JPS6340870B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dry etching method for processing polycrystalline silicon.

Conventionally, as a method for processing polycrystalline silicon, which is often used as a gate material for semiconductor products, a dry etching method that applies a chemical reaction between gas plasma and silicon Si has been used. In this case, the gas used for etching is generally CF ₄ (Freon 14) or a mixture of CF ₄ and oxygen.

FIG. 1 is a sectional view showing Si being processed by this type of conventional dry etching method. In the figure, an oxide film 2 is formed on the main surface of a Si substrate 1, and a polycrystalline Si layer 3 is formed thereon. A photoresist 4 is provided on this polycrystalline Si layer 3, and etching is performed using CF ₄ gas plasma using this as an etching mask.

In this case, etching is caused by fluorine radical particles generated in CF ₄ gas plasma and polycrystalline Si layer 3.
The process proceeds by chemically reacting with Si to produce volatile SiF ₄ . Therefore, the etching is isotropic etching that progresses at the same speed in both the vertical and horizontal directions, and the polycrystalline Si layer 3 after processing is
As shown in FIG. 1, it becomes thinner than the dimension of the photoresist 4 (that is, the desired dimension). In particular, in actual etching of a wafer, in order to ensure accuracy, over-etching is performed for several seconds beyond the point at which the underlying oxide film 2 of the polycrystalline Si layer 3 is thought to be exposed. The difference between the processing dimensions of polycrystalline silicon and the processing dimensions of polycrystalline silicon becomes increasingly large. FIG. 2 shows an example of the relationship between over-etch time and side-etch amount. As is clear from the figure, when the overetch time increases by 10 seconds, the side etching amount increases by 0.3 to 0.4 μm, and the polycrystalline Si
The processing dimensions of layer 3 are reduced. Currently, this polycrystalline Si
Layer 3 is now required to have a processing dimension of 2 μm, but due to the large amount of side etching,
It has been difficult to achieve this by the conventional dry etching method using CF ₄ .

The present invention was made in view of the above circumstances, and its purpose is to fabricate polycrystalline silicon with a line width of approximately 2 μm.
The object of the present invention is to provide a stable dry etching method with a small amount of side etching, which allows processing of.

To achieve this purpose, the dry etching method according to the present invention uses C ₂ ClF ₅ gas plasma. Hereinafter, the dry etching method according to the present invention will be explained in detail using Examples.

FIG. 3 is an internal configuration diagram showing an etching apparatus used in the dry etching method according to the present invention. In the figure, parallel plate electrodes consisting of an upper electrode 12 and a lower electrode 13 are provided inside a chamber 11, and a high frequency power source 14 is connected between the two electrodes. The lower electrode 13 also serves as a wafer mounting table. The chamber 11 is further provided with a gas inlet 15 and an exhaust port 16, each of which is provided with a gas supply source and a vacuum exhaust device (not shown).

When performing the dry etching method according to the present invention using the etching apparatus having the above configuration, first, the wafer 17 as the object to be etched is placed on the lower electrode 13, and the inside of the chamber 11 is removed by operating the vacuum evacuation apparatus. Exhaust. Next, C ₂ ClF ₅ gas is introduced from the gas inlet 15 and the upper electrode 1
Applying a high frequency voltage between 2 and the lower electrode 13,
A high frequency electric field is generated in the space between both electrodes inside the chamber 11. In this case, the high frequency output, gas pressure, gas flow rate, etc. are controlled to appropriate values.

The introduced C ₂ ClF ₅ gas is turned into plasma by the high frequency electric field, and the wafer 17 is etched. Gas generated by the chemical reaction at that time, excess C ₂ ClF ₅ gas, etc. are exhausted from the exhaust port 16 .

Polycrystalline Si etched in this way
Figure 4 shows the machined shape. As is clear from the figure, when C ₂ ClF ₅ is used, the vertical etching rate is much higher than the horizontal etching rate, so the dimensions of the polycrystalline Si layer 3 relative to the photoresist 4 are The thinning will be extremely small.

FIG. 5 shows the relationship between over-etch time and side-etch amount when using C ₂ ClF ₅ gas.
When conventional CF ₄ or a mixed gas of CF ₄ and oxygen is used, the dimensional thinning of polycrystalline Si is already as large as 0.7 μm at an overetch time of 0 seconds, as shown in Fig. The rate of increase in the amount of side etching relative to etching was also large. In contrast,
When using C ₂ ClF ₅ , as shown in Figure 5, the thinning of polycrystalline Si at 0 seconds of overetching is 0.2 μm.
Moreover, the increase rate of the side etching amount with respect to subsequent overetching is extremely small, 0.1 μm after 10 seconds of overetching, so it is possible to process polycrystalline Si with a line width of 2 μm, which was previously impossible.

As explained above, according to the dry etching method of the present invention, the etching gas is
By performing plasma etching using C ₂ ClF ₅ gas, the amount of side etching can be reduced, which has the excellent effect of enabling fine processing of polycrystalline Si with a line width of about 2 μm.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing the processed shape of polycrystalline Si etched by a conventional dry etching method, Fig. 2 is a graph showing the relationship between overetching time and side etching amount in a conventional dry etching method, and Fig. 3 is a graph showing the relationship between overetching time and side etching amount in a conventional dry etching method. FIG. 4 is a cross-sectional view showing the processed shape of polycrystalline Si etched by the dry etching method according to the present invention;
FIG. 5 is a graph showing the relationship between overetch time and side etching amount in the dry etching method according to the present invention. 3... Polycrystalline Si layer, 4... Photoresist, 11
... Chamber, 12 ... Upper electrode, 13 ... Lower electrode, 14 ... High frequency power supply, 15 ... Gas inlet, 16 ... Exhaust port, 17 ... Wafer.

Claims (1)

[Claims] 1. A dry etching method characterized in that C ₂ ClF ₅ gas is used as the etching gas in a dry etching method in which an etching gas is introduced into a high-frequency electric field to generate gas plasma, and polycrystalline Si is etched by the gas plasma. Etching method.