JPH053185A - Cleaning method of semiconductor substrate - Google Patents

Abstract

PURPOSE:To provide a method of cleaning a semiconductor substrate, where the surface of the substrate can be enhanced in cleanness. CONSTITUTION:In a cleaning process where a silicon semiconductor substrate is cleaned when a silicon semiconductor integrated circuit is manufactured, the silicon semiconductor substrate is put in an ozone-containing atmosphere just after it is cleaned, whereby a clean silicon oxide film having a thickness of 20Angstrom or below is formed on the surface of the silicon-exposed part of the silicon semiconductor substrate. If a semiconductor integrated circuit is manufactured by the use of the above cleaning method, it is sharply enhanced in current characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning a silicon semiconductor substrate in the process of manufacturing a silicon semiconductor integrated circuit.

[0002]

SUMMARY OF THE INVENTION According to the present invention, in the step of cleaning a silicon semiconductor substrate when manufacturing a silicon semiconductor integrated circuit, the silicon of the silicon semiconductor substrate is placed in an atmosphere containing ozone immediately after being dried. A feature is that a clean silicon oxide film having a thickness of 20 Å or less is formed on the surface of the exposed portion.

[0003]

2. Description of the Related Art In manufacturing a silicon semiconductor integrated circuit, an oxide film is formed on a silicon semiconductor substrate to selectively
Diffusion of N ⁺ or P ⁺ impurities is performed. These use the existing methods of thermal oxidation and thermal diffusion. Also,
Before these heat treatments, the silicon semiconductor substrate should be washed with a high-purity chemical such as dilute hydrofluoric acid whose content of transition metal is controlled to 1 ppb or less, ammonia water / hydrogen peroxide water, hydrochloric acid / hydrogen peroxide water. Done. This cleaning includes a step of immersing in the chemical, a step of immersing in pure water, and a step of drying.

[0004]

The silicon semiconductor substrate cleaned by the previous cleaning is left in a clean room atmosphere after the cleaning so that a silicon oxide film having a thickness of 5Å to 20Å is naturally formed on the surface of the exposed silicon portion. Formed in. This silicon oxide film is not uniform in the silicon semiconductor substrate, or Al, F
Incorporates impurities such as e, Ni, and Na.

In order to suppress the formation of the silicon oxide film,
Even if the silicon semiconductor substrate is stored in an inert atmosphere such as N ₂ or in a vacuum, a short time is required before the heat treatment.
-For example, 10 minutes-By exposure to the atmosphere, the above-mentioned silicon oxide film is formed and the intended purpose cannot be achieved. Further, it has been attempted to continuously carry out the cleaning and heat treatment by vacuum conveyance, but the equipment becomes huge and the economical efficiency is deteriorated.

When such a thin silicon oxide film is present on the exposed silicon portion of the silicon semiconductor substrate, a silicon oxide film having a constant film thickness due to thermal oxidation--for example, about 100Å.
Even if an attempt is made to form −, a uniform silicon oxide film cannot be formed. In addition, Al, Fe, Ni, Na
Such impurities deteriorate the initial withstand voltage film characteristics of the silicon oxide film and also deteriorate the TDDB reliability characteristics.
Further, Fe and Ni impurities are diffused into the silicon semiconductor substrate in every heat treatment step and deteriorate the reverse current characteristics and carrier recombination characteristics in the PN junction.

An object of the present invention is to eliminate these characteristic deteriorations and easily obtain a high quality semiconductor integrated circuit.

[0008]

According to the present invention, immediately after drying a silicon semiconductor substrate in a pre-cleaning step for heat treating a silicon semiconductor substrate, the silicon semiconductor substrate is exposed to a clean inert gas such as N ₂ in an atmosphere having a constant ozone concentration for a predetermined time. By storing and forming a uniform and clean silicon oxide film on the exposed silicon portion of the silicon semiconductor substrate, such a problem was solved.

[0009]

EXAMPLES Examples of the present invention will be shown below. The pre-cleaning according to the present invention is performed before heat-treating the silicon semiconductor substrate, for example, known thermal oxidation or thermal diffusion. This cleaning is performed by first cleaning the silicon semiconductor substrate with a high-purity chemical.
-For example, ammonia water / hydrogen peroxide water, hydrochloric acid / hydrogen peroxide water, dilute hydrofluoric acid-and alternately immersing in pure water in which the oxygen content is suppressed. Next, it is dried with a spin dryer which is an existing method. The atmosphere during this drying is an inert gas such as N ₂ . Next, the present invention is stored in a clean inert gas having a constant ozone concentration such as N ₂ atmosphere. At this time, the ozone concentration in N ₂ is 2% , The temperature is 23
A uniform and clean silicon oxide film having a thickness of 20 Å is formed on the surface of the exposed silicon portion of the silicon semiconductor substrate at a temperature of 5 minutes and a storage time of 5 minutes. When the spin dryer is used as a storage container, the process of the present invention can be continuously performed from drying,
It goes without saying that a higher effect was obtained.

The relationship between this silicon oxide film thickness, ozone concentration, and storage time is shown in FIG. The higher the ozone concentration, the shorter the time, and the longer the storage time, the thicker the film becomes. The silicon oxide film grows, but it does not become thicker than 30Å.

[0011]

EFFECTS OF THE INVENTION After the cleaned silicon semiconductor substrate is left in the atmosphere in a clean room for 3 hours,
Results of analysis of the surface of the silicon semiconductor substrate Al 16 × 10 ¹⁰ atoms / cm 2 Fe 2 × 10 ¹⁰ atoms / cm 2 Cr 2 × 10 ¹⁰ atoms / cm 2 Ni 3 × 10 ¹⁰ atoms / cm 2 Na 1 × 10 ¹⁰ atoms / cm 2 Became. This value is one-third to one-tenth of the surface analysis value of the silicon semiconductor substrate left to stand in the air for 3 hours in the clean room after the conventional cleaning.

When a 120 Å silicon thermal oxide film was formed on a silicon semiconductor substrate having a diameter of 150 mm cleaned according to the present invention, the standard deviation of the film thickness variation of the silicon thermal oxide film within the silicon semiconductor substrate was 3 Å. ..

[Brief description of drawings]

FIG. 1 Silicon oxide film thickness and N _{2 at a} temperature of 23 ° C.
The graph which shows the relationship between ozone concentration in the inside and storage time.

[Explanation of symbols]

 a Ozone concentration 10% b Ozone concentration 2% c Ozone concentration 0.2%

Claims (1)

Claim: What is claimed is: 1. In cleaning a silicon semiconductor substrate, the silicon semiconductor substrate is placed in an atmosphere of an inert gas containing ozone, and the surface of the exposed silicon portion of the silicon semiconductor substrate has a thickness of 20 Å or less. A method for cleaning a semiconductor substrate, which comprises forming a clean silicon oxide film.