Radiation imagery chemistry: process – composition – or product th – Diazo reproduction – process – composition – or product – Composition or product which contains radiation sensitive...
Reexamination Certificate
1999-08-11
2001-06-05
Chu, John S. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Diazo reproduction, process, composition, or product
Composition or product which contains radiation sensitive...
C430S192000, C430S193000, C430S326000, C430S330000, C528S148000, C528S150000
Reexamination Certificate
active
06242151
ABSTRACT:
This invention relates to a novel polymer in the form of a novolac resin in which some of the hydrogen atoms of hydroxyl groups are replaced by specific groups, a resist composition comprising the polymer, and a patterning method.
BACKGROUND OF THE INVENTION
Prior art novolac resist materials generally use a novolac resin and a photosensitive agent as two main components. Numerous studies have been made on the novolac resin, photosensitive agent and solvent in order to develop a resist material which is improved in sensitivity, resolution, pattern geometry, heat resistance, film retention, adhesion-to-substrate, and shelf stability, and which can accommodate the wavelength of a light source in various steppers.
With respect to the novolac resin, for example, resist characteristics are largely affected by molecular weight fractions of a novolac resin. For example, a tandem type novolac resin consisting of a low molecular weight fraction (Mw=150 to 500) and a high molecular weight fraction (Mw>5,000), with a middle molecular weight fraction (MW=500 to 5,000) excluded, provides a resist composition having a good balance of sensitivity, resolution and heat resistance (see T. Kajita et al., Proc. SPIE, 1446, 161 (1991)).
With respect to the photosensitive agent, research works comply with the change of the stepper light source from g-line to i-line. Since resist compositions comprising conventional benzophenone photosensitive agents have a low transmittance, it was proposed to use non-benzophenone photosensitive agents having less absorption of i-line (see Nikkei Microdevice, April 1992, page 45).
Research works have also been made on the solvent. A resist composition is typically prepared using a conventional cellosolve solvent such as ethyl cellosolve acetate. When it is allowed to stand, even after filtration through a filter with a pore size of 0.2 &mgr;m, very fine microparticulates which are not visible to the naked eyes can form in the resist composition. Some microparticulates have a size of more than 0.5 &mgr;m. If a resist pattern of about 1 &mgr;m is formed on a wafer using the resist composition containing such relatively large microparticulates, the microparticulates are left on the pattern, leading to a lower resolution and exacerbating the manufacture yield of integrated circuits. In this regard, it is proposed in JP-B 3-22619, for example, to formulate a resist composition having improved long-term storage stability by dissolving an alkali-soluble resin and a 1,2-quinonediazide compound in a monooxycarboxylate-containing solvent.
These approaches dealing with the novolac resin and photosensitive agent have drawbacks. In order to realize a high resolution resist composition of good performance by combining the above measures, many additional steps are needed for the resist composition-formulating process, adding to the cost. The approach focusing at the solvent also has drawbacks. Insofar as a 1,2-quinonediazide compound monomer is used as the photosensitive agent in a resist composition as described above, the monomer will precipitate after filtration, detracting from the long-term shelf stability of the resist composition. A further improvement is thus desired.
SUMMARY OF THE INVENTION
An object of the invention is to provide a novel and improved polymer which is formulated into a resist composition having improved uniformity, sensitivity, resolution and pattern geometry as well as improved heat resistance, film retention, substrate adhesion and storage stability. Another object is to provide a resist composition comprising the polymer. A further object is to provide a patterning method using the resist composition.
The inventors have found a novel polymer in the form of a novolac resin in which some of the hydrogen atoms of the hydroxyl groups are replaced by 1,2-naphthoquinonediazidosulfonyl ester groups and some of the hydrogen atoms of the remaining hydroxyl groups are replaced by substituted carbonyl or sulfonyl groups. This polymer is formulated into a resist composition which has improved uniformity, sensitivity, resolution and pattern geometry in microfabrication as well as improved heat resistance, film retention, substrate adhesion and storage stability.
In a first aspect, the invention provides a polymer in the form of a novolac resin comprising recurring units of the following structural formula (1):
wherein m is an integer of 0 to 3, and having a weight average molecular weight calculated as polystyrene of 1,000 to 30,000. Some of the hydrogen atoms of the hydroxyl groups on the novolac resin are replaced by 1,2-naphthoquinonediazidosulfonyl ester groups and some of the hydrogen atoms of the remaining hydroxyl groups are replaced by substituents of at least one type selected from functional groups of the following general formulae (2), (3), and (4).
R is a straight, branched or cyclic alkyl group of 1 to 30 carbon atoms, aryl group of 6 to 20 carbon atoms or aralkyl group of 7 to 20 carbon atoms.
Preferably, the hydrogen atoms of the hydroxyl groups in the novolac resin are replaced by 1,2-naphthoquinonediazidosulfonyl ester groups in a proportion of 0.03 to 0.3 mol per hydrogen atom, and the hydrogen atoms of the remaining hydroxyl groups are replaced by functional groups of formula (2), (3) or (4) in a proportion of 0.01 to 0.8 mol per hydrogen atom.
In a second aspect, the invention provides a resist composition comprising the above-defined polymer.
In a third aspect, the invention provides a method for forming a resist pattern comprising the steps of (i) applying the resist composition onto a substrate, (ii) heat treating the coated film and then exposing it to high-energy radiation having a wavelength of up to 500 nm or electron beams through a photo mask, and (iii) optionally heat treating the exposed film and developing it with a developer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The novel polymer or high molecular weight compound of the invention is in the form of a novolac resin comprising recurring units of the following structural formula (1):
wherein m is an integer of 0 to 3. Some of the hydrogen atoms of the hydroxyl groups in the novolac resin are replaced by 1,2-naphthoquinonediazidosulfonyl ester groups and some of the hydrogen atoms of the remaining hydroxyl groups are replaced by substituents of at least one type selected from functional groups of the following general formulae (2), (3), and (4).
R is a straight, branched or cyclic alkyl group of 1 to 30 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms, an aryl group of 6 to 20 carbon atoms, preferably 6 to 12 carbon atoms, more preferably 6 to 8 carbon atoms, or an aralkyl group of 7 to 20 carbon atoms, preferably 7 to 13 carbon atoms, more preferably 7 to 9 carbon atoms. The polymer has a weight average molecular weight calculated as polystyrene of 1,000 to 30,000.
The letter m is an integer of 0 to 3, preferably equal to 1 or 2.
Of the groups represented by R, examples of the straight, branched or cyclic alkyl group of 1 to 30 carbon atoms include methyl, ethyl, propyl, isoproyl, n-butyl, isobutyl, tert-butyl, n-pentyl, tert-butylmethyl, n-hexyl, n-heptyl, n-octyl, n-decyl, n-dodecyl, n-hexyl, palmityl, n-stearyl, cyclopropyl, cyclopentyl, cyclohexyl and cholesteryl. Examples of the aryl group of 6 to 20 carbon atoms include phenyl, tolyl, ethylphenyl, propylphenyl, dimethylphenyl, methylethylphenyl, naphthyl, furyl and biphenyl. Examples of the aralkyl group of 7 to 20 carbon atoms include benzyl, methylbenzyl, propylbenzyl, and dimethylbenzyl.
In the polymer of the invention, the percent substitution of 1,2-naphthoquinonediazidosulfonyl ester group is preferably 0.03 to 0.3 mol, more preferably 0.05 to 0.2 mol per hydrogen atom of the hydroxyl group in the novolac resin. If the percent substitution of 1,2-naphthoquinonediazidosulfonyl ester group is less than 0.03 mol per hydrogen atom, the retention of a polymer film would be exacerbated, suggesting that a resist composition fails to form a pattern and becomes useless. If
Furihata Tomoyoshi
Kato Hideto
Okazaki Satoshi
Chu John S.
Millen White Zelano & Branigan
Shin-Etsu Chemical Co. , Ltd.
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