OR) ₄ , Nb (OR) ₄ , Zr (OR) ₄ , Hf
There is also known a dopant film using a mixture comprising an inorganic binder, an impurity compound and an organic solvent selected from the group consisting of compounds represented by (OR) ₄ , Ta (OR) ₅ and Be (OR) ₂ . A semiconductor element obtained by performing an impurity diffusion treatment using this dopant film has a shortcoming that the lifetime of minority carriers is short, and the electrical characteristics such as a decrease in reverse breakdown voltage are extremely poor.

[Problems to be solved by the invention]

The present inventors have sought to improve the disadvantages of the conventional dopant film, perform a high-concentration and low-impurity impurity diffusion treatment, obtain a long-lifetime minority carrier, and obtain a semiconductor element having excellent electrical characteristics. As a result of intensive research for the purpose of providing a dopant film, it is possible to achieve the object by a dopant film formed from a specific organic binder, a specific plasticizer, a compound of an impurity element, a mixture of an inorganic binder and an organic solvent. And found the present invention.

[Means for solving the problem]

The present invention provides: (A) at least one kind of organic binder selected from polyvinyl alcohol and polyvinyl butyral; (B) polyethylene glycol, mannitol, a polyalkyl acrylate having an alkyl group having 1 to 3 carbon atoms, glucose and saccharose. At least one plasticizer (C) A compound of an impurity element (D) A mixed solution comprising an inorganic binder and (E) an organic solvent is coated on a support and dried to peel a film obtained from the support. An impurity diffusion method using a dopant film characterized in that the dopant film is brought into close contact with a semiconductor substrate, heated to thermally decompose or burn an organic substance, and then heated to 900 to 1300 ° C.

 Hereinafter, the present invention will be described in detail.

In the present invention, the organic binder used as the component (A) is at least one selected from polyvinyl alcohol and polyvinyl butyral.

The present invention is characterized in that a plasticizer is blended in the preparation of the dopant film. Examples of the plasticizer used as the component (B) include polyethylene glycol, mannite, and alkyl having 1 to 3 carbon atoms. At least one selected from group-containing polyalkyl acrylates, glucose and saccharose, and in combination with the above-mentioned specific organic binder, a dopant capable of producing a semiconductor element having a long minority carrier lifetime and excellent electrical properties, in particular. A film is obtained.

The compound of the impurity element used in the present invention is soluble in an organic solvent or has good dispersibility in an organic solvent, and is hardly affected by outside air when formed into a film. Compounds that have low sublimability even at high temperatures and are vitrified by heat treatment during diffusion are preferred. Specific examples of these compounds include P ₂ O ₅ , NH ₄ H
_{2 · PO 4, (R'O)} 3 P, (R'O) 2 P (OH), (R '
_{O) 3 · PO, (R'O} ) 2 P 2 O 3 (OH) 3, (R'O) P (O
_{H) 2, B 2 O 3} , (R'O) 3 B, R'B (OH) 2, R '2 B (O
_{H), H 3 SbO 4,} (R'O) 3 Sb, SbX '3, SbOX', Sb 4 O 5
X ′, (R′O) ₂ Sb (OH), H ₃ AsO ₃ , H ₃ AsO ₄ , (R ′
O) ₃ As, (R′O) ₅ As, (R′O) ₂ As (OH), R ′ ₃
AsO, (R'O) Zn, ZnX '2, Zn (NO 2) 2, (R'O) 3 G
a, R'Ga (OH), R'Ga (OH) _2, etc. (however,
In the formula, R 'represents a halogen atom, an alkyl group or an aryl group, and X' represents a halogen atom).

As the inorganic binder used in the present invention, Si (OR)
_{4, Ge (OR) 4,} Ti (OR) 4, Zr (OR) 4, Hf (OR) 4, SiO 2, SiC,
Si ₃ N ₄ , Al ₂ O ₃ , GeO ₂ , TiO ₂ , ZrO ₂ , HfO ₂ , Ta ₂ O ₅ , Nb
Examples include ₂ O ₅ and BeO (R represents an alkyl group or an aryl group), and these may be used alone or as a mixture of two or more.

These inorganic binders are preferably used in powder form, and the particle size is preferably 300 μm or less, particularly
Those having a range of 0.01 to 200 μm are preferred. Particle size 300μm
Exceeding this is not preferred because it also causes variations in the impurity diffusion concentration.

To produce the dopant film of the present invention, a coating solution is prepared by dissolving or dispersing the above-mentioned organic binder, plasticizer, compound of an impurity element and an inorganic binder in an organic solvent, and applying the coating solution on an inert substrate. , And then the organic solvent is volatilized to form a solid film, and this film may be peeled from the substrate.

Examples of the organic solvent in this case include methyl alcohol, ethyl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, propylene glycol, and propylene glycol monomethyl. Examples thereof include ether, methyl acetate, ethyl acetate, butyl acetate, acetone, acetylacetone, methyl ethyl ketone, dioxane, tetrahydrofuran, toluene, and xylene. These may be used alone or in combination of two or more.

The solid content concentration in the above coating solution can be changed depending on the coating method, but is usually preferably 10 to 40% by weight. The composition ratio of each component when formed into a dopant film is as follows: organic binder 15 to 70% by weight, plasticizer 2 to 20% by weight, impurity element compound 1 to 20% by weight, and inorganic binder 1 to 80%.
A range of weight percent is used. The thickness of the dopant film is preferably in the range of 10 to 200 μm for practical use.

The method for forming the dopant film of the present invention can be used in the case of small-scale production, a doctor blading method using a doctor knife can be used, but in the case of mass production, a roll coater method, a screen printing method, a flow coater method, or the like. It is valid.

As a step, first, a coating solution is applied to a support, for example, polyethylene, polyethylene terephthalate, polypropylene,
After uniformly applying the above-mentioned coating method on a plate or sheet of a fluororesin or the like and evaporating the organic solvent by a drying treatment, the resulting film is peeled from the support to form a sheet-like film. Can be made.

Next, a method for diffusing impurities into a semiconductor substrate using the dopant film of the present invention will be described.

The dopant film of the present invention is sandwiched between two semiconductor substrates, for example, a silicon wafer, and heated under a stream of nitrogen, oxygen or a mixture of nitrogen and oxygen to thermally decompose or burn organic substances, and then 900 ° C. Diffusion is performed by heating from 1300 ° C. to p ⁺ n type, p ⁺ nn ⁺ type, n ⁺ pn ⁺
It is possible to obtain a silicon wafer having a junction of n-type, n ⁺ pp ⁺ , p ⁺ p, n ⁺ p, n ⁺ n, and p ⁺ np ⁺ . After the diffusion process is completed, the silicon wafer and the dopant film are separated by cooling after cooling. However, the silicon wafer can be easily separated by tweezers or the like without special treatment of the dopant film of the present invention.

〔Example〕

Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples. In Examples and Comparative Examples, “parts” means parts by weight unless otherwise specified.

Example 1 Polyvinyl alcohol 10 parts Mannit 5 parts B ₂ O ₃ 3 parts α-Al ₂ O ₃ 10 parts SiO ₂ 2 parts The above was ethylene glycol monomethyl ether
The solution obtained by dissolving and dispersing in 70 parts was made into a uniform film by a roll coater on a polyethylene terephthalate sheet, and then dried at 100 ° C. for 30 minutes with hot air to obtain 100 μm.
An m-thick dopant film was obtained.

The dopant film thus obtained was peeled off from the sheet, and brought into close contact with a 50-inch silicon wafer having a specific resistance of 50 Ω-cm · n. Next, the wafer is carried into a heat treatment apparatus, and heated at 500 ° C. for 1 hour while introducing nitrogen gas into the apparatus at a rate of 3 l / min.
After decomposing and burning the organic matter in the dopant film, the introduced gas was replaced with oxygen gas, and diffusion treatment was performed at 1250 ° C. for 200 hours. The lifetime of the minority carrier of the wafer was measured by a photoconductive decay method. Numerical values were obtained.

Example 2 Polyvinyl butyral 10 parts Mannit 1 part Ammonium dihydrogen phosphate 4 parts α-Al ₂ O ₃ 20 parts SiO ₂ 5 parts A solution obtained by dissolving and dispersing the above in 60 parts of propylene glycol monomethyl ether. When the lifetime of the minority carrier of the wafer obtained by the same operation as in Example 1 was measured except for using, the value of 7 μsec was obtained.

Example 3 Polyvinyl alcohol 5 parts Polyethylene glycol 1 part B ₂ O ₃ 3 parts α-Al ₂ O ₃ 6 parts SiO ₂ 3 parts The above was ethylene glycol monoethyl ether
When the lifetime of the minority carrier of the wafer obtained by the same operation as in Example 1 was measured except that the solution obtained by dissolving and dispersing in 82 parts was used, a value of 7 μsec was obtained.

Example 4 5 parts of polyvinyl alcohol 1 part of polyethylene glycol 1 part of ammonium dihydrogen phosphate 2 parts of SiO ₂ 2 parts of Example 1 except that a solution obtained by dissolving and dispersing the above in 90 parts of propylene glycol monomethyl ether was used. When the lifetime of the minority carrier of the wafer was measured by the same operation as described above, a value of 9 μsec was obtained.

Comparative Example 1 Polymethyl methacrylate 10 parts B ₂ O ₃ 3 parts α-Al ₂ O ₃ 10 parts
The minority carrier lifetime of the wafer was measured in the same manner as in Example 1 except that the solution obtained by dissolving and dispersing in 77 parts was used, and a value of 4 μsec was obtained.

Comparative Example 2 Polymethyl methacrylate 10 parts Mannit 1 part Ammonium dihydrogen phosphate 4 parts α-Al ₂ O ₃ 20 parts SiO ₂ 5 parts The above is propylene glycol monomethyl ether
The lifetime of the minority carrier of the wafer was measured by the same operation as in Example 1 except that the solution obtained by dissolving and dispersing in 60 parts was used, and a value of 5 μsec was obtained.

〔The invention's effect〕

The dopant film of the present invention can diffuse impurities with a high concentration and a small variation, and has a long minority carrier lifetime, so that a semiconductor element having extremely excellent electric characteristics can be easily and efficiently manufactured. .

Claims (2)

(57) [Claims] 1. An organic binder selected from the group consisting of: (A) at least one organic binder selected from polyvinyl alcohol and polyvinyl butyral; and (B) polyethylene glycol, mannitol, a polyalkyl acrylate having an alkyl group having 1 to 3 carbon atoms, glucose and saccharose. At least one selected plasticizer (C) A compound of an impurity element (D) A mixed solution comprising an inorganic binder and (E) an organic solvent is coated on a support and dried to peel off a film obtained from the support. A dopant film characterized by the above-mentioned. 2. An impurity diffusion method, comprising: adhering the dopant film according to claim 1 to a semiconductor substrate; heating the organic film to thermally decompose or burn the organic substance; and then heating the organic substance to 900 to 1300 ° C.