Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2002-05-01
2004-05-04
Truong, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C528S144000, C528S150000, C430S190000, C430S191000, C430S192000, C430S193000
Reexamination Certificate
active
06730769
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a novolak resin that exhibits excellent sensitivity, definition and short margin (the difference between optimum exposure time period Eop and minimum exposure time period Es) and is advantageously used in positive photoresist compositions for i-line lithography, as well as to a production process of the novolak resin and to a positive photoresist composition using the novolak resin.
2. Description of the Related Art
As positive photoresist composition for i-line (365 nm) lithography, compositions each comprising an alkali-soluble novolak resin and a 1,2-naphthoquinonediazido-group-containing compound are excellent in sensitivity, definition and heat resistance and are widely used in, for example, the manufacture of semiconductor integrated circuits (ICs).
The density of such ICs becomes denser and denser with advance of semiconductor technologies, and demands have been made on photoresist materials that can form ultrafine resist patterns of not more than half a micron with good shapes.
Such photoresist materials should have a higher sensitivity to improve throughput and should have a satisfactory short margin (Eop-Es) to improve yields.
The short margin (Eop-Es) is the difference between the minimum exposure time period (Es) to reproduce separated resist patterns and the exposure time period (Eop) to reproduce patterns in exact accordance with set dimensions of a mask pattern. A larger short margin means a smaller change rate in pattern dimensions depending on exposure conditions. Photoresist materials having a larger short margin exhibit improved yields and are easy to handle.
However, conventional positive photoresist compositions do not satisfy all the required characteristics including sensitivity, definition, short margin and pattern shape upon the formation of ultrafine resist patterns of not more than half a micron. For example, positive photoresist compositions exhibiting a higher sensitivity may cause reduced resist films after development and may have an insufficient definition, pattern shape and short margin. In contrast, those exhibiting a higher definition may have a deteriorated sensitivity.
Conventional alkali-soluble novolak resins for use in the positive photoresist compositions are generally prepared using two or more types of phenols as raw materials. Among them, novolak resins prepared by using m-cresol and p-cresol as essential ingredients are excellent in balance between sensitivity and definition and are widely used.
However, p-cresol is a monomer having low reactivity, and a substantial portion of p-cresol used in the reaction remains as unreacted monomers or as dimers, trimers and other low molecular weight fractions in the resulting product resin, and these substances cause scum in patterning of resists and cause deteriorated the characteristics as the resist.
For these reasons, resist compositions containing novolak resins prepared by using highly reactive 3,4-xylenol instead of lowly reactive p-cresol have been proposed.
For example, Japanese Patent Laid-Open No. 4-365046 discloses a positive photoresist composition comprising a novolak resin and a naphthoquinonediazidosulfonyl ester having a specific structure. The novolak resin is obtained by condensation of formaldehyde with phenols including m-cresol and at least one selected from p-cresol, xylenols and trimethylphenols.
Japanese Patent Laid-Open No. 5-88364 discloses a positive photoresist composition containing a novolak resin prepared by polycondensation of formaldehyde with a phenol mixture comprising 5% to 50% by mole of 3,4-xylenol and 95% to 50% by mole of m-cresol.
Japanese Patent Laid-Open No. 5-204146 discloses a positive photoresist composition containing a polycondensation product (a novolak resin) of an alkyl-substituted phenolic compound with an aldehyde mixture containing formaldehyde and a lower-alkyl-group-containing aldehyde, such as propionaldehyde. The molar ratio of formaldehyde to the lower-alkyl-group containing aldehyde in the aldehyde mixture is 1/99 to 99/1.
Japanese Patent Laid-Open No. 8-234420 mentions a positive photoresist composition containing an alkali-soluble novolak resin that has a weight average molecular weight Mw of from 2000 to 15000 and is prepared by reaction of m-cresol, 3,4-xylenol and formaldehyde in &ggr;-butyrolactone.
These conventional photoresist compositions are, however, still insufficient in the aforementioned required characteristics upon the formation of ultrafine resist patterns of not more than half a micron, although they are suitable for the formation of patterns of about 0.6 &mgr;m.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a positive photoresist composition that satisfies all the required characteristics of sensitivity, definition, short margin and pattern shape even in the formation of ultrafine resist patterns of not more than half a micron.
Another object of the present invention is to provide a novolak resin that is suitable for the preparation of the positive photoresist composition, and a process for producing the novolak resin.
After intensive investigations to accomplish the above objects, the present inventors have found that a positive photoresist composition including an alkali-soluble novolak resin having a specific structure and a naphthoquinonediazidosulfonyl ester of a phenol compound having a specific structure satisfies all the required characteristics of sensitivity, definition, short margin and pattern shape even in the formation of ultrafine resist patterns of not more than half a micron. The present invention has been accomplished based on these findings.
Specifically, the present invention provides, in one aspect, a novolak resin including constitutional units represented by following Formulae (I), (II) and (III) in the molecule:
The present invention provides, in another aspect, a novolak resin that has a weight average molecular weight Mw of from 1000 to 20000 and is a reaction product of a polymer having constitutional units represented by following Formulae (I) and (II) in the molecule with 3,4-xylenol and formaldehyde:
In the novolak resin just mentioned above, the polymer is preferably a reaction product of m-cresol and propionaldehyde.
In a further aspect, the present invention provides a process for producing a novolak resin. The process includes the steps of (i) allowing, as a primary reaction, propionaldehyde to react with m-cresol in the presence of an acid catalyst to thereby yield a polymer, where the amount of propionaldehyde is 0.1 to 0.5 mole per mole of m-cresol; and (ii) allowing, as a secondary reaction, the polymer to react with 3,4-xylenol and formaldehyde to thereby yield a novolak resin having a weight average molecular weight Mw of from 1000 to 20000, where the amounts of 3,4-xylenol and formaldehyde are 0.1 to 0.5 mole per mole of m-cresol and 1 to 5 moles per mole of propionaldehyde, respectively.
The present invention provides, in another aspect, a positive photoresist composition. The positive photoresist composition includes (A) the aforementioned novolak resin and (B) a naphthoquinonediazidosulfonyl ester of a phenol compound represented by following Formula (IV):
wherein R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
7
and R
8
are each independently a hydrogen atom, a halogen atom, an alkyl group having from 1 to 6 carbon atoms, an alkoxy group having from 1 to 6 atoms, or a cycloalkyl group; a, b and c are each independently an integer from 1 to 3; and m is 2 or 3.
In the positive photoresist composition, the phenol compound represented by Formula (IV) may be a linear tetranuclear phenol compound represented by following Formula (V):
Alternatively, the phenol compound represented by Formula (IV) may be a linear pentanuclear phenol compound represented by following Formula (VI):
The naphthoquinonediazidosulfonyl ester (B) is preferably a mixture of a naphthoquinonediazidosulfonyl ester of the linear tetranuclear phenol compound represented by Formula (V)
Hagihara Mitsuo
Katano Akira
Miyagi Ken
Tachi Toshiaki
Tokyo Ohka Kogyo Co. Ltd.
Truong Duc
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