JPS6279625A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To make the side of a polysilicon pattern a tapered surface uniformly within a wafer and between the wafers by making the surface layer of the polysilicon pattern formed on the nitride film on a semiconductor substrate an insulator by oxidization at a low temperature. CONSTITUTION:The first gate oxide film 2 is formed on a semiconductor substrate 1 and a thin silicon nitride film 3 is formed on the film 2. The first polysilicon film 4 which is to be made an electrode is formed on the film 3 and an impurity is introduced in high concentration. Then, the first gate electrode and the film 4 except where is to be made a wiring are etched and a pattern is formed. Then, a polysilicon oxide film 5 is formed by oxidizing the film 4 at a comparatively low-temperature. Since the film 5 is formed by comparatively low-temperature oxidization, it is thin at the region shown by (a') in the figure and the side of residual polysilicon is tapered. Then, the film 5 is totally removed and the first polysilicon film 4' which has the side of a tapered surface can be obtained.

Description

[Detailed description of the invention] (Industrial use portion).

The present invention relates to a method of manufacturing a semiconductor device, and more particularly, to a method of forming a tapered side surface of polysilicon.

(Prior art) Conventionally, in order to make the side surface of polysilicon tapered, for example, it is shown in 1985 Vol. After forming a non-doped CVD oxide film on polysilicon, photoresist buttering is performed, and undercuts are created by wet etching the oxide film.
By dry etching the polysilicon, the sides of the polysilicon were made into a tapered shape.

Due to this taper, the etching residue during etching of the second layer polysilicon and the KT wiring was made into an area.

(Problems to be Solved by the Invention) - However, in the above method, the thickness of the CVD oxide film on polysilicon within the wafer and the etching rate of the etching solution used for wet etching to remove the CVD oxide film Since the taper angle of silicon depends greatly, there is a problem in that it is difficult to form polysilicon with a uniform taper angle.

The present invention has been made in view of the above points, and its object is to taper the sides of a polysilicon pattern with good uniformity within a wafer and between wafers, and in a simple manner.

(Means for Solving the Problems) In the present invention, a nitride film is formed on a semiconductor substrate, a polysilicon pattern is formed on the nitride film, and then the surface layer of the polysilicon pattern is made into an insulator by low-temperature oxidation. ,
This insulator is then removed.

(Function) When the surface layer of a polysilicon pattern formed on a nitride film is made into an insulator by low-temperature oxidation, this insulator is formed so that the side surface of the remaining polysilicon of the polysilicon pattern becomes tapered. Therefore, next, by removing the insulator, a polysilicon pattern made of residual polysilicon and having tapered sides is obtained.

(Example) An embodiment of the present invention will be described below with reference to FIG.

FIGS. 1(a) to 1(e) are cross-sectional views illustrating steps when the present invention is applied to a method of manufacturing an MO8 semiconductor device having a multilayer polysilicon structure containing high concentration impurities.

First, in FIG. 1(a), reference numeral 1 denotes a silicon single crystal semiconductor substrate (hereinafter abbreviated as substrate), and a first gate oxide film 2 is formed on this substrate 1 by thermal oxidation. In order to increase the capacitance of the gate 1, a thin silicon nitride film 3 having a high dielectric constant is formed. Thereafter, a silicon nitride film 3 is applied to improve the dielectric strength of the first gate.
may be oxidized under conditions such that an oxide film of 10 to 30 sizes is formed. A first silicon film 4 serving as an electrode is formed on the first gate oxide film 2 and silicon nitride film 3, which are the first gate films, and this first polysilicon film 4 is made to have conductivity. In order to lower the resistance, impurities such as phosphorus are added to the 3 x 1020 layer using thermal diffusion or ion implantation.
It is introduced at a high concentration of about cm-3 to 6 x 1020 cm-3.

Next, as shown in FIG. 1(b)K, the first portion of the silicon film 4 other than the portion that will become the first gate electrode and wiring is etched by photolithography using the photoresist as a mask, and the photoresist is removed. form a pattern.

Next, the patterned first polysilicon film 4
is oxidized at a relatively low temperature, for example, about 800 to 850°C, under oxidation conditions that form an approximately 1500 to 2500× oxide film, as shown in FIG. 1(c). A polysilicon oxide film 5 (insulator) is formed on the surface of the polysilicon film 4. At this time, parts other than the first polysilicon film 4 are covered with the silicon nitride film 3 and are not oxidized. Furthermore, since the polysilicon oxide film 5 is formed by oxidation at a relatively low temperature,
The portion indicated by A in the figure (the portion in contact with the silicon nitride film 3) is thinned, and as a result, the side surface of the remaining polysilicon of the first polysilicon film 4 is tapered.

Next, as shown in FIG. 1(d), the entire polysilicon oxide film 5 is removed using buffered HF. As a result, a first polysilicon film 4' made of residual polysilicon and having tapered side surfaces is obtained. At this time, the portion other than the polysilicon oxide film 5 is covered with the silicon nitride film 3, and since the functionalized film is difficult to be etched by buffer HF (etchant), it is hardly etched.

Next, as shown in FIG. 1(e), the first bolt J]
Using the silicon film 4' as a mask, the silicon nitride film 3, which is the first gate film, and the first gate oxide film 2 are etched. Thereafter, by performing oxidation at 9000C to 1000C, a second gate oxide film 5 is formed on the substrate 1, and an interlayer insulating film 6 is formed on the first polysilicon film. At this time, the second gate oxide film 5 on the substrate 1 is formed to a thickness of 200 to 400λ, while the interlayer tl! The I edge film 6 is formed to have a thickness of 600 to 1200λ. Further, since this oxidation is performed at a relatively high temperature of 900 to 1000 DEG C., the interlayer insulating film 6 is uniformly formed on the first polysilicon film.

The bale and the second polysilicon film 7, which will become the second electrode, are soaked in salt, impurities are introduced, and a pattern is formed by photolithography. At this time, as shown in the figure, since the side surface of the first polysilicon film 4' is tapered, it is possible to reduce the etching residue when the second polysilicon film 7 is etched. Become.

After that, although not shown in the figure, a diffusion layer, an intermediate insulating film,
A metal pattern for wiring and a protective oxide film are formed using known techniques to complete the MO8 semiconductor device.

(Effect of the invention) As explained in detail above, according to the method of this invention,
The sides of the polysilicon pattern can be tapered by a simple method of low-temperature oxidation of the polysilicon pattern formed on the nitride film and removal of the insulator formed thereby. Further, according to this method, the side surfaces of the polysilicon patterns can be tapered with good uniformity within a wafer and between wafers.

[Brief explanation of drawings]

(Drawings) FIG. 1 is a process sectional view showing an embodiment of the method for manufacturing a semiconductor device of the present invention. DESCRIPTION OF SYMBOLS 1... Silicon single crystal semiconductor substrate, 2... First gate oxide film, 3... Silicon nitride film, 4, 4'...
First polysilicon film, 5... polysilicon oxide film. Representative Patent Attorney Hiroshi Kikuchi,,-1・
-Nini.

Claims (1)

[Claims] (a) A step of forming a nitride film on a semiconductor substrate; (b)
a step of forming a polysilicon pattern on the nitride film; (c) a step of tapering the side surface of the remaining polysilicon by making the surface layer of the polysilicon pattern into an insulator by low-temperature oxidation; and (d) after that. , a step of removing the insulator.