JPS6056286B2 - Method for forming electrode windows in semiconductor devices - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of forming an electrode window in a semiconductor device, and particularly to a method of forming an electrode window using a dry etching technique.

In integrated circuits, when aluminum wiring is applied to electrode windows in a thick silicon dioxide film covering a semiconductor substrate,
Due to the steep step around the electrode window, breaks in the aluminum wiring occur. Therefore, a gentle slope is provided around the electrode window to prevent the above-mentioned accident. A method for forming a slope around the electrode window is, for example, by doping the surface of a thick silicon dioxide film covering the semiconductor substrate with P to make the etch rate on the surface of the film larger than that on the deeper part, and then wet selection. A method is used in which electrode windows are formed by etching.

However, the wet etching method does not have good dimensional accuracy because the etching solution penetrates between the photoresist and the silicon dioxide film. Dry etching may be used to improve dimensional accuracy, but it is not possible to provide a gentle slope around the electrode window.

SUMMARY OF THE INVENTION An object of the present invention is to provide a new manufacturing method for forming an electrode window with good dimensional accuracy and having a sloped periphery using a dry etching method.

For that purpose, the method for forming an electrode window in a semiconductor device of the present invention includes depositing a resist film on a silicon dioxide film formed on a semiconductor substrate, and then applying the steps to the resist film located on the electrode window formation region. A hole with an eave formed around the periphery is provided, and the silicon dioxide film is dry-etched using an etching method using a combination of ion irradiation and chemical reaction using the resist film as a mask to form an electrode window with a gentle slope around the periphery of the silicon dioxide film. Examples thereof will be described in detail below.

FIG. 1 is a cross-sectional view after forming an NPN type transistor on a part of a semiconductor substrate, in which 1 is an N type silicon semiconductor substrate, 2 is an N1 layer buried layer, and 3 is an N- type A collector region, 4 is a P-type base region, 5 is an N1 emitter region, 6 is an isolation region, and 7 is a silicon dioxide (SiO0) film covering the surface.

Next, the process of forming a gently sloped electrode window at the position indicated by the dotted line on the silicon dioxide film 7 will be described. (1) First, a resist film 8 that is sensitive to electron beams is deposited on the silicon dioxide film 7 as shown in FIG. Do this.

At this time, if an exposure dose (~10-4 Cron/Cd) that is about 3 to 4 times the required sensitivity of the resist is applied, the scattering of the electron beam in the resist will cause the resist to become opaque during development as shown in Figure 3. A reverse taper is generated around the hole 9 made in the membrane 8, and an eave 91 is formed. (2) Silicon dioxide film 7
A semiconductor substrate with a resist film 8 on which holes 9 are formed is mounted on the cathode surface of a plasma etching apparatus equipped with two opposed planar electrodes. Then, Freon gas (CxF2x+2(x=
1, 2, 3), (HF3, etc.) is sent in, and the internal gas pressure is set to (0.1 to 1.0 [TOrr]).
After maintaining the temperature at a certain level, a high frequency voltage is applied between the electrodes. Application of a high-frequency voltage causes internal gas discharge, and ions or radicals generated by this gas discharge are accelerated in the cathode dark region and impinge on the semiconductor substrate mounted on the cathode surface in a substantially perpendicular direction. (3) The incident ions or radicals irradiate the silicon dioxide film 7 through the holes 9 provided in the resist film 8 and start etching the film 7.

The etching reaction at this time is thought to be due to the chemical reaction between CF4 radicals generated by dissociation of the etching gas and the silicon dioxide film to generate volatile SiF4. Furthermore, since the gas pressure within the plasma etching apparatus is relatively high as described above, some of the radicals are also supplied to the silicon dioxide in the eaves, and the area under the eaves is also shallowly etched. Therefore, as shown in FIG. 4, the silicon dioxide film 7 has a gently sloped portion 10.
It is etched while producing. Note that due to this etching, the resist film 8 is also consumed from the dotted line to the solid line. However, since the amount is small, the dimensional accuracy of the pattern is maintained. (4) Continue this etching and stop the etching when the etched region reaches the silicon semiconductor substrate.

FIG. 5 is a cross-sectional view of the semiconductor substrate immediately after etching is completed. As is clear from FIG. 5, the width of the lower surface of the electrode window 11 made in the silicon dioxide film 7, that is, the portion in contact with the semiconductor substrate is the width d of the upper end of the hole 9 originally made in the resist film 8. almost matches. A gentle slope 12 is formed around the opened electrode window 11. (5) After that, the semiconductor substrate is taken out from the plasma etching apparatus, the resist film 8 is peeled off, and aluminum wiring is applied to the electrode window 11 portion using a conventional method.

Note that it is impossible to make a hole with a reverse taper in a resist film using a normal photo process.

However, in the method of the present invention, all that is required is to provide an eaves over the holes drilled in the resist film so that there are parts of the silicon dioxide film that are not exposed to ion irradiation. If provided,
As shown in FIG. 6, two types of photoresist films 81 and 82 having different sensitivities were deposited on the silicon dioxide film 7, and the width d1 of the hole made in the photoresist 81 was made in the photoresist film 82. If the eaves 13 are formed with a width larger than the width y of the hole, the same effect as in the embodiment described above can be expected. As explained in detail above, according to the present invention, since dry etching is performed, the dimensional accuracy of the electrode window formed in the silicon dioxide film is better than that of the electrode window formed by wet etching. In addition, since a gentle slope is formed around the electrode window, no breaks occur in the aluminum wiring formed in the electrode portion.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 5 are process sectional views for explaining an embodiment of the present invention, and FIG. 6 is a partial sectional view of another embodiment.

1 is a silicon semiconductor substrate, 7 is a silicon dioxide film, 8 is a resist film, 9 is a hole, 91 is an eave, 11 is an electrode window, and 12 is an inclined surface.

Claims (1)

[Claims] 1. After depositing a resist film on the silicon dioxide film formed on the semiconductor substrate, a hole with an eaves around the periphery is provided in the resist film located on the electrode window formation region, and the silicon dioxide film is deposited using the resist film as a mask. A method for forming an electrode window in a semiconductor device, comprising etching the film using a dry etching method using a combination of ion irradiation and chemical reaction to form an electrode window with a gentle slope around the periphery in a silicon dioxide film.