JPH04113620A - Cleaning method for semiconductor substrate - Google Patents

Abstract

PURPOSE:To eliminate the deterioration of a characteristic and to realize a high quality by a method wherein, at a precleaning operation for a heat treatment process, a silicon semiconductor substrate is immersed in pure water whose ozone concentration is definite and a uniform and clean silicon oxide film is formed in the silicon revealed part of the silicon semiconductor substrate. CONSTITUTION:When a silicon semiconductor substrate is heat treated, e.g. thermally oxidized or thermally diffused, a precleaning operation is executed. For the cleaning operation, the silicon semiconductor substrate is first immersed in chemicals by an existing method, e.g. in dilute hydrofluoric acid, ammonia water/hydrogen peroxide water or hydrochloric acid/hydrogen peroxide water. Then, it is immersed in pure water containing ozone. After that, it is dried by using a spin drier or isopropyl alcohol vapor. At the cleaning operation, the ozone concentration in pure water is set at 5ppm, the temperature of pure water is set at 23 deg.C and the immersion time is set for 5 minutes. Thereby, a uniform and clean silicon oxide film having a thickness of 20Angstrom is formed on the surface of the silicon revealed part of the silicon semiconductor substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of cleaning a silicon semiconductor substrate in the process of manufacturing a silicon semiconductor integrated circuit.

[Summary of the Invention] The present invention provides for cleaning exposed silicon portions of the silicon semiconductor substrate by placing the silicon semiconductor substrate in pure water containing ozone when cleaning the silicon semiconductor substrate in the process of manufacturing a silicon semiconductor integrated circuit. A clean silicon oxide film with a thickness of 20 Å or less is formed on the surface of the silicon oxide film.

[Prior Art] When manufacturing a silicon semiconductor integrated circuit, an oxide film is formed on a silicon semiconductor substrate, and N' or P' impurities are selectively diffused. These methods use existing methods such as thermal oxidation and thermal diffusion. Furthermore, before these heat treatments, the silicon semiconductor substrate is cleaned with chemicals such as dilute hydrofluoric acid, aqueous ammonia/hydrogen peroxide, and hydrochloric acid/hydrogen peroxide. This cleaning consists of a step of immersing in the chemical, a step of immersing in pure water, and a step of drying.

[Problem to be solved by the invention] When the silicon semiconductor substrate cleaned by the previous cleaning is left in the atmosphere, a silicon oxide film with a thickness of 5 to 20 Å is naturally formed on the surface of the exposed silicon part. be done. This silicon oxide film takes in impurities such as AI, Fe, and Na from the atmosphere, which is non-uniform for each silicon semiconductor substrate.

In order to suppress the formation of the silicon oxide film, even if the silicon semiconductor substrate is stored in an N2 atmosphere, the intended purpose can be achieved by exposing it to the atmosphere for a short time, for example, 10 minutes, before heat treatment. It is not possible.

If there is such a thin silicon oxide film on the exposed silicon portion of a silicon semiconductor substrate, even if you try to form a silicon oxide film with a constant thickness (for example, about 100 Å) by thermal oxidation, it will be difficult to form a uniform silicon oxide film. I can't. Further, impurities such as A1, Fe, and Na degrade the initial breakdown voltage of the silicon oxide film and also reduce the reliability of the film characteristics. Furthermore, Fe impurities diffuse into the silicon semiconductor substrate during all heat treatment steps and deteriorate the PN junction characteristics.

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

[Means for Solving the Problems] The present invention provides a method for cleaning exposed silicon portions of a silicon semiconductor substrate by immersing the silicon semiconductor substrate in pure water with a constant ossine concentration during pre-cleaning of the silicon semiconductor substrate in a heat treatment step. This problem was solved by forming a uniform and clean silicon oxide film on the substrate.

[Example] Examples of the present invention will be shown below. Before a silicon semiconductor substrate is subjected to heat treatment, such as known thermal oxidation or thermal diffusion, the precleaning of the present invention is performed. In this cleaning process, the silicon semiconductor substrate is first washed with chemicals, which is an existing method.
For example, immerse in dilute hydrofluoric acid, aqueous ammonia/hydrogen peroxide, hydrochloric acid/hydrogen peroxide. Next, the material of the present invention is immersed in pure water containing ozone. Thereafter, drying is performed using a known method such as a spin dryer or isopropyl alcohol vapor. During this cleaning, the ozone concentration in pure water was 5. ．． 1. The pure water temperature is 23° C. and the immersion time is 5 minutes, and a uniform and clean silicon oxide film with a thickness of 20 Å is formed on the surface of the exposed silicon portion of the silicon semiconductor substrate.

The relationship between the silicon oxide film thickness, ozone concentration, and immersion time is shown in Figure 1. The higher the ozone concentration, the shorter the time, and the longer the immersion time, the thicker the silicon oxide film will grow, but will not become thicker than 30.8 cm.

[Effects of the Invention] The cleaned silicon semiconductor substrate was left in the air in a clean room for 3 hours, and the surface of the silicon semiconductor substrate was analyzed and the results showed that Al 16 x 10 ”
atoms/cm2F e 2 X 10”ato
ms/cm2Cr 2 X 10”atoms/c
u+2N i 3 x 1011Iatoms/cm
2N a 1 x 10"atoms/cm2. This value is the same as that of silicone that was left exposed to the atmosphere in a clean room for 3 hours after conventional cleaning - a cleaning process that involves soaking in pure water that does not contain ozone. This is one-third to one-tenth of the surface analysis value of a semiconductor substrate.

When a silicon thermal oxide film of 120A is formed on a silicon semiconductor substrate with a diameter of 150vn cleaned according to the present invention,
The film thickness variation of the silicon thermal oxide film within the silicon semiconductor substrate had a standard deviation of 38.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between silicon oxide film thickness, ozone concentration in pure water, and immersion time at a pure water temperature of 23°C. a
is an ozone concentration of 5°. 1, b is ozone concentration 1°1, C is ozone concentration 0. 2. ,. Applicant: Seiko Epson Corporation

Claims (1)

[Claims] When cleaning a silicon semiconductor substrate, the silicon semiconductor substrate is placed in pure water containing ozone to form a clean silicon oxide film with a thickness of 20 Å or less on the surface of the exposed silicon portion of the silicon semiconductor substrate. A method for cleaning semiconductor substrates.