JPS5846845B2 - Solid diffusion method and dope composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing semiconductor devices, and more particularly to a technique for solid-state diffusion of impurities that determine conductivity type from doped silicon oxide into semiconductor crystal flakes.

Specifically, we describe a new material composition for use in Q) that covers a semiconductor flake and provides a doped silicon oxide thin film that serves as a source of dopant material for solid-state diffusion.

The use of doped oxide thin films as an impurity source for solid state diffusion in the fabrication of semiconductor devices has been known for many years.

Theoretically, a doped oxide impurity source provides improved control over dopant concentration, a more uniform dopant concentration distribution, and the ability to diffuse n-type impurities at once in a single operational step. .

In practice, however, these advantages have not generally been achieved industrially.

This is probably due to the lack of sufficient economic incentives and the lack of robust low temperature techniques for making doped oxide films.

The idea of creating stable suspensions or solutions of doped oxides, or solutions of the components that would result in thin films of doped oxides, has been proposed.

An example of a technique using suspensions is U.S. Pat. No. 3,660.
No. 156 (Japanese Unexamined Patent Publication No. 47-4816).

However, in order to utilize these technologies commercially, it is difficult in practice to create suspensions or solutions that are sufficiently stable, sufficiently pure, and that can be produced with sufficient reproducibility in a short period of time. Because of this, I have been prevented from doing so.

Accordingly, it is an object of the present invention to create compositions of oxide-forming materials that are sufficiently pure, have sufficient shelf life, and are capable of reproducing accurate properties on a commercial scale.

Another object of the invention is to create compositions of materials that produce certain oxides.

This oxide is such that it imparts a higher doping concentration to the semiconductor to which it is doped as a source of diffusion material compared to the doping concentration obtained in similar operating steps up to now.

It is also an object of the present invention to provide an improved solid state diffusion process.

One feature of the invention is embodied in a material composition comprising a suitable dopant material and a suitable solvent in which is dissolved a reaction product of tetraethylorthosilicate and acetic anhydride or acetic acid.

For example, a desirable composition is made by adding tetraethyl orthosilicate, acetic anhydride, and boron oxide to ethyl alcohol.

Tetraethyl orthosilicate and acetic anhydride react,
At equilibrium, ethyl acetate, triethoxysilicon acetate and jetoxysilicon diacetate are formed.

If an excess number of moles of acetic anhydride is added, cyanide becomes the main product, but this is not essential to the present invention.

Ethyl alcohol is a preferred solvent.

Ethanol is still preferred as a solvent, although some reaction of the alcohol with the jetoxysilicone diacetate species results in the formation of triethoxysilicone aceate, which of course limits the amount of cyanide formed. .

These effects do not substantially reduce the success of the present invention.

Other useful solvents include acetone, methyl ethyl ketone,
Included are toluene, ethyl ether and dialkyl ethers of ethylene glycol, such as dimethyl ether.

Boron, phosphorus, and arsenic are generally selected as doping materials that diffuse into silicon to define its conductivity type.

Gold is also a useful doping material for lifetime control; these doping materials are preferably incorporated into the materials of the present invention in the form of boron oxide, orthophosphoric acid, orthoarsenic acid, and gold chloride, respectively. added into the composition.

Other types of doping materials are also useful, with virtually equivalent results.

Zinc chloride is a suitable source of zinc to diffuse into gallium arsenide.

The compositions of the present invention contain about 50 to 85 parts by weight of solvent, and the ratio of silicon atoms to dog material atoms is about 1, depending primarily on the doping level required for the semiconductor.
．． The ratio is about 5:1 to about 6:1.

In addition to other requirements, by selecting an atomic ratio in this range, higher doping concentrations can be obtained stably and reproducibly compared to doping concentrations obtained in similar previous operating steps.

The molar ratio of acetic anhydride to tetraethylorthosilicate added is from about 1.5 to 1 to 3 to 1, preferably from about 2.0 to 1 to 2.3 to 1.

The undoped solution to which the doping material is to be added is prepared by refluxing acetic anhydride and tetraethylorthosilicate in ethanol or other solvent with stirring for 1 to 8 hours, preferably 2 to 6 hours. .

To minimize the amount of moisture entering the device, a drying tube should be attached to the reflux condenser.

The amount of solvent added determines the final thickness of the resulting thin film for deposition onto a semiconductor.

For example, 45m71! of tetraethylorthosilicate and 40 ml of acetic anhydride in 200 ml of ethanol results in a composition that yields a thin film approximately 1200 angstroms thick.

This composition is applied to the semiconductor surface by a spinning method,
When applied by spraying or dropping, the evaporation of the solvent causes the precipitation of a doped silicon polymer thin film, which is then heated to a low temperature of about 200C to dry the volatile by-products, residual solvent, and remaining moisture. , easily doped Si
Changes to o2.

Subsequent heating to a diffusion temperature of, for example, about 1100 DEG C. causes the dopant material to migrate from the oxide film into the semiconductor, as will be readily understood by those skilled in the art.

The preferred deposition method is a rotational method, which uses a photoresist rotation coater.
st 5pir+coating equipment
) is successfully carried out.

An example of this device is Cupertino, California.
Industrial M in (Cuvertino)
odular System Corporation
It is a model 6604 of the company.

Correct selection of the rotation speed determines the thickness of the thin film obtained.

This thickness also depends on the viscosity of the initial solution.

Examples ■ The basic undoped spin-deposition solution consists of 45 ml of tetraethylorthosilicate, 40 ml of acetic anhydride, and 2
It was obtained by mixing 00 ml of ethanol in a 500 ml round bottom flask.

A reflux condenser and a Teflon-covered magnetic stir bar are then added and the mixture is stirred and warmed to a temperature that slowly refluxes for 6 hours.

3.7 grams of B2O3 was added to the undoped solution made above (285 mg) and the mixture was allowed to warm with stirring overnight.

The doped solution was placed on a clean, dust-free silicon thin piece (4 Ω cm, n-type) at a rotational speed of 3000.
It was applied for about 10 seconds at rpm.

The flakes are baked at 300° C. for 10 minutes to remove excess solvent and densify the resulting oxide film.

The flakes were then placed in a diffusion furnace at 1150°C under N2 for 30 minutes.
Leave it behind.

The resulting sheet resistance was 8.9 ohms/square,
The junction depth was 2.4 microns and the surface dopant concentration was 3 x 1020 atoms/atl.

EXAMPLE ■ To 285 ml of an undoped solution similar to that in Example I, add 7.5 grams of H3AsO4.

The resulting solution was applied to a 100 cm N-type silicon thin piece and placed at 1150°C in 02 air for 120 minutes.

The results obtained are that the junction depth is 1.9 square meters, the sheet resistance is 12.3 ohms/square, and the surface concentration is 2.2×1
020 atoms/cni.

Examples ■ Undoped solution 285 prepared according to Example I
Add 6 grams of phosphoric acid to ml.

The resulting solution was poured onto 100 cm of p-type silicon.
Leave in 02 air at 150°C for 60 minutes.

The result was a sheet resistance of 9.8 microns at a bond depth of 2.8 microns.
0 ohms/square, surface concentration 2 x 1020 atoms/C
It was a.

Example ■ 285ml of undoped solution prepared according to Example ■
Add 9.5 grams of ZnC1 to 1.

The doped solution was immersed in n-type gallium arsenide and
Place in the shape former for 30 minutes at 00°C.

The result was that the depth of the p and n junctions was about 4 microns.

Example V Undoped solution 1007 prepared as in Example ■
Add 1.0 g of HAuCl4.3H20 to 721.

The doped solution was applied to a 0.2 Ωcrn p-type silicon thin plate and heated at 1150°C for 10 minutes in air, 25 minutes in water vapor, and repeatedly heated in air for 20 minutes.

The result was that the gold concentration on the surface was 4 x 1015 atoms/cni.

The compositions of the present invention are particularly useful in obtaining higher doping concentrations than are readily obtainable with conventional methods.

Such high concentrations are possible because the atomic species that make up the solid have a high solubility in the solvent, especially when ethanol is chosen as the solvent.

This allows thicker oxide thin films to be obtained on the semiconductor, which in turn results in higher concentrations of dopant material in the oxide.

Claims (1)

[Claims] 1. A method for solid-state diffusion of impurities that determine the conductivity type into a semiconductor, comprising: depositing a solution forming a doped oxide on the semiconductor; and heating the semiconductor to a diffusion temperature. The depositing solution includes a product obtained by reacting acetic acid or acetic anhydride with tetraethylorthosilicate in a molar ratio of about 1.5:1 to about 3=1, and silicon atoms. a dopant material suitable for solid-state diffusion into the semiconductor in an amount such that the ratio of the number of atoms of the dope material to the number of atoms is from about 1.5:1 to about 6:1, and holding said reaction product and dope material in solution. Possible 50-85
Diffusion method using a solution containing a solvent by weight. 2 A product produced by reacting acetic acid or acetic anhydride with tetraethylorthosilicate in a molar ratio of about 1.5:1 to about 3:1 and a product in which the ratio of the number of atoms of the doping material to the number of silicon atoms is about 1. .5:1 to about 6:1 of a dopant material suitable for solid-state diffusion into the semiconductor and capable of retaining the reaction product and dope material in solution.
0-85% by weight of a solvent.