JPH0390584A - Dry etching method - Google Patents

Abstract

PURPOSE:To efficiently etch an amorphous semiconductor, etc., by incorporating gaseous N2 into a gaseous etchant consisting of CF4 and O2 in a specified ratio. CONSTITUTION:A gaseous mixture of CF4, O2 and N2 is used as a gaseous etchant in dry etching. The gaseous N2 is incorporated by <=20% based on the total flow rate of the gaseous mixture or preferably by 3-15%. The decomposition of the CF4 radical is accelerated by N2, the recrystallization of active F radical is prevented, and consequently the etching rate is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a dry etching method using plasma, and particularly to a dry etching method that can efficiently etch 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 made of quartz or stainless steel, and a pair of electrodes 2 facing each other are provided on the outer periphery of the left and right side walls surrounding the reaction chamber. A support 5 for placing the material to be etched 4 is installed between the pair of electrodes 2.
A mesh shield 7 is provided to surround the support base 5 so that the gas near the electrode 2 becomes a neutral gas and the gas near the electrode 2 becomes an ionic gas.

Furthermore, 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 the other side wall (
An exhaust port 6 for sucking and exhausting gas is provided at the bottom (in the figure).

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, to etch a Si thin film, CF4
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 CF due to inelastic collisions with high-energy electrons of the plasma.
, * (where * indicates a radical) generates other radicals, which diffuse toward the sample to be etched and reach the sample. After that, CF3* and other radicals are once adsorbed to the sample, and after dissociation, S
Reacts with t to produce SiF4, 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, in the past, when etching an amorphous semiconductor, particularly amorphous silicon, there has been no specification of an etching gas suitable for the purpose.

Also, when etching amorphous silicon, CF4 and 02 when etching crystalline silicon.
The etching rate was not sufficient just by using an etching gas consisting of.

SUMMARY OF THE INVENTION An object of the present invention is to provide a dry etching method that can efficiently etch an amorphous semiconductor.

[Means for Solving the Problems] In order to achieve the above object, the present invention firstly provides CF,
A dry etching method using a mixed gas consisting of 02, 02, and N2 as an etching gas, characterized in that a gas containing N2 gas at a ratio of 20% or less to the total mixed gas flow rate is used as the etching gas. Second, the dry etching method described above is characterized in that a gas containing N2 gas at a ratio of 3% to 15% of the total mixed gas flow rate is used as the etching gas. Provides an etching method. Thirdly, the above two dry etching methods are provided as methods for etching amorphous semiconductors, and fourthly, the same methods are provided specifically as methods for etching amorphous silicon.

E-effect When N2 gas is mixed as in the present invention, N2 becomes CF4.
It works to accelerate the decomposition of radicals and prevent the recombination of active F* radicals. Therefore, if dry etching is performed by mixing N2 into a mixed gas of CF4 and 02, the etching speed can be increased.

By mixing 20% or less of N2 gas, the etching rate can be made more efficient than when no N2 gas is mixed.
By increasing the efficiency by 1.5 times or more, it is possible to obtain an efficiency of 1.5 times or more.

It has been confirmed that these methods are extremely excellent dry etching methods for amorphous semiconductors, especially amorphous silicon.

[Example] The apparatus used in this example will be explained according to FIG. 2.

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. Between a pair of electrodes 2 facing each other, an aluminum support stand 5 is installed for placing an object to be etched (substrate 4), and a stainless steel mesh shield 7 is installed to surround this support stand 5. It is being

Furthermore, 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 the other side wall (
An exhaust port 6 for sucking gas is provided at the bottom (in the figure).

The experiment was carried out using such an apparatus under the following conditions.

That is, as the material to be etched, 50o+mX50
A-3i (amorphous silicon) film with a thickness of 5.000 angstroms was deposited on a glass plate of IIffl.
Using a sample formed by method D, half of the a-8L film surface was covered with an aluminum mask, and the sample was placed vertically on a support stand. After that, the flow rate ratio of CF4 and 02 gases was 95.
The etching gas was mixed with N2 gas to form an etching gas, which was introduced into the reaction chamber at a confluence of 1200 seconds. A voltage was applied. In this case, the operating pressure is 0.5 (Torr
)Met.

N2 gas is 0, 3, 5, 10, 1 with respect to the total flow rate.
The tests were carried out at 5%, 20%, and 25%, 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.

FIG. 1 is a graph showing the effect of mixing N2 gas with the etching speed ratio calculated using the etching speed when no N2 gas was mixed as a reference (1.0). This graph shows that by mixing 20% or less of N2 gas, the etching rate can be made faster than when no N2 gas is mixed, and efficient etching can be performed.

Furthermore, it can be seen that by adding 3% or more of N2 gas, it is possible to obtain an efficiency of 1.5 times or more (see the shaded area in the figure).

In addition, by mixing around 5% N2 gas, 1.
It can also be seen that an efficiency of about 8 times can be obtained.

As a result of study, the inventors found that the ratio of 02 is C F
It has been found that 10% or less of the total of 4 and 02 is desirable. That is, if the ratio of 0□ is greater than 10%, the etching rate becomes slow and the effects of the present invention cannot be sufficiently obtained.

Further, the operating pressure can be applied in the range of 10 -3 to I Torr, but is preferably in the range of 0.2 to 0.7 Torr, and optimally around 0.5 Torr.

The sample to be etched by the method of the present invention is not limited to the a-St thin film listed in the Examples, but also the CF4
The effects of the present invention can be obtained as long as the sample can be etched using gas; for example, 5i1SiO
2, Si, N4, Mo1W, etc. However, it is best to do so on a-3L.

Furthermore, the present invention is not limited to active ion etching as described in the above embodiments, but any etching method that uses a chemical reaction as an etching mechanism may be used, and similar effects can be obtained even with plasma etching, ion beam etching, etc. be able to.

Furthermore, it goes without saying that the dry etching apparatus that can be used is not limited to those listed in the examples.

[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 drawings]

FIG. 1 is an etching rate curve when N2 gas is added according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of a 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 (4)

[Claims] (1) In a dry etching method using a mixed gas consisting of CF_4, O_2, and N_2 as an etching gas, a gas containing N_2 gas at a ratio of 20% or less to the total mixed gas flow rate is used as the etching gas. A dry etching method characterized by: (2) The dry etching method according to claim 1, wherein a gas containing N_2 gas at a ratio of 3% to 15% of the total mixed gas flow rate is used as the etching gas. (3) The method according to claim 1 or 2, wherein the material to be etched is an amorphous semiconductor. (4) The method according to claim 3, wherein the material to be etched is amorphous silicon.