JPH06163471A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To enable a silicon nitride film of semiconductor to be anisotropically dry-etched and enhanced in selectivity to a silicon oxide film which serves as a base of the silicon nitride. CONSTITUTION:A quartz bell jar 2 provided with a domed roof is provided under a waveguide 1, microwaves are fed towards the quartz bell jar 2 from the waveguide 1, and a substrate holder 3 connected to a power supply of high frequency is provided under the quartz bell jar 2 to constitute a microwave downstream etching device. Processing gas of mixed gas of nitrogen trifluoride and oxygen is introduced into a vacuum chamber 6 through a gas feed pipe 7. Plasma generated by discharge in the vacuum chamber 6 is guided to a specimen 4 for etching. By this setup, the side wall of the silicon nitride film 10 is protected by nitrogen dissociated from nitrogen trifluoride and reaction products, and the film 10 can be etched into an anisotropic shape and enhanced in selectivity by making oxygen content optimal in mixing ratio.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method, and more particularly to a semiconductor manufacturing method for manufacturing semiconductors such as semiconductor devices and semiconductor integrated circuits by dry etching using microwave downstream plasma.

[0002]

2. Description of the Related Art Recently, it has been considered to manufacture a semiconductor integrated circuit by dry etching using microwave downstream plasma. For example, it is being put to practical use in a dry etching process or a resist ashing process of a passivation film (silicon nitride film formed by plasma CVD) after forming an aluminum wiring film. In the above method, a reactive gas (mainly CF ₄ and O ₂ ) having a pressure of about 0.2 to 1.5 Torr is introduced into a vacuum chamber, and plasma is generated by a microwave (2.45 GHz) electric field to generate gas molecules. The sample is dry-etched by reactive radicals and ions generated by dissociation from the sample.

However, when the above-mentioned dry etching method is used, when a silicon oxide film, a silicon nitride film, and a photoresist are laminated in this order on a silicon substrate to etch the silicon nitride film, isotropicity with a large side etch occurs. The shape arises. Therefore, there is a problem that it cannot be applied to the etching of the silicon nitride film during the LOCOS forming process which requires an anisotropic shape.

Further, in order to obtain an anisotropic shape, it is conventionally necessary to use the method shown in FIG.
There is a method of etching by a parallel plate type plasma etching method as shown in FIG. In FIG. 3, a sample 22 is placed on a substrate holder 21, and a quartz chamber 23 having a downward concave shape is provided on the substrate holder 21 so as to cover the sample together with the substrate holder 21. An anode electrode 24 is provided in the upper center of the quartz chamber 23, and the substrate holder 21 is grounded. And
A high frequency voltage is applied to the anode electrode 24, a process gas is supplied into the quartz chamber 23 from the upper portion of the quartz chamber 23, and the process gas is exhausted from an exhaust port provided in the substrate holder 22.

However, in the above plasma etching apparatus, the selectivity is low (selection ratio is about 2 to 3), and when the underlying silicon oxide film is thinned (150 to 100 Å), the oxide film is etched during overetching. There was a problem of turning it off.

[0006]

SUMMARY OF THE INVENTION In view of the above problems of the prior art, the main object of the present invention is to provide an anisotropic shape when a silicon nitride film is dry-etched using microwave downstream plasma. Another object of the present invention is to provide a method of manufacturing a semiconductor which can be etched to a high degree and can enhance the selectivity of a silicon nitride film with respect to an underlying silicon oxide film.

[0007]

According to the present invention, there is provided a semiconductor manufacturing method for manufacturing a silicon nitride film by dry etching using microwave downstream plasma, the process being used for the dry etching. This is achieved by providing a semiconductor manufacturing method characterized in that the gas is a mixture of nitrogen trifluoride and oxygen.

[0008]

In this way, by using a mixture of nitrogen trifluoride and oxygen gas as the process gas for dry etching the silicon nitride film, the etching rate for the silicon nitride film can be improved. Further, a protective film is formed on the side wall of the silicon nitride film by reaction products such as nitrogen and SiNxOy dissociated from nitrogen trifluoride,
Since the etching progresses in the depth direction, the processing pressure of the process gas can be lowered, and at the same time, the etching on the side wall can be prevented and a good anisotropic shape can be formed. Further, by mixing the process gas with the oxygen gas, when the underlying silicon oxide film is exposed, the silicon oxide film reacts with the nitrogen trifluoride gas and the oxygen gas to form SiFxOy, SiNxOy on the silicon oxide film.
Is formed, which reduces the reaction rate of the fluorine radical with SiO ₂ . Therefore, the selectivity of the silicon nitride film with respect to the silicon oxide film is enhanced, and the silicon oxide film can be prevented from being exposed and further etched.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic sectional view showing an example of a microwave downstream etching apparatus to which the present invention is applied. The present apparatus is formed by a waveguide 1, a dome-shaped quartz bell jar 2 provided below the waveguide 1, and a substrate holder 3 provided below the quartz bell jar 2. A sample 4 to be processed is placed on the upper surface of the substrate holder 3.

The waveguide 1 is formed so as to expand downward so as to cover the quartz bell jar 2, and a mesh portion 5 is provided on the lower peripheral wall portion thereof. In addition, a process gas is supplied from a gas supply device (not shown) located outside to a decompression chamber 6 surrounded by the concave inner surface of the quartz bell jar 2 and the substrate holder 3. At the same time, a high frequency power source is connected to the substrate holder 3.

In the microwave downstream etching apparatus thus constructed, microwaves (2.45 GHz) are supplied from the waveguide 1 toward the quartz bell jar 2, and discharge is generated in the decompression chamber 6. The surface of the sample 4 is etched by guiding the plasma (radicals and ions) generated thereby to the sample 4. At this time, the process gas supplied from the gas supply pipe 7 is a mixture of nitrogen trifluoride and oxygen, and nitrogen trifluoride is introduced at a flow rate of 40 SCCM and oxygen is introduced at a flow rate of 10 SCCM.

Then, with the apparatus of FIG. 1, 0.15 Tor
Under the pressure of r, the microwave power is set to 600 W and the high frequency bias power applied to the substrate holder 3 is set to 3 W.
FIG. 2 shows an etching cross-sectional shape when the silicon nitride film (silicon nitride film for forming the active region) in the LOCOS formation step is etched by setting it to 0 W. In FIG. 2, a base silicon oxide film 9 is formed on a silicon substrate 8, an etching mask 11 made of a resist is partially provided on a silicon nitride film 10 laminated on the silicon oxide film 9, and A shape is shown in which the silicon nitride film 10 in a portion excluding the etching mask 11 is etched.

By the way, in the conventional plasma etching apparatus shown in FIG. 3, CF ₄ is 80 SCCM and oxygen is 2
Introduced at each flow rate of 0 SCCM and set microwave power to 1
In some cases, the etching was performed under a pressure of 0.6 Torr as well as 000 W, and in that case, the shape was isotropic. On the other hand, according to the etching by the apparatus of the present invention, since the process gas in which nitrogen trifluoride and oxygen are mixed is used, nitrogen dissociated from nitrogen trifluoride and reaction products such as SiNxOy are generated. The object protects the side wall of the etched portion of the silicon nitride film 10. Therefore, it is possible to prevent side etching due to fluorine radicals during the etching of the silicon nitride film 10 and to advance the etching only in the depth direction, so that the anisotropic shape shown in FIG. 2 can be easily obtained. Further, it is possible to perform the etching of the wiring shape which is further miniaturized.

When the unnecessary silicon nitride film 10 is etched and the underlying silicon oxide film 9 begins to be partially exposed, a reaction product of SiFxOy produces SiO _{2 due} to the reaction between SiO ₂ and oxygen in the process gas. Deposit on top. Therefore, by increasing the mixing ratio of the oxygen gas in the process gas, the silicon oxide film 9 of the silicon nitride film 10
It is possible to drastically improve the selectivity of the base silicon oxide film 9 to 200 Å as compared with the conventional 300 Å.
Or even if the thickness is further reduced to 100 Å, the underlying silicon oxide film 9 is not etched. Incidentally, the selection ratio is conventionally 2 to
Although it was 3, it is 10 to 20 according to the present invention. Further, if the mixing ratio of the oxygen gas is increased to 35% or more, the etching rate of the silicon nitride film 10 will be decreased. Therefore, an appropriate mixing ratio of 35% or less is preferable.

[0016]

As described above, according to the present invention, by using a mixture of nitrogen trifluoride gas and oxygen gas as a process gas in the microwave downstream etching, the silicon nitride film for the active region is formed. Can be etched into an anisotropic shape with a vertical surface without side etching, which can be applied to miniaturized shapes for high-density and high-integration of semiconductor circuits, and can significantly improve selectivity. Therefore, an extremely good etching cross-sectional shape can be formed.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a microwave downstream etching apparatus to which the present invention is applied.

FIG. 2 is a sectional view of an essential part of a semiconductor according to the etching of the present invention.

FIG. 3 is a schematic sectional view of a conventional dry etching apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Waveguide 2 Quartz bell jar 3 Substrate holder 4 Sample 5 Mesh part 6 Decompression chamber 7 Gas supply pipe 8 Silicon substrate 9 Silicon oxide film 10 Silicon nitride film 11 Etching mask 21 Substrate holder 22 Substrate holder 23 Quartz chamber 24 Anode electrode

Claims (1)

[Claims] 1. A semiconductor manufacturing method for manufacturing a silicon nitride film by dry etching using microwave downstream plasma, wherein the process gas used for the dry etching is a mixture of nitrogen trifluoride and oxygen. A semiconductor manufacturing method characterized by the above.