Method of forming isolation region

A method of forming an isolation region exerts no adverse influence upon steps after forming the isolation region and is, besides, capable of forming the isolation region having a narrow isolation width. After a mask has been formed of an oxidationproof material such as Si.sub.3 N.sub.4 on a silicon substrate, a field oxide is formed by effecting selective oxidation in a high-pressure dry oxygen atmosphere. Thereafter, a portion, protruded from the silicon substrate, of the formed field oxide is removed, thereby forming the isolation region.

What is claimed is:

1. A method of forming an isolation region, comprising:

forming a first layer of an oxidation-proof material on the semiconductor substrate;

forming a second layer on the first layer, wherein the second layer has an opening in an area corresponding to an area of the substrate where the isolation region should be formed, and is composed of a material whose volume increases when oxidized;

oxidizing the second layer within the opening;

after the oxidizing, etching the first layer with the oxidized second layer used as an etching mask, to pattern the first layer;

forming an oxide on a portion of the substrate corresponding to the opening of the oxidized second layer, by thermally treating the substrate in an oxidative atmosphere of such a pressure that oxidation in a thicknesswise direction of the substrate progresses faster than oxidation in a direction orthogonal to the thicknesswise direction; and

polishing the substrate so as to remove a protruding portion of the oxide formed in said oxide forming.

2. A method of forming an isolation region, comprising:

forming a first layer of an oxidation-proof material on the substrate;

forming a second layer on the first layer, wherein the second layer has an opening in an area corresponding to an area of the substrate where the isolation region should be formed, and is composed of a material whose volume increases when oxidized;

oxidizing the second layer within the opening:

after the oxidizing etching the first layer with said oxidized second layer used as an etching mask, to pattern the first layer;

processing the substrate so as to form a recess in an area of the substrate corresponding to the opening of the oxidized second layer; and

after said processing the substrate, forming an oxide on a portion of the substrate corresponding to the opening of the oxidized second layer, by thermally treating the substrate in an oxidative atmosphere of such a pressure that oxidation in a thicknesswise direction of the substrate progresses faster than oxidation in a direction orthogonal to the thicknesswise direction.

3. A method of forming an isolation region according to claim 2, further comprising:

polishing the substrate so as to remove a protruding portion of the oxide formed in said oxide forming step.

4. A method of forming an isolation region according to claim 2, wherein the substrate is a silicon substrate, the first layer is composed of silicon nitride, and the second layer is composed of silicon.

5. A method of forming an isolation region according to claim 1, wherein the substrate is a silicon substrate, the first layer is composed of silicon nitride, and the second layer is composed of silicon.