JPS6151416B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for forming an oxide film on a semiconductor surface. The following description will be made using silicon as an example of a semiconductor.

Conventionally, in order to generate a silicon oxide film on the surface of a silicon substrate, a method has been used in which the silicon substrate is thermally oxidized at a high temperature of several hundred degrees Celsius or higher in dry oxygen or oxygen containing moisture. In particular, in order to form a thick silicon oxide film, it was necessary to leave silicon in moist oxygen for a long time at high temperatures.

For example, in the case of silicon with crystal axis <100>, 95
When thermally oxidized at 1150°C for 5 hours in oxygen containing moisture at 1.5°C, a silicon oxide film of about 1.5μ is produced. However, it is well known that when silicon is thermally oxidized at high temperatures, stacking faults occur along the 111 plane near the silicon surface. These stacking faults can cause an increase in leakage current at the p-n junction in semiconductor devices made using silicon, a decrease in charge storage time when used as a charge-coupled device, or a decrease in refresh rate when a dynamic memory device is configured. This will have negative effects such as a decrease in spacing.

Although the mechanism by which stacking faults occur has not yet been fully elucidated, the density and size of stacking faults depend on the silicon oxide film formation temperature and formation time; generally, the lower the temperature and the shorter the formation time, the higher the It is known that both the density and size of stacking faults are small. In particular, it has been found that temperature has a more significant effect on the density and size of stacking faults. Therefore, in order to generate a silicon oxide film of a predetermined thickness and reduce stacking faults, it has been necessary to carry out thermal oxidation at a low temperature for a long time.

This invention was made in view of the above-mentioned conventional problems, and does not cause stacking faults.
It is an object of the present invention to provide a method for forming a semiconductor oxide film that can form a semiconductor oxide film of a predetermined thickness in a relatively short time.

An embodiment of the present invention will be described below.

First, experimental facts regarding the occurrence of stacking faults in the case of one thermal oxidation and the case of two thermal oxidations at low and high temperatures, as confirmed by the inventors, will be described. As the substrate material, an N-type silicon single crystal wafer with a crystal axis <100> and a specific resistance of 4 to 6 Ω-cm was used. This wafer was divided into two pieces, and the first wafer piece was thermally oxidized at 1000°C for 2 hours in oxygen containing moisture at 95°C to form a silicon oxide film of approximately 6000 Å. Together with the wafer pieces from No. 2, they were thermally oxidized at 150° C. for 5 hours in oxygen containing moisture at 95° C. As a result, a silicon oxide film of about 1.7 μm was formed on the first wafer piece that had been thermally oxidized twice, and about 1.5 μm on the second wafer piece that had been thermally oxidized once. At this time, in order to find out the number of stacking faults generated on the surfaces of the first and second wafer pieces, the surface of the formed oxide film was etched with hydrofluoric acid, and then a Secco etchant (hydrogen fluoride) was applied. 2000c.c., water 1000c.c., dichromic acid 46.5g
Etching was performed using ultrasonic waves for 5 minutes using a mixed solution of As a result, the first wafer piece had about 10 ² etching pits/cm ² , and the second wafer piece had about 10 ³ etching pits/cm ² , and the first wafer piece had more silicon. The interesting result was that the density of stacking faults was low despite the thick oxide film.

This invention is based on the above new knowledge,
The thermal oxidation process is divided into two stages, and after performing the first oxidation at a low temperature, the second thermal oxidation is performed at a high temperature.

Here, it is better to make the first thermal oxidation time at low temperature long to prevent the occurrence of stacking faults, but it is not practical to make it too long, and the effect of preventing the occurrence of stacking faults is as described above. This can be fully expected by providing a first thermal oxidation at a low temperature followed by a second thermal oxidation at a high temperature. The difference in oxidation temperature between the two stages of thermal oxidation may theoretically be any number of times, but in practice no significant effect can be expected unless this difference is 50°C or more.

In the above embodiments, the case where the substrate material is silicon has been described, but other semiconductor substrate materials may be used.

As detailed above, according to the present invention, the thermal oxidation process is divided into two stages, first performing the first thermal oxidation at a low temperature, and then performing the second thermal oxidation at a high temperature. There is an effect that a semiconductor oxide film with a low density of stacking faults can be obtained without significantly increasing the time required for oxidation.

Claims (1)

[Claims] 1. Performing a first thermal oxidation on a semiconductor at a predetermined temperature, and then performing a second thermal oxidation at a temperature higher than the predetermined temperature.
1. A method for producing a semiconductor oxide film, which comprises performing thermal oxidation to obtain a semiconductor oxide film. 2. The method for producing a semiconductor oxide film according to claim 1, wherein the second temperature is 50° C. higher than the first temperature.