JPH02309633A - Dry etching - Google Patents

Abstract

PURPOSE:To protect a ground silicon oxide film and to secure a steep pattern shape by removing first etching with Cl2 as a reaction gas and then second etching with a specific mixed gas as a reaction gas. CONSTITUTION:After forming a silicon oxide film 2 for ground on an Si wafer 1, a polycrystalline silicon film 3 is accumulated and an etching mask 4 is completed. Then, a Cl2 gas 5 is introduced into an ECR(electron cycrotron resonance) etching device for forming etching plasma and then a polycrystalline silicon film 3 is etched by this first etching halfway to allow a pattern with a trailing to be formed. Then, the succeeding etching is performed by the second etching with a mixed gas 6 of Cl2, SF6, and O2 being as a reaction gas, thus protecting the ground silicon oxide film 2 and eliminating the trailing part of pattern for obtaining a highly accurate and steep pattern.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an etching method for forming fine patterns required in semiconductor integrated circuits, and in particular to an etching method for forming fine patterns required in semiconductor integrated circuits. This invention relates to a dry etching method for etching a crystalline silicon film.

[Conventional technology]

In silicon semiconductor integrated circuits, miniaturization of batten dimensions is required to improve speed performance, and along with this miniaturization, there is also a demand for extremely thin gate oxide films. In this rounding and etching of the polycrystalline silicon gate electrode,
Etching techniques that can create fine patterns without damaging the underlying film, which is a thin silicon oxide film, are becoming important.

Conventional methods for etching polycrystalline silicon films include, for example, a method in which only 43 gas is used as a reactant gas.The batten etched by this method tends to leave tails and easily forms a trapezoidal batten shape. On the other hand, the etching rate near the bottom of the button is locally high and the underlying silicon oxide film in that area is exposed earlier than in other parts, so the underlying silicon oxide film 2 near the bottom of the button is overgrown as shown in FIG. There is a problem in that it disappears during etching, resulting in the formation of a damaged base film 8. Therefore, especially in samples where the base silicon oxide film is extremely thin, over-etching is limited, resulting in a trapezoidal shape. The actual situation is that it is used for practical purposes.

On the other hand, Ct! In the etching process using a two-component mixed gas containing a small amount of SF as the reaction gas, isotropic etching occurs due to F radicals, so over-etching results in an inverted platform with a large undercut where the bottom of the pattern recedes. There was a drawback of the shape being a trap (see Figure 5). In addition, although there is no local etching under these conditions, the etching selectivity ratio (81/810g) is smaller than the former (approximately 20), so there is a risk that the extremely thin underlying silicon oxide film may disappear during overetching. There were drawbacks. However, in Figures 4 and 5, 1 is S
t wafer, 2 a base silicon oxide film, 4 an etching mask, and T an etching pattern of polycrystalline silicon, respectively.

On the other hand, in an etching process using a three-component mixture of Ct2, a small amount of SF, and 02 as the reaction gas, 100
Very large etching selection ratio (si/5t
oz) can be easily obtained, and the underlying silicon oxide film is improved so that it is hardly etched. but,
As with the 2m mixed gas, a/da cut occurred due to isotropic etching accompanying F radicals, and the drawback remained that the batten shape became an inverted trapezoid (see FIG. 5).

[Problem to be solved by the invention]

In this way, with the conventional dry etching method for polycrystalline silicon films, it is difficult to simultaneously maintain the extremely thin underlying silicon oxide film and ensure a highly precise and steep pattern with little undercut. there were.

The present invention has been made in view of the above points, and its purpose is to solve the above-mentioned drawbacks of the prior art, and simultaneously satisfy the requirements of preserving the underlying silicon oxide film and ensuring a highly accurate and steep button shape. The objective is to provide a new and satisfying dry etching method.

[Means to solve the problem]

To achieve the above object, the present invention provides a dry etching method for etching a polycrystalline silicon film deposited on a silicon oxide film, in which the polycrystalline silicon film is etched halfway through the first etching using Ct2 as a reactive gas. Form a batten with a hem, and then perform etching with Ct2, SF-, and 0! By carrying out the second etching using a mixed gas as the reactive gas, the base silicon oxide film is protected and the trailing portion of the pattern is removed, resulting in a highly precise and steep pattern. be.

[Effect]

In the present invention, by performing a first etching using Cl2 as a reactive gas and a second etching using a 3y11 mixed gas of Cl2, SF-, and O3 as a reactive gas,
Preserves the underlying silicon oxide film, 1! It is possible to obtain a highly accurate and steep polycrystalline silicon pattern while keeping the temperature high.

[! ! Example]

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIGS. 1(a) to 1(d) are etching process diagrams showing an embodiment of the dry etching method according to the present invention;
1 wafer, 2 is a base silicon oxide film, 3 is a polycrystalline silicon film, 4 is an etching mask, 5 is Ct2 gas used as a reaction gas for the first etching, and 8 is Ct2 and SF6 used as a reaction gas for the second etching. and 02, and γ is a polycrystalline silicon etching batt, that is, a completed polycrystalline silicon batt.

That is, in FIG. 1(a), after forming a base silicon oxide film 2 with a thickness of 7 OA on the S1 wafer 1,
A polycrystalline silicon film 3 having a thickness of 0.000A is deposited.

Next, in FIG. 1(b), first, a silicon oxide film to be used as an etching mask material is deposited on the polycrystalline silicon film 3, and a desired resist pattern is further formed thereon. Next, the upper silicon oxide film is dry etched using the resist pattern as a mask, and then the resist is removed by ashing to complete the etching mask 4. Next, in Fig. 1(c), ECR using electron cyclotron resonance (ECR) plasma by microwave excitation is shown.
Ot3 gas 5 is introduced into the etching device and the gas pressure is 0.6.
An etching plasma of mTorr and microwave power of so low is formed, and the first etching is performed to the middle of the polycrystalline silicon. At this time, the amount of etching is determined by the sample conditions such as the thickness of the polycrystalline silicon, the thickness of the underlying silicon oxide film, and the ratio of these film thicknesses, but even in the abnormally etched area (called trenching) near the button, Set within a range where the underlying silicon oxide film is not exposed. After that, in FIG. 1(d), CL! is applied to the ECR etching device. A three-component mixed gas 6 consisting of , SF, and 02 was introduced, and the gas pressure was 0.6 mTorr.

A subsequent second etching including overetching is performed under the condition of a microwave power of 600 W, thereby completing a highly precise and steep polycrystalline silicon batten T.

Figure 2 shows the three types of mixed gas (
This figure shows an example of the etching rate and etching selectivity characteristics of polycrystalline silicon and a silicon oxide film using Ctz-SF6-02) as a reaction gas. The dotted line indicated by Y indicates the etching rate characteristic of the silicon oxide film, and the dotted line indicated by 2 indicates the etching selectivity characteristic. At this time, the results are obtained when the waste flow rate was kept constant at Clz = 24aaem18F@-3sec and the amount of 02 gas added was varied. - Gas pressure is 0.6 mTorr and microwave power is 600W. Here, the etching rate of polycrystalline silicon is almost constant regardless of the amount of 02 gas added, as shown by its characteristic ,Cl,
2-24meem, SF1m3secm, 0202
It can be seen that under the -1ac condition, an extremely high etching selectivity (st/5toz) of about 300 can be secured (%2), and the underlying silicon oxide film is hardly etched under this condition.

FIG. 3 shows an example of the cross-sectional shape of a polycrystalline silicon pattern etched by the two-stage etching method of the present invention.

Here, approximately 50% of the total etching amount is etched in the first etching using C20 as a reaction gas to form a pattern with a tail, and 50% of the remaining etching amount including over-etching is etched.
% etching is performed in the second etching using a mixed gas of ct2, SF-, and 02 as the reaction gas. As a result, there was no damage to the underlying silicon oxide film, and it was possible to achieve a highly accurate and steep slam. The amount of dimensional change in the batten in this case was about 172 times the amount of dimensional change in the case of 100% etching using only two or 381 mixed gases, which was as expected. Thus, it was confirmed that the present etching method is very effective in improving dimensional accuracy.

Note that the first (C
20) and the second (Ctz +13F@+02) etching amount settings may be determined as follows. For example, a sample with a large difference in polycrystalline silicon film thickness (for example, a sample with multiple steps) requires a long overetch.

Therefore, if the underlying silicon oxide film is extremely thin, there is a high risk that the silicon oxide film near the bottom of the button will disappear quickly. All you have to do is set it until the exposure of the exposed part starts. On the other hand, for samples with similar step differences but with a thick underlying silicon oxide film, there is less risk of the silicon oxide film disappearing early, so the first etching can be extended to some extent. For a sample with a thicker base film, the process can be extended until the exposure of the portion where the polycrystalline silicon film is the thickest and the base silicon oxide film is exposed the slowest is completed. On the other hand, since the overetching of a sample with a relatively uniform polycrystalline silicon film thickness (for example, a flat sample) is shorter than that of the former (a multi-step sample), The amount of overetching of the silicon oxide film is also smaller than in the former (sample with multiple steps). For this reason, it can be said that the first etching for such a flat sample can be set to be somewhat longer than for each of the former samples (sample with steps).

In this way, the first (
The setting of the etching amount of Ctz) and the second (Cl2+ SF s +Ox) is determined according to the sample conditions, etc., and is not limited to a specific value. However, the basic idea of this method regarding this is that as much polycrystalline silicon as possible is etched in the first etching without damaging the underlying silicon oxide film, and the second etching is performed while protecting the underlying silicon oxide film. By shortening the etching, the occurrence of undercuts can be minimized and a batten with little dimensional change can be realized. Therefore, it goes without saying that it is inappropriate to unnecessarily reduce the first etching amount and increase the second etching amount because it will cause a large undercut. The etching distribution used in the above example (50
%, second 50%) was determined from the distribution of polycrystalline silicon thickness within the sample and the thickness of the underlying silicon/oxide film.

In this way, the present invention solves the problem of damage to the underlying silicon oxide film that occurred in the conventional method of 100% etching using only CTL, and also solves the problem of damage to the underlying silicon oxide film that occurs in the conventional method of etching 100% using only CTL. , +SF, +02)
This simultaneously solves the problem of deterioration in dimensional accuracy due to undercuts that occurred in the conventional method of 100% etching, and realized a highly accurate and steep polycrystalline silicon pattern.

In the above example, Ct2 w 24accmXSF6 is used as an example of the mixed gas used for the second etching.
= 3secm, 02 = lsecm, high etching selection ratio (st/sto*)
For example, Cl2-24acem, SF6-6sc
It has been confirmed that it can be obtained under mixing conditions such as cm, 02-2 sccm, etc.

In this way, the mixed gas flow rate used for the second etching is not limited to the above conditions, but other flow rate conditions may be used as long as a sufficiently large etching selectivity can be ensured with respect to the thickness of the underlying silicon oxide film. But it goes without saying that it doesn't matter. Note that instead of 02, a gas such as N2 or CO2 having some oxidizing properties may be added.

Furthermore, in the above embodiments, the case where a silicon oxide film is used as the etching mask material is described; however, if the material has a sufficient etching selectivity with silicon, for example,
Needless to say, resist, silicon nitride film, etc. may also be used.

Furthermore, the present invention is applicable not only to the etching of a single layer of polycrystalline silicon film, but also to the multilayer structure of high melting point metal silicide called polycide and polycrystalline silicon film, or the multilayer structure of high melting point metal and polycrystalline silicon film. Needless to say, this method can also be applied to etching crystalline silicon film layers.

〔Effect of the invention〕

As explained above, in the dry etching method of the present invention, Ct! After performing the first etching process using a reaction gas of This method has the great advantage of being able to simultaneously satisfy both conditions of securing a good batten shape, and etching a fine and highly accurate polycrystalline silicon pattern even on a thin underlying silicon oxide film.

Therefore, the technology of the present invention that enables etching on such a base thin film has never existed before, and is essential for future VLSI manufacturing, and its contribution is extremely important industrially.

[Brief explanation of drawings]

1(a) to (d) are etching process diagrams explaining one embodiment of the present invention, and FIG.
A diagram showing an example of the etching rate and selection characteristics of silicon and silicon oxide films when etched with a mixed gas system,
FIG. 3 is an enlarged cross-sectional view of a polycrystalline silicon pattern on an ultra-thin silicon/oxide film formed by the multi-stage etching method of the present invention, and FIG. An enlarged cross-sectional view of a polycrystalline silicon baton on a silicon oxide film, FIG.
r@)Mixed gas is an enlarged sectional view of a polycrystalline silicon pattern on an ultra-thin silicon oxide film formed by a conventional etching method using a (Cl2SF602) mixed gas as a reactive gas. DESCRIPTION OF SYMBOLS 1--Si wafer, 2--Based silicon oxide film, 3--Polycrystalline silicon film, 4-Mirror/etching mask, 5--CT2 residue, 6--3 Seed mixed gas (Ct2-8Fa O2), Tφ self-condensed/polymerized J%
Silicone etching button. Figure 1 Figure 3 Figure 2 Figure 4 Figure 5

Claims (1)

[Claims] In a dry etching method for etching a polycrystalline silicon film deposited on a base film made of a silicon oxide film, after performing the first etching using Cl_2 as a reaction gas, a mixture of three gases of Cl_2, SF_6, and O_2 is reacted. A dry etching method characterized in that a fine pattern of the polycrystalline silicon film is formed by performing a second etching using gas.