JPH04158514A - Impurity diffusion to semiconductor substrate - Google Patents

Abstract

PURPOSE:To suppress generation of rosettes at the time when impurity diffused layers are formed and thereby form satisfactory diffused layers by putting a silicon semiconductor substrate into a thermal diffusion furnace in which the gas atmosphere is kept oxidative and then by switching the gas atmosphere into an inactive one to diffuse arsenic or antimony in a coating film into the silicon substrate. CONSTITUTION:After a silicon semiconductor substrate is coated with a coating solution resulting from dissolution of a silica film containing arsenic or antimony to form a coating film, the silicon semiconductor substrate is put into a thermal diffusion furnace to keep its gas atmosphere oxidative, which is then switched into an inactive gas atmosphere to diffuse arsenic or antimony in the coating film into the silicon substrate. Diffusion temperature for diffusion using the above-mentioned coating solution is 1000-1500 deg.C, preferably, close to 1250 deg.C. The oxidative gas atmosphere at the beginning of diffusion is a mixture gas of oxygen and an inactive gas. The oxygen concentration is 5-50vol%, preferably, 5-10vol%, and the remaining inactive gas is preferably nitrogen. It is favorable that the time of switching into an inactive gas atmosphere is within 1/2Thr where the total treatment time for diffusion is Thr.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for diffusing impurities into a semiconductor substrate, particularly arsenic,
Alternatively, the present invention relates to an impurity diffusion method in which a coating liquid in which a silica film containing antimony is dissolved is applied onto a silicon substrate and thermally diffused.

[Prior Art] Conventionally, one method for forming an impurity diffusion layer such as arsenic or antimony on a silicon semiconductor substrate is to use a coating liquid (hereinafter referred to as coating) in which a silica film containing impurities such as arsenic or antimony is dissolved in an organic solvent. A conventional method has been to supply a liquid (referred to as liquid) onto a substrate, form a film using a spin code method, and then thermally diffuse impurities. This method is
Forming a silicon dioxide (SiL) film on a silicon substrate,
A window is opened in the SiO□ film to expose the surface of the silicon substrate where the diffusion layer is to be formed, and a coating liquid is applied thereon using a spin code method to form a silica film layer, and then heat treatment is performed to remove impurities. This was done by forming a diffusion layer.

However, the above-mentioned technique has a problem in that crystallized glass is generated due to heat treatment of the coating liquid. This crystallized glass is commonly called a rosette, but if such a rosette is formed in the area where the impurity diffusion layer is to be formed on the substrate, the adhesion between the rosette and silicon is extremely strong, so the coating solution is removed in a later process. There was a problem in that even if the silica film layer formed by the method was removed, the rosette remained as it was.

Furthermore, it has been experienced that rosettes are formed in SiO□ films, and in these rosette regions, impurities penetrate the SiL film and diffuse into the substrate, creating an unnecessary impurity diffusion layer. there were.

These rosettes are particularly noticeable when arsenic or antimony, which has an atomic radius larger than that of the silicon constituting the substrate, is diffused for a long period of time to lower the sheet resistance value of the silicon substrate surface.

In response to this phenomenon, several methods have been developed to prevent the generation of rosettes. One such method is disclosed in, for example, Japanese Unexamined Patent Publication No. 143031/1982.

The same report states that before the silica film formed on the SiO2 film, which does not substantially contribute to diffusion into the silicon substrate, is removed, only the apertured portion is left and removed before the diffusion treatment, resulting in a rosette. It describes how to prevent this from happening. Other similar methods include JP-A-62-
216322, JP-A-63-117419, JP-A-1-53414, etc. However, although this method can prevent the formation of rosettes I on the 5i02 film, it still does not solve the problem of rosettes occurring in the diffusion layer formation area, that is, the apertured area. This is a problem because the number of steps required for formation increases, which puts pressure on product yield and manufacturing costs.

In JP-A-2-178920, after applying a coating liquid, 02 plasma treatment or 03 treatment is performed to oxidize impurities in the silica film, and then diffused, thereby reducing the occurrence of rosettes and forming a low sheet. A semiconductor substrate with a high resistance value is obtained. A similar method is JP-A-2-1
There is a publication No. 78921. However, even with this method,
The number of steps required to form the diffusion layer increases, which continues to be a factor that puts pressure on product yield and manufacturing costs.

[Problems to be Solved by the Invention] The present invention solves the drawbacks of the prior art, namely, the generation of rosettes that occur when forming an impurity diffusion layer when a silica film containing arsenic or antimony is formed on a silicon substrate and thermally diffused. It is an object of the present invention to provide a method for suppressing this in an extremely simple manner and thereby forming a good diffusion layer.

[Means for Solving the Problems] The present invention applies a coating solution in which a silica film containing arsenic or antimony is dissolved to a silicon semiconductor substrate to form a coating film, and then places the silicon semiconductor substrate in a thermal diffusion furnace.
This method of diffusing impurities into a semiconductor substrate is characterized by keeping the gas atmosphere in a thermal diffusion furnace oxidizing and then switching to an inert gas atmosphere to diffuse arsenic or antimony in a coating film into a silicon substrate.

That is, by performing diffusion in an oxidizing gas atmosphere at the initial stage and then switching to an inert gas atmosphere, 510
The present invention was completed by discovering that the occurrence of rosettes is extremely small and a good sheet resistance value can be obtained not only on the top of the two films but also in the portion where the diffusion layer is formed.

The coating liquid used in the present invention is prepared by dissolving a silica film containing several percent of arsenic and antimony in an organic solvent such as acetone. Commercially available coating liquids include Ac
cuspin @ 5b-273 (manufactured by Sumiya Kagaku Kogyo ■),
OCD Type [F] (manufactured by Tokyo Ohka Kogyo ■) etc. can be used.

The diffusion temperature when diffusing using the above coating liquid is determined depending on the desired sheet resistance, but is usually 1000℃~
1500″C1, preferably around 1250°C.

At temperatures below 3,000°C, a very long time is required for impurity diffusion, and at temperatures above 1,500°C, there is a limit to the performance of the electric furnace for diffusion used.

A mixed gas of oxygen and an inert gas is used as the oxidizing gas atmosphere at the initial stage of diffusion. Oxygen concentration ranges from 5vo1% to 50
vo1%, preferably 5 vo1% to loVOI%. The remaining inert gases include helium, argon,
Although nitrogen etc. can be used, nitrogen is particularly preferred. If the oxygen concentration is less than 5 vol.chi., the sheet resistance value after diffusion will not be lowered, and if it exceeds 50 VOI%, the occurrence of rosettes will become noticeable.

The concentration of the inert gas used to switch from the oxidizing gas atmosphere to the inert gas atmosphere is one that does not contain oxygen.

The timing of switching to the inert gas atmosphere should be within 1/2 T hr, preferably 1/2 T hr to 1/4 T hr, assuming the total processing time for diffusion is T hr.
It is between. If the diffusion is performed in an oxidizing gas atmosphere for more than 1/2 Thr, rosettes will be noticeable, and if the diffusion time is less than 1/4th of an oxidizing gas atmosphere, the desired sheet resistance value will not be achieved. can't get it.

[Example] Although the method of the present inventor will be specifically explained, the present invention is not limited to the examples described below.

Examples 1, 2, 3 Acetone solution of silica film containing 1% Sb on P-type silicon substrate (Accuspin @ 5b-27
3. A silica film was formed by the spin-coding method using a silica film manufactured by Sumitomo Chemical Co., Ltd. ■Made in C0BRA) 125
Diffusion was performed at 0°C for 5 hours. In this case, the gas composition during the 5-hour diffusion process is such that the initial stage of the diffusion is an atmosphere of 10 VOI% oxygen and 90 VO1% nitrogen, and the remaining time is 100 VOI% nitrogen.
The treatment time was 2.5 hr, 1.5 hr, 1.25 hr in an atmosphere containing 10vol% oxygen.
I changed it.

After diffusion, take out the silicon substrate from the diffusion furnace and heat it to 30%H.
After removing the silica film on the silicon substrate at F,
An optical microscope with a 200x lens and an IC microscope made by Kon
6F-M), and the number of rosettes generated was measured.

Further, the sheet resistance value of the surface of the silicon substrate was measured using a resistivity measuring device (1705RD manufactured by Kyowa Riken Co., Ltd.).

The results are shown in Table 1.

As the treatment time in the oxygen-containing gas atmosphere became shorter, the number of crystallized glass produced decreased significantly.

Comparative Examples 1 and 2 The treatment time in an atmosphere containing 10vol% oxygen was 1. Oh
Example 1.2.3, except that r, 0.5 hr.
Table 2 shows the number of rosettes and sheet resistance values measured after diffusion under exactly the same conditions as above.

Table 2 Although there was almost no rosette, the sheet resistance value of the silicon substrate surface was higher than that of Examples 1, 2, and 3.

Comparative Examples 3, 4, 5 Without changing the gas composition during diffusion,
0! /N2=0/100, 10/90, 25/75
．． Example 1 except that 50150 gas was used.
．． It was diffused under exactly the same conditions as 2.3.

Table 3 shows the number of rosettes and sheet resistance values.

Although no rosettes were observed on the silicon surface after diffusion with 100 vol 1% nitrogen, the sheet resistance value of the surface was as high as that of Example! , 2.3, was much higher.

On the silicon surface after diffusion with 10 vol% oxygen and 90 vol% nitrogen, the sheet resistance value equivalent to that of Example 1.2.3 was obtained, and the occurrence of rosettes was remarkable.

Oxygen 25vol1%, Nitrogen 75vol1%, Oxygen 50vol1
On the silicon surface after diffusion with 50vol% and nitrogen, the occurrence of crystallized glass became more noticeable, and the sheet resistance value also showed a higher value than in the example.

[Effects of the Invention] As described above, according to the present invention, a silica film containing arsenic or antimony is formed on a silicon semiconductor substrate, and the problem of rosette generation during thermal diffusion is solved by oxidizing the gas atmosphere during diffusion. By switching from a reactive material to an inactive material, which is an extremely simple method, its occurrence can be significantly suppressed and a good diffusion layer can be formed.

Claims (1)

[Claims] (1) After coating a silicon semiconductor substrate with a coating solution containing dissolved silica film containing arsenic or antimony to form a coating film, the silicon semiconductor substrate is placed in a thermal diffusion furnace, and the gas atmosphere in the thermal diffusion furnace is made oxidizing. 1. A method for diffusing impurities into a semiconductor substrate, the method comprising: maintaining the silicon substrate, and then switching to an inert gas atmosphere to diffuse arsenic or antimony in the coating film into the silicon substrate.