JPH06289592A - Production of photomask - Google Patents

Abstract

PURPOSE:To provide the method capable of stably plotting exact patterns without accumulating the electrons projected from an electron gun on an electron beam resist at the time of producing the photomask having light absorptive insulating thin films by an electron beam exposing method. CONSTITUTION:A tantalum nitride thin film 2 is formed on a transparent substrate 1. A light shieldable thin film 32 and the light absorptive insulating thin films 31 and 33 are formed thereon exclusive of its end. The patterns are then plotted on the electron beam resist 4 in the state of pressing a grounding pin 5 to the surface at the end. The electron irradiated from the electron gun are discharged to the grounding pin via the tantalum nitride 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a photomask using an electron beam exposure method, and more particularly to a method capable of preventing the generation of static electricity in the manufacturing process and improving the yield thereof.

[0002]

2. Description of the Related Art Generally, a method of manufacturing a photomask using an electron beam exposure method forms a light-shielding metal thin film such as metallic chromium on a transparent substrate and deposits an electron beam resist on the light-shielding metal thin film. This electron beam resist is applied in a pattern by an electron beam emitted from an electron gun to expose the resist in a pattern, and the electron beam resist remaining after development is used as an etching resist to form the light-shielding metal thin film. A method of manufacturing the above photomask having a light shielding pattern by etching is adopted.
Then, according to this method, it is possible to form a fine pattern with higher accuracy as compared with the method using a photoresist and ultraviolet rays.

However, since the light-shielding pattern thus formed is composed of the light-shielding metal thin film, its light reflectance is high. For example, when the exposure light beam is radiated over the photoresist coated on the semiconductor substrate. The reflected light from the light-shielding metal thin film may become ambient light, resulting in a decrease in the accuracy of the pattern reproduced on the photoresist. In order to avoid this, the light-shielding metal thin film and the light-absorbing insulating thin film such as chromium oxide are formed on the transparent substrate, and the electron beam resist is applied and electron beam drawing is performed, followed by development, and the remaining electron beam resist is removed. There is a method of forming a light shielding pattern by etching the light absorbing insulating thin film and the light shielding metal thin film as an etching resist. Further, according to this method, since the light-absorbing insulating thin film is formed on the light-shielding metallic thin film, the light rays incident on this light-shielding pattern are absorbed by the light-absorbing insulating thin film and do not generate reflected light. .

However, unlike the above-mentioned metal thin film, this light-absorbing insulating thin film is electrically insulating, so that the electrons emitted from the electron gun are easily accumulated on the electron beam resist,
Then, the electrons thus accumulated on the electron beam resist generate an electric field to distort the flight direction of the electrons irradiated from the electron gun, and distort the pattern originally to be drawn on the electron beam resist.

In order to prevent the deterioration of the drawing pattern accuracy due to such accumulation of electrons, in general, as shown in FIG.
A ground pin is pierced from above the resist to ground the light-shielding metal thin film. That is, in FIG.
Is a transparent substrate, b is a light-shielding metal thin film such as metal chromium, c is a light absorbing insulating thin film such as chromium oxide, and d is an electron beam resist coated on the light absorbing insulating thin film. Then, the earth pin e is pierced from above the electron beam resist d so that the tip of the earth pin e is made into the light-shielding metal thin film c.
It is stopped inside and the light-shielding metal thin film c is grounded at this tip. Since the light absorbing insulating thin film d is formed as a thin film having a thickness of several hundred angstroms, the electrons emitted from the electron gun pass through the light absorbing insulating thin film d and reach the light shielding metal thin film c. However, it is discharged through the ground pin e.

[0006]

However, the light-shielding metal thin film is still formed as a thin film having a thickness of about several hundred angstroms. Therefore, it is extremely difficult to stop the tip of the ground pin e inside the light-shielding metal thin film c, and the tip may not reach the metal thin film c or may penetrate the metal thin film c. .

In any of the cases, the conductivity between the electron beam resist and the ground pin is insufficient to prevent sufficient grounding, or it seems that sufficient conductivity is ensured. There is a problem in that conductivity changes during electron beam writing and grounding becomes insufficient, and as a result, electrons are accumulated on the electron beam resist and the writing pattern is easily distorted.

The present invention has been made based on such a technical background, that is, an object of the present invention is to provide a photomask having the above-mentioned light-absorbing insulating thin film and therefore having a small light reflectance. To provide a method for producing the above photomask, which is capable of stably and accurately drawing a pattern without causing the electrons irradiated from the electron gun to be accumulated on the electron beam resist in producing the electron beam by the electron beam exposure method. is there.

[0009]

That is, the invention according to claim 1 forms a tantalum nitride thin film on a transparent substrate, and then, on this tantalum nitride thin film, the tantalum nitride thin film end has a smaller area than this tantalum nitride thin film. A light-shielding thin film composed of a light-shielding metal thin film and a light-absorbing insulating thin film is formed at a position where the portion is exposed, and then an electron is formed on the light-shielding thin film so that the end of the tantalum nitride thin film is exposed. A line resist is applied, and an electron beam is drawn in the state where the ground pin is brought into contact with the end surface of the tantalum nitride thin film and grounded, then the electron beam resist is developed, and the electron beam resist thus left is used as an etching resist. The exposed portion of the light-shielding thin film is etched.

In such a technical means, the tantalum nitride thin film is used for surely and easily guiding the electrons irradiated on the electron beam resist from the electron gun to the ground pin at the time of electron beam drawing. Since the ground pin is in contact with the ground pin, the conductivity between the tantalum nitride thin film and the ground pin is sufficiently and surely secured, and is stably maintained even during electron beam drawing. Since the electrons are surely discharged through the tantalum nitride thin film, it is possible to accurately draw the pattern originally intended to be drawn.

As such a tantalum nitride thin film, for example, a tantalum nitride thin film having a composition of TaNx (where x is 1 or less) can be used, and the conductivity between the electron beam resist and the ground pin is sufficiently high. In order to secure it, it is necessary to have a film thickness of 30 Å or more.
Further, if this tantalum nitride thin film is too thick, the accuracy of the drawing pattern may be deteriorated, so it is desirable to have a film thickness of 100 angstroms or less.

This tantalum nitride thin film is a thin film having a high light transmittance. For example, when the tantalum nitride thin film is exposed to a photoresist on a semiconductor substrate by a contact exposure method, if the thickness is about 80 angstroms, the nitriding is performed. It is not necessary to remove the tantalum thin film, but rather it is desirable to leave it as it is to form a photomask in order to prevent the generation of static electricity between the photoresist and the photomask.

On the other hand, when the tantalum nitride thin film has a thickness of 80 angstroms or more, the light transmittance decreases. Therefore, after the light shielding thin film is etched to form the light transmitting region of the photomask, the exposed light transmitting portion is exposed. It is desirable to etch away the conductive thin film in the area.
Further, even when the thickness is 80 angstroms or less, for example, when a photomask is overlaid on a photoresist on a semiconductor substrate by using a stepper and exposed, the light transmittance is further improved. It is desirable to etch away the tantalum nitride thin film in the light transmitting region.

The invention according to claim 2 is based on such a technical background, that is, the invention according to claim 2 is based on the invention according to claim 1, and the above-mentioned light-shielding thin film is etched. After that, the exposed portion of the tantalum nitride thin film is etched.

The tantalum nitride thin film is, for example,
It is possible to remove it by alkaline etching using an alkaline etching solution such as NaOH or KOH.

The tantalum nitride thin film is preferably formed by a reactive sputtering method. For example, nitrogen gas is added in an amount of 0.5 to 0.5 with respect to argon gas at a molar ratio of 10.
Introduced at a rate of 2.5, the pressure in the sputter chamber is 10 ^-3 ~
An example is a spattering method in which the target is metallic tantalum in the DC magnetron system set to about 10 ⁻⁵ Torr.

As the light-shielding thin film, a multilayer film in which a light-absorbing insulating thin film is applied to the upper surface (opposite side of the transparent substrate) of the light-shielding metal thin film or both upper and lower surfaces thereof can be used. As the thin film, a thin film of metal chrome or metal nickel having a thickness of 100 to 1000 angstrom can be used. The light absorbing insulating thin film has a thickness of 100.
A thin film of chromium oxide having a thickness of about 500 Å can be used, and electrons irradiated on the electron beam resist can pass through this thin insulating film and reach the tantalum nitride thin film. When the light-shielding thin film is composed of metallic chromium, it is possible to form a metallic chromium thin film by sputtering metallic chromium as a target in a mixed gas of nitrogen and argon. It is possible to form a chromium oxide thin film by mixing a slight amount of oxygen gas in a mixed gas of argon and argon. Therefore, the metal chromium thin film and the chromium oxide thin film can be continuously formed.

[0018]

According to the invention of claim 1, a tantalum nitride thin film is formed on a transparent substrate, and then, on the tantalum nitride thin film, at a position where the end portion of the tantalum nitride thin film is exposed in a smaller area than the tantalum nitride thin film. A light-shielding thin film composed of a light-shielding metal thin film and a light-absorbing insulating thin film is formed, and then an electron beam resist is applied on the light-shielding thin film so that the end of the tantalum nitride thin film is exposed. In order to draw an electron beam with the ground pin abutting on the end surface of the tantalum nitride thin film and grounding it, the tantalum nitride thin film and the ground pin are used to manufacture a photomask having a light absorbing insulating thin film by an electron beam exposure method. The conductivity between the two is ensured sufficiently and reliably, and is stably maintained even during electron beam writing.

According to the second aspect of the present invention, since the exposed portion of the tantalum nitride thin film is etched after etching the light shielding thin film, the light transmittance of the light transmitting region of the photomask is improved.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram for explaining an embodiment of the present invention.

As shown in FIG. 1, a tantalum nitride thin film 2 is formed on the entire surface of a transparent substrate 1 made of quartz glass, and the tantalum nitride thin film 2 is formed on the tantalum nitride thin film 2.
A light-shielding thin film 3 composed of three layers of a chromium oxide thin film 31, a metal chromium thin film 32, and a chromium oxide thin film 33 is formed at a position where the tantalum nitride thin film end portion 21 is exposed in a smaller area to form a photomask blank. Manufactured.

The photomask blank is manufactured by the following method. That is, using a magnetron sputtering device, using metal tantalum as a target, an argon flow rate of 30 SCCM, and a nitrogen gas flow rate of 4
SCCM is set, target current is 0.5 A, target voltage is 350 to 400 V, and sputter discharge pressure is 5.
The tantalum nitride thin film 2 was formed into a film having a thickness of about 60 angstrom by sputtering under the condition of 8 to 10 ^-4 Torr. The surface resistance of this tantalum nitride thin film 2 is about 3 kΩ /
It was cm ² .

Next, a portion having a width of about 5 mm from the end face of the transparent substrate 1 is covered with a metal plate to form a mask, and in this state, a mixed gas of nitrogen gas, argon gas and oxygen gas is flowed using a magnetron sputtering device. Meanwhile, a chromium oxide thin film (thickness: 200 angstrom) 31 is formed by sputtering using metallic chromium as a target, and then the gas composition is changed to continuously form a chromium metal thin film (thickness: 800 angstrom) 32 and a chromium oxide thin film ( Thickness 20
0 angstrom) 33 was deposited.

A polyimide tape is attached to the exposed portion 21 of the tantalum nitride thin film 2 of the photomask blank thus obtained, and an electron beam resist 4 is applied to the thickness of 4 to 5 μm by a spin coating method. The tape was peeled off to expose the tantalum nitride thin film 2 at this portion, which was used as a grounding portion 21.

Then, as shown in FIG. 1, the tip of the ground pin 5 is brought into contact with the surface of the tantalum nitride thin film 2 at the ground portion 21 to ground it, and a photomask pattern is drawn by an electron beam exposure device (not shown). did. Then, the electron beam resist is developed to expose the chromium oxide thin film 33, and the chromium oxide thin film 33, the metal chromium thin film 32, and the chromium oxide thin film 31 at the exposed portions are etched with an etching solution composed of cerium ammonium nitrate and hydrogen peroxide. The light shielding pattern was formed by etching.

Finally, the photomask was manufactured by immersing the exposed tantalum nitride thin film 2 in the 4% NaOH aqueous solution at 40 ° C. for 15 minutes by etching.

When the pattern of the photomask thus obtained was examined, it was completely in agreement with the originally intended drawing pattern, and no pattern distortion was observed.

Further, it was confirmed that the photomask has a high light transmittance in the light-transmitting region and a small light reflectance in the light-shielding region, so that it can accurately perform pattern exposure on the photoresist on the semiconductor substrate.

[0029]

According to the first aspect of the present invention, when the photomask having the light absorbing insulating thin film is manufactured by the electron beam exposure method, the conductivity between the tantalum nitride thin film and the ground pin is sufficient and reliable. Since it is ensured and stable even during electron beam drawing, it is possible to accurately draw the originally intended drawing pattern. Further, according to the second aspect of the invention, the light transmittance of the light transmitting region of the photomask thus accurately drawn is improved, so that there is an effect that the pattern exposure can be accurately performed on the photoresist.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of the present invention.

FIG. 2 is an explanatory view showing a conventional example.

[Explanation of symbols]

 1 Transparent Substrate 2 Tantalum Nitride Thin Film 21 Grounding Part 3 Light-Shielding Thin Film 31 Chromium Oxide Thin Film 32 Metal Chrome Thin Film 33 Chrome Oxide Thin Film 4 Electron Beam Resist 5 Earth Pin

Claims (2)

[Claims] 1. A tantalum nitride thin film is formed on a transparent substrate,
Then, on this tantalum nitride thin film, a light-shielding thin film composed of a light-blocking metal thin film and a light-absorbing insulating thin film is formed at a position where the tantalum nitride thin film end portion is exposed in a smaller area than this tantalum nitride thin film, Next, an electron beam resist is applied on the light-shielding thin film so that the end portion of the tantalum nitride thin film is exposed, and an electron beam is drawn in a state where the earth pin is brought into contact with the end surface of the tantalum nitride thin film and grounded, Then, the electron beam resist is developed, and the exposed portion of the light-shielding thin film is etched by using the remaining electron beam resist as an etching resist. 2. The method of manufacturing a photomask according to claim 1, wherein the exposed portion of the tantalum nitride thin film is etched after the light-shielding thin film is etched.