JPS5860537A - Dry type pattern forming method - Google Patents

Abstract

PURPOSE:To remove faults due to a wet method, such as the swelling of an image part, by a method wherein actinic rays are applied selectively on a photoresist, heat treatment is applied thereto at least 5min at the temperature of 80-180 deg.C, a plasme gas is then applied thereto, and thereby the part thereof whereon the actinic rays are not applied selectively is removed. CONSTITUTION:Actinic rays are applied selectively to a photoresist layer to make its molecular structure varied. A photoresist irradiated by the actinic rays is subjected to heat treatment at least for 5min at the temperature of 80- 180 deg.C, and thereby its appropriateness for development is increased when the development is performed by a plasma gas. When the photoresist is not subjected to this heat treatment, but subjected only to the selective irradiation of the actinic rays, undesirable film reduction occures also in an image part to the same degree as in a non-image part when the development is performed by the plasma gas. Meanwhile, the heat treatment is not practical under the condition that the temperature is lower than 80 deg.C or that the time therefor is shorter than 5min, since the remaining film thickness is reduced to a large extent. When the temperature exceeds 180 deg.C, the appropriateness of the non-image part for development by the plasma gas is damaged.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a pattern on a photoresist, and more particularly to a method for forming a negative dry pattern in which a photoresist is selectively irradiated with active radiation, heat treated, and then dry developed with plasma gas.

There are many steps in the manufacturing of semiconductor devices in the semiconductor industry, and photolithography is one of them. The commonly used photolithography technique relies on ultraviolet irradiation, which requires a photosensitive material, ie, a photoresist, designed to be compatible with the irradiation technique and its processing. In other words, AI is several hundred nanometers thick on a silicon wafer.

After forming a thin film to be etched such as S i 02.8 i3N or polysilicon, a photoresist is applied and active rays such as ultraviolet rays, far ultraviolet rays, X-rays, and electron beams are applied through a required patterning mask. irradiation, predetermined wet development and rinsing treatment.

The underlying thin film to be etched is etched, and the process consisting of peeling off the photoresist, cleaning and drying the silicon wafer, and diffusing and implanting impurities into the exposed silicon area is repeated several times, and electrodes and wiring are created. to obtain semiconductor devices.

There are two types of photoresists commonly used in the semiconductor industry: negative type, which becomes crosslinked and insolubilized by actinic irradiation, and positive type, which decomposes and becomes solubilized. A desired pattern is formed from the photoresist irradiated with actinic radiation by removing non-irradiated areas or irradiated areas using an organic solvent or alkaline solution called a developer. As described above, conventional photoresists are processed in a wet manner using organic solvents or alkaline solutions as developing solutions and rinsing solutions. Using the photoresist image thus obtained as a mask, the silicon wafer substrate is etched with a hydrofluoric acid-based etching solution.

Recently, instead of these etching solutions, CF
4+ CF4-O2 system, CC14, CC1'4-Ar
A method of dry etching by converting a reactive gas such as 0CI4-He, 0CI4-He, etc. into plasma has begun to be widely used. After the etching process, the photoresist image is removed using a stripping solution mainly composed of organic solvents, but in some cases, ashing and stripping in oxygen gas plasma and cleaning of the substrate are also performed. It's here. However, as for the development process, the wet method is still used as described above.

When developing and rinsing using an organic solvent, the image area of the photoresist may swell.

Organic solvent enters between the photoresist and the substrate, resulting in decreased image dimensional reproducibility and processing accuracy.

This is undesirable because it causes a decrease in production yield.

In addition, there are various problems such as deterioration of the working environment, decreased safety for workers, the need for waste liquid treatment, which requires longer working hours, and the generation of pollution.

Taking these problems into consideration, the present inventors have conducted extensive research into a dry pattern forming method that can be fully put to practical use.As a result, when forming a pattern on a photoresist, the inventors have found that: a) active rays are selectively applied to the photoresist; We have discovered that it is possible to form a dry pattern by irradiating it with b) heat treatment at 80-18 Or for at least 5 minutes, and then (c) irradiating it with plasma gas and selectively removing the portions that were not irradiated with active rays. The present invention was made based on this knowledge.

The present invention will be explained in detail below.

The photoresist that can be used in the present invention is a conventionally used negative type photoresist, but
In particular, a photoresist made of an acrylic polymer and an azide compound is suitable. Examples of acrylic polymers include homopolymers containing methyl isoprobenylgedone, methyl vinyl ketone, methyl methacrylate, butyl methacrylate, or glycidyl methacrylate as monomers, or copolymers containing at least one of these monomers. The azide compounds include 1-azidopyrene, 1,8-diazidonaphthalene, 4,4'-diazidostilbene, 4,4'-diazidochalcone, 4,41
-Diazidobenzalua 7ton, 26-di(41-azidohenzal)cyclohexanone, 2,6-di(4'-azidohenzal)-4-methylstilbene, 4,4'-diazido diphenyl ether, 4,4'-diazidomethane 1
44'-Diazidiphenyl sulfide.

4.4'-Diazidodiphenyl sulfone, 2.2'-diazidostilbene, 4.4'-diazidobiphenyl.

83'-Dimethyl-4,4'-diazidobiphenyl.

■-Azidnaphthalene, 1-azidoanthracene, ■-
Examples include azidophenanthrene. Then, the acrylic polymer and the azide compound are mixed in a suitable solvent such as cyclohexanone, methyl n-butyl ketone, methyl n-propyl ketone.

Ethyl n-butyl ketone, methyl cellosolve acetate, ethyl cellosolve acetate, toluene, xylene,
■-nitropropane, 2-nitropropane, 1.1.2
．． 2-tetrachloroethane.

It is dissolved in N,N-dimethylformamide or the like, coated on a support such as a silicon wafer, and dried to form a photoresist layer. The photoresist layer thus obtained is selectively irradiated with actinic radiation to cause the photoresist to undergo molecular structural changes. Here, "selective" refers to creating areas that are irradiated with actinic radiation and areas that are not irradiated, and is achieved by irradiating through a suitable mask or the like to create a desired pattern. Next, photoresist irradiated with active rays was applied at 80%
Heat treatment at ~180C for at least 5 minutes can improve development suitability for development with plasma gas.

In the case of a photoresist that is only selectively irradiated without this heat treatment, film thinning occurs in the image area to the same extent as the non-image area during development with plasma gas, which is not preferable. Further, heat treatment is the same as when no heat treatment is performed if the temperature is less than sor or if 1 hour is less than 5 minutes.

The film loss in the image area (decrease in remaining film thickness) is large and becomes impractical. On the other hand, if the temperature exceeds 18011:', the suitability for developing with plasma gas in non-image areas will be impaired. Furthermore, the pattern fidelity is also inferior, which is not preferable. Temperature is 80~
At 180C, the goal can be achieved in as little as 5 minutes, but
Even if the length is longer than that, pattern formation will not be affected much. However, in actual operation, it is preferable not to take extra time. More preferable heat treatment conditions are 100-15
0t? It is 10 to 10 minutes. A specific method for heat treatment is to expose the material to an atmosphere at a desired temperature for a predetermined period of time, and therefore it is preferable to use a dryer or the like maintained at such a temperature.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 05 to 3 parts by weight of 2,6-di(4'-azidopenzal)-4-methylcyclohexanone was added to 10 parts by weight of PMIPK (polymethyl isopropenyl ketone) having a molecular weight of 210,000, and about 90 parts by weight of cyclohexanone was added. A photosensitive composition was prepared by dissolving it in This composition was spin-coated onto a silicon wafer having a thermal oxidation (Si02) film with a thickness of about 5,000 μm and dried for 20 minutes in a hot air dryer kept at 90C to create a solidified resist film with a thickness of 1 μm. did. Ultraviolet rays with a wavelength of 350 to 450 nm were irradiated in vacuum by contact exposure using a mask aligner PLA520F manufactured by Canon. The mask used has a minimum line width of 0.5μ
This is a quartz resolving power test mask with a pattern of m. Samples exposed in this way were baked in the air for 30 minutes using a hot air dryer maintained at 14 Orr, ■ baked at 120C in the same way, ■1
Oxygen gas plasma treatment was performed on four types: one that was beta-baked at 80C for 80 minutes, and one that was not baked.

The plasma device used was OAPM30 manufactured by Tokyo Ohka Kogyo Co., Ltd.
0, pure oxygen was used as the etching gas, and parallel plate electrodes were attached. The processing conditions were: first, the pressure inside the plasma reaction chamber was reduced to 15 Torr, then oxygen gas was introduced to bring the internal pressure to 1.0 Torr, the RF specific output was 100 W, and the wafer table temperature was set to 100 C. This was done using a monochromator.

As a result of processing in this manner, if post-exposure baking was not performed, there was almost no difference in etching rate between exposed and non-exposed areas, so no development was performed. On the other hand, when baking was performed, a negative image could be obtained. Therefore, it is clear that baking after exposure is necessary.

The baking temperature is 140C and 120tl? In the case of 180C, a pattern of 05 μm was obtained with almost no change in the obtained image, whereas a pattern of only 1 μm was obtained in the case of baking at 180C. In the range of 0.5 to 3 parts by weight of the azide compound relative to 10 parts by weight of PMIPK, the higher the amount of the azide compound added, the higher the residual film after development. When 3 parts by weight of the azide compound is added, the residual film percentage reached is about 70%, although it depends on the plasma conditions.

Example 2 Molecular weight 860,000 PMMA (polymethyl methacrylate)
A photosensitive composition was prepared by adding 0.5 to 8 parts by weight of 4.4'-diazide chalcone to 10 parts by weight and dissolving it in about 100 parts by weight of ethyl 7'rosolve acetate, as in Example 1. When processed in the same way, those that were not beta-beta were not developed, and only those that were beta-beta were developed.

Example 8 Conventionally used. ■ Cyclized rubber-based negative photoresist, ■ Novolac-based positive photoresist, ■ Boryl C
The same treatment as in Example] was carried out for four types of romethylstyrene and (2) novolac resin + azide compound, but in all cases, development could not be carried out regardless of the presence or absence of baking.

This indicates that dry development is difficult when the main chain and side chains of the polymer have aromatic rings or similar substances.

Patent applicant Tokyo Ohka Kogyo Co., Ltd. Representative Patent Attorney Akira Ito

Claims (2)

[Claims] (1) When forming a pattern on the photoresist, the photoresist is a) selectively irradiated with actinic radiation (b) 8
A dry pattern forming method comprising a step of heat treatment at 0 to 180C for at least 5 minutes, and (c) a step of irradiating with plasma gas and removing portions not selectively irradiated with active rays. (2) A dry pattern forming method according to claim (1), wherein the photoresist is composed of an acrylic polymer and an azide compound. (3) The acrylic polymer is methyl isopropenyl ketone, methyl vinyl ketone, or methyl methacrylate. , a homopolymer containing butyl methacrylate or glycidyl methacrylate as a monomer, or a copolymer containing at least one such monomer, the dry pattern forming method according to claim (2).