JPH03277788A - Dry etching method - Google Patents

Abstract

PURPOSE:To increase dry etching efficiency by forming the inner wall of an etching chamber out of a material not reacting with etching gas contg. CF4, O2 and N<2> and accelerating the radical decomposition of CF4. CONSTITUTION:A gaseous mixture of CF4 with O2 and N2 is introduced as etching gas into an etching chamber and plasma is generated to etch a material to be etched such as amorphous silicon. In this dry etching method, at least the surface of the inner wall of the etching chamber is formed of a material hardly reacting with the etching gas and accelerating the radical decomposition of CF4. At least the surfaces of tools in the chamber are also formed of the material as required. Al or an Al alloy is suitable for use as the material. The radical decomposition of CF4 is accelerated, the recombination of active radicals is prevented and etching speed and dry etching efficiency are increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a dry etching method using plasma, and more particularly to a dry etching method capable of efficiently etching an amorphous semiconductor thin film.

[Prior Art] In recent years, dry etching has been widely used as a method for etching amorphous semiconductor thin films, as it enables fine processing and provides excellent uniformity of the film after etching.

Dry etching includes sputter etching, which performs mechanical etching using ion bombardment, plasma etching, which performs chemical etching by exposing the sample to plasma by introducing a reactive gas, and introducing a reactive gas to generate a voltage drop. There are reactive ion etching methods in which a sample is chemically etched by exposing it to plasma while the etching process is being performed, and ion beam etching methods in which etching is performed by irradiating an ion beam.

The mechanism will be explained below using reactive ion etching as an example.

First, FIG. 2 schematically shows the equipment necessary for dry etching.

The dry etching apparatus shown in Fig. 2 consists of a reaction chamber 1 surrounded by walls made of quartz or stainless steel. A pair of electrodes 2 are provided. A support 5 for placing the material to be etched 4 is installed between the pair of electrodes 2, and the gas near the support 5 becomes a neutral gas, and the gas near the electrode 2 becomes an ionic gas. A mesh shield 7 is provided so as to surround the support base 5 so that the gas becomes . Further, a gas inlet 3 for introducing gas is provided on one side wall (the upper part in the figure) of the reaction chamber 1, and an exhaust port 6 for sucking and exhausting the gas is provided in the other side wall (the lower part in the figure). is provided.

Using such an apparatus, the material to be etched 4 coated with a mask or resist having a predetermined opening is placed on the support base 5.
put it on top. Thereafter, etching gas is introduced into the reaction chamber 1, and while the gas is exhausted from the exhaust port 6, a high frequency voltage is applied between the electrodes. Plasma is generated between the electrodes by applying a voltage, and high-energy electrons of the plasma cause inelastic collisions with gas molecules contained in the etching gas, generating radicals. The radicals cause a chemical reaction with the thin film of the object to be etched, and etching progresses.

For example, in order to etch a Si thin film, CF,
It is known that a mixed gas of and 02 can be used;
The reaction mechanism in this case is as follows.

When plasma is generated, CF4 molecules become Cr due to inelastic collisions with high-energy electrons of the plasma.
Two other radicals (*indicates a radical) are generated, and these radicals diffuse toward the sample to be etched and reach the sample. After that, CF, *other radicals are once adsorbed to the sample, and after dissociation, St
reacts with S i F4 etc. This reactant is highly volatile and therefore diffuses. As a result, Si is etched.

In addition, 02 not only generates radicals and etches them, but also removes the carbon layer formed on the sample surface.
It works to remove O2 or CO and has the effect of increasing the etching rate.

[Problems to be Solved by the Invention] However, when etching amorphous semiconductors, particularly amorphous silicon, it has not been recognized in the past that the material of the inner wall of the reaction chamber, that is, the etching chamber, can have an important effect on the etching efficiency. There was no recognition of this.

The present inventor unexpectedly discovered that the selection of the material for the inner wall of the chamber is extremely important for the purpose of efficiently etching an amorphous semiconductor.

It is an object of the present invention to develop an improved dry etching method based on this knowledge.

[Means for Solving the Problems] As a result of repeated research to solve the above problems, we have found that at least the inner wall surface of the chamber, which has conventionally been made of stainless steel, and more preferably, various types of etching required for the etching provided inside the chamber. We have learned that it is extremely effective to coat at least the surfaces of tools such as mesh shields and substrate supports with materials such as aluminum or aluminum alloys to improve the etching speed. We have developed a unique dry etching method.

The reason why aluminum or aluminum alloy is effective for the above purpose is that these metal materials contain CF4, O2 and N.
This is because it is a material that does not react, or at least hardly reacts, with the etching gas consisting of two gases, and has a catalytic function that accelerates the radical decomposition of CF 4 .

This new dry etching method has been found to be extremely effective as an etching method for amorphous semiconductors, and particularly for etching amorphous silicon.

[Function] According to the present invention, the inner wall surface of the chamber and preferably at least the surface of various articles necessary for etching disposed inside the chamber, particularly articles as etching auxiliary tools made of stainless steel, are made of or coated with an aluminum-based material. By doing so, products due to chemical reactions between Fe5Ni, etc., which are components of stainless steel, and etching gases, such as CF4, are not generated, or at least are made difficult to form, and the radical decomposition of CF4 is accelerated and active F*
Since recombination of radicals can be prevented, dry etching using the method of the present invention using a mixed gas of CF4, O2 and N2 will not damage the inner wall surface of the stainless steel chamber or the surface of the articles placed inside the chamber, as in the conventional method. Compared to dry etching performed without covering with aluminum material at all, the etching speed can be significantly increased.
It was found that an average efficiency increase of about 1.6 times could be obtained. These methods can be applied to amorphous semiconductors,
It has been confirmed that this method is particularly excellent as a dry etching method for amorphous silicon.

This will be explained in detail below using examples.

[Example] The apparatus used in this example will be explained with reference to FIG.

A pair of aluminum electrodes 2 facing each other are provided on one side and the other side of a reaction chamber 1 made of stainless steel. An aluminum support 5 for placing the object to be etched (substrate 4) is installed between a pair of electrodes 2 facing each other, and an aluminum mesh shield 7 is provided to surround this support 5. It is being Furthermore, a gas inlet 3 for introducing gas is provided on one side wall (upper part in the figure) of the reaction chamber 1, and an exhaust port 6 for sucking gas is provided in the other side wall (lower part in the figure). It is provided.

Dry etching was carried out using such an apparatus under the following conditions.

That is, as the material to be etched, 50w+m×50
■Using a sample in which a 5,000 angstrom thick a-3T (amorphous silicon) film was formed on a glass plate by the CVD method, half of the a-3T film surface was covered with an aluminum mask, and placed on a support stand. It was placed vertically. Thereafter, CF4 and 02 gases were mixed at a flow rate ratio of 95:5, and N2 gas was mixed with the gas at the ratio described below to form an etching gas, which was introduced into the reaction chamber at a total flow rate of 200 seconds, and from the exhaust port. While evacuating the gas, a high frequency voltage of 0 W was applied to the throw-in cuff between the electrodes. In this case, the operating pressure is 0.5 (Torr)
Met.

N2 gas has a ratio of 0.3.5.10.1 to the total flow rate.
5, 20, and 25% by volume, respectively.

Dry etching was performed in this manner for 5 minutes each, and the etching rate was evaluated based on the thickness of the etched film. The results are shown in FIG.

Figure 1 shows CF4 and 02 gas, which do not mix any N2 gas, in a chamber whose inner wall surface is made of stainless steel.
This is a diagram showing the change in the etching speed ratio with respect to the N2 gas mixture ratio, which was calculated using the etching speed as a reference value (1,0) when etching was performed using a mixed gas of Curve B shows the combined effect of the mixing effect of N2 gas and the effect of using aluminum as the chamber inner wall material. From these graphs, it can be seen that when the inner wall surface material of the chamber and preferably the surface material of the various etching tools placed inside the chamber are made of aluminum, the etching speed is faster than when the materials are made of stainless steel. It can be seen that the etching is improved and very effective etching can be performed.

As a result of studies by the present inventors, even when aluminum is used as the material for the surface material of the inner wall of the chamber and the material for the surfaces of various tools installed in the chamber,
Instead of dry etching using only a mixed gas of CF4 gas and 02 gas, we also add N2 gas from several percent to 14%.
If dry etching is performed using a gas mixed with N
It has been found that the etching rate increases compared to the case where the two gases are not mixed, and in particular, when the mixing ratio of N2 gas is around 8% to 10%, the efficiency of the etching rate increases to about 1.4 times. Therefore, the method of the present invention uses a mixed gas of CF4 gas and 02 gas without mixing N2 gas, and also maintains the material of the inner wall surface of the chamber and the surface material of the tools disposed in the chamber as stainless steel. When etching -Si, that is, when compared with the reference value, it can be seen that the efficiency is increased by 1, B Xl, 4 times, or approximately 2.2 times.

Further, the operating pressure can be applied in the range of 10-3 to I Torr, but preferably in the range of 0.2 to Q.7 Torr, and optimally around 0.5 Torr.

The sample that can be effectively etched by the method of the present invention is not limited to the a-3i thin film listed in the examples, but any sample that can be etched using CF4 gas may be used.For example, Si, 5io2
, Si3N4, MO%W, etc., the method of the present invention can be effectively applied.

However, this method was most effective when applied to a-8i.

Furthermore, the application of the method of the present invention is not limited to the case of active ion etching as shown in the above embodiments, but may be applied to any method in which a chemical reaction is utilized as an etching mechanism. Even when the method of the present invention is applied to etching, ion beam etching, etc., the same effects as described above can be obtained.

Furthermore, it goes without saying that the dry etching apparatus that can be used in carrying out the present invention is not limited to that shown in the above embodiments.

[Effects of the Invention] As can be seen from the above, the present invention provides a dry etching method that can efficiently etch a sample.

[Brief explanation of the drawing]

Figure 1 shows the etching rate when dry etching was performed using an etching chamber whose inner wall surface was made of stainless steel and an etching gas that did not mix any N2 gas, with the reference value (1,0) being calculated. This is a curve in which the etching speed ratio (vertical axis) is plotted against the mixing ratio (%) of N2 gas in the etching gas (horizontal axis). Curve A is a curve showing the effect of mixing N2 gas into the etching gas, and curve B is a curve showing the overall effect of adding the effect of using aluminum to the mixing effect of N2 gas. FIG. 2 is a schematic diagram of the dry etching apparatus. Explanation of symbols 1...Reaction chamber 2...Electrode 3...Gas inlet port 4...Substrate 5...Substrate support stand 6...Exhaust port a... mesh shield

Claims (6)

[Claims] (1) As an etching chamber, the inner wall or at least the surface part of the inner wall is used for etching CF_4, O_2 and N.
Using an etching chamber made of a material that does not react or at least does not easily react with the etching gas consisting of the mixed gas of _2, and has the function of accelerating the radical decomposition of CF_4, the material to be etched placed inside the chamber is etched. A dry etching method characterized in that dry etching is carried out using an etching gas made of the above-mentioned mixed gas introduced into a chamber. (2) The various tools for etching installed in the chamber, or at least their surface parts, do not react with the etching gas consisting of the mixed gas, or at least do not react easily, and have the function of accelerating the radical decomposition of CF_4. Claim 1 characterized in that it is made of a material that has
Dry etching method described. (3) The method according to claim 1, wherein aluminum or an aluminum alloy is used as a component of the inner wall of the chamber or at least the surface of the inner wall. (4) The dry etching method according to claim 2, wherein aluminum or an aluminum alloy is used as a constituent material of various tools for etching arranged in the chamber or at least their surface parts. (5) The dry etching method according to any one of claims 1 to 4, wherein the material to be etched is an amorphous semiconductor. (6) The dry etching method according to claim 5, wherein the material to be etched is amorphous silicon.