JPS5994844A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To make the element finer and higher integrated by a method wherein an oxide film separating process preventing or restricting a projecting or a inroading of a field oxide film into an element region from occuring is performed. CONSTITUTION:An oxide film 2 and a nitride silicon film 3 are formed on a silicon substrate 1 to be etched leaving the nitride silicon film 3 only in the element forming region. Then the oxide film 2 is selectively removed exposing the silicon substrate 1 to enter slightly into the part right below the end of the nitride silicon film 3. Another nitride silicon film is formed on the surface of a field region to be selectively removed forming the other nitride silicon film 5'. Then a field oxide film 4 is formed by thermal oxidation. In such a constitution, any bird beak and bird head may be prevented or restricted from occuring since the nitride silicon films 5' restrict any oxidation at the ends.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device, and more particularly to an improvement in an oxide film isolation method for isolating elements using an oxide film.

In recent years, IC-? In the manufacture of LSIs and the like, an oxide film isolation method is often used as a method of electrically and gaseously isolating each element. This is to selectively oxidize the surface of a semiconductor substrate using a silicon nitride (SiaN4) film as a mask.

FIGS. 1A to 1C are process cross-sectional views for explaining a conventional oxide film separation method.

First, as shown in FIG. 1(a) K, an oxide film 2 is provided on the surface of a silicon substrate 1, and a silicon nitride film 3 is deposited thereon by the CVD method.

Next, as shown in FIG. 1(b), the I/c% silicon nitride 83° oxide film 2 is patterned so as to remain only in the element formation region.

Next, as shown in FIG. 1C, field oxide film 4 is formed by thermal oxidation.

However, in this conventional method, as shown in FIG. 1C, a protuberance A called a bird's head and a bite B into the device region called a bird's beak occur at the end of the field oxide film 4. This protrusion A causes a break in the wiring, and the bite B causes the dimensions of the element area to deviate from the design value.
This has the disadvantage that it hinders the miniaturization and high integration of elements.

The present invention eliminates the above-mentioned drawbacks and develops an oxide film separation method that can prevent or suppress the protrusion of the field oxide film and its encroachment into the device area, and a method for manufacturing semiconductor devices that achieves miniaturization and high integration of devices. It provides:

The method for manufacturing a semiconductor device of the present invention includes the steps of forming an oxide film on a semiconductor substrate, forming a first oxidation-resistant film on the oxide film, and selectively controlling all of the oxidation-resistant film and the oxide film. selectively forming a thin second nitride film on the exposed edge of the field region of the semiconductor substrate; and forming a field oxide film on the exposed semiconductor substrate by performing thermal oxidation. and a step of removing the first and second oxidation-resistant films to form an element.

Next, embodiments of the present invention will be explained using the drawings.

FIGS. 2(a) to 2(e) are cross-sectional views showing main manufacturing steps for explaining the first embodiment of the present invention.

First, as shown in FIG. 2(a) VC, an oxide film 2 with a thickness of 50 OA is formed on a silicon substrate 1 by thermal oxidation.
Thereon, a silicon nitride film 3 is formed as an oxidation-resistant film to a thickness of 100 OA by CVD.

Next, as shown in FIG. 2(b), dry etching is performed by photolithography using a normal photoresist V so that the silicon nitride film 3 is left only in the element formation region. Next, the oxide film 2 is selectively removed by wet etching using a film using the silicon nitride film 3 as a mask. At this time, it is important to expose the surface of the silicon substrate by slightly over-etching so as to penetrate slightly inside the silicon nitride film 3 just below the edge.

Next, as shown in FIG. 2C, a silicon nitride film 5 is formed as a second oxidation-resistant film on the exposed surface of the field region of the silicon substrate. The thickness of silicon nitride film 5 as the second oxidation-resistant film varies depending on the thickness of the field oxide film to be formed later. Usually values are in the tens to hundreds.

The silicon nitride film 5 is made using ultra-high purity ammonia gas.
It is formed by nitriding a silicon substrate at 000°0.

Next, as shown in FIG. 2fd), the silicon nitride film 5 is selectively removed by an anisotropic etching method, and a silicon nitride film 5' is formed only directly under the silicon nitride film 3.

Next, as shown in FIG. 2(e), thermal oxidation is performed to form a field oxide film 4 with a thickness of 1 μm. At this time, the silicon nitride film 5' left at the end of the field region suppresses the progress of oxidation at the end, thereby suppressing the formation of sea urchins, bird's beaks, and bird's heads as shown in the figure.

FIGS. 3(a) and 3(b) are cross-sectional views showing the main manufacturing steps for explaining the second embodiment of the present invention.

The structure shown in FIG. 2(d) is formed using the same method as in the first embodiment.

Next, as shown in FIG. 3fa), the silicon substrate 1 is etched by an anisotropic etching method.

Next, as shown in FIG. 3(b), a field oxide film 4 is formed by thermal oxidation. In this way, the step difference in the field oxide film 4 can be made extremely small, and by properly adjusting the etching depth and oxidation conditions, the step difference can be eliminated.

As explained in detail above, according to the present invention, it is possible to perform oxide film separation that suppresses the occurrence of bird's beaks and bird's heads, and suppresses the penetration of oxide into the element region, and allows for miniaturization and high quasi-integration of elements. This method has a great effect because it provides a method for manufacturing a semiconductor device that achieves this.

[Brief explanation of the drawing]

1(a) to (C) are process cross-sectional views for explaining the conventional oxide film separation method, and FIGS. 21'g(a1 to (e) are cross-sectional views for explaining the entire first embodiment of the present invention. Process cross-sectional diagram, Figure 3 (
a). (b) is a process sectional view for explaining the second embodiment of the present invention. 1...Silicon substrate, 2...River/thermal oxide film, 3...
River: silicon nitride film, 4: field oxide film,
5.5'...Silicon nitride film. Goo / (e) Cow 2 Figure (σ2 Figure 3

Claims (3)

[Claims] (1) forming an oxide film on a semiconductor substrate, forming a first oxidation-resistant film on the oxide film; and selectively removing all of the oxidation-resistant film and the oxide film; selectively forming a thin second nitride film on the exposed edge of the field region of the semiconductor substrate; performing thermal oxidation to form a field oxide film on the exposed semiconductor substrate;
A method for manufacturing a semiconductor device, comprising the step of completely removing the first and second oxidation-resistant films to form an element. (2) Claim No. 1, wherein the second oxidation-resistant film is formed by nitriding using ammonia gas.
A method for manufacturing a semiconductor device according to section 1. (3) The second oxidation-resistant film is selectively removed by an anisotropic dry etching method so that it remains only directly under the first oxidation-resistant film. A method for manufacturing a semiconductor device according to item (1).