Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2000-06-01
2001-08-28
Chu, John S. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S905000
Reexamination Certificate
active
06280902
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a photoresist composition suitable for lithography utilizing high-energy radiation such as a far ultraviolet ray including eximer laser, electron beam, X-ray, radiation or the like.
Recently, with development of higher integration of an integrated circuit, formation of a submicron pattern is required. Eximer laser lithography has attracted special interest for such a requirement, particularly for it enables production of 64 MDRAM and 256MDRAM. As aresist suitable for such eximer laser lithography process, a so-called chemical amplification type resist has been adopted which utilizes an acid catalyst and chemical amplification effect. In the chemical amplification type resist, solubility of portion irradiated with a radiation in an alkaline developer is changed through a reaction utilizing an acid catalyst generated from an acid generator in the irradiated portion, and by this, a positive or negative pattern is obtained.
In the chemical amplification type positive resist, an acid generated in the irradiated portion diffuses by post heat treatment (post exposure bake: hereinafter, abbreviated as PEB), and acts as a catalyst for changing solubility of irradiated portion in a developer. Such a chemical amplification type positive resist generally comprises a resin component which is alkali-insoluble or alkali slightly soluble by itself, but is converted to alkali-soluble by the action of an acid, and an acid generator which generates an acid by the action of an radiation.
Excimer lasers have a defect that they generate a standing wave formed by interference of t he reflected light and the incident light in a film when they are irradiated on a resist film placed on a substrate having a high reflectivity, because they have a high coherence. For example, when the intensity of the light in a resist film becomes uneven by such a standing wave, a phenomenon occurs in which a side of resist pattern becomes wave-shaped, so-called the standing wave effect. When a side of resist pattern becomes wave-shaped due to the standing wave effect, it is difficult to keep a fixed width of pattern line. In order to suppress the standing wave effect, it is general to suppress the interference in the film by adding a light-absorbing ingredient in the resist. When, however, such a light-absorbing ingredient is used, a problem arises that the light energy in the bottom of the resist film becomes weak and the profile of pattern becomes a tapered shape of a bottom-expanded form. This phenomenon lowers the resolution. In addition, due to the light interference described above, when the light exposure is carried out through a so-called half-tone mask having a small transmittance even at a ask ed part, sometimes a phenomenon (called side lobe) occurs that a perforation that is not present in the mask is formed in an unexposed part. Formation of such a side lobe causes a serious problem in the production of semiconductor integrated circuits.
In addition, generally in the lithography, it is demanded to form a pattern of high fidelity to the original mask pattern even if the focus is somewhat moved during the radiation irradiation. In other words, a photoresist having a deeper depth of focus or a wide focus margin is demanded.
The purpose of the present invention is to provide a positive working photoresist composition which is excellent in various resist properties including sensitivity, resolution, film-forming property, coating property, heat resistance and so on; excellent also in pattern profile and depth of focus; hard to cause standing wave effect in particular, and capable of forming an almost perpendicular and smooth pattern side face even on a substrate having a high reflection. As the result of extensive studies for attaining such purpose, the present inventors have found that a positive working photoresist composition having excellent properties can be obtained by adding a specific compound in the resist together with a resin and an acid-generator. The present invention has been completed based on such fact.
SUMMARY OF THE INVENTION
The present invention provides a positive working photoresist composition which comprises a resin which is converted to alkali-soluble from alkali-insoluble or alkali slightly soluble by the action of an acid; an acid generator; and a nitrogen-containing cyclic compound represented by the following formula (I):
wherein X represents CH
2
or C(═O), two of R
1
, R
2
, R
3
and R
4
represent a lower alkyl and the rest two represent hydrogen.
PREFERRED EMBODIMENT OF THE INVENTION
The resin which is a main component of the photoresist component is by itself alkali-insoluble or alkali slightly soluble, and becomes alkali-soluble by a chemical reaction caused by the action of an acid. For example, such a resin can be produced by protecting at least a part of a phenolic hydroxyl group in an alkali soluble resin having a phenol skeleton with a group which has dissolution inhibiting ability against alkaline developers and is insecure against acid.
Examples of the alkali soluble resin used for producing the resin in the resist composition include novolak resins, polyvinylphenol resins, polyisopropenylphenol resins, copolymers of vinylphenol with another vinyl monomer, and copolymers of isopropenylphenol with another vinyl monomer. Examples of the vinyl monomer copolymerized with vinylphenol or isopropenylphenol include (meth)acrylate such as methyl, ethyl, propyl, isopropyl, butyl or cyclohexyl ester of acrylic acid or methacrylic acid, acrylonitrile and styrene. Positional relation between a hydroxy group and a vinyl group or an isopropenyl group in vinylphenol or isopropenylphenol is not particularly limited, although, in general, p-vinylphenol or p-isopropenylphenol is preferred. Hydrogen may also be added to these resins for improving transparency. An alkyl group, alkoxy group and the like may be introduced into a phenol nucleus of the above-described resins, as long as the resulting resin is alkali-soluble. Among these alkali soluble resins, polyvinylphenol-based resins, that is, a homopolymer of vinylphenol or copolymer of vinylphenol with other monomer are preferably used.
The group to be introduced in the alkali soluble resin which has dissolution inhibiting ability against an alkali developer and is insecure against acid can be selected from various known protecting groups. Examples thereof include a tert-butoxycarbonyl group, tert-butoxycarbonylmethyl group, tetrahydro-2-pyranyl group, tetrahydro-2-furyl group, methoxymethyl group, 1-ethoxyethyl group, 1-propoxyethyl group, 1-(2-methylpropoxy)ethyl group and 1-ethoxypropyl group. These groups shall be substituted for hydrogen on a phenolic hydroxyl group. Among these protecting groups, particularly, 1-alkoxyalkyl group is preferred. Examples of the preferred 1-alkoxyalkyl group include 1-ethoxyethyl group, 1-propoxyethyl group, 1-(2-methylpropoxy)ethyl group and 1-ethoxypropyl group. The ratio of the phenolic hydroxyl groups substituted by the protecting group to the all phenolic hydroxyl groups in the alkali soluble resin (protective group introducing ratio) is preferably from 10 to 50%, in general. In the present invention, it is preferable to use a polyvinylphenol resin among those described above in which a part of the phenolic hydroxyl group is protected by the one or more kinds of 1-alkoxyalkyl groups selected from those mentioned above, as a part or whole of the resin component in the resist composition of the present invention.
The acid generator in the resist composition of the present invention can be selected from various compounds which generate an acid by irradiation to the substance itself or to a resist composition containing the substance. The acid generator can be used as a single compound or a mixture of two or more thereof. Examples thereof include onium salts such as sulfonium salt and iodonium salt, organic halogen compounds, particularly haloalkyl-s-triazine compound, compounds having a diazomethanedisulfonyl skeleton, disulfone compo
Takeyama Naoki
Yako Yuko
Birch & Stewart Kolasch & Birch, LLP
Chu John S.
Sumitomo Chemical Company Limited
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