JPH04167524A - Via-hole formation method of semiconductor device - Google Patents

Abstract

PURPOSE:To enable the title via-hole to be formed taking an arbitrary shape by a method wherein the mixed gas of tetrafluoromethane and trifluoromethane is used for mild etching step while the mixing ratio of the two gasses is continuously varied in proportion to the advancement of the etching steps. CONSTITUTION:A resist 101 is formed on the interlayer film 102 of a substrate 103 and then the mixing ratio of tetrafluoromethane and trifluoromethane used for a reactive gas is varied using the resist 101 as a mask so that the sidewall of an oxide film via hole 102a may be controlled to take a taper shape swelling inward. That is, at the etching step starting point, the mixing ratio of tetrafluoromethane is specified to be 100% (flow rate to total mixture amount) to be linearly decreased in proportion to the advancement of etching step down to 10% immediately before finishing the etching step and then increased again up to 50% at the finishing time of the overetching step. Through these procedures, the taper shape of the oxide film via hole 102a can be arbitrarily controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for forming a via hole in a semiconductor device, and particularly to a method for forming a tapered via hole.

[Prior art] In the via hole forming process of a semiconductor device, the glabellar membrane 30
The formation of the second via hole 302a is shown in FIGS.
), (c), the interlayer film 30 on the substrate 301
2, a resist 303 obtained by a lithography process is formed, and using the resist 302 as a mask, reactive ion etching (hereinafter referred to as RI) is performed using a fluorine-based gas as a reactive gas.
(referred to as E).

In the above process, a via hole 30 with a vertical side wall angle is
2a is obtained. After opening this via hole, a sputtering method is used to form an aluminum or aluminum alloy film for forming wiring. In film formation using the sputtering method, coverage at stepped portions largely depends on the aspect ratio, and in fine via holes, if the sidewall shape of the via hole 302a is vertical, sputtered aluminum will not be formed in the via hole. Poor wiring contact occurs. In order to solve this problem, a via hole etching method that combines isotropic wet etching and anisotropic dry etching was used, as shown in Figures 4(a) and 4(a).
A via hole with a rounded upper part and a vertical lower part as shown in b) and (c) is obtained. By enlarging the opening system above the via hole, aspect ratio dependence is alleviated.

[Problem to be solved by the invention]

As mentioned above, in film formation using the sputtering method, the coverage at the step part is largely dependent on the aspect ratio, and in the case of fine via holes, if the via hole is vertical, sputtered aluminum will not be formed in the via hole. , resulting in poor wiring contact. In order to solve this problem, via holes are etched using a combination of isotropic wet etching and anisotropic dry etching, and via holes as shown in FIG. 4 can be obtained. However, even with this method, when the diameter of the via hole becomes submicron, the coverage at the contact area between the rounded part at the top of the via hole and the vertical part at the bottom, and the film formation thickness at the vertical part at the bottom decrease. , resulting in poor wiring contact.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for forming a via hole in a semiconductor device, which enables formation of a via hole in an arbitrary tapered shape.

[Means to solve the problem]

In order to achieve the above object, a method for forming a via hole in a semiconductor device according to the present invention includes a dry etching process, and the dry etching process includes the following steps: trifluoromethane and trifluoromethane. This process uses a mixed gas of tetrafluoromethane and continuously changes the gas mixture ratio of trifluoromethane and tetrafluoromethane as etching progresses.

The dry etching process uses a magnetron reactive ion etching method, an electron cyclotron resonance plasma etching method, or a microwave etching method in which a magnetic field is applied to increase the density of active species.

[Operation] Dry etching of the oxide film is performed by reactive ion etching using a chlorofluorocarbon gas such as tetrafluoromethane or trifluoromethane as a reactive gas. It has been revealed that the addition of hydrogen in this etching plasma promotes the formation of a polymer film mainly composed of carbon, and in the oxide film via hole opening process,
The above method is widely used for the purpose of improving the selectivity with respect to the underlying silicon substrate. Trifluoromethane has hydrogen in its constituent atoms and is a gas that easily forms a carbon-based polymer film.

In the present invention, a via hole having a tapered shape is formed by actively using this polymer film and utilizing a competitive reaction between the formation of the polymer film and etching. Furthermore, using trifluoromethane and tetrafluoromethane as reaction gases,
By continuously changing this mixing ratio, the tapered shape of the oxide film via hole can be controlled to an arbitrary shape.

In addition to this, the etching device can etching via holes of any tapered shape by applying a magnetic field to increase the density of active species using a magnetron reactive ion etching method, an electron cyclotron resonance plasma etching method, or a microwave etching method. get.

[Example 1 Next, the present invention will be described in detail with reference to the drawings.

(Example 1) FIGS. 1(a) and 1(b) are explanatory diagrams for explaining the outline of Example 1 according to the present invention.

In Example 1, as shown in FIG. 1(b), a resist 101 is formed on an interlayer film l○2 of a substrate 103, and the resist 101 is
By using 01 as a mask, using tetrafluoromethane and trifluoromethane as reaction gases, and continuously changing the mixing ratio, the side wall of the oxide film via hole 102a as shown in FIG. It is controlled to have a tapered shape that protrudes.

In this example, a magnetron reactive ion etching apparatus was used. Using a high frequency of 13.56MHz,
A power of 500 W was applied, and a magnetic field of 200 Gauss was applied on the wafer surface. The total flow rate of tetrafluoromethane and trifluoromethane was set to 50 cc/min, and the mixing ratio was changed as shown in FIG. 1(a). At the start of etching, the mixing ratio of tetrafluoromethane is 1.
00% (flow rate ratio to the total mixing ratio of tetrafluoromethane and trifluoromethane), and decrease linearly as etching progresses. Immediately before the end of via hole etching, the mixing ratio is decreased to 10%, then increased again, and then increased to 50% when overetching is completed.

At the beginning of etching, add 100% tetrafluoromethane.
%, in the initial stage of etching, the formation of a polymer film is dominant and taper etching is performed. Vertical etching is achieved by decreasing the flow rate ratio of tetrafluoromethane as etching progresses. Furthermore, during the overetching time when the silicon surface is exposed,
By increasing the mixing ratio of tetrafluoromethane,
Ensure selectivity with silicon.

By performing the above etching, a via hole shape as shown in FIG. 1(b) was obtained.

(Example 2) FIGS. 2(a) and 2(b) are explanatory diagrams for explaining the outline of Example 2 according to the present invention.

In Example 2, tetrafluoromethane was used as the reaction gas.

By using trifluoromethane and continuously changing the mixing ratio, the side wall of the oxide film via hole 102a is controlled to have a concave tapered shape as shown in FIG. 2(b).

In this example, a magnetron reactive ion etching device was used. Using a high frequency of 13.56MHz,
A power of 400 W was applied, and a magnetic field of 100 Gauss was applied on the wafer surface. The total flow rate of tetrafluoromethane and trifluoromethane was set to 50 cc/min, and the mixing ratio was changed as shown in FIG. 2(a). At the start of etching, the mixing ratio of tetrafluoromethane is 0.
% (flow rate ratio to the total mixing ratio of tetrafluoromethane and trifluoromethane), etching is performed using only trifluoromethane, and the mixing ratio of tetrafluoromethane is linearly increased as etching progresses. Immediately before the end of via hole etching, the mixing ratio is increased to 100%, and then increased again to 60% when over etching is completed.
increase to

The reason why tetrafluoromethane is set to 0% at the start of etching is to suppress the formation of a polymer film and perform vertical etching at the initial stage of etching. Taper etching is achieved by increasing the flow rate ratio of tetrafluoromethane as etching progresses. Furthermore, during the overetching period when the silicon surface is exposed, contamination due to polymer film formation is suppressed by reducing the mixing ratio of tetrafluoromethane.

By performing the above etching, a via hole shape as shown in FIG. 2(b) was obtained.

[Effects of the Invention] As explained above, in the formation of via holes in semiconductor devices, the present invention can form via holes having a tapered shape by utilizing competitive reactions between the formation of a polymer film and etching.

Further, by using trifluoromethane and tetrafluoromethane as reaction gases and continuously changing the mixing ratio, the tapered shape of the oxide film via hole can be controlled to an arbitrary shape. In addition, via holes of any tapered shape can be obtained by using a magnetron reactive ion etching method, an electron cyclotron resonance plasma etching method, or a microwave etching method in which the density of active species is increased by applying a magnetic field. can.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the concept of Embodiment 1 of the present invention,
(a) is a diagram showing changes in the mixing ratio of trifluoromethane and tetrafluoromethane, (b) is a longitudinal cross-sectional view showing the via hole shape obtained by this etching, and FIG. 2 is a diagram showing the implementation of the present invention. FIG. 3 is a diagram showing the concept of Example 2, in which (a) is a diagram showing changes in the mixing ratio of trifluoromethane and tetrafluoromethane, and (b) is a vertical cross section showing the shape of a via hole obtained by this etching. Figure 3(a). (b) and (C) are cross-sectional views showing the conventional example in the order of steps;
Figures (a), (b), and (c) are cross-sectional views showing a conventional example in the order of steps.

Claims (2)

[Claims] (1) A method for forming via holes in semiconductor devices that includes a dry etching process, and the dry etching process uses a mixed gas of trifluoromethane and tetrafluoromethane. A method for forming a via hole in a semiconductor device, characterized in that the process involves continuously changing a gas mixture ratio as etching progresses. (2) The dry etching step uses a magnetron reactive ion etching method, an electron cyclotron resonance plasma etching method, or a microwave etching method in which a magnetic field is applied to increase the density of active species. A method for forming a via hole in a semiconductor device according to item (1).