JPS6161431A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To improve the flatness of the surface of a polycrytstalline silicon film in a groove by a method wherein a silica thin film is formed by spin coating after the formation of a polycrystalline silicon film, the silica thin film is subjected to etching foir the partial exposure of the surface of the polycrystalline silicon film, and then the polycrystalline silicon film, and then the polycrystalline silicon film is subjected to etching. CONSTITUTION:A polycrystalline silicon film 16 is formed on a silicon substrate 11 provided with a silicon oxide film 12, silicon nitride film 13, and a groove, whereafter a silica thin film 18 is formed by the spin coating mkethod. The silica thin film 18 is then subjected to anisotropic dry etching, for the exposure of the polycrystalline silicon 16 except in the groove. A process follows wherein the polycrystalline silicon film 16 is subjected to etching by anisotropic plasma IA. A relatively flat surface appears in the groove because at its center etching is less effective due to the remaining silica film 18. An element isolating region is formed when the remaining polycrystalline silicon film 16 is converted into a silicon oxide film 17 by thermal oxidation.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for forming a buried polycrystalline silicon film for element isolation.

(Prior art) Conventionally, as a method for forming a buried polycrystalline silicon film for element isolation, a trench formed on the surface of a semiconductor substrate is filled with a polycrystalline silicon film, and the polycrystalline silicon film on an active region is removed by etching. A method is mainly used in which a polycrystalline silicon film remains only inside. In this method, the step of etching and removing the polycrystalline silicon film on the active region is difficult, and various methods have been proposed. For example, after forming a polycrystalline silicon film, there is a method of etching the entire surface, taking advantage of the difference in film thickness between the trench and the active region, leaving the polycrystalline silicon film only in the trench. (See, TEDM
82, 9-6) The above method will be explained in detail with reference to FIGS. 1 to 4.

FIG. 1 shows that after a silicon oxide film 12 and a silicon nitride film 13 are formed on the surface of a silicon semiconductor substrate 11, the silicon nitride film 13, silicon oxide M12, and silicon substrate 11 are partially etched in sequence using a photo process method. After forming a groove 14 having a desired depth on the surface of the substrate, a silicon oxide film 1 is formed on the surface of the groove 14 by thermal oxidation.
This is where 5 was formed. Next, a polycrystalline silicon film 16 is formed on the substrate surface to a desired thickness (FIG. 2). Next, the polycrystalline silicon film is partially removed by plasma etching to expose the surface of the silicon nitride film 13. As a result, since the effective 1/CM thickness is thick in the trench, the trench is filled with a polycrystalline silicon film (FIG. 3). After that, the surface of the polycrystalline silicon film is selectively oxidized thermally to form a silicon oxide film 17.
form.

Through the above steps, a buried polycrystalline silicon film is formed (fourth
figure).

According to the above-mentioned conventional manufacturing method, the surface shape of the polycrystalline silicon film remaining in the groove is a direct copy of the surface shape when the polycrystalline silicon film was formed, and even if the surface shape around the groove is flat, The central part has a deeply etched shape. This shape does not change in the subsequent element forming process, and has become a major problem, such as causing defects such as pattern breakage in the element forming process and blanking between wires in the wiring process.

(Objective of the Invention) An object of the present invention is to provide a novel manufacturing method that eliminates the aforementioned defects and flattens the surface of the buried polycrystalline silicon film.

(Structure of the Invention) The main feature of the present invention is that after forming a polycrystalline silicon film,
A step of forming a silica thin film on a polycrystalline silicon film by spin coating, a step of etching the silica thin film to partially expose the surface of the polycrystalline silicon film, and then etching the polycrystalline silicon film. It is characterized by having a process.

(Operations and Effects of the Invention) When the manufacturing method of the present invention is used, since the silica film is present in the trench and on the polycrystalline silicon film, the silica film acts as a partial mask material for etching, and the remaining polycrystalline silicon film acts as a partial mask material for etching. It becomes possible to flatten the surface of the crystalline silicon film. Tsuma-υ,
The difference in etch rate between the polycrystalline silicon film and the silica film can be changed arbitrarily by changing the plasma etching conditions.By setting this etch rate difference to a desired value, the polycrystalline silicon film at the center of the groove can be Reduce the amount of etching,
It becomes possible to perform flattening.

In addition, the selection ratio between the silica film and the polycrystalline silicon film can be increased.
Planarization can also be achieved by etching a polycrystalline silicon film by a combination of anisotropic plasma etching and isotropic plasma etching.

As a result, the surface of the polycrystalline silicon film within the groove is not flat, which improves the processing accuracy in the subsequent element forming process.
A system that can significantly reduce disconnection defects in the wiring process.
As a result, it becomes possible to significantly improve yield.

(Example) Next, it will be explained in detail using examples.

The process up to the step of forming polycrystalline silicon and a film on a silicon substrate is the same as the conventional manufacturing method (FIGS. 1 and 2) (FIG. 5). Next, a silica thin film 18 is formed by spin coating. When a solution with a silica concentration of about 6 J% is applied at a rotational speed of 300 Orr and pm, the film thickness on the flat part is approximately so! , about 2 soo at the center of the groove! It becomes a tax (Figure 6). Thereafter, the silica film is etched using anisotropic dry etching. CF, and H! Etching is performed for 1 minute using plasma etching using a mixed gas. Then, the silica film is etched to a thickness of about 50A, and the polycrystalline silicon surface other than the ports is exposed (FIG. 7).

Next, the polycrystalline silicon film is coated with anisotropic plasma 1. A) Etching. At this time, the selectivity ratio between the polycrystalline silicon film and the silica film is set to about 3 to 4, and the etching rate of the silica film is made slower than the etching rate of the polycrystalline silicon film.

For example, CC4F +0. (10%) etching gas and a vacuum degree of 0.4 to 0.6 Torv are suitable. As a result, the amount of etching in the central part of the groove is smaller than that in other parts due to the silica film, resulting in a smooth and relatively flat shape as shown in FIG. After this, the remaining polycrystalline silicon film surface is thermally oxidized, and the silicon oxide film 1
By forming 7, an element isolation region is formed (FIG. 9).

(Summary of the Invention) As described in detail above, according to the present invention, after forming a trench for element isolation on the surface of a silicon substrate, an insulating film is formed on the surface of the trench, and then a trench embedding film is formed on the surface of one substrate. A polycrystalline silicon film is formed, and a silica film pattern is formed near the center of the groove on the polycrystalline silicon film. Then, when the polycrystalline silicon film is etched, a groove is filled in with the polycrystalline silicon film.

This improves the flatness of the surface of the polycrystalline silicon film within the buried trench, facilitating the subsequent device formation process).
It is also possible to significantly reduce disconnection defects in the wiring process, and it is therefore expected to improve yield.

The explanation was about the method of using silica membrane, but
Alternative #) A similar effect can be expected by using a VC resist film. Also, the same result can be obtained even if holes are formed in place of grooves! It is easy to guess that he will be rejected.

[Brief explanation of the drawing]

1 to 4 are cross-sectional views showing a manufacturing method according to the prior art, and FIGS. 5 to 9 are cross-sectional views showing main steps of a manufacturing method according to an embodiment of the present invention. 11...Semiconductor substrate, 12,15.17...
... silicon oxide film, 13 ... silicon nitride film, 14 ... groove, 16 ... polycrystalline silicon film, 18 ... group silica film.

Claims (1)

[Claims] 1. A step of forming a groove or a hole on the surface of a semiconductor substrate, a step of forming a polycrystalline silicon film on the surface of the semiconductor substrate,
In the method for manufacturing a semiconductor device, the method includes the step of etching the polycrystalline silicon film and leaving the polycrystalline silicon film in the groove or hole, before the step of etching the polycrystalline silicon film. Manufacturing a semiconductor device comprising the steps of: forming a silica thin film on a crystalline silicon film by spin coating; and etching the silica thin film to partially expose the surface of the polycrystalline silicon film. Method. 2. A method of manufacturing a semiconductor device according to claim (1), characterized in that a photoresist film is used in place of the silica thin film.