JPH0322425A - Manufacture of photomask - Google Patents

Abstract

PURPOSE:To remove an ionizing radiation resist composed of a high molecular compound completely in a short time by applying energy beams in an oxidizing gas atmosphere. CONSTITUTION:When an organic high molecular compound is irradiated with energy beams in an oxidizing gas atmosphere such as oxygen gas containing ozone, the chemical bonds of the compound are cut. The compound is oxidative- destructed by oxygen atoms under an excitation state generated and gasified by simultaneously irradiating ozone with energy beams. The action of oxidative destruction gives damage to the surface of a substrate 1 because oxidizing power is too strong. However, oxidizing power can be controlled by mixing an inert gas into an oxidizing gas. Accordingly, the substrate 1 on which a reflecting chromium 2 layer is formed particularly is not damaged, and the ashing of the organic high molecular compound such as a resist 3 can be conducted in a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a photomask used for manufacturing high-density integrated circuits such as LSIs and VLSIs, and particularly to a manufacturing method with high productivity.

[Conventional technology]

In recent years, many high-precision products such as photomasks for manufacturing semiconductor integrated circuits, reticles for Stesopar exposure, and master masks for aligner exposure are manufactured by etching processing using electron beam lithography.

This manufacturing process will be explained according to the drawings.

FIG. 1 is a cross-sectional diagram showing the process of creating a photomask, where l is the substrate, 2 is the chromium film, 3 is the resist layer, 4 is the ionizing radiation, 5 is the exposed area, 6 is the etching gas plasma, 7 indicates oxygen plasma.

First, an ionizing radiation resist such as chloromethylated polystyrene is uniformly applied onto an optically polished mask substrate l having a chromium film 2 by a conventional method such as spin coating, and then heated and dried to a thickness of 0. A resist thin film 3 having a thickness of about .1 to 2.1 μm is provided (a). The heat drying process depends on the type of resist, but is usually 80 to 150°C and 20°C.
~60 minutes.

Next, a pattern is drawn on the ionizing radiation resist layer 3 using an ionizing radiation 4 exposure device such as an electron beam drawing device according to a conventional method (b), and then a developer containing an organic solvent such as ethyl cellosolve or ester as a main ingredient is used. After development, a resist pattern (C) is formed by rinsing with alcohol.

Furthermore, after performing heat treatment and descum treatment to remove unnecessary resist such as resist scraps and whiskers remaining at the edges of the resist pattern as necessary, wet the processed portion exposed from the opening of the resist pattern. Alternatively, dry etching is performed using etching gas plasma 6 to form the pattern (d).

After ethoching in this manner, the remaining resist indicated by 5 in (e) is removed by solvent stripping or ashing with oxygen plasma 7 (e), and the photomask is completely destroyed (f).

[Problem to be solved by the invention]

However, recent advances in semiconductor integrated circuits, plasma displays, etc. have become increasingly highly integrated and highly efficient.
Demand for miniaturization, higher precision, and shorter delivery times for photomasks and the like is rapidly increasing. In order to meet these demands, in the production of photo-1 masks using electron beam lithography, an integrated production line including electron beam exposure, development, baking, etching, and film removal is being attempted. The current situation is that the film removal process takes a long time, reducing production efficiency.

That is, the conventional method of stripping a resist film using oxygen plasma associating requires a vacuum device, which causes problems such as low productivity and insufficient associating on the side and back surfaces of the substrate.

Furthermore, although resist stripping using a solvent can process a larger number of resists than oxygen plasma associating, it is difficult to control the fatigue level of the solvent, it takes time to replace the solvent, and some solvents are extremely dangerous. There are some problems.

? Therefore, the present inventor ethoched a substrate to be processed on which a resist pattern made of an organic polymer compound was first formed,
To remove the resist remaining after ethoching, we proposed removing the resist by irradiating it with energy rays in an oxidizing gas atmosphere (Japanese Patent Application No. 1983-
No. 15290).

This method is extremely effective for ashing organic polymer compounds from chromium masks, molybdenum silicide masks, SiO2 masks, and substrates, but photomasks with antireflection films such as chromium oxide and chromium nitride cannot be used with oxidizing power. It has been found that there is a problem in that not only the resist but also anti-reflection films such as chromium oxide and chromium nitride films are damaged because the oxidation is too strong.

An object of the present invention is to further improve a method for ashing a resist made of an organic polymer compound using an oxidizing gas, and to provide a method for stripping a resist that is simple and easy to form into lines.

[Means to solve the problem]

The present invention manufactures a photomask by etching a processed substrate on which a resist pattern made of an organic polymer compound is formed, and removing the resist remaining after etching by irradiating energy rays in an oxidizing gas atmosphere. The method is characterized in that an inert gas is mixed into the oxidizing gas.

The substrate to be processed used in the present invention is a glass substrate made of quartz glass, low expansion glass, soda glass, etc., on which a film of chromium, molybdenum, molybdenum silicide, etc. is deposited to a thickness of 0.05 to 0.2 μm by sputtering. Further, as an anti-reflection film, a film formed by laminating chromium oxide, chromium nitride, molybdenum oxide, molybdenum nitride, etc. to a thickness of 0.01 to 0.1 μm by sputtering is used.

Examples of the resist material made of an organic polymer compound to be laminated on the antireflection film on the substrate to be processed include polyglycidyl methacrylate, glycidyl methacrylate-acrylic acid copolymer, cross-methylated polystyrene, polybutene-1 sulfone, and poly(α-chlorotrifluoride). In addition to resists for exposure to ionizing radiation such as fluoroethyl acrylate 1, there are novolak-based positive-type photoresists, cyclized rubber-based negative-type photoresists, and the like.

In the photomask manufacturing method of the present invention, the pattern drawing step shown in FIG. 1(b) and the etching step of the chrome mask etc. shown in FIG. 1(d) are carried out in the same manner as in the conventional method described above. In the process of removing the resist 5 shown in FIG. 1(e), the oxidizing power is moderately controlled by introducing an inert gas into the oxidizing gas when irradiating the energy beam in an oxidizing gas atmosphere. It is something to do.

Further, as the oxidizing gas, oxygen gas containing ozone, which is produced by a normal ozone generator, is preferable.
In this case, the ozone concentration is preferably 1 to 10%. Also, Uesoto, which can be obtained by passing air through water,
Air, or a mixture of air or oxygen, can also be used as a good oxidizing gas.

As the inert gas mixed into this oxidizing gas, nitrogen, air, helium, argon, etc. can be used, and the partial pressure in the oxidizing gas is 0.3 to 15V.
o It is preferable to contain it so that it becomes 1%.

Energy rays include deep ultraviolet light, electron beams and A wavelength with a strong intensity is preferable.

[Effect]

Generally, when organic polymer compounds are irradiated with energy rays in an oxidizing gas atmosphere such as ozone-containing oxygen gas, their chemical bonds are broken, and at the same time, excited oxygen atoms are generated when ozone is irradiated with energy rays. It is oxidized and decomposed and gasified.

However, although this action is effective in ashing the organic polymer compound in a short time, the oxidizing power is too strong and damages the substrate surface. Therefore, the present invention has discovered that it is possible to control the oxidizing power by mixing an inert gas into the oxidizing gas, and as a result, the oxidizing power can be controlled without causing damage to the substrate provided with the low-reflection chromium layer. It is capable of ashing organic polymer compounds such as resist in a short time.

Examples will be described below.

[Example 1] A resist solution of chloromethylated polystyrene was applied by spin coating onto a photomask substrate on which a chromium layer and a low-reflection chromium layer were sequentially laminated, and the coating was heated at 120°C for 30 minutes.
A uniform resist film having a thickness of 0.6 μm was obtained by buri-paking for a minute. Next, the beam diameter is 0.5μm, and the acceleration voltage is 10KV.
exposed to an electron beam at a dose of 1 μC/all,
I drew a pattern. After exposure, this substrate was treated with a developer consisting of a mixture of isoacetate and ethyl cellosolve for 60 minutes.
After developing for a second, the resist pattern was rinsed with isopropyl alcohol for 30 seconds to obtain a resist pattern. After boss-baking this at 140°C for 30 minutes, it was descumed for 2 minutes in oxygen plasma of 100W Torrs, and exposed using the resist pattern as a mask. Dry ethoched.

While heating this substrate to 80° C., the remaining resist film was ashed and removed by irradiating it with far ultraviolet light in an oxygen atmosphere containing 5 vol% ozone and 10 vol% nitrogen.

The resist was completely removed in the required time of 3 minutes, and the damage to the low-reflection chromium film was only 10~15%.

For comparison, when the resist film was removed in the same manner as above in an oxygen atmosphere containing no nitrogen, that is, an oxygen atmosphere containing 5 vol% ozone, the damage to the low-reflection chromium film reached 30%. did.

[Example 2] A resist solution of poly(α-chlorotrifluoroethyl methacrylate) was applied by spin coating onto a photomask substrate on which a chromium layer and a low-reflection chromium layer were sequentially laminated, and prebaked at 200°C for 30 minutes. thickness 0
．． A uniform resist film of 5 μm was obtained.

Next, in the same manner as in Example 1, pattern irradiation was performed with an electron beam at an exposure dose of 3 μC/aa, and development was performed to obtain a resist pattern. This was etched for 1 minute with an aqueous solution containing ceric ammonium nitrate as the main ingredient. Subsequently, without heating this substrate, ozone 5ν01% and argon 8νol
The remaining resist film was ashed and removed by irradiation with deep ultraviolet light for 3 minutes in an oxygen atmosphere containing %. The resist was completely removed from this substrate, and the damage to the low-reflection chromium film was only 0 to 3%.

〔Effect of the invention〕

The present invention provides a method for removing organic polymer-based ionizing radiation resist remaining after ethoching by irradiating energy rays in an oxidizing gas atmosphere, compared to conventional solvent stripping and oxygen plasma ansing methods. It can be removed completely and in a short time. In particular, the oxidizing power used to be too strong and could damage the substrate, but the oxidizing power can be easily controlled, and it is made of aromatic organic polymer compounds such as polystyrene, which were previously difficult to remove. The ionizing radiation resist 1 can be completely removed in a short time, and the time required for the resist stripping process, which was a rate-determining step in the photomask manufacturing process, can be significantly shortened.

Furthermore, compared to conventional solvent stripping and oxygen plasma associating methods, the present invention is a simple method of irradiating energy rays in an oxidizing gas atmosphere, and does not require a solvent tank, waste liquid treatment, or vacuum equipment. This makes it easier to integrate the process into a production line.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the process of making a conventional photomask. 1 is a substrate, 2 is a chromium film, 3 is a resist layer, 4 is an ionizing radiation, 5 is an exposed part, 6 is an etching gas plasma, 7
indicates oxygen plasma.

Claims (4)

[Claims] (1) A substrate to be processed on which a resist pattern made of an organic polymer compound is formed is etched, and the resist remaining after the etching is removed by irradiating energy rays in an oxidizing gas atmosphere to produce a photomask. A method for manufacturing a photomask, characterized in that an inert gas is mixed into the oxidizing gas. (2) The photomask manufacturing method according to claim 1, wherein a chromium film and a low reflection chromium layer are laminated on the substrate to be processed. (3) The photomask manufacturing method according to claim 1 or 2, wherein the inert gas is nitrogen. (4) Claims 1 and 2, wherein the energy beam is an electron beam.
Or the photomask manufacturing method described in 3.