JPH0563935B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of forming a contact hole for contacting an electrode.

Conventional Structures and Problems Conventionally, in forming contact holes in insulating films on semiconductor devices, due to miniaturization of processing dimensions, anisotropic etching without side etching using a parallel plate type dry etching system has recently become possible. It has been put into practical use.

However, in anisotropic etching of contact holes, it is difficult to obtain sufficient etching selectivity for the underlying etching film of the photoresist mask used as an etching mask, which causes significant damage to the photoresist mask due to gas plasma, which causes a drop in breakdown voltage of the underlying interlayer insulating film. It is becoming. Further, the contact hole formed by anisotropic etching has a steep hole edge, which causes a problem in that the aluminum wiring is easily disconnected.

Figure 1 is a cross-sectional view of a contact hole formed using a conventional anisotropic etching method.
In the figure, 1 is a silicon substrate, 2 is a silicon oxide film for a gate, 3 is a polysilicon film which is a gate electrode,
4 is an aluminum film for wiring, 5 is a CVD silicon oxide film as an interlayer insulating film, and 6 is a contact hole. As the pattern size of the contact hole 6 becomes finer and the thickness of the interlayer insulating film 5 becomes thicker, a deep contact hole must be formed, and as a result, the aluminum wiring is likely to break at the edge of the hole. .

Purpose of the Invention The present invention aims to solve the above-mentioned problems, and by using a first etching mask that has high etching selectivity with respect to the insulating film, pattern dimensions can be achieved without reducing the withstand voltage of the interlayer insulating film. A method for manufacturing a semiconductor device that can form contact holes with high precision and further perform taper etching by controlling the etching selectivity between the resist and the insulating film using a second etching mask made of photoresist. The purpose is to provide the following.

Structure of the Invention In the present invention, a polycrystalline silicon film or an aluminum film, which is a first etching mask material, is formed on an insulating film. These films have extremely high etching selectivity compared to a photoresist mask, so they can be formed with a thin film thickness, and the first etching mask having high pattern dimensional accuracy is formed by anisotropic etching. A second etching mask having contact windows smaller than the first etching mask pattern size is then formed using a photoresist mask. After that, using the first and second etching masks as masks, dry etching was performed using gas plasma in which oxygen gas was added to fluorine gas in order to reduce the dry etching selectivity between the resist and the insulating film. An opening in the insulating film is formed.

DESCRIPTION OF EMBODIMENTS Embodiments of the present invention will be described below, taking as an example a case where a contact hole is formed in a silicon substrate.
First, as shown in FIG. 2a, polycrystalline silicon 13, which will serve as a first etching mask, is formed to a thickness of about 2000 to 5000 Å on the surface of interlayer insulating film 12 on semiconductor substrate 11 by low pressure CVD. Next, the polycrystalline silicon 13 is anisotropically etched using the photoresist film 14 to form a first etching mask using the polycrystalline silicon 13 (FIG. 3(b)). Furthermore, a second etching mask 15 having a contact window smaller than that of the first etching mask 13 is formed using a photoresist film by a photolithography process (FIG. 3(c)). For such a pattern having two layers of etching masks 13 and 15, oxygen gas was added to the fluorine gas plasma in order to accelerate the etching of the resist etching mask 15 and reduce the etching selectivity with respect to the insulating film. Etching is performed using plasma. At this time, the etching mask 15 is etched not only in the vertical direction but also in the horizontal direction, and the resist pattern edge recedes. By utilizing this receding of the resist pattern edge, the etched shape of the insulating film becomes tapered (see d in the figure).

In this example, the etching rate ratio between the resist and the insulating film, that is, the etching selectivity was approximately
Control the amount of oxygen gas added so that the ratio is 1.5:1,
The taper angle of the contact hole was approximately 70 degrees.
According to the present invention, even if the resist etching mask 15 disappears during dry etching of the insulating film, the etching mask 13 exists, and the etching of the insulating film does not proceed, and the breakdown voltage of the interlayer insulating film does not decrease due to pinholes etc. do not have. Next, the first and second etching masks 13 and 15 are removed to obtain a tapered contact hole 16 (see e in the figure). Then, an aluminum film 17 as an electrode is formed on this (FIG. 5f).

Effects of the Invention According to the method of the present invention, since the first etching mask has high etching selectivity, its film thickness can be reduced, and a fine etching pattern can be formed using a photoresist film. Furthermore, since the etching mask has a two-layer structure, the influence of etching on the interlayer insulating film can be reduced. Furthermore, by controlling the etching selectivity of the resist and insulating film using the second etching mask, the taper angle of the contact hole can be independently controlled. Furthermore, since the first etching mask is formed under the second etching mask, the thickness of the photoresist film that is the second etching mask can be made thinner, making it easier to pattern very fine contact windows using the photolithography process. This has the effect of significantly improving the quality of semiconductor devices, such as reducing breakdown voltage due to dry etching of interlayer insulating films and breaking aluminum wiring, and improving pattern processing dimensional accuracy.

[Brief explanation of the drawing]

FIG. 1 is a sectional view for explaining a conventional contact hole forming method, and FIGS. 2 a to 2 f are process sectional views showing a method for manufacturing a semiconductor device according to the present invention. 11...Semiconductor substrate, 12...Interlayer insulating film, 1
3...first etching mask, 15...second etching mask, 17...aluminum film.

Claims (1)

[Claims] 1. A step of forming an insulating film on a semiconductor substrate, and then forming a first etching mask having higher etching selectivity than a photoresist film for forming a contact hole, the first etching a step of forming a second etching mask of a photoresist film with a window for forming a contact hole smaller than the mask; and a step of dry etching the insulating film while performing lateral etching on the window of the second etching mask. A method for manufacturing a semiconductor device, comprising: 2. The method of manufacturing a semiconductor device according to claim 1, wherein the first etching mask is a polycrystalline silicon film.