JPH02229426A - Dopant film - Google Patents

Abstract

PURPOSE:To execute a diffusion operation without lowering a lifetime value of a nondiffusion layer by a method wherein a support body is coated with a mixed liquid composed of an organic binder of a vinyl-based synthetic resin, a compound of impurity elements, a solvent and an inorganic binder which is composed of high-purity silicon and this liquid is dried and stripped off from the support body. CONSTITUTION:The dopant film 1 is formed, e.g. in the following manner. An amount of B2O3 as a compound of impurity elements is contained at 12.3(wt.%); an amount of a high-purity silicon powder as an inorganic binder is contained at 39.9(wt.%); an amount of an organic binder is contained at 47.8(wt.%). The dopant film 1 is stacked so as to be brought into close contact between semiconductor substrates 2, 2. After that, this assembly is heated inside a diffusion furnace at 40.0 deg.C for 30 minutes. The assembly is heated at 500 deg.C for 120 minutes; after that, it is heated at 1200 deg.C or higher for a definite time. By this continuous heat treatment, boron in the dopant film 1 is diffused into the semiconductor substrate 2. Accordingly, it is possible to restrain inessential impurities such as Al from being diffused to the semiconductor substrate such as an Si substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to improvements in dopant films.

2. Description of the Related Art Various methods for impurity diffusion, which are important for manufacturing semiconductor devices, have been proposed. In the solid phase-solid phase diffusion method, an impurity source must be deposited on the semiconductor substrate before the drive diffusion process.

Examples of this deposition method include a vapor phase decomposition method, a BN disk method, an electroplating method, a sputtering method, a dipping method, a spray method, and a spin-on method. When manufacturing graded junction semiconductors such as transistors and diodes,
There is a need for a method that allows for deep diffusion at high concentrations and is highly productive in mass production.

A commonly used method is boron nitride (B).
There is a BN disk method in which N) is formed into a disk shape and placed alternately with a semiconductor substrate to perform thermal diffusion.

This method is a method of depositing and thermally diffusing B203 while keeping the semiconductor substrate and the BN disk at a constant distance and flowing carrier gas, and is suitable for PN junctions. However, like +P-N-N+ junction, N type and P type (P and B)
It is not suitable for simultaneous diffusion of different types of impurities such as.

On the other hand, spray methods, spin-on methods, brush coating methods, etc.
It is also possible to apply an impurity source to one side of a semiconductor substrate and dry it to form an impurity layer, and then apply the impurity to another side, facing the same type of impurity layers, and arranging them alternately to perform simultaneous diffusion. However, these methods have the disadvantage that the number of steps is increased because the impurity layer must be deposited on the semiconductor substrate one by one.

In addition, if the film is thick, cracks are likely to occur during heat treatment, so it must be made thinner, making it unsuitable for high-concentration, deep diffusion such as in rectifiers.

A magazine published in the United States [Electronics (E le
clronics) October 14, 1968 issue (Volume 41, No. 21), pages 242 to 244,
A dopant film released by Semi-Elements is introduced. This dopant film is made by dispersing an arsenic compound, a phosphorus compound, or a boron compound in cyanocell or ethyl cellulose.

Solvents that dissolve this resin are limited to those with a high boiling point and strong toxicity, such as dimethylformamide, so using this resin is inefficient. When cyanoethylcellulose or ethylcellulose is used, since these substances are manufactured using cellulose as a raw material, it is difficult to sufficiently remove alkali metal or noble metal compounds when they are mixed in.

U.S. Patent No. 3,971,870 (197
(July 27, 2006, Semi-Elements, Inc.) has a finely divided compound selected from the group consisting of phosphorus pentoxide, arsenic, antimony, iron, cobalt, boron nitride, boric acid, indium, methyl borate and gallium. and a volatile organic binder selected from the group consisting of cyanoethylated cellulose, methylcellulose, polyvinyl alcohol, starch, and polyvinyl butyral.
A self-supporting flexible film is described consisting essentially of %.

This film not only has the same drawbacks as the above film, but also has the drawback that it is not possible to produce a film of uniform quality.

It is also described that alumina powder is used as an inorganic binder, but the alumina powder has the disadvantage that it does not mix uniformly with the organic binder.

Therefore, the following dopant films have been proposed. In other words, it is a dopant film made by processing a liquid mixture consisting of an organic binder of vinyl-based synthetic resin, an inorganic binder made from an aluminum compound, a compound of impurity elements, and a solvent.

Problems to be Solved by the Invention This conventional dopant film is intended to achieve uniform and high concentration diffusion.

However, during diffusion, Al in the aluminum compound is diffused into the semiconductor substrate, causing a decrease in the lifetime value of the non-diffusion layer of the substrate.

For this reason, dopant films that use aluminum compounds as inorganic binders cannot be applied to semiconductor substrates for transistors, which have strict device characteristics.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a dopant film in which impurities can be diffused into a semiconductor substrate without reducing the lifetime value of the non-diffused layer.

SUMMARY OF THE INVENTION The gist of the present invention is a dopant film as set forth in the claims.

Means for Solving the Problems The dopant film of the present invention is produced by applying a liquid mixture consisting of an organic binder made of a vinyl-based synthetic resin, an inorganic binder made of a compound of impurity elements, a solvent, and high-purity silicon onto a support, and drying the mixture. It was then peeled off from the support.

Al. Since high-purity silicon is used instead of chemical compounds,
Diffusion of unnecessary impurities such as A1 into the substrate is eliminated.

Structure of the Invention The dopant film of the present invention comprises an organic binder, an inorganic binder, a compound of a diffusion impurity element, and a solvent.

[Organic binder] Vinyl synthetic resin is used as the organic binder.

In this invention, the vinyl synthetic resin excludes polyvinyl alcohol and polyvinyl butyral.

The conditions required for an organic binder are that the inorganic binder, diffusion impurities, and solvent have good compatibility, that it decomposes easily at relatively low temperatures, that no toxic gas is generated during decomposition, and that there are no interfering impurities (alkali). It contains no metals), has high mechanical strength when made into a dopant film, and is easy to handle.

A vinyl-based synthetic resin satisfies these conditions.

For example, polyvinyl acetate, polymethyl vinyl ketone,
Polyvinylpyrrolidone, as well as methyl acrylate, ethyl acrylate, ethyl methacrylate, probyl methacrylate, tetrahydrofurfuryl acrylate, tetrahydrofurfuryl methacrylate, 2-methoxyethyl acrylate, 2-methoxyethyl methacrylate, 2-
Polymers such as ethoxyethyl acrylate, 2-butoxyethyl acrylate, 2-hydroxyethyl acrylate, cyclohexyl acrylate, cyclohexyl methacrylate, and their copolymers alone or in mixtures of two or more are suitable.

Furthermore, other easily decomposable resins such as nitrocellulose may be mixed in up to about 30% by weight of the vinyl synthetic resin.

Vinyl synthetic resins are completely suitable for the purpose of the present invention because the content of interfering impurities (alkali metals) can be extremely reduced.

Since polyvinyl alcohol is produced by hydrolyzing polyvinyl acetate with an alkali, it is inevitable that alkali metals will be mixed into polyvinyl alcohol. It is extremely difficult to remove it to an acceptable level. Therefore, polyvinyl alcohol is not suitable from an industrial standpoint.

Since polyvinyl butyral is produced using polyvinyl alcohol as a raw material, it is not suitable for the same reason.

[Inorganic Binder] High purity silicon is used as the inorganic binder. This is because the organic binder has good compatibility with the diffusion impurities and the solvent used, there is little shrinkage when the organic substance is decomposed, and it forms a doped oxide film at high temperatures (during diffusion), resulting in uniform diffusion. , not to become interfering impurities;
The wafers must be easy to separate from each other after diffusion.

The content of harmful impurities in high-purity silicon that satisfies these conditions is O. ippm～ipp
It is m. If the content of the harmful impurity is greater than ippm, it is unfavorable in terms of electrical characteristics after diffusion.

On the other hand, if it is smaller than ippm, it is not preferable because it causes an increase in cost in the production of high-purity silicon.

[Impurity compound for diffusion] As the impurity compound for diffusion, boric anhydride (B203) is most preferable. When a phosphorus compound is used as a diffusion impurity compound, it is easy to obtain a sheet-like dopant film from the support, but when other impurity compounds are used, the peelability from the support is good. Therefore, it is preferable to use a peeling aid.

The impurity compounds for diffusion must be compatible with the above binder, soluble in solvents, and not easily affected by the outside air when made into a film (this is because compounds with strong hygroscopicity become sticky and difficult to handle), and The compound must have low sublimation even at high temperatures.

Among the compounds that meet these conditions, phosphorus compounds are:
(R' O) 3P, (R″O) 2P (OH).
(R' 0) 3PO, (R' O)2 P203
(OH). (R' 0)P (OH)2, etc. (R' represents a halogen atom, an alkyl group, an alkylene group, or an aryl group.

same as below. ).

As the boron compound, the above-mentioned B203, (R' O)
3B, R' B (OH) 2. R' 2B (OH
) etc.

As an antimony compound, H3SbO4, (R' 0
) 3Sb, SbX3, SbOX, Sb4 0s X
(However, X represents a halogen atom.

same as below. ) (HO)Sb (OR' )2.

Examples of arsenic compounds include H3ASO3, H2ASO4. (
R' O) 3As, (R' 0) 5As, (R'
O) 2As (OH), R' 3ASo, R' AS
=ASR'.

Zinc compounds include Zn(OR″)2, ZnX2,'
Zn (No. 2) 2.

As a gallium compound, (R'O)3Ga, R' G
a (OH), R'Ga (OH2), R2
G a [OC (CH3) = CH c
(CH3)=O).

Examples of gold compounds include HAUCl, AUX3, R',
, AUX, R' 2AU (0 (CH3)=CH-C
o (CH3)), etc. can be used.

To produce the dopant film of the present invention, a coating solution is prepared by dissolving an organic binder, an inorganic binder, and a diffusion impurity compound in a solvent. This coating solution may be applied onto an inert substrate, the solvent may then be evaporated to form a solid film, and this solid film may be peeled off from the substrate.

[Solvent] Any solvent may be used as long as it can dissolve the organic binder, inorganic binder, and diffusion impurities, and can easily form a film.

For example, methanol, ethanol, methyl cellosolve,
Alcohols such as ethyl cellosolve and butyl cellosolve, methyl cellosolve acetate, ethyl cellosolve acetate, esters such as methyl acetate, ethyl acetate, butyl acetate, acetone, acetylacetone, methyl ethylacetone, dioxane, tetrahydrofuran, toluene, xylene, trichlor Ethylene, trichloroethane, methylene chloride, etc. are used.

The concentration of solids in the above-mentioned coating liquid can be varied depending on the coating method, but is usually preferably 10 to 40 weight percent. As for the composition ratio when forming a dopant film, the organic binder is used in the range of 20 to 60% by weight, the inorganic binder is used in the range of 30 to 60% by weight, and the diffusion impurity compound is used in the range of 1 to 30% by weight. The thickness of the dopant film is preferably 10 to 300 μm.

The amount of B 2 O 3 is determined according to the layer resistance ρS of the diffusion layer of the semiconductor substrate. If the organic binder content is less than 201%, it will be dry and will not form a film. Organic binder is 60W
If it is more than 1%, combustion gas will increase. In addition, during use, it shrinks and becomes smaller than the wafer diameter, and cannot be diffused to the outer circumference of the wafer. If the inorganic binder is less than 30W1%, the organic binder may be more than 60W1%, which is not preferable for the reasons mentioned above. Inorganic binder is 60W
If it is more than 1%, the organic binder may be less than 2011%, which is not preferable for the reasons mentioned above.

The dopant film formation method is as follows for small quantity production:
This can easily be done by the doctor plating method using a doctor knife.

For mass production, the slip casting method, screen printing method, flow coater method, etc. are preferable.

The process is to first pour the coating solution onto a support such as a plate or sheet made of polyethylene, polypropylene, fluororesin, etc. so that it can be easily peeled off in the later process, apply it evenly using the above coating method, and dry it. The solvent is evaporated, and the film is then peeled off from the support to form a sheet-like film, which is further cut into a wafer shape using a cutting machine to create a dopant film.

Example The dopant film 1 is, for example, as follows. The amount of 8203 as a compound of impurity element is 12.3
(wl%), the amount of high purity silicon powder as an inorganic binder is 39.9 (vj%), and the amount of organic binder is 47.8 (vj%).

The semiconductor substrate 2 in FIG. 1 is a SiC substrate.

This dopant film 1 is tightly scooped between semiconductor substrates 2, 2. Thereafter, it is heated in a diffusion furnace at 40.0° C. for 30 minutes as shown in FIG. and 500℃
After heating for 120 minutes, heat treatment is performed at 1200° C. or higher for a certain period of time. Through such continuous heat treatment, Boton in the dopant film 1 is diffused into the semiconductor substrate 2. 3 in FIG. 1 is a SIC boat. Note that the amount of B203, the amount of inorganic binder, and the amount of organic binder are not particularly limited to the values in the examples.

Since high-purity silicon is used in this manner, unnecessary impurities such as AI are prevented from diffusing into a semiconductor substrate such as the 81 substrate. In other words, the quality (characteristics) of the product diffusion wafer is improved. Ultimately, the yield of semiconductor devices
Improve reliability.

Here, in Table 1 below, when impurity diffusion is performed using the dopant film according to the present invention, the lifetime value of the non-diffusion layer of the semiconductor substrate is compared with that of a conventional product.

As is clear from Table 1, in the case of the dopant film according to the present invention, the lifetime value of the non-diffusion layer is 3.03 times higher than that of the conventional dopant film using an aluminum compound. . This value allows application to semiconductor substrates for transistors.

Effects As explained above, since high-purity silicon is used as the inorganic binder, when impurities are diffused into the semiconductor substrate, desired diffusion can be performed without reducing the lifetime value of the non-diffusion layer.

Therefore, it can be applied to semiconductors for transistors, which have strict device characteristics.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an intimate cooking state using the dopant film of the present invention, and FIG. 2 is a diagram showing an example of heat treatment process conditions. 1... Dopant film 2... Semiconductor substrate 3... SiC boat schedule time procedure amendment (voluntary) March 9, 1989 6. 7. "Detailed Description of the Invention" of the specification to be amended Contents of the amendment Column 2 as shown in the attached sheet. 3. 4. Name of the invention Relationship to the dopant film corrector case Patent applicant address 1-26-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Name Toshiba Ceramics Corporation

Claims (1)

[Claims] 1. A mixed liquid consisting of an organic binder made of vinyl synthetic resin (excluding polyvinyl alcohol and polyvinyl butyral), an inorganic binder made of high-purity silicon, a compound of impurity elements, and a solvent. 1. A dopant film characterized in that it has a structure in which it is coated on a support, dried, and peeled off from the support.