JP2002075893A - Liquid impurity source material, and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem of difficulty in forming a diffusion region with a high impurity density by using liquid impurity source. SOLUTION: An impurity source solution containing organic phosphorus compound as a conductivity type determining impurity and a solvent is applied on a semiconductor substrate 1 and a thick liquid impurity source layer 2 is formed and dried. The substrate 1 is heated at a temperature lower than the phosphorus diffusion temperature. After that, the substrate 1 is heated at a higher temperature to diffuse the impurity in the substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid impurity source material for diffusing impurities into a semiconductor substrate, and a transistor, a thyristor and a diode formed by forming a diffusion region in the semiconductor substrate using the liquid impurity source material. The present invention relates to a method for manufacturing a semiconductor device such as a semiconductor device.

[0002]

2. Description of the Related Art A liquid impurity source material is known as an impurity source material for forming an impurity diffusion region in a silicon semiconductor substrate. When an impurity diffusion region is formed by using this, a liquid impurity obtained by dissolving an impurity such as phosphorus or boron in an organic solvent such as alcohol is applied to the surface of the silicon semiconductor substrate by a well-known spinner method to form a liquid. An impurity film is formed, and then the silicon semiconductor substrate is subjected to a heat treatment at about 120 to 140 ° C., and the liquid impurity film is baked to evaporate an organic solvent to form a diffusion source film. By subjecting the silicon semiconductor substrate to a heat treatment at about 1200 ° C. in a nitrogen atmosphere, impurities such as phosphorus in the diffusion source film are diffused into the semiconductor substrate.

[0003]

The conventional liquid impurity source has a relatively low viscosity because it is composed of a mixture of an organic solvent such as alcohol and an impurity such as phosphorus or boron. Therefore, a liquid impurity film cannot be formed thickly on the surface of the semiconductor substrate by a spinner method or the like, and it is difficult to easily form a deep diffusion region having a high impurity concentration. Therefore, the diffusion region that can be formed by the liquid impurity source is limited.

Accordingly, an object of the present invention is to provide a liquid impurity source material capable of forming a diffusion region having a high impurity concentration,
And a method for manufacturing a semiconductor device using the same.

[0005]

According to a first aspect of the present invention, there is provided a liquid impurity source material comprising a conductivity determining impurity, a solvent, and a thickener comprising a polymer. It is characterized by the following. According to a second aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising the steps of: forming a liquid impurity source material containing a solvent and a polymer thickener as impurities for determining conductivity type on a surface of a semiconductor substrate; And applying a heat treatment at a temperature lower than the diffusion temperature of the impurities to the applied liquid impurity source material to volatilize the solvent and form an impurity source film,
Subjecting the impurity source film to a heat treatment at a temperature higher than the diffusion temperature of the impurity to diffuse the impurity into the semiconductor substrate.

[0006] The impurities in the claimed invention are phosphorus,
N-type and P such as boron, organophosphorus compound, phosphoric acid compound
It is a form impurity.

[0007] The solvent in the claimed invention is selected from those capable of dissolving impurities and thickeners and having relatively low volatility, for example, methanol, ethanol, 2-propanol, 2-methoxyethanol. And glycol-based substances such as ethylene glycol and propylene glycol. Particularly, 2-propanol has a property of dissolving a thickener (polymer) swollen with water, and is suitable as a solvent of the present invention.

The thickener according to the present invention is used to increase the content of impurities by forming a relatively thick liquid impurity source material on the surface of the semiconductor substrate. Therefore, this thickener
It is selected from those which do not remain as a residue by burning in the diffusion step or the preceding heat treatment and are soluble in water or a solvent and do not generate dangerous gas when decomposed or burned. For example, polyvinyl butyral ( PVB), polyvinyl alcohol (PVA), polyvinyl methyl ether (PV
ME) and polyvinylpyrrolidone (PVP). In particular, polyvinyl alcohol is a polymer that is water-soluble and soluble in alcohols and can favorably increase the viscosity of liquid impurities, and is therefore suitable as the thickener of the present invention.

[0009]

According to the invention of each claim, since the viscosity of the liquid impurity raw material can be increased by the thickener, the liquid impurity material can be thickly applied to the surface of the semiconductor substrate. Therefore, the amount of impurities in the impurity source film can be increased, and a diffusion region having a high impurity concentration can be formed in the semiconductor substrate.

[0010]

Embodiments and Examples Next, embodiments and examples of the present invention will be described with reference to FIGS.

First, a P-type silicon semiconductor substrate 1, ie, a wafer, was prepared as a semiconductor substrate. Further, a liquid impurity source material having the following composition was prepared. 8. Ammonium dihydrogen phosphate as a phosphate compound:
40% by weight Water as a wettable powder: 68.55% by weight 2-propanol as a solvent: 14.70% by weight Polyvinyl alcohol as a thickener: 7.35% by weight

When the above-mentioned liquid impurity source material is prepared, polyvinyl alcohol as a thickener is swelled in water, and then an organic solvent (2-propanol) is added thereto to uniformly dissolve the swollen polyvinyl alcohol. I do. Next, a phosphoric acid compound is added to such an extent that polyvinyl alcohol does not salt out, and is uniformly dissolved. Thereby, the target liquid impurity source material is obtained. If ammonium dihydrogen phosphate as a phosphoric acid compound is added in an amount not exceeding 10% by weight based on a polymer such as polyvinyl alcohol, the polymer does not precipitate. Accordingly, phosphorus (impurity for determining the conductivity type) can be contained in the liquid impurity source material at a relatively high concentration.

Next, this liquid impurity source material is uniformly applied to one main surface of the semiconductor substrate 1, that is, the surface of the region where the impurity is to be diffused, by a well-known spinner method, so that the liquid impurity source layer 2 is formed as shown in FIG. Is formed as shown conceptually in FIG. In this embodiment, the number of revolutions of the semiconductor substrate during spinner coating of the liquid impurity source is set to 3000 to 4000 rpm. In this embodiment, since the phosphoric acid compound having low hygroscopicity is used, the storage stability of the liquid impurity source layer 2 formed by the spinner is good, and the liquid impurity source layer 2 reaches the back surface of the semiconductor wafer even after a lapse of time. Material does not run around. Further, since the liquid impurity source material contains a thickener, the liquid impurity source layer 2 can be formed relatively thick on the semiconductor substrate 1. Further, by using the liquid impurity source material having the above composition, the liquid impurity source layer 2 can be formed to have a substantially uniform thickness with little application unevenness.

Next, the semiconductor substrate 1 on which the impurity source layer 2 shown in FIG. 1B has been formed is hot-plated (heat-plate).
The semiconductor substrate 1 having the impurity source layer 2 disposed thereon is subjected to a heat treatment at 150 to 200 ° C. lower than the diffusion temperature of phosphorus to volatilize the solvent contained in the liquid impurity source layer 2. As shown in FIG. 1C, an impurity source film 3 containing a phosphoric acid compound and a thickener is formed on one main surface of the semiconductor substrate 1. This solvent volatilization treatment is performed in the air. Since the impurity source film 3 after the solvent volatilization treatment is made of a material having a low absorption property, no water droplet is formed on the impurity source film 3 even when left in the air.

Next, the semiconductor substrate 1 having the impurity source film 3 shown in FIG. 1C is charged to a semiconductor substrate diffusion holder made of quartz or SiC (silicon carbide).
After that, it is put into a process tube made of quartz, SiC, or the like, and subjected to a heat treatment at a predetermined temperature profile. That is, the semiconductor substrate is gradually heated to a temperature of 500 to 1000 ° C. lower than the diffusion temperature (1260 ° C.) in a state where oxygen is introduced into the tube and the inside of the tube is in an oxidizing atmosphere. Hold for 30-100 minutes. By heating the impurity source film 3 in an oxygen atmosphere, an oxide of phosphorus is generated and the thickener is burned out, so that an impurity source film 4 made of the oxide of phosphorus shown in FIG. 1 is formed.

Next, the temperature is maintained at 500 to 1000 ° C., the atmosphere is replaced with a nitrogen (N 2) atmosphere (non-oxidizing atmosphere), and a heat treatment is performed for about 30 minutes.
Raise the temperature to 0 ° C for a predetermined time (eg, 5 hours) in a nitrogen atmosphere.
Heat treatment to remove phosphorus from the impurity source film 4 to the semiconductor substrate 1.
To obtain an N-type semiconductor region 5 shown in FIG. Note that the P-type semiconductor region 1a remains in the semiconductor substrate 1, and a PN junction is formed.

Next, the semiconductor substrate 1 shown in FIG. 2E is etched with hydrofluoric acid or a hydrofluoric acid-based etchant containing the same as a main component, so that an impurity source film remaining on one main surface of the semiconductor substrate 1 is formed. 4 is removed to expose the N-type semiconductor region 5 on one main surface of the semiconductor substrate 1 as shown in FIG. In the present embodiment, since one main surface of the silicon semiconductor substrate 1 is not nitrided as described above, the residual film formed of the impurity source film 4 formed on one main surface of the semiconductor substrate 1 can be easily formed. And it can be completely removed.

Next, a metal ohmic electrode 6 is formed on the N-type semiconductor region 5 as shown in FIG. In addition,
Although omitted in FIG. 2G, the N-type semiconductor region 1a
An N-type semiconductor region or the like is formed as necessary to form a well-known transistor, thyristor, or the like.

According to this embodiment, the following effects can be obtained. (1) Since the liquid impurity material contains a thickener made of a polymer (polyvinyl alcohol), the liquid impurity source layer 2 and the impurity source film 3 can be formed thicker than in the prior art, and can be 10 ²⁰ cm ^−3. Above high surface impurity concentration, 55 μm
A diffusion region having the above depth can be formed. (2) Since the liquid impurity source material containing the phosphoric acid compound having low hygroscopicity is used, when the liquid impurity source layer 2 is formed by the spinner, the liquid impurity reduced material goes around the back surface of the wafer, that is, the semiconductor substrate 1. Can be prevented. In other words, even if the wettability to the semiconductor substrate 1 is kept relatively good, it is possible to prevent the liquid impurity source material from sneaking into the back surface of the wafer. (3) Since the phosphoric acid compound having low hygroscopicity is used, the impurity source film 3 after the liquid impurity source is heat-treated at 150 to 200 ° C. also has low hygroscopicity, and water droplets are formed even when left in the air. However, a highly stable impurity source film can be provided. (4) The concentration of phosphorus and the amount of the thickener added in the liquid impurity source material can be easily adjusted, and as a result, the impurity concentration and the depth of the phosphorus diffusion region in the semiconductor substrate 1 can be easily controlled. (5) What remains on the surface of the semiconductor substrate 1 after diffusion can be easily removed with hydrofluoric acid.

[0020]

[Modifications] The present invention is not limited to the above embodiment, and for example, the following modifications are possible. (1) Organic phosphorus, inorganic phosphorus, boron, boron compounds and the like can be used as impurities. (2) The composition of the liquid impurity source can be changed. However, the following range is desirable. Impurities: 5 to 15% by weight Water: 40 to 80% by weight Solvent: 5 to 25% by weight Thickener: 5 to 15% by weight (3) Impurities are diffused in a non-oxidizing atmosphere such as argon instead of a nitrogen atmosphere. be able to. (4) The liquid impurity source can be applied only to a specific region of the semiconductor substrate 1, that is, a region to be diffused. (5) Instead of the ohmic electrode 9, a Schottky barrier electrode, a gate insulating film of an FET or the like can be formed on the surface of the N-type semiconductor region 5. (6) In order to improve the wettability to the semiconductor substrate 1, a surfactant composed of, for example, a fluorine-based surfactant may be added to the liquid impurity source.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view for explaining a method of manufacturing a semiconductor device according to an embodiment of the present invention in the order of steps.

FIG. 2 is a cross-sectional view illustrating a step that follows the step of FIG.

[Explanation of symbols]

 Reference Signs List 1 semiconductor substrate 2 liquid impurity source layer 5 N-type semiconductor region

Claims (2)

[Claims] 1. A liquid impurity source material used for diffusing an impurity into a semiconductor substrate, comprising a conductivity type determining impurity, a solvent and a thickener comprising a polymer. . 2. A step of applying a liquid impurity source material containing an impurity for determining conductivity type, a solvent and a thickener made of a polymer to a surface of a semiconductor substrate, and applying the impurity to the applied liquid impurity source material. Performing a heat treatment at a temperature lower than the diffusion temperature to volatilize the solvent to form an impurity source film; and performing a heat treatment at a temperature higher than the diffusion temperature of the impurity on the impurity source film. And a step of diffusing the impurity.