JPS6234835B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel dry etching method for masks.

Mask plates, which are photomask materials used in the manufacturing process of semiconductor devices, are coated with light-shielding substances such as chromium, chromium, etc. on glass substrates.
It is constructed by forming a single layer or multiple layers of thin film layers made of iron, silicon, or their oxides. As the light-shielding substance, chromium-based materials are generally used because of their excellent adhesion to glass, which is a transparent substrate, their excellent light-shielding properties, and their ability to form fine patterns. Note that in the present invention, the chromium-based film refers to a single layer or multilayer film of chromium or its oxide.

By the way, ceric ammonium nitrate [Ce( _NH4 ) ₃
Wet chemical etching using chemicals such as a mixed solution of (NO ₃ ) ₆ ] and perchloric acid [HClO ₄ ] is applied.

However, wet chemical etching has many drawbacks such as difficulty in forming fine patterns, difficulty in controlling dimensions, high defect density, and complicated waste liquid treatment.Recently, gas plasma etching or reactive ion etching has been Dry etching techniques such as these have been developed and put into practical use. Reactive ion etching is a method in which gas plasma is generated between parallel plate electrodes and etching is performed in situ.

Conventionally, in these dry etching methods, a mixed gas containing at least chlorine gas such as carbon tetrachloride and oxygen gas is heated to Cr+20+ by glow discharge.
The chromium thin film is etched away through a reaction thought to be 2Cl→CrO ₂ Cl ₂ ↑. As is clear from the above chemical reaction equation, the presence of oxygen atoms is essential for dry etching a chromium-based film. However, in conventional dry etching using a mixed gas plasma of chlorine gas and oxygen gas or air, the oxygen gas plasma decomposes the photosensitive resin film that is the etching-resistant mask material for the chromium film. Therefore, if the partial pressure of oxygen gas in the mixed gas is increased, the etching rate of the chromium-based film can be increased, but at the same time, the decomposition speed of the photosensitive resin film is also increased. Therefore, if the oxygen partial pressure is increased in order to increase the etch rate of the chromium-based film to a practical level, the decomposition of the resist will also be accelerated, resulting in increased dimensional variation within the mask surface, making dimensional control extremely difficult. This is causing various problems such as

Recently, electron beam exposure technology has been developed as a high-precision exposure technology to replace light exposure technology, but the dry etching resistance of resists for electron beam exposure is even worse than that of photosensitive resists. Therefore, if a resist for electron beam exposure is used as an etching mask material and a mixed gas plasma containing chlorine-based gas and oxygen gas is used, dry etching is basically impossible because the resist film is greatly reduced. There is a problem.

An example is shown in FIG. Figure 1 shows a mixed gas containing carbon tetrachloride ( _CCl4) as an etchant gas.
₂ is a graph showing the etching rate of a chromium-based film and the etching rate of a photosensitive resin film in the case of plasma etching using +O 2 +He) using the carrier gas composition ratio (O ₂ /O ₂ +He x 100) as a parameter. The photosensitive resin film used here was a negative electron beam resist OEBR-100 (manufactured by Tokyo Ohka Kogyo Co., Ltd.).

The inventors of the present invention have conducted extensive research to overcome the above-mentioned drawbacks, and have found that a material to be etched, in which a photosensitive resin film with a predetermined pattern is provided on a chromium-based film, is treated with at least a halogen-based gas, nitrogen monoxide, or When dry etching is performed using a mixed gas plasma containing nitrogen oxide gas such as nitrogen dioxide, it is possible to suppress the loss of the photosensitive resin film, which is a masking material for etching, and at the same time obtain a high etching rate of the chromium-based film. Therefore, the inventors discovered that it is possible to obtain a chromium-based film pattern with extremely high dimensional accuracy, and completed the present invention.

As the halogen gas used in the present invention, a chlorine gas such as dichloromethylene is preferable.

Next, the dry etching method of the present invention will be explained with reference to Examples.

Example 1 A mixed gas plasma consisting of dichloromethylene, nitrogen monoxide, and helium was used as an etchant gas on a sample in which a desired pattern was formed using a negative electron beam resist OEBR-100 on a plate made of a chromium film. Plasma etching was performed.

A plasma etching device having a cylindrical electrode was used as the etching device. Also, the etching conditions are
A high frequency power of 13.56 MHz and 200 W was applied, and the gas pressure was 0.2 Torr. The mixed gas was created by bubbling carbon tetrachloride with a carrier gas (CO+He).

FIG. 2 is a graph showing the etching rate of the chromium film and the etching rate of OEBR-100, which is a mask-resistant material, using the composition ratio of the carrier gas, that is, the composition ratio of nitrogen monoxide and helium, as a parameter.

Here, in FIG. 1 and FIG. 2, the composition ratio of the carrier gas is a value shown as O ₂ /O ₂ +He×100 (%) in FIG. 1, and NO/NO + He in FIG. The value is expressed as ×100 (%).

As is clear from FIG. 2, as the amount of nitrogen monoxide in the carrier gas increases, the etch rate of the chromium film increases rapidly. On the other hand, OEBR
Although there are some changes in the etching rate of 100,
It has been suppressed to an almost acceptable level for practical purposes.

For example, as shown in Figure 1, when a mixed gas of oxygen gas and helium is used as the carrier gas, the etching rate of a chromium film is 75 Å/min when the carrier gas composition ratio is 50%, that is, O ₂ :He = 1:1. Yes, the etching rate of OEBR-100 is 160 Å/min.

On the other hand, as shown in Figure 2, when a mixed gas of nitrogen monoxide and helium is used as the carrier gas, the composition ratio of the carrier gas is 50%, i.e.
When NO:He=1:1, the same degree of etching rate of the chromium film is obtained, and the etching rate of OEBR-100 at this time is about 1/3 of that when oxygen gas and helium are used at 50 Å/min. By adding nitrogen monoxide in this way, a large etching rate of the chromium film can be obtained, but decomposition of the photosensitive resin film is suppressed.

This is a phenomenon that does not occur with conventional dry etching techniques in which oxygen gas is added. Therefore, dry etching technology using a mixed gas plasma in which nitrogen monoxide is added to a halogen-based gas, especially a chlorine-based gas, has made it possible to manufacture high-precision chromium-based masks. Dry etching of chrome-based masks using line resist has become possible.

Further, in the above embodiment, a gas plasma etching apparatus having a cylindrical electrode was used as the dry etching apparatus, but a so-called reactive ion etching (R.I.E.) etching apparatus having a parallel plate type electrode was used. It can also be applied to equipment. Note that although helium was mixed with nitrogen monoxide as the carrier gas, other inert gases such as argon nitrogen are also effective instead of helium, and of course, the same effect can be obtained with nitrogen monoxide alone.

Furthermore, in the above example, a plate consisting of a single layer of chromium film was used as an etching sample, but it is also possible to use a so-called low-reflection chrome plate, which is a two-layered chromium film and chromium oxide film formed on a glass substrate. It was confirmed that it had a similar effect.

As described above, according to the mask dry etching method according to the present invention, a material to be etched, which has a photosensitive resin film having a predetermined pattern on a mask plate made of chromium or chromium oxide, is etched with dichloromethylene monoxide. Since the dry etching is performed using a mixed gas plasma containing carbon, the dimensional accuracy can be improved and a highly accurate mask can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the etching rates of a conventional chromium-based film and a photosensitive resin film, and FIG. 2 is a graph showing the etching rates of a chromium film and a photosensitive resin film in an embodiment of the present invention.

Claims (1)

[Claims] 1. A material to be etched, on which a photosensitive resin film having a predetermined pattern is provided on a mask plate made of chromium or chromium oxide, is etched using a mixed gas plasma containing dichloromethylene and nitrogen monoxide. 1. A dry etching method for a mask, which comprises performing dry etching to form a mask having the above-mentioned predetermined pattern. 2. The dry etching method for a mask according to claim 1, wherein the dry etching is gas plasma etching or reactive ion etching.