JP3128837B2 - Dry etching method - Google Patents

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 dry etching of a silicon-based thin film such as polysilicon or polycide used for a semiconductor device.

[0002]

2. Description of the Related Art Recent dry etching methods for a polysilicon film and a polycide film of this kind include, for example,
Proceedings of the Fall Meeting of the 1990s, p.462, 26p-ZF-
1, page 463, 26p-ZF-2, 26p-ZF-3
Are known.

(1) In the method described in 26p-ZF-1, when etching tungsten polycide, oxygen (O ₂ ) gas is added to chlorine (Cl ₂ ) gas,
This is a method of performing anisotropic etching while using iO ₂ as a protective film.

(2) The method described in the above 26p-ZF-2 is a method of performing time-modulated (TM) etching for alternately repeating formation of a protective film and etching when etching tungsten polycide.

(3) In the method described in 26p-ZF-3, when etching tungsten polycide or polysilicon, the wafer temperature is cooled to about -70 ° C.
In this method, anisotropic etching is performed using hexafluorine sulfur (SF ₆ /) hydrogen bromide (HBr) -based gas. In this method, since a bromine-based gas is used, sidewall protection is performed by SiBr _x generated during etching. This method has an advantage that the selectivity with respect to SiO ₂ can be increased.

[0006]

However, the above-mentioned prior art has various problems described below.

That is, in the conventional method described in the above (1), there is a problem that the oxygen selectivity is added to the etching gas, so that the selectivity to the resist cannot be reduced.

Further, in the conventional method described in the above (2), since a protective film is formed by polymer deposition, there is a problem that dust is generated due to the use of a deposition gas (deposition gas).

Further, in the conventional method described in the above (3), at the time of overetching after etching the tungsten polycide or polysilicon and exposing the base,
Since the supply of SiBr _x having a side wall protecting effect is reduced, as shown in FIG. 12, there is a problem that the deterioration of the shape due to the over-etching cannot be avoided. In FIG. 12, 10 is a silicon substrate and 11 is SiO
₂ film, 12 is a polysilicon film, 13 SiO ₂ film, 14 denotes a resist.

The present invention has been made in view of such problems of the conventional method. The present invention can provide a large selectivity with respect to the base, can reduce the pattern conversion difference, and can reduce the shape deterioration at the time of overetching. It is an object of the present invention to obtain a dry etching method for preventing anisotropic processing.

[0011]

Accordingly, the present invention provides a method for dry etching a polysilicon film and a polycide film formed on a substrate, comprising the steps of: forming the polysilicon film and the polycide film on the substrate; Patterning a stopper film having etching resistance on the polysilicon film and the polycide film;
After etching the polycide film and performing oxygen plasma treatment when the substrate is exposed , the stopper film is masked.
And a step of performing over-etching as a mask .

[0012]

When the polysilicon film or the polycide film is etched and the underlying substrate is exposed, oxygen plasma treatment is performed to completely remove the resist used as the etching mask, exposing the stopper film. Since the carbon source (resist) is eliminated from the reaction system in this manner, it is possible to increase the selectivity in the next step of over-etching as compared with the case where the resist is used as a mask. Further, by performing the oxygen plasma treatment, a silicon oxide film is formed on the etched side wall of the polysilicon film or the polycide film, and the silicon oxide film has a function of preventing the shape from being deteriorated in overetching performed later.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the dry etching method according to the present invention will be described below based on embodiments shown in the drawings.

(First Embodiment) FIGS. 1 to 4 show a first embodiment of a dry etching method according to the present invention.

First, as shown in FIG. 1, an SiO ₂ film 1 as a gate oxide film is formed on a surface of a silicon substrate 10 as a substrate.
Form one. Next, a phosphorus (P) -doped polysilicon film (hereinafter referred to as an n ⁺ -PolySi film) 12 serving as a gate electrode on the SiO ₂ film 11 and an oxidation resistant film serving as a mask at the time of over-etching. The films 13 are sequentially formed by, for example, a CVD method.

Next, patterning is performed on oxide film 13 using resist 14 separately. Using the patterned resist 14 as a mask, n ⁺ -P
The processing is performed by etching the polycrystalline Si film 12.

In this etching, an RF bias application type
ECR etcher was used. First, as shown in FIG.
In addition, an oxide film that serves as a mask during overetching13
With CHF as a reaction gas_Three50 gas and oxygen_SCCMVs. 2
_SCCMAnd a pressure of 10 mtorr,
Microwave output 300mA, RF bias (2MHz) 30
The etching was performed while setting to W.

Next, as shown in FIG. 3, the n ⁺ -PolySi film 12 is formed by using the resist 14 and the oxide film 13 as a mask.
Is etched. For this etching, hydrogen bromide (HBr) gas was used at a flow rate of 50 _SCCM , and a pressure of 1 _SCCM was used.
0 mtorr, μ wave output = 300 mA, RF bias (2 MHz) 20 W, and the underlying SiO ₂ film 1
Etch until 1 is exposed. At this time, if further etching is performed for over-etching, SiBr _x contributing to sidewall protection will not be generated from the etched surface.
As shown in FIG. 12, the n ⁺ -PolySi film 12
A problem that an undercut occurs in the film.

Therefore, in this embodiment, when the underlying SiO ₂ film 11 is exposed, oxygen (O ₂ ) is 100 _SCCM , pressure is 20 mtorr, μ-wave output is 300 mA, RF
Oxygen plasma processing is performed with the bias (2 MHz) set to 0 W (FIG. 4). At this time, the resist 14 serving as a mask is used.
It is desirable that the treatment be carried out until completely removed.

As shown in FIGS. 5 and 6, by this process, SiBr _x formed as a protective film on the side wall of the n ⁺ -PolySi film 12 becomes SiO _X and the side wall is oxidized to SiO _2. .

The bonding energy of Si—O is 192
Kcal / mol, and the binding energy of Si—Br is 70 Kcal / mol. For this reason, Si-Br
Bonding is performed by applying oxygen plasma treatment to form Si—O
It is easy to change to binding. That is, when the change in the binding energy is represented by the equation, Si—Br + ／ O ₂ → Si—
O + 1 / 2Br ₂ -122 Kcal / mol;
When the generation energy at which iBr ₄ is changed to SiO ₂ is expressed by an equation, SiBr ₄ + O ₂ → SiO ₂ + 2Br (ΔHf = −
111 KJ / mol), and both are exothermic reactions, so that the reaction proceeds spontaneously.

After the oxygen plasma treatment, over-etching is performed under the same conditions as the above-described etching in the state shown in FIG. The pattern sidewalls, as described above, since that is a SiO _X, the etching does not proceed, the etched surface has an incident ion, it is possible to etch the remaining removal. At the time of this over-etching, the resist 14 has been removed, and there is no carbon (C) in the reaction system. Therefore, there is an advantage that the selectivity can be increased as compared with using the resist as a mask.

(Second Embodiment) FIGS. 7 to 11 show a second embodiment of the present invention. In this embodiment, the silicon substrate 1
In the case where a material on the oxide film 20 having a step with a step on the surface of the oxide film 20 is etched, the polycide film 22 of that material is etched.
This is an example in which the present invention is applied to the case of (12, 21).
An n + -PolySi film 12 on the oxide film 20 having a step,
Then, a tungsten silicide (hereinafter WSi _x ) film 21 is sequentially formed to form a polycide film 22, on which an oxide film 13 and a resist 14 are sequentially formed as in the first embodiment.

First, as in the first embodiment, the oxide film 13 serving as a mask during over-etching is etched (FIG. 8).

Next, the resist 14, but polycide film 22 an oxide film 13 as a mask (12, 21) is not etched, this etching SF ₆ gas and HB
The r gas was used at a flow rate ratio of 5 _SCCM to 30 _SCCM , the pressure was set at 10 mtorr, the microwave output was set at 300 mA, and the wafer substrate temperature was set at -70 ° C.

Next, as shown in FIG. 9, when the underlying oxide film 20 is partially exposed, the resist 14 is removed by oxygen gas plasma treatment as described in the first embodiment.

At this time, n ⁺ -PolySi
The etching residue 12a of the film 12 is generated, and the surface thereof is oxidized similarly to the side wall of polycide. Therefore, simply HBr
It is difficult to remove even if additional etching is performed using only gas. Therefore, stepwise etching is performed under the following conditions a) and b).

A) SF ₆ / HBr = _{2/50 SCCM} , 10
mtorr, μ wave = 300 W, RF bias = 20 W b) HBr = 50 _SCCM , 10 mtorr, μ wave = 300
W, RF bias = 20 W That is, after removing the oxide film on the unetched portion 12a with a gas system containing SF ₆ , over-etching is performed under the condition b) to maintain the anisotropy, and It is possible to remove the etching residue 12a while keeping the selectivity large.

Although both embodiments have been described above, the present invention is not limited to this, and various design changes are possible.

For example, in the first and second embodiments, the HBr gas alone or the mixed gas of the HBr gas and the SF ₆ gas was used.
Similar effects can be obtained by using r ₂ , BBr ₃ , CBr ₃ H gas, and using NF ₃ , CF ₄ gas or the like instead of SF ₆ gas.

Further, as the insulating film formed under the resist, SiO ₂ by the CVD method is used in the above embodiment, but PSG, BPSG, AsSG, SiN
Etc. can also be used. In addition, by optimizing the film thickness, it is possible to reduce the influence of reflection at the time of resist patterning on the upper portion.

Further, for removing the resist, a mixed gas of O ₂ + N ₂ , O ₂ + NH ₃ , O ₂ + H ₂ O system other than the O ₂ gas of the embodiment can be used. Before removing the resist, the gas species (Br system) or the reaction product (SiBr _x ) adsorbed on the wafer surface should be easily removed.
Heating to 300 ° C. is also applicable.

Furthermore, in the above embodiment, a reactive gas was selected as a method of removing the oxide film layer of the etching residue 12a, but a method of temporarily increasing the RF bias for increasing ion energy was used. Removing the oxide film is also applicable.

[0034]

As is apparent from the above description, it is possible to perform anisotropic processing of polysilicon and polycide without using a deposition gas while maintaining a high selectivity with respect to the base.

In particular, at the time of over-etching, the polysilicon and the sidewalls of the polysilicon are stable oxide films. Since the resist is removed in advance and carbon is excluded from the reaction system, over-etching is performed at a high selectivity. There is a possible effect.

[Brief description of the drawings]

FIG. 1 is a process chart of a first embodiment.

FIG. 2 is a process chart of the first embodiment.

FIG. 3 is a process chart of the first embodiment.

FIG. 4 is a process chart of the first embodiment.

FIG. 5 is an explanatory cross-sectional view showing a state of a side wall when a base is exposed by etching in the first embodiment.

FIG. 6 is a sectional view showing a state of a side wall when oxygen plasma processing is performed in the first embodiment.

FIG. 7 is a process chart of the second embodiment.

FIG. 8 is a process chart of the second embodiment.

FIG. 9 is a process chart of the second embodiment.

FIG. 10 is a process chart of the second embodiment.

FIG. 11 is a process chart of the second embodiment.

FIG. 12 is a cross-sectional view showing a state where conventional over-etching is performed.

[Explanation of symbols]

11 SiO ₂ film, 12 polysilicon film, 13 oxide film, 14 resist, 21 tungsten silicide film, 22 polycide film.

Claims (2)

(57) [Claims] 1. A polysilicon film formed on a substrate.
A method for forming the polysilicon film on the substrate,,  An etching resistant storage on the polysilicon film
Patterning the film,  Etching the polysilicon film, exposing the substrate
Oxygen plasma treatmentAfter performing, the stopper
A step of performing over-etching using the film as a mask,To
A dry etching method, comprising: 2. A drive for a polycide film formed on a substrate.
In the etching method, a step of forming the polycide film on the base;,  An etching resistant stopper on the polycide film
Patterning the film and,  Etching the polysilicon film, exposing the substrate
Oxygen plasma treatmentAfter performing, the stopper
A step of performing over-etching using the film as a mask,To
A dry etching method, comprising: