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
2000-10-12
2002-10-08
Baxter, Janet (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
C430S311000, C430S325000, C430S326000, C430S330000, C521S027000, C526S242000
Reexamination Certificate
active
06461791
ABSTRACT:
This invention relates to polymers useful as the base polymer 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 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 a resin based on a polystyrene derivative of a fluorinated backbone comprising recurring units of the general formula (1) defined below, especially a polymer comprising recurring units of the general formula (2) defined below, a resist material featuring transparency and alkali solubility is obtained.
Herein R
1
is hydrogen, fluorine or an unsubstituted or fluorinated, straight, branched or cyclic alkyl group of 1 to 20 carbon atoms; R
2
is fluorine or an unsubstituted or fluorinated, straight, branched or cyclic alkyl group of 1 to 20 carbon atoms; R
3
is an aryl group of 6 to 20 carbon atoms which may have attached thereto a hydroxyl group and/or a hydroxyl group substituted with an OR
4
roup; R
4
is an acid labile group; letters o, p, q, r, s and t are numbers in the range: 0≦o<5, 0<p≦5, 0≦q<5, 0≦r≦5, 0≦s≦5, 0≦t≦5 , 0<o+q<5, and 0≦s+t≦5, k, m and n are numbers in the range: 0<k<1, 0≦m<1, and 0≦n<1.
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 has found that use of a fluorine-substituted polystyrene derivative is effective for improving transparency while maintaining the desired dry etching resistance. Specifically, among halogen atoms, fluorine atoms are effective for improving transparency whereas chlorine atoms are not effective and bromine atoms detract from transparency. The effect is obtained whether the position of fluorine substitution is on the benzene ring or on the polymer 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. Since the energy of C—F bonds is greater than the energy of C—C bonds and C—H bonds, the C—F bonds are less damageable upon exposure. In particular, fluorination of the backbone is effective to prevent crosslinking.
In a first aspect, the invention provides a polymer comprising a polystyrene derivative of a fluorinated backbone having recurring units of the following general formula (1).
Herein R
1
is hydrogen, fluorine or an unsubstituted or fluorinated, straight, branched or cyclic alkyl group of 1 to 20 carbon atoms; R
2
is fluorine or an unsubstituted or fluorinated, straight, branched or cyclic alkyl group of 1 to 20 carbon atoms; R
3
is an aryl group of 6 to 20 carbon atoms which may have attached thereto a hydroxyl group and/or a hydroxyl group substituted with an OR
4
group; and R
4
is an acid labile group.
The invention also provides a polymer comprising recurring units of the following general formula (2).
Herein R
1
, R
2
and R
4
are as defined above, letters o, p, q, r, s and t are numbers in the range: 0≦o<5, 0<p≦5, 0≦q<5, 0≦r≦5, 0≦s≦5, 0≦t≦5, 0<o+q<5, and 0≦s+t≦5, k, m and n are numbers in the range: 0<k<1, 0≦m<1, and 0≦n <1.
In another aspect, the invention provides a photoresist composition comprising the polymer defined above.
One embodiment of the invention is a chemical amplification, positive resist composition comp
Harada Yuji
Hatakeyama Jun
Nakashima Mutsuo
Watanabe Jun
Baxter Janet
Millen White Zelano & Branigan P.C.
Shin-Etsu Chemical Co. , Ltd.
Walke Amanda C.
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