JP2003218049A - Liquid form impurity source material and method of forming diffusion region using the material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem of difficulty of forming an n-type diffusion region in a good condition using liquid form impurity source. <P>SOLUTION: The liquid form impurity source material, which consists of ammonium dihydrogen phosphate as conduction-deciding impurity, solvent, poly N-vinylacetamide as a thickever, and water, is coated on a semiconductor substrate 1 to form as liquid impurity source film 2, and the film is dried. Next, the film is heated at a temperature lower than the phosphorous diffusion temperature, and subsequently is heated at a temperature higher than the temperature of phosphorous diffusion in the semiconductor substrate 1. Thus, it is possible to properly form the n-type diffusion region using the liquid form impurity source. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

The present invention relates to a liquid impurity source material used for diffusing phosphorus as an n-type impurity in a silicon semiconductor substrate, and an n-type diffusion region in a semiconductor substrate using this liquid impurity source material. To a method of forming.

[0002]

2. Description of the Related Art A liquid impurity source material containing phosphorus is known as an impurity source material for forming an n-type diffusion region in a silicon semiconductor substrate for manufacturing diodes, transistors, thyristors and the like. When the n-type impurity diffusion region is formed using this, a liquid impurity source obtained by dissolving phosphorus as an n-type impurity in an organic solvent such as alcohol is applied to the surface of the silicon semiconductor substrate by a well-known spinner method. A liquid impurity film is formed, then the silicon semiconductor substrate is subjected to heat treatment at about 140 to 200 ° C., the liquid impurity film is baked to evaporate the organic solvent, and a diffusion source film is formed. By subjecting the silicon semiconductor substrate to a heat treatment at about 1200 ° C. in a nitrogen atmosphere, phosphorus in the diffusion source film is diffused into the semiconductor substrate.

[0003]

The conventional liquid impurity source containing phosphorus is composed of a mixture of an organic solvent such as alcohol and an inorganic phosphorus compound. Here, the reason why the inorganic phosphorus compound such as ammonium dihydrogen phosphate is used as the phosphorus compound is that the inorganic phosphorus compound is well dissolved in the organic solvent. However, since the inorganic phosphorus compound has high hygroscopicity, there is a problem that a diffusion source film cannot be stably formed on the surface of a silicon semiconductor substrate when a liquid impurity obtained by mixing the inorganic phosphorus compound and an organic solvent is used. . That is, the liquid impurity source wraps around to the back surface side of the semiconductor substrate due to the moisture absorption of the phosphorus compound, or if the liquid impurity film is left for a while after baking, the moisture content of the phosphorus compound causes water droplets containing phosphorus to the surface of the diffusion source film. It was sometimes formed. The wraparound of these impurity sources and the generation of water droplets pose a problem in stably forming a homogeneous diffusion region in the silicon semiconductor substrate. Here, it is possible to use an inorganic phosphorus compound having a low hygroscopicity as an inorganic phosphorus compound, but this kind of a low hygroscopic inorganic phosphorus compound is relatively well dissolved in water, but in an organic solvent such as alcohol. Since it does not dissolve well, it could not be used as a phosphorus compound as a liquid impurity source. In order to solve this kind of problem, the present applicant has tried to add polyvinyl alcohol as a thickener to the inorganic phosphorus compound.
However, it had the following drawbacks. (1) The liquid impurity source has a poor compatibility between polyvinyl alcohol and an inorganic phosphorus compound, and the amount of the inorganic phosphorus compound is 15
When the concentration is higher than 0.1%, the polymer and the phosphorus compound are separated during baking. (2) The liquid impurity source has a poor wettability with respect to the silicon semiconductor substrate, and it is difficult to obtain a uniform film especially on the mirror surface. It was not possible to obtain a proper diffusion layer. (3) Polyvinyl alcohol is a polymer that is less likely to salt out with respect to inorganic phosphorus compounds than other water-soluble polymers.
However, when the polyvinyl alcohol concentration is 10%,
The concentration of the inorganic phosphorus compound that can be dissolved without salting out is about 10%, and the high concentration N close to the solid solubility limit in the silicon semiconductor substrate.
100μ at high concentration of mold diffusion layer and surface concentration of 10 ²⁰ cm ^-3
An n-type diffusion layer of m or more could not be formed.

Therefore, an object of the present invention is to provide a liquid impurity source material capable of easily and satisfactorily forming a diffusion source film containing phosphorus, and a diffusion method using the same.

[0005]

The present invention for solving the above problems and achieving the above objects provides a liquid impurity source material used when diffusing n-type impurities into a silicon semiconductor substrate, A thickener comprising an inorganic phosphorus compound and at least one water-soluble organic polymer selected from nitrogen-containing vinyl polymer, cellulose polymer and acrylic polymer; The present invention relates to a liquid impurity source material composed of a solvent and water.

In order to achieve the above-mentioned object, the invention of the method of claim 3 is selected from an inorganic phosphorus compound, a nitrogen-containing vinyl polymer material, a cellulose polymer material and an acrylic polymer material. And a step of preparing a liquid impurity source material composed of at least one water-soluble organic polymer substance, an organic solvent, and water, and applying the liquid impurity source material to the surface of the silicon semiconductor substrate. A step of forming a liquid impurity source film by applying a first heat treatment to the liquid impurity source film at a temperature lower than a diffusion temperature of phosphorus to evaporate the solvent and the water, and the inorganic phosphorus compound and the inorganic phosphorus compound. Forming a dry impurity source film comprising a thickener; and subjecting the semiconductor substrate having the dry impurity source film to a second heat treatment in an atmosphere containing oxygen to increase the viscosity of the thickener. Remove And a step of forming a silicon oxide film containing phosphorus on the surface of the semiconductor substrate, and a third temperature higher than the second heat treatment in a non-oxidizing atmosphere for the semiconductor substrate having the silicon oxide film containing phosphorus. And a step of diffusing phosphorus into the semiconductor substrate by applying the heat treatment described in 1. above.

The inorganic phosphorus compound in the invention of each claim is preferably ammonium dihydrogen phosphate, diammonium hydrogen phosphate, or diethyl ammonium dihydrogen phosphate. In particular, ammonium phosphorus dihydrogen
High safety, low hygroscopicity, melting point 190 ° C, solubility in water at 25 ° C 40.3g / 100g
It is water, and is suitable as the inorganic phosphorus compound according to the present invention because it starts to decompose at 190.5 ° C. and becomes a metaphosphate. Further, as shown in claim 2, the thickener is at least one selected from poly N-vinylacetamide, poly N-vinylformamide, polyamidine, polyamine, carboxymethylcellulose ammonium salt, polyacrylic acid and polyacrylamide. Seed is desirable.

The solvent in the invention of each claim is selected from those capable of dissolving both the inorganic phosphorus compound and the swollen thickener. As a solvent satisfying these conditions, for example, alcohol-based substances such as methanol, ethanol, 2-propanol and 2-methoxyethanol,
Alternatively, there are glycol-based substances such as ethylene glycol and propylene glycol.

[0009]

The invention of each claim has the following effects. (1) The thickener comprising a water-soluble organic polymer substance according to the present invention is a water-soluble substance having a stronger polarity than polyvinyl alcohol, and has better compatibility with inorganic phosphorus compounds than polyvinyl alcohol. Therefore, the inorganic phosphorus compound can be uniformly mixed with the thickener, and a phosphorus diffusion region having a uniform impurity concentration can be formed. (2) The thickener is a substance that can ensure good wettability with respect to the silicon semiconductor substrate. For this reason,
A uniform and excellent impurity source film can be formed, and a uniform phosphorus diffusion region can be formed. (3) Salting out can be prevented and the inorganic phosphorus compound can be dissolved in a relatively high concentration (for example, 20%). Therefore, it is possible to form the n-type diffusion region having a high concentration of the n-type impurity (phosphorus), and it is possible to form the deep n-type diffusion region. (4) The proportions of the inorganic phosphorus compound and the thickener can be adjusted in a relatively wide range, and the impurity concentration and depth of the n-type diffusion region can be easily adjusted.

Next, an embodiment of the present invention will be described with reference to FIG.

1A to 1G are views for explaining a method of manufacturing a diode as a semiconductor device according to an embodiment of the present invention in the order of steps. Although a diode is shown in FIG. 1G, the present invention can be applied to formation of an n-type diffusion region in a semiconductor device such as a transistor or a thyristor.

First, the p-type semiconductor substrate 1 shown in FIG.
And the liquid impurity source material. The semiconductor substrate 1 may have ap ⁺ semiconductor region on the back surface side to form a p ⁺ pn diode. When forming a transistor, a semiconductor substrate 1 having an n-type semiconductor region on the back side is used.

As a liquid impurity source material, Water-soluble organic phosphorus compound 10-20% by weight Thickener 10-20% by weight Organic solvent 5-10% by weight Remaining water The total of 100% by weight is used.

A more preferable example of the composition represented by weight% of the liquid impurity source material is as follows. Ammonium dihydrogen phosphate as an inorganic phosphorus compound: 1
0 to 20% by weight Poly N-vinyl amide as a thickener: 10 to 20% by weight 2-methoxyethanol as an organic solvent: 5 to 10% by weight Water: balance

When the liquid impurity source material having the above composition is prepared, poly N-vinylacetamide is dissolved in 2-methoxyethanol and water, and ammonium dihydrogen is dissolved therein. When poly N-vinylacetamide, which is more polar than polyvinyl alcohol, is used as a thickener, the concentration of the inorganic phosphoric acid compound in the liquid impurity source material, that is, the proportion thereof can be increased to about 20% by weight.
In addition, the concentration or ratio of the thickener in the liquid impurity source material can be increased to 20% by weight.

Next, this liquid impurity source material is uniformly applied to one main surface of the semiconductor substrate 1 by a well-known spinner method to form a liquid impurity source film 2 as schematically shown in FIG. 1 (B). Form. By using the thickener made of a highly polar organic polymer substance according to the present embodiment, the liquid impurity source film 2 in which the inorganic phosphorus compound is uniformly contained can be favorably formed on the silicon semiconductor substrate 1 by the spinner method. Further, due to the action of the thickener, the liquid impurity source film 2 has good storage stability, and the liquid impurity source material does not reach the back surface of the semiconductor substrate 1 even after a lapse of time. Further, the liquid impurity source film 2 can be formed relatively thick on the semiconductor substrate 1.
Further, by making the liquid impurity source material have the above composition,
The liquid impurity source film 2 can be formed to have a substantially uniform thickness with less coating unevenness.

Next, the semiconductor substrate 1 on which the impurity source film 2 shown in FIG. 1B is formed is placed on a hot plate (heat plate), and phosphorus is applied to the semiconductor substrate 1 with the impurity source film 2. 150 ~ 200 ℃ lower than the diffusion temperature of
1st heat treatment for 30 to 60 seconds at a temperature of 1 to evaporate the solvent and water contained in the liquid impurity film 2,
As shown in (C), an impurity source film 3 made of a polymer film in a dry state containing an inorganic phosphorus compound and a thickener is formed on one main surface of the semiconductor substrate 1. This drying process is performed in the air.

Next, after the semiconductor substrate 1 having the impurity source film 3 shown in FIG. 1 (C) is charged in a semiconductor substrate diffusion holder made of quartz or SiC (silicon carbide) or the like, it is charged with quartz or quartz. It is put in a process tube made of SiC or the like and subjected to a second heat treatment with a predetermined temperature profile. That is, oxygen is introduced into the tube to create an oxygen atmosphere in the tube and the diffusion temperature (126
Semiconductor substrate 1 up to a temperature of about 1000 ° C, which is lower than 0 ° C)
The temperature is gradually increased and this state is maintained for 30 to 100 minutes. By heating the impurity source film 3 in an oxygen atmosphere, that is, an oxidizing atmosphere, the silicon oxide film 4 containing phosphorus shown in FIG. 1D is produced. By this second heat treatment, the thickener is pyrolyzed and burned to be removed. Further, the inorganic phosphorus compound is also thermally decomposed.

Next, after keeping the temperature at 1000.degree. C. and replacing the oxidizing atmosphere with a nitrogen (N.sub.2) atmosphere (non-oxidizing atmosphere), the semiconductor substrate 1 shown in FIG.
A heat treatment (third heat treatment) at 260 ° C. is performed for a predetermined time (for example, 10 hours) to diffuse phosphorus from the silicon oxide film 4 containing phosphorus into the semiconductor substrate 1, and the phosphorus diffusion region shown in FIG. ^{A + type} semiconductor region 5 is obtained. The p-type semiconductor region 1a remains on the semiconductor substrate 1 and a pn junction is formed.

Next, the semiconductor substrate 1 of FIG. 1 (E) is etched with hydrofluoric acid or a hydrofluoric acid-based etching solution containing it as a main component to contain phosphorus remaining on one main surface of the semiconductor substrate 1. The silicon oxide film 4a is removed to expose the n-type semiconductor region 5 on one main surface of the semiconductor substrate 1 as shown in FIG. In this embodiment, as described above, one main surface of the silicon semiconductor substrate 1 is not nitrided,
The residual film formed of the silicon oxide film 4a containing phosphorus formed on one main surface of the semiconductor substrate 1 can be easily and completely removed.

Next, as shown in FIG. 1G, a first metal ohmic electrode 6 is formed on the n-type semiconductor region 5, and p
The second metal ohmic electrode 7 is formed in the shaped semiconductor region 1a. Although omitted in FIG. 1G, a p ^{+ -type} semiconductor region may be formed in the p-type semiconductor region 1a as necessary, and the second metal ohmic electrode 7 may be formed therein.

According to this embodiment, the following effects can be obtained. (1) Since an organic polymer substance having a stronger polarity than polyvinyl alcohol is used as a thickener, even if the main surface of the silicon semiconductor substrate 1 is a lap surface, a mirror surface, a back grind surface, etc., it is liquid. Good wettability of the impurity source material can be secured, and the diffusion region 5 having a uniform thickness can be formed. (2) Since a thickener composed of a highly polar organic polymer substance is used, the compatibility between the thickener and the inorganic phosphorus compound is good, and the inorganic phosphorus and the compound are evenly dispersed in the thickener. The liquid impurity source film 2 and the dry impurity source film 4 thus obtained can be obtained, and the uniform and excellent diffusion region 5 can be formed. (3) By using the thickener of the present embodiment, it is possible to prevent salting out and to include an inorganic phosphorus compound in a high concentration, and the diffusion region 5 includes phosphorus in a high concentration close to the solid solubility limit. Therefore, it is possible to form the n-type diffusion region 5 having a high surface impurity concentration of 10 ²⁰ cm ⁻³ and a depth of 100 μm or more. (4) Since the ratios of the thickener and the inorganic phosphorus compound can be changed within a wide range, it is possible to easily adjust the impurity concentration and the diffusion depth of the n-type diffusion region 5. (5) Since the viscosity can be adjusted by the thickener, it is possible to prevent the liquid impurity source material from flowing around to the back surface side of the semiconductor substrate 1. (6) What remains on the surface of the semiconductor substrate 1 after diffusion can be easily removed with hydrofluoric acid.

[0023]

[Modification] The present invention is not limited to the above-described embodiment, and the following modifications are possible. (1) Impurities can be diffused in a non-oxidizing atmosphere such as argon instead of a nitrogen atmosphere. (2) The liquid impurity source can be applied only to a specific region of the semiconductor substrate 1, that is, a region to be diffused. (3) Instead of the ohmic electrode 6, a Schottky barrier electrode, a FET gate insulating film, or the like can be formed on the surface of the n-type semiconductor region 5. (4) By adding the fluorine surfactant, the wettability with respect to the semiconductor substrate can be improved.

[Brief description of drawings]

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

[Explanation of symbols]

1 p-type semiconductor substrate 2 Liquid impurity source film 3 Dry impurity source film 4 Silicon oxide film containing phosphorus 5 n-type semiconductor region

Claims (3)

[Claims] 1. A liquid impurity source material used when diffusing n-type impurities into a silicon semiconductor substrate, which comprises an inorganic phosphorus compound and a nitrogen-containing vinyl polymer substance, cellulose polymer substance, and acryl. A liquid impurity source material comprising a thickener composed of at least one water-soluble organic polymeric material selected from the group of polymeric materials, an organic solvent, and water. 2. The thickener is at least one selected from poly N-vinyl acetamide, poly N-vinyl formamide, polyamidine, polyamine, carboxymethylcellulose ammonium salt, polyacrylic acid and polyacrylamide. The liquid impurity source material according to claim 1, which is characterized in that. 3. An inorganic phosphorous compound and at least one water-soluble organic polymer substance selected from a nitrogen-containing vinyl polymer substance, a cellulose polymer substance and an acrylic polymer substance. A step of preparing a liquid impurity source material composed of a viscous agent, an organic solvent, and water; a step of applying the liquid impurity source material to the surface of a silicon semiconductor substrate to form a liquid impurity source film; The source film is subjected to a first heat treatment at a temperature lower than the diffusion temperature of phosphorus to evaporate the solvent and the water to form a dry impurity source film composed of the inorganic phosphorus compound and the thickener. A second heat treatment in an atmosphere containing oxygen to the semiconductor substrate having the impurity source film in a dry state to remove the thickener and to add phosphorus to the surface of the semiconductor substrate. A step of forming a silicon oxide film, and performing a third heat treatment at a temperature higher than the second heat treatment in the non-oxidizing atmosphere on the semiconductor substrate having the silicon oxide film containing phosphorus to form a semiconductor film in the semiconductor substrate. And a step of diffusing phosphorus.