Polymers and positive resist compositions

Details Polymers and positive resist compositions Polymers and positive resist compositions

2001-02-07

2002-08-20

Truong, Duc (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S504000, C525S505000, C528S143000, C528S158000, C528S159000, C528S162000, C528S171000, C528S290000, C528S373000, C528S422000, C430S190000, C430S192000

Reexamination Certificate

active

06437058

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 1,2-naphthoquinonediazidosulfonyl ester groups and acid labile groups, and a positive resist composition comprising the polymer.
BACKGROUND OF THE INVENTION
Prior art novolac resist materials generally use a novolac resin and a photoactive compound as two main components. Numerous studies have been made on the novolac resin, photoactive compound and solvent in order to develop a resist material which is improved in sensitivity, resolution, pattern profile, heat resistance, film retention, adhesion-to-substrate, and shelf stability, and which can accommodate the wavelength of a light source in various aligner.
With respect to the novolac resin, for example, reducing the average molecular weight of a novolac resin being synthesized leads to an increased resolution at the sacrifice of heat resistance and film retention (see BREAK THROUGH, February 1992, page 18). One prior art solution is to remove a low molecular weight fraction from the novolac resin by re-precipitation treatment.
In order that the novolac resin be improved in contrast without lowering sensitivity, a method of optimizing the bond mode of methylene is considered (see Handbook of Semiconductor IC Resist Materials, 72, 1996). Allegedly a high-ortho-novolac is effective in enhancing the contrast of a resist without lowering the dissolution rate of exposed areas.
A combination of a base polymer in the form of a novolac resin having at least three acid-decomposable acetal bonds with a photoacid generator is proposed in JP-A 62-215947 as having improved resolution and storage stability.
With respect to the photoactive compound, research works comply with the change of the stepper light source from g-line to i-line. Since resist compositions comprising conventional benzophenone photoactive compounds have a low transmittance, it was proposed to use non-benzophenone photoactive compounds having less absorption of i-line (see Nikkei Microdevice, April 1992, page 45).
Research works have also been made on the solvent. A positive 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 microparticle 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 positive 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 photoactive compound 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 photoactive compound 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 positive resist composition having improved uniformity, sensitivity, resolution and pattern profile as well as improved heat resistance, film retention, substrate adhesion and storage stability. Another object is to provide a positive resist composition comprising the polymer.
The inventors have found that a 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 specific acid labile groups or crosslinked with acid labile crosslinking groups, that is, one component novolac polymer having both photosensitive groups and acid labile or acid labile crosslinking groups incorporated in its molecule is improved in dissolution contrast, that is, differential dissolution rate in a developer between radiation-exposed areas and unexposed areas. This polymer is formulated into a positive resist composition which has improved uniformity, sensitivity, resolution and pattern profile in microfabrication as well as improved heat resistance, film retention, substrate adhesion and storage stability.
In one aspect, the invention provides a polymer in the form of a novolac resin comprising recurring units of the following structural formula (1) and having a weight average molecular weight of 1,000 to 30,000 calculated as polystyrene. Some of the hydrogen atoms of 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 acid labile groups of the following general formula (2) and/or crosslinked within a molecule or between molecules with crosslinking groups having C—O—C linkages of the following general formula (3).
Herein m is an integer of 0 to 3.
Herein R
1
and R
2
are independently hydrogen or a straight, branched or cyclic alkyl group of 1 to 6 carbon atoms, R
3
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, or R
1
and R
2
, R
1
and R
3
, or R
2
and R
3
, taken together, may form a ring, and each of R
1
, R
2
and R
3
is a straight of branched alkylene group of 1 to 18 carbon atoms when they form a ring.
Herein R
4
, R
5
, R
7
and R
8
are independently hydrogen or a straight, branched or cyclic alkyl group of 1 to 6 carbon atoms, or R
4
and R
5
, and R
7
and R
8
, taken together, may form a ring, and each of R
4
, R
5
, R
7
and R
8
is a straight of branched alkylene group of 1 to 17 carbon atoms when they form a ring, and R
6
is a divalent hydrocarbon group of 1 to 6 carbon atoms which may contain an oxygen atom.
In another aspect, the invention provides a positive resist composition comprising the polymer defined above.
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 structural formula (1), wherein some of the hydrogen atoms of hydroxyl groups are replaced by 1,2-naphthoquinonediazidosulfonyl ester groups, and some of the hydrogen atoms of the remaining hydroxyl groups are replaced by acid labile groups of the general formula (2) and/or some of the hydrogen atoms of the remaining hydroxyl groups are crosslinked within a molecule or between molecules with crosslinking groups having C—O—C linkages of the general formula (3).
In formula (1), m is an integer of 0 to 3, and preferably 1 or 2.
In formula (2), R
1
and R
2
may be the same or different and stand for hydrogen or straight, branched or cyclic alkyl groups of 1 to 6 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, hexyl, cyclopentyl, and cyclohexyl.
Examples of the straight, branched or cyclic alkyl group of 1 to 30 carbon atoms represented by R
3
include methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, n-hexyl, n-heptyl, n-octyl, n-decyl, n-dodecyl, n-hexyl, palmityl, n-stearyl, cyclopropyl, and cholesteryl. Examples of the aryl groups of 6 to 20 carbon atoms include phenyl, tolyl, ethylphenyl, pro

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