JPH06163443A - Method of diffusing impurity into thin film - Google Patents

Abstract

PURPOSE:To evenly diffuse impurities into a thin film uniform in distribution by a method wherein a semiconductor thin film is formed on a film where impurity element or its compound is attached. CONSTITUTION:An SiO2 film 3 which serves to prevent impurities from diffusing is formed on an Si substrate 1, a certain amount of boron or boron compound which is diffused into a semiconductor thin film (polysilicon film) 4 formed on the film 3 is attached to the film 3 in an atmosphere which contains boron or boron compound, and then a polysilicon film 4 is formed on the SiO2 film 3. Then, boron or boron compound is diffused into the polysilicon film (polysilicon film) 4 through a thermal treatment. By this setup, required impurities (e.g. boron) are uniformly diffused into the semiconductor thin film 4 without deteriorating it in quality.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for diffusing impurities into a thin film.

[0002]

2. Description of the Related Art Conventionally, the diffusion of impurities into a thin film is carried out by depositing the thin film on a sample and then diffusing the impurities from the surface of the thin film by heat, or by giving energy to the ions of the impurities as in ion implantation. It has been done by the driving method.

[0003]

However, the methods of diffusing impurities into a thin film by these methods have problems such as uneven diffusion of impurities and damage to the underlying layer when the thickness of the thin film is reduced. That is, in the method of diffusing impurities from the surface of the thin film by heat, there is a problem that the oxide film and the contaminants growing on the outermost surface hinder the diffusion and uniform diffusion of the impurities cannot be achieved.

In the diffusion of impurity ions by ion implantation, the distribution after implantation becomes larger than the film thickness of the thin film, the impurity distribution varies, and a non-implanted region occurs due to a stepped portion. There was a problem that the base was damaged by the implanted ions.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a method for diffusing impurities into a thin film, which can diffuse impurities in the thin film with a uniform distribution without damaging the thin film. Has an aim.

[0006]

According to the present invention, (i)
A step of forming a film that prevents diffusion of impurities on the sample surface,
(ii) the film, in an atmosphere containing an impurity element or a compound thereof to be diffused in a semiconductor film formed on the film,
Attaching a fixed amount of an impurity element or a compound thereof,
There is provided a method of diffusing impurities into a thin film, including (iii) a step of forming a semiconductor thin film on the film, and (iv) a step of diffusing the impurity element or a compound thereof into the semiconductor thin film by heat treatment.

The sample in the present invention refers to a semiconductor substrate of a semiconductor device or the like, or a semiconductor substrate on which an insulating film, an electrode material or the like is deposited to form elements such as transistors or capacitors, or wiring. The film that inhibits diffusion of impurities formed on the surface of the sample is not particularly limited, but examples thereof include an oxide film such as SiO ₂ and a nitride such as SiN. It is preferably a SiO ₂ film. The film thickness in this case can be appropriately selected and used depending on the material, but is preferably about 5 nm or more. The SiO ₂ film can be formed by a known method, for example, a CVD method using SiCl ₄ or SiH ₄ and oxygen gas or the like. In addition, in order to prevent contamination of impurities in the atmosphere,
The SiO ₂ film is formed in an atmosphere containing only the O ₂ source gas, or first, the SiO ₂ film is formed to a desired thickness in the air and then in the atmosphere containing only the SiO ₂ source gas. Further, a SiO ₂ film may be formed with a film thickness of about 5 nm or more.

Further, in the present invention, after forming a film which inhibits diffusion of impurities, a certain amount of the impurity element or its compound to be diffused is contained in a semiconductor thin film formed on the film. Impurity element or its compound is attached. In this case, the impurity element or the compound thereof is not particularly limited as long as it is usually doped in the semiconductor as an impurity, and examples thereof include boron, phosphorus, arsenic and the like, or compounds thereof. As an atmosphere containing these impurity elements or their compounds, only the impurity elements or their compounds are 1 × 10 ^−12.
It is an atmosphere containing 1 × 10 ⁻⁹ mol / liter.
The pressure of this atmosphere is preferably about 1 atom, and its temperature is preferably in the range of about 0 to 300 ° C. Also, the time for introducing the sample into this atmosphere is preferably about 5 minutes,
As a result, about 1 × 10 ¹⁰ to 1 × 10 ¹³ pieces / cm ² of the impurity element or its compound are attached to the film surface.

Then, a semiconductor thin film is formed on the film having the impurity element or its compound attached to the surface as described above. The semiconductor thin film is not particularly limited as long as it can be used for electrodes, wirings and the like, and diamond, GaAs, ZnS or the like can be used, but polysilicon is preferable. When forming a polysilicon thin film, a known method such as Si ₂ H ₆ or SiH ₄ and N is used.
It can be formed by a CVD method using _two gases or the like. In that case, it is preferable that the polysilicon thin film is continuously formed in an airtight container from the above steps. The thickness of the polysilicon thin film is preferably about 0.1 μm. After laminating the polysilicon thin films, an insulating film having a film thickness of about 5 nm or more, for example, S, is formed so as to further cover the polysilicon thin films.
An iO ₂ film or the like may be formed.

Next, heat treatment is performed. This heat treatment is performed in the air or in an oxidizing or inert atmosphere at a pressure of 1 atom.
The temperature is preferably about 800 to 1000 ° C. for about 30 minutes. In the present invention, the above steps (i) to (iv) are most preferably performed in an airtight container containing a gas having a known component.

[0011]

According to the method of diffusing impurities into a thin film of the present invention, the step of forming a film that inhibits the diffusion of impurities on the surface of the sample, and the impurity element to be diffused in the semiconductor film formed on the film Or a step of depositing a certain amount of an impurity element or a compound thereof in an atmosphere containing the compound, a step of forming a semiconductor thin film on the thin film, and a step of diffusing the impurity element or the compound into the semiconductor thin film by heat treatment, Therefore, a certain amount of impurity element or its compound,
It will be evenly deposited on the film that inhibits the diffusion of impurities. Then, the impurities are uniformly diffused into the semiconductor thin film formed on the film by the subsequent heat treatment without causing defects.

[0012]

Embodiments of the method for diffusing impurities into a thin film of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments.

[0013] Example 1 First, on a silicon substrate 1, the polysilicon 2 is formed through the SiO ₂ film, an SiO ₂ film 3 having a film thickness of about 0.1μm as a film for inhibiting the diffusion of impurities. Then, it is exposed to an atmosphere 5 containing boron (B in FIG. 1) of 2 μg / m ³ for 1 minute at room temperature to deposit about 1 × 10 ¹² boron / cm ² of boron on the surface of the SiO ₂ film 3. (Figure 1).

Then, SiO₂SiH on the film 3_FourAnd N
₂By using a vapor phase decomposition method to form polysilicon 4
Deposit about 100 nm (FIG. 2). Furthermore, at 950 ° C
Annealing is performed at temperature for 30 minutes. This allows Si
O ₂Boron adhered to the film 3 becomes 1 in the polysilicon 4.
× 10¹⁷Pieces / cm³It diffuses uniformly at the concentration of (Fig. 3).

When formed in this manner, boron, which is an impurity element, is uniformly diffused in the polysilicon 4, which is a semiconductor thin film.

[0016] Example 2 First, as in Example 1, on a silicon substrate 1, the polysilicon 2 is formed through the SiO ₂ film, first, an SiO ₂ film 3a having a thickness of about 0.1μm . On this occasion,
Since contaminants from the atmosphere tend to adhere to the surface of the SiO ₂ film 3a, unnecessary impurities (C in FIG. 4) adhere (FIG. 4).

Next, in a sealed state, SiH
SiO ₂ film 3 by the vapor phase epitaxy method using ₄ and N ₂ O.
A SiO ₂ film 3b having a film thickness of about 0.1 μm is further formed on a as a film that prevents diffusion of impurities (FIG. 5).
At this time, since the SiO ₂ film 3b is formed in a sealed state, the adhesion of impurities can be extremely reduced.

Then, by exposing to the atmosphere 5 containing 2 μg / m ^{3 of} boron at room temperature for 1 minute, about 1 × 10 ¹² boron / cm ² of boron is attached to the surface of the SiO ₂ film 3b (FIG. 6). ). Furthermore, using SiH ₄ and N ₂ on the SiO ₂ film 3b, polysilicon 4 is formed by a vapor phase decomposition method,
After depositing a film thickness of about 100 nm, the SiO ₂ film 3 is continuously formed.
c was laminated (FIG. 7).

Then, anneal at a temperature of 950 ° C. for 30 minutes.
Process. As a result, SiO ₂Attached to the membrane 3b
Boron is 1 × 10 in the polysilicon film 4.¹⁷Pieces / cm
³It uniformly diffuses at a concentration of (Fig. 8). Form like this
Then, the steps after the formation of the film 3b that inhibits the diffusion of impurities
Impurities that are unnecessary to carry out in an atmosphere of known composition
Quality of the semiconductor thin film 4 without contacting the semiconductor thin film 4.
The desired impurity can be diffused uniformly without reducing the
it can.

[0020]

According to the method of diffusing impurities into a thin film of the present invention, the step of forming a film that inhibits the diffusion of impurities on the sample surface, and the film should be diffused into the semiconductor film formed on the film. In an atmosphere containing an impurity element or its compound,
Attaching a fixed amount of an impurity element or a compound thereof,
Since a step of forming a semiconductor thin film on the thin film and a step of diffusing the impurity element or a compound thereof into the semiconductor thin film by heat treatment are included, a certain amount of the impurity element or a compound thereof is formed on the film that inhibits the diffusion of impurities. Will be attached. And, this impurity, by the subsequent heat treatment,
The semiconductor thin film formed on the film can be uniformly diffused without causing defects. Therefore, it becomes possible to greatly contribute to industry as a method for diffusing impurities into a thin film.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram showing a first embodiment of a method for diffusing impurities into a thin film according to the present invention.

FIG. 2 is a manufacturing process diagram showing a first embodiment of a method for diffusing impurities into a thin film according to the present invention.

FIG. 3 is a manufacturing process diagram showing a first embodiment of a method for diffusing impurities into a thin film according to the present invention.

FIG. 4 is a manufacturing process diagram showing a second embodiment of the method for diffusing impurities into a thin film according to the present invention.

FIG. 5 is a manufacturing process diagram showing a second embodiment of the method for diffusing impurities into a thin film according to the present invention.

FIG. 6 is a manufacturing process diagram showing a second embodiment of the method for diffusing impurities into a thin film according to the present invention.

FIG. 7 is a manufacturing process diagram showing a second embodiment of the method for diffusing impurities into a thin film according to the present invention.

FIG. 8 is a manufacturing process diagram showing a second embodiment of the method for diffusing impurities into a thin film according to the present invention.

[Explanation of symbols]

 1 Silicon Substrate 2 Polysilicon 3,3a, 3b, 3c Film that Impedes Diffusion of Impurity 4 Semiconductor Film (Polysilicon Film) 5 Atmosphere Containing Impurity Element or Compound thereof B Boron C Unnecessary Impurity

Claims (1)

[Claims] 1. (i) a step of forming a film which inhibits diffusion of impurities on a sample surface, (ii) the film contains an impurity element or a compound thereof to be diffused in a semiconductor film formed on the film In an atmosphere to deposit a certain amount of an impurity element or a compound thereof, (iii) a step of forming a semiconductor thin film on the thin film, (iv) a step of diffusing the impurity element or a compound thereof into a semiconductor thin film by heat treatment A method for diffusing impurities into a thin film, which comprises: