JPH03269533A - Production of photomask and substrate used therein - Google Patents

Abstract

PURPOSE:To prevent electrification and to allow production with high accuracy by forming a resist layer on a substrate to be worked, and forming a thin metallic film for preventing the electrification by ionizing radiations thereon, then irradiating the film with the ionization radiations as patterns. CONSTITUTION:A chromium film 2 is formed on the optically polished substrate 1 to form the substrate to be worked. The resist layer 3 is formed on this substrate to be worked; further, the thin metallic film 9 for preventing electrification by the ionizing radiations 4 is formed on the resist layer 3. The thin metallic film is irradiated with the ionizing radiations 4 as patterns to form resist patterns 5. The substrate to be worked is etched with the resist patterns 5 as a mask and the resist layer 3 remaining after the etching is removed. The electrification is prevented in this way and the high-accuracy mask is stably produced.

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 LSI and VLSI, and in particular, a method for manufacturing a photomask having a pattern with good dimensional accuracy. The present invention relates to a photomask manufacturing method and a substrate used therein.

[Prior Art] In recent years, many high-viscosity products such as photomasks for manufacturing semiconductor integrated circuits, reticles for stepper exposure, and master masks for aligner exposure have been manufactured by etching using electron beam lithography. This conventional manufacturing process will be explained below with reference to the drawings.

FIG. 2 is a cross-sectional view showing the process of creating a photomask. In the figure, 11 is a substrate, 12 is a chrome film, 13 is a resist layer, and 14 is a ?? l! 11 radiation, 15 Rennost pattern, 16 etching gas plasma, 17 chrome pattern, and 18 oxygen plasma.

First, a chromium film 12 is formed on an optically polished substrate 11 to form a substrate to be processed, and a mm radiation resist such as chloromethylated polystyrene is uniformly applied onto the substrate by a conventional method such as spin coating. The film is coated on the surface and heated and dried to give a thickness of 0.1 to 0.1 cm, as shown in Figure 2 (a).
A resist layer 13 of about 2.0 μm is formed. The heat drying process depends on the type of resist used, but it is usually 80%
~! The temperature is 50°C for about 20 to 60 minutes.

Next, as shown in FIG. 6(b), a pattern is drawn on the resist layer 13 using ionizing radiation 14 using an exposure device such as an electron beam drawing device according to a conventional method, and an organic solvent such as ethyl cellosolve or ester is used as the main component. After development with a developer solution, the resist pattern 15 is rinsed with alcohol to form a resist pattern 15 as shown in FIG.

Next, heat treatment and descum treatment are performed as necessary to remove the resist layer remaining in the esso portions of the resist pattern 15, and unnecessary renost such as whiskers.
As shown in d), the portion to be processed exposed through the opening of the resist pattern 15, that is, the chromium layer 12, is dry etched using the etching gas plasma 16 to form a chromium pattern 17. It is clear to those skilled in the art that the chromium pattern 17 may be formed by wet etching instead of dry etching using the etching gas plasma 16.

Thereafter, as shown in FIG. 5(e), the remaining resist pattern 15 is removed by ashes using oxygen plasma 18, thereby completing a photomask as shown in FIG. 1(f).

Note that this treatment can also be performed by solvent stripping instead of the ashing treatment using the oxygen plasma 18.

The ionizing radiation resist described in "U" can be made from organic polymer compounds such as polyglycidyl methacrylate, glycidyl methacrylate-acrylic acid copolymer, chloromethylated polystyrene, polybutene-1-sulfone, and poly-α-chlorotrifluoroethyl acrylate. A similar resist is used.

[Problem to be solved by the invention] However, recent advances in semiconductor integrated circuits, etc. have continued to increase in density and performance, and photomasks are also becoming smaller, more precise, and more efficient. Demand is increasing rapidly.

As mentioned above, photomasks are manufactured using so-called electron beam lithography using an electron beam lithography system, which involves drawing a pattern with an electron beam, followed by a development process, a baking process, a descum process, an etching process, and a film peeling process. A consistent production line that goes through each process is used. However, conventional electron beam resists made of organic polymer compounds such as polyglycidyl methacrylate, glycidyl methacrylate-acrylic acid copolymer chloromethylated polystyrene, polybutene-1-sulfone, and poly-α-chlorotrifluoroethyl acrylate in electron beam lithography are , because it has no conductivity, and even though the photomask substrate is a thin film of metal such as chromium, it has extremely low conductivity because the surface is coated with an anti-reflection layer.
There was a problem in that the pattern was distorted due to charging during pattern irradiation with ff111 radiation.

For example, taking the in-plane dimensional accuracy of a photomask for DRAM manufacturing as an example, the dimensional deviation of a 5x reticle for a 2511i K-bit DRAM, that is, a reticle with a size 5 times the size of the pattern to be exposed, is ± the average value. When taking 3σ (σ is the standard deviation), the accuracy is 0.1 to 0.3 μm, whereas the 5x reticle for IM bit DRAM has a dimensional accuracy of 0.07 to 0.15 μm (3σ ) is 4
A 5x reticle for M-bit DRAM is required to have a dimension lFi[(3σ) of 0.1 μm or less, and it is extremely difficult to stably manufacture such a photomask using the conventional Rennost process.

In addition, although various conductive resists have been proposed,
A practical conductive renost has not yet been developed.

The present invention solves the above-mentioned problems, and includes a method for manufacturing a photomask that can prevent electrification when creating a photomask using an electron beam lithography process, and thereby can manufacture a photomask with a high sheath density. The purpose is to provide a substrate for use in this process.

[Means for Solving the Problems] In view of the above-mentioned problems, the present inventor has devised a highly accurate photomask that can prevent the charging phenomenon without significantly changing the photomask manufacturing process using conventional electron beam lithography. As a result of research to develop a method that can stably produce
By forming a resist layer on the substrate to be processed, forming a metal thin film to prevent charging due to ionizing radiation, and then irradiating the pattern with ionizing radiation, pattern distortion caused by charging is eliminated and high-precision photo The inventors have discovered that masks can be manufactured stably, and have completed the present invention based on this knowledge.

That is, the method for manufacturing a photomask according to the present invention includes a step of forming a resist layer on a substrate to be processed, a step of forming a metal thin film for preventing charging caused by ionizing radiation on the resist layer, and a step of forming a pattern using ionizing radiation. It is characterized by comprising a step of irradiating and developing to form a resist pattern, a step of etching the substrate to be processed using the resist pattern as a mask, and a step of removing the resist layer remaining after etching, and The substrate used in the photomask manufacturing method according to the present invention is characterized in that a resist layer and a metal thin film are formed in this order on the substrate to be processed.

Hereinafter, the present invention will be explained using the drawings.

FIG. 1 is a cross-sectional view showing the method for manufacturing a photomask of the present invention, in which 1 is a substrate, 2 is a chromium film, 3 is a resist layer, and 4
5 is an ionizing radiation, 5 is a resist pattern, 6 is an etching gas plasma, 7 is a chromium pattern, 8 is an oxygen plasma, and 9 is a metal thin film.

First, as shown in FIG. 2(a), an optically polished substrate 1
A chromium film 2 is formed thereon to form a substrate to be processed, and an ionizing radiation resist such as 5 made by Sibley Co., Ltd. is further applied thereon.
AL-601, etc. is applied uniformly by a conventional method such as spin coating, and then heated and dried to a thickness of 0.1 to 2.
．． A resist layer 3 with a thickness of about 0 μm is formed, and the second part of the resist layer 3 is coated with a thickness of 10 μm to 10 μm using a low-temperature sputtering device or the like.
A metal thin film 9 having a thickness of about 1000λ is formed. Note that the heat drying treatment for the resist layer 3 is usually performed at 80 to 200° C. for about 1 to 60 minutes, although it depends on the type of resist.

Moreover, as a material for forming the metal thin film 9, AI
, T+ , N+ + Cu + Mo + W r P
t, Tar A g + A u, etc. can be used.

Furthermore, as the TIi radiation-absorbing resist, organic polymer compounds such as polyglycidyl methacrylate, glycidyl methacrylate-acrylic acid copolymer, chloromethylated polystyrene, polybutene-1-sulfone, poly-α-chlorotrifluoroethyl acrylate, etc. Lennost consisting of can be used.

Next, as shown in FIG. 5B, a predetermined pattern is drawn on the resist layer 3 using ionizing radiation 4 such as an electron beam drawing device according to a conventional method, and then, as shown in FIG. After developing with an alkaline aqueous solution containing tetramethylammonium hydroxide as the main component, rinsing with pure water was performed.
) A Rennost pattern 5 as shown in FIG. At this time, the metal thin film 9 formed on the resist layer 3 is also dissolved and removed at the same time.

Next, heat treatment and descum treatment are performed as necessary to remove unnecessary resist such as the resist layer remaining on the edges of the Renost pattern 5, whiskers, etc. (d) in the same figure.
), the portion to be processed exposed through the opening of the resist pattern 5, that is, the chromium layer 2, is dry etched with an etching gas plasma 6 to form a chromium pattern 7.

The chrome pattern 7 can also be formed by wet etching instead of dry etching using the etching gas plasma 6.

Thereafter, as shown in FIG. 5(e), the remaining resist pattern 5 is removed by ashing with oxygen plasma 8, thereby completing a photomask as shown in FIG. 2(f). Note that the resist pattern 5 can be removed by solvent stripping instead of the ashing treatment using the oxygen plasma 8.

[Operation and Effects of the Invention] When drawing a pattern using m-separate radiation, charged particles such as electrons are irradiated onto the substrate to be processed, so as the irradiation area increases, the substrate becomes charged, and due to the repulsion between the charged particles, The beam is deflected, causing pattern distortion. This phenomenon becomes more pronounced as the irradiation area becomes larger, and as the sensitivity of the resist becomes lower and the irradiation dose becomes larger. Therefore, in the production of photomasks for future high-density integrated circuits, long-term exposure and high-density exposure due to huge amounts of data will be required, which will lead to charging phenomena, so anti-static measures will be necessary. Ta.

On the other hand, in the present invention, charging can be almost completely eliminated by a simple method of forming a thin metal film that is inert to charged particles on the resist layer, and the thin metal film can be removed using a normal photomask manufacturing process. This is a method that can also remove oxides, making it extremely useful for manufacturing high-precision masks.

[Example code] Examples of the present invention will be described below.

[Example 1] A resist solution of 5AL-1i01 manufactured by Koshiplay was applied onto a chrome mask substrate by spin coating, and 9
Prebaking was performed at 0° C. for 30 minutes to obtain a uniform resist film with a thickness of 0.5 μm. Next, a 200-layer thick 0A1 film was formed on the resist film of the substrate using a low-temperature sputtering device. Subsequently, using an electron beam exposure device (manufactured by Hitachi [IL-70014]) with an accelerating voltage of 20 KV, IOμC/cm"
A pattern on the level of the aluminum wiring layer of a 4M-bit DRAM was drawn by exposing to light at a dose of . After exposure, this substrate was developed for 2 minutes using 5AL-822 developer manufactured by Sibley Co., Ltd. whose main component is tetramethylammonium hydroxide, and rinsed with pure water to obtain a resist pattern. At this time, the A1 film was dissolved in the developer and was completely removed.

Subsequently, using the resist pattern as a mask, the exposed substrate to be processed was dry-etched for 8 minutes in a plasma consisting of carbon tetrachloride and oxygen at an output of 300 W to remove it by ashing.

The ratio of carbon tetrachloride and oxygen is 4 carbon tetrachloride by volume.
to 1% oxygen.

Finally, the remaining resist was heated to 2 Torr 1400
A photomask was obtained by ashing and removing with W oxygen plasma.

The photomask manufactured in this way has no pattern distortion (
, the in-plane dimensional accuracy (3δ) at the 2.5 μm line is 0.
The accuracy was as high as 0.3 μm.

[Example 2 A resist solution of cochloromethylated polystyrene was applied onto a chrome mask substrate by spin coating, and
Prebaking was performed at 0° C. for 30 minutes to obtain a uniform resist M having a thickness of 0.6 μm. Next, in the same manner as in Example 1 above, A11g having a thickness of +oo was formed on the resist film. Next, an electron beam exposure system (MEBE) with an accelerating voltage of 10 KV was used.
Using S-I [[), exposure was performed at a dose of 1 μC/cm 2 to draw a grating pattern of 0.5 μm. After exposure, this substrate was treated with a developer consisting of a mixture of 35% by weight of isoamyl acetate and 65% by weight of ethyl cellosolve.
After developing for 0 seconds, the resist pattern was rinsed with isopropyl alcohol for 30 seconds to obtain a resist pattern. At this time, the AIgg present in the dissolved portion of the Lenost film was removed together with the resist, but the A1 film on the remaining pattern portion of the resist remained. This was post-baked at 140° C. for 30 minutes, then descumed for 2 minutes with oxygen plasma at I Torr and +00 W, and the exposed substrate was etched using ceric ammonium nitrate as a main component using the resist pattern as a mask. Etched with liquid for 1 minute. As a result, the Al film remaining on the resist was also thoroughly removed.

Finally, the remaining resist was heated to 2 Torr, 400
A photomask was obtained by ashing and removing with W oxygen plasma.

The thus manufactured photomask having a grating pattern of 0.5 .mu.m had high precision with no distortion of the pattern even in the periphery.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a method for manufacturing a photomask according to the present invention, and FIG. 2 is a sectional view showing a conventional photomask manufacturing process. l...Substrate, 2...Chromium film, 3...Resist layer, 4...Ionizing radiation, 5...Resist pattern, 6
... Etching gas plasma, 7... Chrome pattern, 8... Oxygen plasma, 9... Metal thin film, 11.
...Substrate, 12...Chromium film, 13...Resist layer, 14...Ionizing radiation, 15...Resist pattern, 16...Etching gas plasma, 17...Chromium pattern, 18...・Oxygen plasma. Applicant Dai Nippon Printing Co., Ltd.

Claims (2)

[Claims] (1) A step of forming a resist layer on a substrate to be processed, a step of forming a thin metal film on the resist layer to prevent charging caused by ionizing radiation, and a step of irradiating the pattern with ionizing radiation and developing to form a resist pattern. A method for manufacturing a photomask, comprising the steps of: etching a substrate to be processed using the resist pattern as a mask; and removing a resist layer remaining after etching. (2) A substrate characterized in that a resist layer and a metal thin film are formed in this order on a substrate to be processed.