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
2001-10-25
2003-09-30
Baxter, Janet (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
Reexamination Certificate
active
06627381
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a resist composition suitable for lithography by the action of such high-energy rays as far ultraviolet rays (including excimer laser and others), electron beam, X-ray or other rays.
BACKGROUND TECHNOLOGY
With an increasing demand for higher integration of integrated circuits in recent years, formation of submicron patterns has been required. Particularly, since lithography with the use of krypton fluoride (KrF) excimer laser or argon fluoride (ArF) excimer laser makes the production of integrated circuits of 64 M DRAM to 1 G DRAM possible, the lithographic process is drawing attention. As a resist suitable for the above-mentioned excimer laser lithographic process, so-called a chemical amplification type resist utilizing an acid catalyst and the chemical amplification effect has been increasingly adopted. In the chemical amplification type resist, an acid generated from an acid generating agent at areas irradiated with a ray is diffused in the following heat treatment (post exposure bake: hereinafter sometimes abbreviated as PEB) and a reaction catalyzed by this acid changes the solubility of the exposed areas in an alkaline developer, providing positive or negative patterns.
For a positive resist of the chemical amplification type, particularly a positive resist for KrF excimer laser lithography, a poly(hydroxystyrene) resin with part of its phenolic hydroxyl group protected by a group which undergoes cleavage by the action of an acid is employed, in many cases in combination with an acid generating agent. As the group which undergoes cleavage by the action of an acid, from the viewpoints of resolution, sensitivity, and others, those forming acetal-type bonds with oxygen atoms derived from phenolic hydroxyl groups, such as resins having a structure in which tetrahydro-2-pyranyl, tetrahydro-2-furyl, or 1-ethoxyethyl is bound to an oxygen atom, are arousing interest. However, even the use of such resins has been faced with limitations in improvement in resolution.
Moreover, in the formation of a pattern by photolithography, generally, variations in exposure dose are liable to lead to variations in the finished dimensions of the resulting resist pattern, indicating its small exposure latitude (also referred to as exposure margin). As described above, resist compositions conventionally known in the art have limits in resolution, sensitivity, exposure capacity, and others. Furthermore, since the manufacture of integrated circuits involves dry etching through a resist pattern formed by photolithography as a mask, the resist employed therefor is also required to have heat resistance and dry etching resistance.
DISCLOSURE OF INVENTION
The object of the present invention is to provide a chemical amplification type positive resist composition excellent in such properties as sensitivity, resolution, heat resistance, the ratio of residual thickness, coatability, exposure latitude, dry etching resistance, and others, particularly one that is further improved in resolution and exposure latitude.
The inventors of the present invention made intensive studies to achieve the above-mentioned object and have found that the use of a hydroxystyrene/3-hydroxy-1-adamanty methacrylate copolymer as a resin component for the chemical amplification type positive resist provides excellent performance. The present invention was accomplished based on this finding.
Accordingly, the present invention provides a chemical amplification type positive resist composition containing: a resin which has a hydroxystyrene-based polymerization unit, a 3-hydroxy-1-adamantyl methacrylate-based polymerization unit, and a polymerization unit having a group unstable toward an acid, and, though insoluble or hardly soluble in an alkali in itself, becomes alkali-soluble after the acid-unstable group described above has been cleaved by the action of an acid; and an acid generating agent.
Although the resin component which is a main constituent of the resist composition of the present invention is insoluble or hardly soluble in an alkali in itself, it is rendered alkali-soluble through a reaction by the action of an acid, and has a polymerization unit resulting from the opening of the double bond of the vinyl group of hydroxystyrene, and a polymerization unit which results from the opening of the double bond of the vinyl group of 3-hydroxy-1-adamantyl methacrylate, as essential constituents. These polymerization units can be represented by the following formulae (I) and (II), respectively.
In the polymerization unit formed from hydroxystyrene shown by the formula (I), the position of the hydroxyl group is not particularly restricted, but the polymerization unit is generally one that is formed from p-hydroxystyrene.
Moreover, this resin is insoluble or hardly soluble in an alkali in itself. However, for becoming alkali-soluble through a chemical reaction by the action of an acid, it comprises a polymerization unit having a group unstable toward an acid. Usually, the group unstable toward an acid has been introduced to the resin so as to protect such an alkali-soluble group as hydroxyl group and carboxyl group. Concrete examples of such acid-unstable group for protecting an alkali-soluble group include tert-butyl, tert-butoxycarbonyl, an acetal-type group of the following formula (III):
wherein, R
1
represents for an alkyl group having 1 to 4 carbon atoms, R
2
represents an alkyl group having 1 to 6 carbon atoms or a cycloalkyl group having 5 to 7 carbon atoms, or R
1
and R
2
together form a trimethylene or tetramethylene chain, and a 2-alkyl-2-adamantyl represented by the following formula (IV):
wherein, R
3
represents an alkyl group having 1 to 4 carbon atoms. These groups each substitutes for the hydrogen atom of the hydroxyl or carboxyl group.
Those suitable as the acetal-type group represented by the formula (III) include tetrahydro-2-furyl, tetrahydro-2-pyranyl, 1-ethoxyethyl, 1-isopropoxyethyl, 1-isobutoxyethyl, 1-ethoxypropyl, 1-ethoxy-2-methylpropyl, and 1-cyclohexyloxyethyl. Of these, 1-ethoxyethyl, 1-isobutoxyethyl, 1-isopropoxyethyl, 1-ethoxypropyl, and others are preferred. Moreover, examples of suitable 2-alkyl-2-adamantyl groups represented by the formula (IV) are 2-methyl-2-adamantyl and 2-ethyl-2-adamantyl.
Among the groups unstable toward an acid enumerated above, tert-butoxycarbonyl usually substitutes for hydroxyl group and a 2-alkyl-2-adamantyl group represented by the formula (IV) usually substitutes for carboxyl group. Other tert-butyl and acetal-type groups represented by the formula (III) can substitute for both hydroxyl group and carboxyl group.
In the case of a resist for KrF excimer laser exposure, the group unstable toward an acid is generally such as to protect the hydroxyl group of a hydroxystyrene unit. A unit in which the acid-unstable group is bound to the hydroxyl group of a hydroxylstyrene unit can be represented by the following formula (V):
In the formula, Q represents the acid-unstable group. Tert-butyl, tert-butoxycarbonyl, acetal-type groups represented by the formula (III) shown above, and the like are mentioned as concrete examples of Q in this formula. Among these, the acetal-type groups represented by the above-shown formula (III) are preferred. Its preferred embodiment as a polymerization unit can be represented by the following formula
wherein, R
1
and R
2
have the same meanings as defined in the formula (III). A particularly preferred is the case where R
1
in the formula (III) or (VI) is an alkyl group having 1 to 4 carbon atoms and R
2
is an alkyl group having 1 to 6 carbon atoms or a cycloalkyl having 5 to 7 carbon atoms.
The resin having a hydroxystyrene-based polymerization unit, a 3-hydroxy-1-adamantyl methacrylate-based polymerization unit, and such a polymerization unit having a group unstable toward an acid as was described above can be produced, for example, in the following manner. Firstly, in the case where tert-butyl serves as the acid-unstable group and substitutes for the hydroxyl group of hydroxystyrene,
Kamabuchi Akira
Uetani Yasunori
Baxter Janet
Sumitomo Chemical Company Limited
Walke Amanda C.
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