JPH0472082A - Dry etching method - Google Patents

Abstract

PURPOSE:To prevent the resticking of a reaction product and to obtain a high selection ratio by mixing gaseous sulfur hexafluoride and/or gaseous oxygen into gaseous chlorine in the ECR discharge plasma dry etching using the gaseous chlorine. CONSTITUTION:A microwave is introduced into a plasma chamber 1 to be evacuated from a microwave inlet window 3 through a waveguide 4. A magnetic field generating coil 5 is set outside the chamber 1, an ECR discharge is excited in the chamber 1 by the magnetic field and the electric field of the microwave, and the gaseous chlorine introduced into the chamber 1 through a gas introducing system 10 is converted to plasma. Sulfur hexachloride (SF6) is mixed into the reactive gaseous chlorine (Cl2). The reactive ion in the formed plasma is vertically injected into a substrate 7 set close to the resonance point of the ECR discharge in an etching chamber 2. Consequently, the resticking of the reaction product is prevented, and dry etching is carried out while maintaining a high selection ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a dry etching method for etching the surface of a substrate using electron cyclotron resonance (hereinafter referred to as rECRJ) discharge plasma of chlorine gas.

(Prior Art) Conventionally, a low-pressure reactive gas on the order of 10' to 10-" Torr is introduced into a vacuum chamber, and this vacuum chamber is exposed to a magnetic field and microwaves (
2,45GH2) Apply an electric field to ECR the reactive gas
A method is known in which the surface of a substrate is etched using reactive ions and radicals that are dissociated from a reactive gas and generated by plasma generated by a discharge.

This dry etching method using ECR discharge discharge plus can process fine patterns with high precision, so in recent years it has been
It has come to be adopted in the manufacturing and processing of semiconductor integrated circuits.

(Problems to be Solved by the Invention) When etching, for example, a tungsten polycide film formed on a silicon oxide film of a substrate using the ECR discharge discharge plus, chlorine gas is used as the reactive gas, and the substrate holder is was often carried out by applying a high frequency bias of 13.56 MHz, but this causes a lot of damage to the substrate surface, and the selectivity ratio of chlorine ions and chlorine radicals to tungsten polycide and silicon oxide film is about 5, so it is not very effective. It wasn't good.

In addition, in order to avoid damage to the substrate surface, when etching is performed without applying the bias, WCP is generated by the reaction between reactive ions and radicals dissociated from chlorine gas and tungsten polycide.
Since the vapor pressure of tungsten chlorides such as 2, WC, and P3 is low, there is a problem that they re-adhere to the substrate surface. This redeposition of tungsten chloride is closely related to the substrate temperature, and as shown in Figure 6, redeposition occurs when the substrate temperature is lower than 80°C, and as shown in Figure 7, The photoresist 31 is covered and redeposited 33 onto the sidewalls of the patterned portions 32 that remain on the substrate without being etched.
It was something to do.

On the other hand, the shape of the side wall of the pattern portion 32 is also closely related to the substrate temperature during etching, and in order to obtain an anisotropic etched shape as shown in FIG. 8, it is necessary to keep the temperature below 60°C. there were. Therefore, it has not been possible to simultaneously prevent re-deposition of reaction products and achieve anisotropy by controlling the substrate temperature.

This invention was made in view of the above-mentioned characteristics of ECR discharge plasma etching, and provides a dry etching method that prevents reaction products from re-deposition and provides a high selectivity through control of reactive gas. It is intended to.

(Means for Solving the Problems) A dry etching method of the present invention that achieves the above-mentioned object is a method of dry etching the surface of a substrate using an electron cyclotron resonance discharge plasma of chlorine gas. Sulfur fluoride gas and/or
Or it is characterized by mixing oxygen gas.

In the above, the mixing ratio of sulfur hexafluoride gas needs to be about 3.5% or more of the total introduced gas, but since increasing the mixing ratio deteriorates the selectivity, it is preferably about 5%.

Further, the mixing ratio of oxygen gas needs to be within about 5% of the total introduced gas; if it exceeds 5%, the etching rate will be reduced and the reaction products will be redeposited.

(Function) In the etching method of the present invention, fluorine generated from sulfur hexafluoride by ECR discharge plasma reacts with the material of the etched film to become a substance with high vapor pressure, which contributes to preventing redeposition. . Furthermore, the etching of the underlying film of the film to be etched is limited by the oxygen gas, contributing to maintaining a high selectivity.

(Example) The present invention will be described in more detail below based on examples.

First, an outline of the ECR discharge plasma etching apparatus used in the examples will be explained. The device is as shown in Figure 1.
It consists of a plasma chamber 1 and an etching chamber 2 connected in series, and microwaves are guided from a microwave oscillator (not shown) through a waveguide 4 to a microwave introduction window 3 provided in the plasma chamber 1. It looks like this. A magnetic field generating coil 5 is installed outside the plasma chamber 1, and an ECR discharge is excited within the plasma chamber 1 by the magnetic field generated by the magnetic field generating coil 5 and the electric field of the microwave guided by the waveguide 4. The gas introduced into the plasma chamber 1 through the gas introduction system 10 is turned into plasma. In the figure, reference numeral 9 denotes a cooling means for the plasma chamber 1, which allows water to circulate as indicated by an arrow 11.

Inside the etching chamber 2, there is a resonance point 87 of the ECR discharge.
A substrate holder 6 is installed so as to be located close to 5 Gauss), so that reactive ions are perpendicularly incident on the substrate 7 to be etched. Further, an exhaust system 8 is connected to the etching chamber 2 so that the etching chamber 2 and the plasma chamber 1 can be evacuated.

Using such an ECR discharge plasma etching apparatus, a two-layer film of tungsten silicide and polysilicon formed on a silicon oxide film (SiO2) was etched.

The etching conditions were a processing pressure of 5 x 10' Torr.
r microwave power was set to IKW, high frequency bias was not applied to avoid damage to the substrate, and the temperature of the substrate 7 was set to 60° C. to perform anisotropic etching. The reactive gas is a mixture of chlorine gas (C, Q2) and sulfur hexafluoride (SFe), and the total flow rate is 208ccI1.
It was set to 1.

Figure 2 shows the etching rate of a tungsten polycide film (a two-layer film of tungsten silicide and polysilicon) and the etching rate of the underlying silicon oxide film when the mixing ratio of sulfur hexafluoride in the reactive gas is changed. This is a graph showing the following. Moreover, FIGS. 3(a) to 3(C) are diagrams showing the etching shape at this time. (a) is the shape when sulfur hexafluoride gas is 0%, (b) is 2°5%, and (C) is 5%.

From the results shown in Figures 2 and 3, mixing 3.5% or more of sulfur hexafluoride prevents the re-deposition of tungsten chloride that was observed when etching was performed using only chlorine gas. It was confirmed that extremely good anisotropic etching could be achieved. The reaction between tungsten in tungsten polycide and fluorine in sulfur hexafluoride produces tungsten fluoride with a high vapor pressure, making it possible to avoid the formation of deposits.

As the mixing ratio of sulfur hexafluoride increases, the etching rate of the underlying silicon oxide film also increases, and the selectivity with respect to the tungsten polycide film decreases. Therefore, it is desirable that the mixing ratio of sulfur hexafluoride be about 5%.

Next, the substrate on which the polysilicon film was formed on the base of the silicon oxide film was etched.

The etching conditions are almost the same as above, processing pressure 5 x
The temperature was 10 −4 Torr, microwave power IKW, no bias was applied, and the substrate temperature was 70° C.

In addition, the reactive gas was a mixture of chlorine gas and oxygen gas (02), and the total flow rate was set to 2 Q 5 eeli.

FIG. 4 is a graph showing the etching rate of a polysilicon film and the underlying silicon oxide film when the mixing ratio of oxygen gas is changed.

From this example, it was confirmed that by mixing oxygen gas within 5%, the etching rate of the polysilicon film can be lowered and the selectivity can be improved. When oxygen gas was mixed in an amount exceeding 5%, the etching rate of the polysilicon film rapidly decreased, and redeposition of reaction products was observed.

Therefore, next, a substrate on which a tungsten polycide film was formed on a silicon oxide film was etched by mixing chlorine gas with sulfur hexafluoride gas and oxygen gas. The etching conditions were a processing pressure of 5 x 10' Torr.
, ? Microwave power IKW, no bias, substrate temperature 6
The temperature was 0°C. The reactive gases are 1.9 sec+n of chlorine gas, 1 cell of sulfur hexafluoride gas, and 0~n of oxygen gas.
The mixture was mixed for 2 seconds.

FIG. 5 is a graph showing the etching rate of the tungsten polycide film and the underlying silicon oxide film when the mixing ratio of oxygen gas is changed.

In this example, it was found that re-deposition of reaction products could be prevented and the selectivity between the tungsten polycide film and the silicon oxide film could be increased.

From the above examples, it was confirmed that by mixing sulfur hexafluoride gas and/or oxygen gas with chlorine gas, redeposition of reaction products can be prevented and etching can be performed without reducing the selectivity. .

Therefore, without applying a high frequency bias to the substrate and under conditions where the temperature is kept low, plasma damage is eliminated and anisotropic etching is possible, making it possible to perform extremely ideal dry etching. can.

Although etching of tungsten polycide and polysilicon has been described in the embodiment, the same etching can be performed using chlorine gas. Etching using chlorine gas can be applied to films of transition metals such as tungsten, titanium, and molybdenum, films of compounds of these transition metals, films of compounds of transition metals and silicon, films of compounds of transition metals and silicon, and polycrystalline silicon films. multilayer film, aluminum alloy film (e.g. Ag5i-
There are multilayer films of compound films of Cu) and transition metals, etc.
It can be implemented in either case.

(Effects of the Invention) As explained above, according to the present invention, there is an effect that re-deposition of reaction products can be prevented and etching can be performed while maintaining a high selectivity.

However, since it is possible to lower the substrate temperature, anisotropic etching can be performed, and there is no need to apply a bias to a 4° substrate, so etching can be performed without damage. .

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an apparatus in which the present invention is implemented, and FIG. 2 is a graph of the etching rate when the mixing ratio of the sulfur hexafluoride gas is varied in an example in which the sulfur hexafluoride gas of the present invention is mixed. 3(a), 3(b), and 3(C) are explanatory diagrams of the etching shape, and FIG. 4 is a graph of the etching rate when the mixing ratio of oxygen gas is changed in an embodiment of the present invention in which oxygen gas is mixed. FIG. 5 is a graph of the etching rate when the mixing ratio of oxygen gas is changed in an embodiment of the present invention in which sulfur hexafluoride gas and oxygen gas are mixed, and FIG. 6 is a graph of the substrate temperature and etching rate of the conventional method. , Figure 7 is the same〈
FIG. 8, which is a diagram illustrating deposits in the conventional method, is a graph showing the relationship between substrate temperature and pattern sidewall shape in the conventional method. 1... Plasma chamber 2... Etching chamber 3.
...Microwave introduction window 5...Magnetic field generating coil 7...
・Substrate 10...Gas introduction system diagram SFs liquid t (SFs/fclz+5Fs1%) 4th 02 flow t (02/FC+2+02J%) Figure 5 Figure 6 1ixz degrees (°C) Figure 7

Claims (1)

[Claims] 1. A method of dry etching the surface of a substrate using electron cyclotron resonance discharge plasma of chlorine gas, in which sulfur hexafluoride gas and/or
Or a dry etching method characterized by mixing oxygen gas