JPH08124850A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE: To provide a method of forming a polycrystalline silicon film, wherein the silicon film is separately controlled in grain diameter of silicon crystal and impurity concentration, enhanced in processing accuracy and electrical properties, and decreased in number of manufacturing processes and cost. CONSTITUTION: For instance, phosphorus P is introduced into a polycrystalline silicon film 13 and thermally diffused to form silicon crystals of required grain diameter. In succession, a silicon oxide film 14 is removed by NH4 F, then the polycrystalline silicon film 13 is thermally treated in an N2 gas atmosphere, and phosphorus P contained in the polycrystalline silicon film 13 is diffused outwards. By this setup, controlling phosphorous P in outward diffusion, phosphorous P contained in the polycrystalline silicon film 13 is controlled in concentration independent of the grain diameter of silicon crystals without forming a metal silicide film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, for example, a ULSI (Ultra).
Large Scale Integrated C
The present invention relates to control of grain size and impurity concentration of polycrystalline silicon or amorphous silicon used for gate electrodes of ircuit).

[0002]

2. Description of the Related Art Conventionally, polycrystalline silicon or amorphous silicon, which has been used for a gate electrode of ULSI, has a high resistance as it is formed, so that the resistance can be reduced by introducing impurities such as phosphorus and boron. ing. Moreover, when introducing the impurities, heat treatment is performed for the purpose of diffusing the impurities, but due to the effect of the impurities and the temperature, the crystal grains of polycrystalline silicon or amorphous silicon grow, and the grain size of the crystals increases and becomes uniform. And the surface is flattened at the same time.

From the point of view of the growth of the crystal grains, it is preferable that the impurity concentration and the heat treatment temperature are both high. It is desirable to carry out the heat treatment process at the lowest possible temperature, as the required film changes and reactions may occur.

Also, from the viewpoint of electrical characteristics, the concentration has an optimum value. Therefore, at present, the impurity concentration and the heat treatment temperature are determined from these requirements, and the crystal grain size is dependently determined by these conditions, and it cannot be said that they are independently controlled. .

However, as devices become finer in the future,
When various dimensions reach the level of several times the grain size, the uniformity and flatness of the surface of the silicon film affect the electrostatic breakdown voltage. Is important, and it becomes necessary to control the crystal grain size of silicon independently of the impurity concentration in the silicon film.

[0006] In response to such a demand, a technique has already been proposed which can control the crystal grain size of silicon and the impurity concentration in the silicon film independently (for example, Japanese Patent Application No. 6-89).
No. 20).

This is a metal silicide having a high melting point on the surface of a silicon film after introducing a high concentration of impurities into a polycrystalline silicon film or an amorphous silicon film to perform thermal diffusion to obtain a desired crystal grain size. Form a film. Then, heat treatment is performed in an oxidizing atmosphere, and the impurity concentration in the silicon film is controlled by the impurity absorption effect of the metal silicide film.

However, in this method, the inside of the furnace is contaminated by the metal by the heat treatment performed after the metal silicide film is formed. When the furnace contaminated with this metal is used for another heat treatment, the metal adheres to the substrate and adversely affects the device characteristics. Therefore, a dedicated furnace is required for the heat treatment after the metal silicide film is formed, which may lead to a complicated manufacturing process and an increase in cost.

[0009]

As described above, in the prior art, when the crystal grain size of silicon and the impurity concentration in the silicon film are independently controlled by forming the metal silicide film, the wafer (substrate There is a risk that a dedicated furnace will be required due to the contamination of), which will complicate the manufacturing process and increase the cost.

Therefore, according to the present invention, the crystal grain size of silicon and the impurity concentration in the silicon film can be controlled independently, the processing accuracy and electrical characteristics can be improved, and the manufacturing process and cost can be reduced. It is an object of the present invention to provide a method for manufacturing a semiconductor device.

[0011]

In order to achieve the above object, in the method of manufacturing a semiconductor device of the present invention, a silicon film in which crystals grow in the film is formed on a semiconductor substrate by heat treatment. A process, a process of thermally diffusing impurities having a predetermined conductivity type into the silicon film, and a process of performing heat treatment in a gas atmosphere capable of outwardly diffusing the impurities in the silicon film are used.

[0012]

According to the present invention, the crystal grain size of silicon and the impurity concentration in the silicon film can be independently controlled by the means described above without forming a metal silicide film. It is possible to eliminate the need.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 schematically shows a method for manufacturing a semiconductor device according to the present invention.

First, as shown in FIG. 1A, after a predetermined layer (not shown) is formed on the surface region of the semiconductor substrate 11, a silicon oxide film 12 and a polycrystalline silicon film 13 are formed on the predetermined layer. Are formed respectively. For example, the polycrystalline silicon film 13 is formed at 620 ° C. by the chemical vapor deposition method.
A film is formed to a thickness of 0.2 μm at the heat treatment temperature. In this case, the grain size of the polycrystalline silicon film 13 is 0.1 μm or less.

Subsequently, as shown in FIG. 3B, phosphorus diffusion using phosphorus oxychloride as a source is performed at a heat treatment temperature of about 900 ° C. for about 60 minutes to set the grain size of the polycrystalline silicon film 13 to a desired value. It is grown to a size, for example, 0.5 to 0.6 μm.

Then, as shown in FIG. 3C, the thin silicon oxide film 14 grown on the polycrystalline silicon film 13 is removed by NH ₄ F during the phosphorus diffusion. The concentration of phosphorus P in the polycrystalline silicon film 13 at this point is about 5 × 10 ²⁰ atoms / cm ³ .

After that, as shown in FIG. 3D, for example, a heat treatment is performed for 20 minutes at a temperature of 850 ° C. in an N ₂ gas atmosphere which is an inert gas, and then the polycrystalline silicon film 13 is formed.
The phosphorus P inside is diffused outward. As a result, phosphorus P in the polycrystalline silicon film 13 remains almost unchanged in grain size.
The concentration of is reduced to 9 × 10 ¹⁹ atoms / cm ³ or less.

In this case, the same furnace as the above phosphorus diffusion can be used only by changing the gas. Further, the heat treatment temperature is preferably lower than that during phosphorus diffusion so that the grain size of the polycrystalline silicon film 13 does not grow to 0.5 to 0.6 μm or more.

FIG. 2 shows an element profile in the depth direction by Auger electron spectroscopy. It should be noted that FIG. 11A shows a profile before heat treatment in an N ₂ gas atmosphere, and FIG. 11B shows a profile after heat treatment. 2 (a) and 2 (b),
21 is Si (silicon), 22 is P (phosphorus), 23 is O
It is each elemental profile of (oxygen).

As is apparent from this figure, the concentration of phosphorus P existing in the polycrystalline silicon film 13 is limited by the Auger electron spectroscopy analysis by outward diffusion after the heat treatment in the N ₂ gas atmosphere ( About 9 × 10 ¹⁹ atoms / cm
³ ) It can be seen that it has been reduced to below.

As described above, the crystal grain size of the polycrystalline silicon film 13 can be grown to an arbitrary size by changing the phosphorus P diffusion conditions. Moreover, the subsequent N ₂
By controlling the outward diffusion of phosphorus P by changing the heat treatment conditions in a gas atmosphere, the concentration of phosphorus P in the polycrystalline silicon film 13 can be controlled to an arbitrary concentration while maintaining the grain size. it can. As a result, it is possible to easily obtain the polycrystalline silicon film 13 having a large grain size and a low concentration.

As described above, the crystal grain size of polycrystalline silicon and the concentration of phosphorus in the polycrystalline silicon film can be independently controlled without forming a metal silicide film.

That is, after the grain size of polycrystalline silicon is grown to a desired size, phosphorus is diffused outward,
The concentration of phosphorus can be controlled independently. As a result, the grain size of polycrystalline silicon and the concentration of phosphorus can be controlled independently without using a metal silicide film. Therefore, since the inside of the furnace is not contaminated with metal, the furnace can be used for both the phosphorus diffusion and the heat treatment, and the dedicated furnace can be eliminated.

Further, since the grain size of polycrystalline silicon and the concentration of phosphorus can be obtained in an arbitrary combination, the uniformity and flatness of the surface and interface of the polycrystalline silicon film can be easily achieved regardless of the device. It is possible to secure the same, the processing accuracy is improved, and the variation in electrical characteristics can be greatly reduced.

Moreover, since the furnace is shared and the steps of forming a metal silicide film, post-oxidizing and removing the metal silicide film are not required, the steps (manufacturing process) can be shortened and the cost can be reduced accordingly. It is a thing.

In the above embodiments, polycrystalline silicon has been described as an example, but the present invention is not limited to this and can be similarly applied to, for example, film formation of amorphous silicon. The impurities may be boron or arsenic other than phosphorus.

In addition to the thermal diffusion described above, the impurities can be introduced by a method such as ion implantation. Furthermore, the heat treatment is not limited to the case where the heat treatment is performed in an N ₂ gas atmosphere, and the heat treatment may be performed using another inert gas (for example, He
Similar effects can be expected even in an atmosphere of Ne, Ar, Kr, Xe) or in an atmosphere of a reducing gas such as H ₂ .

In particular, when the heat treatment is performed using a reducing gas, the reducing gas has an effect of etching the silicon oxide film grown on the polycrystalline silicon film after phosphorus diffusion, so that the phosphorus diffusion and the heat treatment are performed. Can be continuously processed in the same furnace. That is, when heat treatment is performed in a reducing gas atmosphere, it is not necessary to take out the semiconductor substrate from the furnace and etch the silicon oxide film with NH ₄ F. Of course, various modifications can be made without departing from the scope of the invention.

[0029]

As described above in detail, according to the present invention, the crystal grain size of silicon and the impurity concentration in the silicon film can be controlled independently, the processing accuracy and the electrical characteristics can be improved, and the manufacturing process can be improved. It is possible to provide a method for manufacturing a semiconductor device capable of reducing the process and cost.

[Brief description of drawings]

FIG. 1 is a sectional view shown for explaining a method for manufacturing a semiconductor device according to an embodiment of the present invention.

FIG. 2 is a diagram which similarly illustrates the method for manufacturing the semiconductor device.

[Explanation of symbols]

11 ... Semiconductor substrate, 12 ... Silicon oxide film, 13 ... Polycrystalline silicon film, 21 ... Silicon element profile, 2
2 ... Elemental profile of phosphorus, 23 ... Elemental profile of oxygen, P ... Phosphorus.

Claims (7)

[Claims] 1. A step of forming, on a semiconductor substrate, a silicon film in which crystals grow in the film by heat treatment, a step of thermally diffusing an impurity having a predetermined conductivity type in the silicon film, and And a step of performing heat treatment in a gas atmosphere capable of outwardly diffusing the impurities. 2. The silicon film in which crystals grow in the film is a polycrystalline silicon film.
A method of manufacturing a semiconductor device according to item 1. 3. The method of manufacturing a semiconductor device according to claim 1, wherein the silicon film on which crystals grow in the film is an amorphous silicon film. 4. The method of manufacturing a semiconductor device according to claim 1, wherein the gas is an inert gas. 5. The semiconductor according to claim 4, wherein the heat treatment using the inert gas is performed after removing an oxide film formed on the surface of the silicon film by thermal diffusion of the impurities. Device manufacturing method. 6. The method of manufacturing a semiconductor device according to claim 1, wherein the gas is a reducing gas. 7. The semiconductor device according to claim 6, wherein the heat treatment using the reducing gas is continuously performed in the same furnace in a step of thermally diffusing impurities into the silicon film. Manufacturing method.