JPS63260133A - Dry etching method - Google Patents

Abstract

PURPOSE:To control the cross-sectional shape of polycrystalline silicon in etching as a desired shape with good reproducibility, when the polycrystalline silicon is etched in ECR discharge plasma, by further mixing nitriding gas with chlorine and sufur hexafluoride. CONSTITUTION:A gas, which is introduced through a gas introducing system 6, is made to be ECR plasma with a magnetic field, which is produced by a magnetic field producing coil 5 that is provided at the outer surface of a plasma chamber 1 and a microwave electric field. The plasma is guided by the divergent magnetic field produced by the magnetic field producing coil 5 and inputted into a sample 9 through a plasma-stream lead-out window 8. Then the surface of the sample 9 is etched. Here, in addition to chlorine with a specified flow rate and sulfur hexafluoride, nitrogen is introduced at a specified flow rate. When etching is performed at a specified pressure, an anisotropic shape is readily obtained. The cross-sectional shape in etching can be adjusted by changing the mixing ratio of nitrogen gas. When nitrogen gas is added by 10-20%, polycrystalline silicon having the desirable etching cross-sectional shape with a forward taper angle of 80-90 degrees can be etched.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an ECR discharge plasma etching method in the manufacturing process of semiconductor elements, semiconductor devices, etc.

(Conventional technology).

The dry etching method using ECR discharge plasma is as follows:
It is well known as a method that can process fine patterns with high precision, and has recently been adopted in the manufacturing process of semiconductor integrated circuits.

This method introduces a low-pressure reactive gas on the order of 10-2 to 10 iPa into a vacuum chamber, and a magnetic field and microwave (2,45G
In this method, an ECR plasma is created by applying an electric field (Hz), and the sample is etched by reactive ions and radicals that are dissociated and generated from gas molecules.

(Problems to be Solved by the Invention) The etched cross-sectional shape of a thin film pattern such as polycrystalline silicon formed by this dry etching method (Fig. 2a)
, b, c) have a rectangular shape in most cases. However, since the side wall of such a thin film pattern (14 in Fig. 2) with a rectangular etched cross section forms a sharp step, there is a problem of disconnection when metal wiring is deposited across this pattern. arise.

In order to solve this problem, it is necessary to adjust the etched cross-sectional shape of the thin film pattern to a desired shape.

In conventional etching processing using ECR discharge, various gases mainly containing sulfur hexafluoride are used to adjust the shape, but as shown in Figure 2a, side etching tends to occur and shape control is difficult. Ta.

(Object of the Invention) An object of the present invention is to provide a dry etching method that solves the above-mentioned problems and can control the etched cross-sectional shape of polycrystalline silicon to a nova shape with good reproducibility.

(Means for Solving the Problems) The present invention provides a method for etching polycrystalline silicon in ECR discharge plasma, in which the etched cross-sectional shape is controlled by a method in which nitrogen gas is further mixed with chlorine and sulfur hexafluoride. This is what I did.

(Function) By the method of the present invention, the rise of the side wall of the etched cross-sectional shape of polycrystalline silicon can be tilted at any angle, for example, from vertical to slightly tapered. This forward tapered etched cross-sectional shape is an extremely preferable shape for microfabrication of semiconductor substrates.

(Implemented materials) Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 schematically shows an ECR discharge plasma flow etching apparatus used in the present invention.

In FIG. 1, 3 is a rectangular waveguide for propagating microwaves with a side wave number of 2.45 GHz.

1 is a plasma chamber, which has a microwave introduction window 4. The plasma chamber 1 and the etching chamber 2 are kept in vacuum. The sample 9 is placed on a water-cooled substrate holder 10. The exhaust system 11 includes a plasma chamber 1 and an etching chamber 20.
The degree of vacuum in both chambers is maintained at a predetermined value. The gas introduced from the gas introduction system 6 is converted into ECR plasma by a magnetic field and a microwave electric field generated by a magnetic field generating coil 5 provided on the outer periphery of the plasma chamber 1. The generated plasma is guided by the diverging magnetic field created by the magnetic field generating coil 5 and enters the sample 9 through the plasma flow extraction window 8, etching the surface of the sample 90. Furthermore, this apparatus does not use a grid, and it is also possible to apply a DC voltage 12 to the plasma chamber as shown in the figure.

In FIG. 2, 13 is an etching mask, 14 is a side wall of the material to be etched, 15 is a gate oxide film, and 16 is a silicon substrate. This is an etched cross-sectional shape when polycrystalline silicon is etched at a pressure of 0.13 Pa by introducing the polycrystalline silicon at a flow rate of 2 seconds. In this case, although the etching speed is high, the shape has side etching as shown in the figure.

On the other hand, Figure 2 shows 9.5 seconds of chlorine and 0.0 seconds of sulfur hexafluoride. This is the etched cross-sectional shape of polycrystalline silicon when etching was performed at the same pressure of <0.13 Pa by introducing nitrogen at a flow rate of 5 sec in addition to 5 s c Cm. In this case, an anisotropic shape can be obtained more easily than in FIG. 2a, and there is an advantage that the etched cross-sectional shape can be finely controlled. Silicon residue on the sample surface caused by chlorine gas can be eliminated by adding sulfur hexafluoride, increasing the etching rate.

Here, the etching cross-sectional shape can be adjusted by changing the mixing ratio of nitrogen gas.

Figure 2C shows the mixture of nitrogen gas in the introduced gas in Figure 2.
0105e, which is etched into a completely inverted tapered shape (inverted trapezoidal shape). When the mixing ratio of nitrogen gas is gradually reduced, the shape changes from a reverse tapered shape to a vertical shape as shown in FIG. 2, and then to a forward tapered shape as shown in FIG. 2a.

It has been found that a practical forward taper angle of around 85 degrees can be obtained when the nitrogen gas mixing ratio is 10 to 20%. The addition of nitrogen gas also has the advantage that the N radicals generated in the plasma convert C and O in carbide and oxide residues, which are thought to be generated due to the resist mask, into CN and ON, thereby removing them. be.

On the other hand, the etching rate decreases due to the addition of nitrogen gas.
It has also been found that it is possible to compensate by applying the aforementioned DC voltage to the plasma chamber.

(Effects of the Invention) The present invention is as described above, and the nitrogen gas is reduced to 10 to 20%.
By adding this, it is possible to etch polycrystalline silicon with a desirable etching cross-sectional shape in which the forward taper angle of the cross-section is 80 to 90 degrees.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an ECR discharge plasma stream etching apparatus used to explain an embodiment of the method of the present invention. Figures 2a-C are cross-sectional views showing various etching shapes. 1... plasma chamber, 2... etching chamber, 3...
Rectangular waveguide, 4...Microwave introduction window, 5...Magnetic field generation coil, 6...Gas introduction system, 7...Insulator, 8
...Plasma flow drawer window, 9...Sample, 10...
Substrate holder, 11... Exhaust system, 12... DC power supply, 13... Etching mask, 14... Side wall of material to be etched, 15... Gate oxide film, 16...-Silicon substrate.

Claims (1)

[Claims] (1) A dry etching method for etching polycrystalline silicon in ECR discharge plasma, which is characterized by controlling the etching cross-sectional shape by further mixing nitrogen gas with chlorine and sulfur hexafluoride.