Polymer, resist composition and patterning process

Details Polymer, resist composition and patterning process Polymer, resist composition and patterning process

2001-09-27

2004-08-24

Thornton, Yvette C. (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

C430S313000, C430S323000, C526S271000, C526S270000, C526S279000

Reexamination Certificate

active

06780563

ABSTRACT:

This invention relates to polymers suitable as the base resin in chemically amplified positive resist compositions used for micropatterning in a process for the fabrication of semiconductor devices. It also relates to chemically amplified positive resist compositions adapted for exposure to high-energy radiation such as deep-UV, KrF excimer laser light (248 nm), ArF excimer laser light (193 nm), electron beams or x-rays and a process for forming a pattern.
BACKGROUND OF THE INVENTION
While a number of recent efforts are being made to achieve a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, the commonly used light exposure technology is approaching the essential limit of resolution determined by the light source wavelength. For the light exposure using g-line (436 nm) or i-line (365 nm), a pattern rule of about 0.5 &mgr;m is thought to be the limit. The LSI fabricated using such light exposure has a maximum degree of integration corresponding to 16 M-bit dynamic random access memory (DRAM). However, the laboratory fabrication of LSI already reached this stage, and the development of a further micropatterning technology is in urgent demand.
One means for reducing the pattern size is to reduce the wavelength of exposure light used in forming a resist pattern. For the mass production process of 256 M-bit DRAM (processing size up to 0.25 &mgr;m), it is now under intensive consideration to replace i-line (365 nm) as the exposure light source by KrF excimer laser light of a shorter wavelength of 248 nm. However, for the fabrication of DRAM with a degree of integration of 1 G or more requiring a finer patterning technology (processing size up to 0.2 &mgr;m), a shorter wavelength light source is required, and in particular, photolithography using ArF excimer laser light (193 nm) is now under investigation.
Since H. Ito, G. C. Willson et al of IBM proposed a chemically amplified positive resist composition comprising a resin in the form of polyhydroxystyrene having hydroxyl groups blocked with tert-butoxycarbonyloxy (tBOC) groups, that is, poly(4-t-butoxycarbonyloxystyrene) (PBOCST) and a photoacid generator in the form of an onium salt, a number of resist compositions having a high sensitivity and resolution have been developed. These chemically amplified positive resist compositions all have a high sensitivity and resolution, but are difficult to form fine patterns with a high aspect ratio because the patterns' strength is low.
A number of chemically amplified positive resist compositions using the above-mentioned polyhydroxystyrene as the base resin and having sensitivity to deep-UV, electron beams and x-rays are known in the art. These resist compositions, however, rely on the single-layer resist method although the bi-layer resist method is advantageous in forming a pattern with a high aspect ratio on a stepped substrate. These resist compositions are not yet practically acceptable because of the outstanding problems of substrate steps, light reflection from substrates, and difficulty of forming high-aspect ratio patterns.
As is known in the art, the bi-layer resist method is advantageous in forming a high-aspect ratio pattern on a stepped substrate. It is also known that in order to develop a bi-layer resist film with a common alkaline developer, high molecular weight silicone compounds having hydrophilic groups such as hydroxyl and carboxyl groups must be used.
Among silicone base chemically amplified positive resist compositions, recently proposed were those compositions comprising a base resin in the form of polyhydroxybenzylsilsesquioxane, which is a stable alkali-soluble silicone polymer, in which some phenolic hydroxyl groups are blocked with tBOC groups, in combination with a photoacid generator (see JP-A 7-118651 and SPIE vol. 1925 (1993), 377). Also JP-A 9-110938 discloses a silicone-containing polymer using a silicon-containing acrylic monomer.
The silicon-containing polymer of the acrylic pendant type has the drawback that its resistance to dry etching with oxygen plasma is weak as compared with The silsesquioxane polymer. A low silicon content accounts for this weak dry etching resistance. The silicon-containing polymer of the siloxane pendant type has the drawback that it is repellent to developer and less wettable therewith. Then SPIE vol. 3678, pp. 214, 241 and 562 describes a polymer containing a monomer of the trisilane or tetrasilane pendant type having an increased silicon content and a silicon-containing substituent which can be eliminated with acid. However, since silane compounds of at least disilane exhibit strong absorption at the wavelength of ArF excimer laser, an increased introduction of such silanes undesirably leads to a lower transmittance. Besides, an attempt of introducing silicon into acid labile groups is reported in SPIE vol. 3678, p. 420. Because of a low acid elimination ability, there are drawbacks including low environmental stability and a T-top profile.
SUMMARY OF THE INVENTION
An object of the invention is to provide a novel polymer which is useful as the base polymer in a chemically amplified positive resist composition having a high sensitivity and high resolution, especially suitable as a material for use in the bi-layer resist method adapted to form a high-aspect ratio pattern, and capable of forming a pattern having improved heat resistance. Another object of the invention is to provide a chemically amplified positive resist composition comprising the polymer as the base resin, and a method for forming a pattern using the same.
We have found that by incorporating silicon-containing substituent groups of the general formula (1) to be shown below, the silicon content of a polymer can be increased to an effective level to prevent the transmittance of ArF excimer laser light from lowering. The silicon-containing substituent group of formula (1) functions as an acid-eliminatable substituent group by substituting for the lo hydroxyl group on a carboxylic acid, alcohol or phenol, and especially the hydroxyl group of a phenol or carboxyl group as shown by the general formula (2) to (5) to be shown below. This substituent group has so high an acid eliminating ability that the environmental stability following exposure is improved and a T-top profile is thus precluded.
In a first aspect, the invention provides a polymer having silicon-containing groups of the general formula (1):
Herein R
1
to R
4
each are independently hydrogen or a straight, branched or cyclic alkyl group of 1 to 20 carbon atoms, or R
1
and R
2
, taken together, may form an aliphatic hydrocarbon ring in which —CH
2
— may be substituted with a —Si(R
8
)
2
— group, and R
3
and R
4
, taken together, may form an aliphatic hydrocarbon ring in which —CH
2
— may be substituted with a —Si(R
8
)
2
— group. R
5
to R
7
each are independently a straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms or aryl group of 6 to 20 carbon atoms. R
8
is independently a straight or branched alkyl group of 1 to 4 carbon atoms, and m is 1 or 2.
Preferably, hydrogen atoms of hydroxyl groups on a carboxylic acid, alcohol or phenol are substituted with the silicon-containing groups of the general formula (1).
A preferred embodiment of the invention provides a polymer comprising recurring units of one of the general formulae (2) to (5).
Herein R
1
to R
7
and m are as defined above. R
9
is hydrogen, a straight, branched or cyclic alkyl group of 1 to 20 carbon atoms, or CH
2
CO
2
R
12
. R
10
is hydrogen or a straight, branched or cyclic alkyl group of 1 to 20 carbon atoms. R
11
is a straight, branched or cyclic alkylene group of 1 to 10 carbon atoms. R
12
is hydrogen or a straight, branched or cyclic alkyl group of 1 to 20 carbon atoms, n is a number of 0 to 5, p is a number of 1 to 5, each of q and r is 0 or 1.
In a second aspect, the invention provides a chemically amplified positive resist composition comprising (A) the polymer defined above, (B) a photoacid generator, and (C) an organic solvent. Also conte

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