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
2001-02-15
2004-12-28
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
C430S296000, C430S322000, C430S326000, C430S330000, C430S905000, C430S907000, C430S942000, C526S246000, C526S271000
Reexamination Certificate
active
06835524
ABSTRACT:
This invention relates to novel polymers useful as the base resin in chemical amplification resist compositions suited for microfabrication. It also relates to chemical amplification resist compositions comprising the polymers and a patterning process using the same.
BACKGROUND OF THE INVENTION
In the drive for higher integration and operating speeds in LSI devices, the pattern rule is made drastically finer. The rapid advance toward finer pattern rules is grounded on the development of a projection lens with an increased NA, a resist material with improved performance, and exposure light of a shorter wavelength. In particular, the change-over from i-line (365 nm) to shorter wavelength KrF laser (248 nm) brought about a significant innovation, enabling mass-scale production of 0.18 micron rule devices. To the demand for a resist material with a higher resolution and sensitivity, acid-catalyzed chemical amplification positive working resist materials are effective as disclosed in U.S. Pat. Nos. 4,491,628 and 5,310,619 (JP-B 2-27660 and JP-A 63-27829). They now become predominant resist materials especially adapted for deep UV lithography.
Resist materials adapted for KrF excimer lasers enjoyed early use on the 0.3 micron process, went through the 0.25 micron rule, and currently entered the mass production phase on the 0.18 micron rule. Engineers have started investigation on the 0.15 micron rule, with the trend toward a finer pattern rule being accelerated. A wavelength change-over from KrF to shorter wavelength ArF laser (193 nm) is expected to enable miniaturization of the design rule to 0.13 &mgr;m or less. Since conventionally used novolac resins and polyvinylphenol resins have very strong absorption in proximity to 193 nm, they cannot be used as the base resin for resists. To ensure transparency and dry etching resistance, some engineers investigated acrylic and alicyclic (typically cycloolefin) resins as disclosed in JP-A 9-73173, JP-A 10-10739, JP-A 9-230595 and WO 97/33198. With respect to F
2
excimer laser (157 nm) which is expected to enable further miniaturization to 0.10 &mgr;m or less, more difficulty arises in insuring transparency because it was found that acrylic resins are not transmissive to light at all and those cycloolefin resins having carbonyl bonds have strong absorption.
SUMMARY OF THE INVENTION
An object of the invention is to provide a novel polymer having a high transmittance to vacuum ultraviolet radiation of up to 300 nm, especially an F
2
excimer laser beam (157 nm), Kr
2
excimer laser beam (146 nm), KrAr excimer laser beam (134 nm) and Ar
2
excimer laser beam (126 nm), and improved anti-ablation of the backbone, and useful as the base polymer in a chemical amplification resist composition. Another object is to provide a chemical amplification resist composition comprising the polymer, and a patterning process using the same.
It has been found that using as the base resin a polymer comprising recurring units of an acrylic derivative having a fluorinated backbone represented by the general formula (1) defined below, a resist composition featuring transparency and alkali solubility is obtained.
Herein R
1
, R
2
and R
3
are independently hydrogen, fluorine or unsubstituted or fluorinated, straight, branched or cyclic alkyl groups of 1 to 20 carbon atoms, at least one of R
1
, R
2
and R
3
contains fluorine, and R
4
is a hydrophilic group.
It has also been found that the polymer becomes more effective when it contains recurring units of the general formula (2) defined below in addition to the recurring units of formula (1), and further effective when it contains recurring units of the general formula (3) defined below in addition to the recurring units of formulas (1) and (2).
Herein R
5
, R
6
and R
7
are independently hydrogen, fluorine or unsubstituted or fluorinated, straight, branched or cyclic alkyl groups of 1 to 20 carbon atoms, and R
8
is an acid labile group.
Herein R
9
, R
10
and R
11
are independently hydrogen, fluorine or unsubstituted or fluorinated, straight, branched or cyclic alkyl groups of 1 to 20 carbon atoms, and R
12
is an acid stable group.
As long as the inventor has confirmed, polyvinyl phenol is somewhat improved in transmittance near 160 nm, but far below the practical level, and reducing carbonyl and carbon-to-carbon double bonds is essential for insuring a transmittance.
However, cyclic structures and carbon-to-carbon double bonds greatly contribute to an improvement in dry etching resistance. A polymer for use with an ArF excimer laser, in which a benzene ring is excluded and instead, an alicyclic structure is introduced for improving etching resistance, is difficult to provide transparency since it acquires solubility by relying on carboxylic acid. The inventor found that use of a fluorine-substituted polymer is effective for improving transparency. Through studies on how to improve the transparency of acrylic polymers used in ArF resists, the inventor has arrived at the use of an acrylic derivative having a fluorine-substituted backbone.
What becomes a problem as a result of wavelength reduction is a lowering of transparency, and in the case of a positive resist material, a negative working phenomenon that the exposed areas become insoluble as the dose of exposure is increased. Those portions which have turned negative are insoluble not only in alkali developers, but also in organic solvents such as acetone. This indicates that gel forms as a result of crosslinking of molecules together. Radical generation is probably one cause of crosslinking. As a result of wavelength reduction, the exposure energy is increased so that even C—C bonds and C-H bonds may be excited in the case of F
2
exposure (157 nm). As a result of excitation, radicals are generated with a possibility that molecules are bonded together. For polymers having an alicyclic structure for use in ArF exposure, for example, polynorbornene, an outstanding negative working phenomenon was observed. It is believed that these polymers have a structure susceptible to crosslinking since the alicyclic group has many C-H bonds at the bridgehead. On the other hand, it is well known that &agr;-methylstyrene and derivatives thereof are effective for preventing crosslinking. Alpha-methylstyrene can mitigate the negative working phenomenon, but fail to completely eliminate the phenomenon. Moreover, since oxygen absorption is considerable in the VUV region, exposure is effected under the conditions that oxygen is purged, with an inert gas such as nitrogen or argon, to an oxygen concentration of 1 ppm or lower. Since oxygen is an effective radical trapping agent, this means that the radicals generated have a long lifetime and more crosslinking takes place. As a result of the ensuing studies, an outstanding negative working phenomenon was observed for a resist composition comprising a polyhydroxystyrene base polymer among many other types of resist polymers, but rarely for a resist composition based on acrylate. This indicates that using a polyacrylate having a fluorinated backbone, a resist composition featuring both transparency and alkali solubility is obtainable.
In one aspect, the invention provides a polymer comprising recurring units of an acrylic derivative having a fluorinated backbone represented by the above general formula (1).
In another embodiment, the invention provides a polymer comprising recurring units represented by the above general formulas (1) and (2).
In a further embodiment, the invention provides a polymer comprising recurring units represented by the above general formulas (1), (2) and (3).
Preferably in formula (1), the hydrophilic group represented by R
4
contains an alcohol, ester, lactone, carbonate, acid anhydride, carboxylic acid, carboxylic amide, sulfonic acid or sulfonic amide.
In another aspect, the invention provides a chemical amplification type positive resist composition comprising (A) the polymer defined above, (B) an organic solvent, and (C) a photoacid generator. In preferred embodiments, the resist composition fur
Harada Yuji
Hatakeyama Jun
Watanabe Jun
Millen White Zelano & Branigan P.C.
Shin-Etsu Chemical Co. , Ltd.
Thornton Yvette C.
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