JPS60192334A - Dry etching method - Google Patents

Abstract

PURPOSE:To enable to bring the shape of etching cross-section of an insulating film into an arbitrarily and easily controllable state using a cylindrical plasma etching device by a method wherein the amount of side etching given to the film to be etched is controlled by the partial voltage ratio of the inert gas for reaction gas. CONSTITUTION:When a microscopic work is going to be performed on the insulating film consisting of a poly silicon film, a silicon nitride film, a silicon nitride film and the like using a cylindrical plasma etching device, the partial voltage ratio of dilute gas with Freon gas is brought to 1 or above by performing an etching wherein dilute gas is mixed to Freon gas, for example, if said insulating film is to be formed in the vertical cross-sectional form same as the size of photoresist coated on the insulating film. Also, when an inclination is given to the cross-sectional form of the insulating film for the purpose of preventing generation of an unsatisfactory step coverage, a plasma etching is performed in the state wherein the partial voltage ratio is brought to 1 or below. Through the above-mentioned procedures, the cross-sectional form after etching performed on the insulating film can be determined arbitrarily.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field to Which the Invention Pertains The present invention relates to a dry etching method for finely processing thin films such as insulating films provided on semiconductor devices.

[Prior art and its problems]

For example, improvements in etching technology are expected as a microfabrication method for forming fine patterns in highly integrated semiconductor integrated circuits. Generally, in this etching process, an insulating film 2 is provided on the surface of a silicon substrate 1, as shown in the cross-sectional view in FIG.
Etching is performed to remove unnecessary parts of the
Etching methods include wet etching, which utilizes a chemical reaction using a chemical solution, and dry etching, which uses radicals by discharging gas at high frequency in a reduced pressure container.

However, in wet etching, the insulating film 2 to be etched is
Since the etching speed in the vertical and horizontal directions progresses at approximately the same rate in both directions, the insulating film 2 has a trapezoidal cross-sectional shape with respect to the silicon substrate 1, as shown in the cross-sectional view of FIG. This tends to cause undercutting, resulting in a finished product that is smaller than the resist 3 dimension. On the other hand, with the increase in the diameter of silicon wafers, dry etching methods, which are superior in etching accuracy and etching uniformity, have come into widespread use. For dry etching, for example, a cylindrical plasma etching apparatus whose main part is shown in cross section in FIG. 3 is used. In FIG. 3, a wafer 7 supported by a wafer boat 6 is placed through an etch tunnel 5 in a quartz tube 4 for plasma protection, and is reacted by high frequency output from a high frequency electrode 8 provided on the outer periphery of the quartz tube 4. For example, the fluorine of the freon (CCFa) gas containing oxygen, which is introduced from the gas port 9, becomes active radicals and etches the wafer 7, but in this method, as in the case of wet etching, etching is performed laterally from the edge of the mask material. There is a problem in forming a fine pattern with large intrusion.

In order to avoid this problem, etching can be made anisotropic, and parallel plate type reactive ion etching has also been carried out, which causes less side etching in accordance with the dimensions of the photoresist. For example, FIG. 4 shows a cross-sectional view of the main parts of this parallel plate type reactive ion etching apparatus.
The high-frequency electrode 11 and the wafer to be etched 12 are placed opposite each other in the reaction vessel 10, and an etching gas is introduced from the reaction gas port 13, and a high-frequency voltage is applied to the wafer 1.
2 etching is performed.

However, in this dry etching method, as shown in FIG. 5, after etching, for example, the polysilicon oxide film 2 provided on the silicon substrate 1 is vertically etched directly under the photoresist 3, but the resist 3 is removed in the subsequent process. When the wiring metal film 14 is deposited, the step coverage etching method as shown in FIG. 6 can be used as quickly as a conventional plasma etching device, but it has a lower throughput than, for example, cylindrical plasma etching. %, and it has drawbacks such as difficulty in controlling the amount of side etching of the insulating film.

OBJECT OF THE INVENTION The object of the present invention is to eliminate the above-mentioned drawbacks and to provide a dry etching method that allows etching of an insulating film to any desired cross-sectional shape using a cylindrical plasma etching device and easily. be.

[Summary of the Invention] The present invention uses a cylindrical plasma etching device to finely process insulating films made of polysilicon, silicon nitride, etc., so that the photoresist coated on these insulating films has a vertical cross-sectional shape that matches the dimensions. When forming as shown in FIG.
Furthermore, when the cross-sectional shape of the insulating film is made to have a slope in order to prevent defective step coverage, by performing plasma etching with the partial pressure ratio of the etching gas set to 1 or less, the cross-sectional shape of the insulating film after etching can be determined arbitrarily. It has been made possible.

[Embodiments of the invention]

The present invention will be explained below based on examples.

First, a polysilicon insulating film with a thickness of 0.5 μm is formed on the surface of a silicon substrate, a photoresist is applied to predetermined locations on this insulating film, and then the film is loaded into a cylindrical plasma etching device. A reaction gas, which is a mixture of Freon (CF4) gas containing % of acid g(02) and Helium (He) gas, is introduced into the apparatus, and the partial pressure ratio of helium gas to Freon gas is changed, and this partial pressure ratio and side We looked at the relationship between the amount of sex. The side etch amount is determined by the length of the base of the trapezoidal cross-sectional shape of the insulating film 2 formed between the silicon substrate 1 and the resist 3, as shown in FIG. The results shown in Table 1 were obtained by expressing the difference L-s between t and the length S of the upper side.

Note that t is approximately the same as the width of the resist 3 due to just etching. In Table 1, X is the average value for five points within a 4-inch diameter silicon substrate.

From Table 1, it can be seen that as the partial pressure ratio of helium gas to Freon gas increases, the etching rate slows down, but the amount of side etching decreases. In particular, when the partial pressure ratio exceeds 1, the side effect (6) amount begins to decrease significantly. Therefore, as the partial pressure ratio of helium gas to Freon gas increases, the inclination angle of the insulating film after etching becomes steeper; however, this inclination angle can be estimated from the partial pressure ratio and side etching amount for a given film thickness. It becomes possible to carry out microfabrication according to the resist dimensions from (force). Regarding the results shown in Table 1, FIG. 8 shows the relationship between the partial pressure ratio of helium gas to Freon gas and the inclination angle of the insulating film.

In this example, helium was used as the cloth waste to be mixed with the Freon gas, but the same results can be obtained by using other inert gases such as argon (Ar), without being limited to helium. can get.

〔Effect of the invention〕

When dry etching is performed using a cylindrical plasma etching device for microfabrication of insulating films and the like provided on semiconductor devices, conventionally the amount of side etching becomes large and etching perpendicular to the substrate cannot be performed directly under the resist. For this reason, parallel plate type etching equipment is often used despite its low processing capacity.However, according to the method of the present invention, a cylindrical plasma etching equipment is used and a rare gas is mixed with the etching gas. By setting the partial pressure ratio to 1 or more, it is not only possible to perform vertical etching with good reproducibility to the same degree as the parallel plate type, but also by setting the partial pressure ratio of the etching gas to an appropriate value as necessary, it is possible to achieve a partial pressure ratio of 1.
In the following, defective step coverage can be avoided by making the etching angle of the insulating film directly under the resist inclined with respect to the semiconductor substrate.

That is, the method of the present invention allows the amount of side etching of the film to be etched to be arbitrarily controlled by appropriately selecting the partial pressure ratio of the etching gas and the rare gas, and also provides mass production effects using a cylindrical plasma etching apparatus. be.

[Brief explanation of drawings]

Fig. 1 is a partial cross-sectional view of a semiconductor element before etching, Fig. 2 is a partial cross-sectional view of the same after wet etching, Fig. 3 is a cross-sectional view of a main part of a cylindrical plasma etching apparatus, and Fig. 4 is a parallel plate. 5 is a partial sectional view after etching by the apparatus shown in FIG. 4, FIG. 6 is a partial sectional view showing poor step coverage, and FIG. 7 is a partial sectional view showing side etching. FIG. 8 is a graph showing the relationship between the gas partial pressure ratio and the inclination angle of the insulating film. 1... Silicon substrate, 2... Polysilicon insulation film,
3... Photoresist, 14... Wiring metal. (9) Figure 1 Figure 2 Figure 3 Figure 11 Figure 4 Figure 5 Figure 4 Figure 6

Claims (1)

[Scope of Claims] l) In a method of processing fine patterns of semiconductor devices by mixing an inert gas with a reactive gas using a plasma etching apparatus, the film to be etched is A dry etching method characterized by controlling the amount of side etching 82. A dry etching method according to claim 1, characterized in that the inert gas is 1-1e or Ar.