JPH05304217A - Etching method for insulation film - Google Patents

Abstract

PURPOSE:To provide an etching method for insulation film through which a reverse conical through hole having constant aperture can be made with an insulation film. CONSTITUTION:An interlayer insulation film 3 is formed on a conductor layer 2 formed on a semiconductor substrate 1 and an etching mask 4 of silicon nitride is formed thereon. When the insulation film 3 is etched selectively using the etching mask 4, an ECR etching system is used and RF power is lowered at the initial and final stages of etching. Alternatively, microwave power is increased at the initial and final stages of etching. This method provide a through hole having constant aperture irrespective of the thickness of insulation film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulating film etching method, and more particularly to an etching method for forming a through hole in an interlayer insulating film of a semiconductor integrated circuit device.

[0002]

2. Description of the Related Art Through holes in an interlayer insulating film in a semiconductor integrated circuit device are etched so that the cross-sectional shape thereof is an inverted conical shape (surveillance shape). The reason is that in the sputtering method used to form a conductor layer on the interlayer insulating film after the opening of the through hole, it is necessary for the inner surface of the through hole unless the through hole has a cross-sectional shape to some extent. This is because a conductor film having a different thickness cannot be attached. As a method of etching the through hole in a scuttle shape in this manner, conventionally, a method has been employed in which the mask film used as a mask during the etching of the through hole is laterally etched as the etching progresses.

2A to 2E are diagrams showing an example thereof. First, as shown in FIG. 2A, the conductor layer 2 is formed on the silicon substrate 1, the interlayer insulating film 3 is formed, and then the etching mask 4 is formed on the interlayer insulating film 3. At this time, an etching mask having an etching rate that is about 1/3 to 1/4 lower than that of the interlayer insulating film is provided. For example, when a polyimide film is used as the interlayer insulating film, a plasma silicon nitride film is used for the etching mask 4.

Next, as shown in FIG. 2B, a plasma silicon nitride film 4 in a desired region is formed by a photolithography technique.
To remove. Further, as shown in FIG. 2 (c), a parallel plate type reactive ion etching apparatus is used to remove CF ₄ by about 40
%, O ₂ of about 60% and a pressure of 100 mtorr for 10 m
A high frequency power of about w / cm ² is introduced, and the interlayer insulating film 3 is etched using the plasma silicon nitride film 4 as a mask. At this time, the silicon nitride film is about 400 A / min, and the photoresist is about 600 A / min. Then, as shown in FIG. 2D, the opening region expands as the silicon nitride film is etched in the lateral direction, whereby the interlayer insulating film opens like a mortar. Thereafter, as shown in FIG. 2 (e), the the CF ₄ to about 80
%, Oxygen gas of about 20% is introduced, and plasma etching is performed by a barrel type dry etching apparatus having a pressure of about 0.6 torr to remove the silicon nitride film.

[0005]

However, such a conventional etching method has a problem that the through-hole opening diameter increases in proportion to the increase in etching time. This is an unavoidable problem because the mask is etched in proportion to the etching of the interlayer insulating film as described above. On the other hand, the interlayer insulating film is subjected to flattening the step of the underlying layer of the interlayer insulating film so that the upper conductive film can be covered with a sufficient film thickness.
There is a portion where the thickness is partially different. As a result, the through-hole portion at the crest of the step portion is etched more than necessary until the through-hole located at the valley of the step portion of the underlayer is opened, and as shown in FIG. The bottom is small in the valley and the bottom is large.

From the viewpoint of cost, the controllability of the film thickness of the interlayer insulating film is inevitably about ± 10% of the regulation, but as the film thickness increases or decreases, the etching time of the through hole is set. I need to start over. Therefore, as shown in FIG. 3B, there is a problem that the size of the upper portion of the through hole changes.
As described above, the difference in the opening diameter of the through hole imposes restrictions on the characteristics of the arrangement of the elements and wirings of the semiconductor integrated circuit device, which makes the layout design difficult. An object of the present invention is to provide an insulating film etching method capable of forming through holes formed in an insulating film with a uniform opening diameter.

[0007]

According to the present invention, when the insulating film is selectively etched using an etching mask, EC
The R etching apparatus is used to reduce the RF power in the initial stage of the etching and reduce the RF power in the final stage of the etching. Alternatively, the microwave power is increased at the beginning of etching and the microwave power is increased at the end of etching. As the etching gas, an etching gas mainly containing oxygen gas and fluoride gas is used.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a part of a semiconductor chip showing an embodiment of the present invention in the order of manufacturing steps. First, as shown in FIG. 1A, a conductor layer 2 is formed on a silicon substrate 1, and a polyimide solution is applied on the conductor layer 2 and heated at about 400 ° C. to form a polyimide interlayer insulating film 3 at about 1 μm. It is formed thick. Then, as shown in FIG. 1B, plasma C is formed on the interlayer insulating film 3.
The silicon nitride film 4 is formed to a thickness of about 0.2 μm by the VD method.
Then, as shown in FIG. 1C, after the photoresist 5 is applied, the photoresist 5 is removed only in the through hole region by using the photolithography technique, and the ordinary reactive ion etching method is mainly used by using CF ₄ gas. Then, the silicon nitride film 4 in the photoresist opening region is removed.

Then, as shown in FIG. 1 (d), after removing the photoresist 5 with an organic solvent, an ECR etching apparatus is used, and oxygen gas containing 10% of SF ₆ gas is used as the first stage etching, and the pressure is 1 mtorr. and then, to set the microwave 2.45 GHz _Z was 200w applied magnetic field 875 Gauss immediately above the wafer to generate the etching gas plasma by electron resonance is about 0.3μm etched in the polyimide depth. At this time, SF _{6 is used} as an etching gas component.
The reason for mixing the gas is that polyimide for semiconductors generally contains a silicon component. Fluorine gas is not particularly required as long as the polyimide film does not contain a silicon component.

Further, as shown in FIG. 1E, RF power is applied to the substrate through the substrate holder as the second stage etching. RF power 100 mw / cm of this time 13.56MH _Z
^{2 was} applied to further etch the polyimide by 0.3 μm. Then, as shown in FIG. 1 (f), RF power was set to 600 mw / cm ² as the third stage etching and 0.8 μm etching was performed in terms of polyimide etching. The substrate bias at this time was about 100V.

As described above, by increasing the RF power, the number of etchants involved in etching was relatively large in the first-step etching, whereas the ion etching effect was large in the third-step etching, and the etching was large. Etching is achieved. At this time, if the interlayer insulating film is thick, the third stage etching time may be increased according to the increase in the film thickness. In the third-stage etching, the opening diameter of the silicon nitride film mask hardly changes even if the etching time is increased, so that the opening diameter of the through hole does not fluctuate in the vertical direction of the sectional structure. Here, the same effect can be obtained by increasing the microwave power in the initial stage and decreasing it in the final stage instead of increasing the RF power.

A silicon oxide film may be used as the interlayer insulating film, and a photoresist film may be used as the etching mask. That is, after forming an interlayer insulating film and a photoresist mask in the same manner as in the above embodiment, through hole etching is performed using the ECR etching apparatus as in the above embodiment. Further, regarding the etching conditions at this time, the point different from the above embodiment is the composition ratio of the etching gas. In this case, in order to increase the etching rate of the silicon oxide film as compared with photoresist, CF ₄ 80%,
By using a gas containing 20% of O _2, a through hole having the same shape as that of the above-mentioned embodiment was obtained.

When the siloxane-containing polyimide film is used as the interlayer insulating film, the following can be used as the etching mask. A silicon nitride film formed by plasma CVD, a silicon nitride / oxide film formed by plasma CVD, a silicon oxide film formed by plasma CVD, an aluminum film formed by sputtering, a tungsten silicide film formed by sputtering, and a titanium film formed by sputtering. Further, as an interlayer insulating film, a silicon oxide film formed by thermal oxidation of silicon, a silicon oxide film containing phosphorus and boron formed by a thermal CVD method, a silicon nitride film formed by a plasma CVD method, a silicon nitride / oxide film formed by a plasma CVD method, and a plasma CVD method.
In the case of a silicon oxide film formed by the method, a silicon oxide film formed by a solution coating method, or a laminated film of these, a photoresist film can be used as an etching mask.

[0014]

As described above, according to the present invention, the insulating film is etched while gradually changing the RF power or the microwave power in the ECR etching apparatus.
The insulating film can be etched with almost no etching mask, and the opening diameter is uniform even if the through-hole etching time is changed due to the local film thickness difference of the insulating film or the film thickness deviation at the time of forming the insulating film. Since such a through hole is formed, it has the effect of facilitating the design of the semiconductor integrated circuit device.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention in the order of manufacturing steps.

FIG. 2 is a cross-sectional view showing a conventional manufacturing method in process order.

FIG. 3 is a cross-sectional view for explaining problems of the conventional method.

[Explanation of symbols]

 1 Silicon Substrate 2 Conductor Layer 3 Interlayer Insulation Film 4 Silicon Nitride Film 5 Photoresist

Claims (3)

[Claims] 1. A method comprising the steps of forming an insulating film on a semiconductor substrate and forming an etching mask on the insulating film in a desired pattern, and selectively etching the insulating film using the etching mask. An etching method for an insulating film, characterized in that an ECR etching apparatus is used for etching, and RF power is reduced at an initial stage of etching and RF power is reduced at a final stage of etching. 2. A method comprising the steps of forming an insulating film on a semiconductor substrate and forming an etching mask on the insulating film in a desired pattern, and selectively etching the insulating film using the etching mask. An etching method of an insulating film, characterized in that an ECR etching apparatus is used for etching, and microwave power is increased at an initial stage of etching and is increased at a final stage of etching. 3. The method for etching an insulating film according to claim 1, wherein an etching gas mainly composed of oxygen gas and fluoride gas is used for etching in the ECR etching apparatus.