Chapter 5
Acid-Catalyzed Dehydration A New Mechanism for Chemically Amplified Lithographic Imaging 1
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H. Ito, Y. Maekawa , R. Sooriyakumaran , and E. A. Mash
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Downloaded by GEORGE MASON UNIV on June 4, 2016 | http://pubs.acs.org Publication Date: November 23, 1993 | doi: 10.1021/bk-1994-0537.ch005
IBM Research Division, Almaden Research Center, 650 Harry Road, San Jose, CA 95120-6099 New chemical amplification resist systems based on acid-catalyzed dehydration reactions are described. Intramolecular dehydration of poly[4-(2-hydroxy-2propyl)styrene]results in the change of the polarityfroma polar to a nonpolar state, allowing swelling-free negative imaging with alcohol as a developer. The pendantα-methylstyrenicmoieties generated by dehydration further undergo dimerization, resulting in concomitant crosslinking, which disallows positive imaging. Thetertiary-alcoholresist provides an extremely high sensitivity. Polystyrene with a pendant secondary alcohol group has been also prepared and evaluated as a resist material. Its unexpectedly high sensitivity is a result of crosslinking through ether linkage produced via intermolecular dehydra tion. The O-alkylation product is then converted to a linear dimer of styrene. Lithographic evaluations and mechanistic studies are presented.
Chemical amplification (I) based on radiation-induced acidolysis is a very attractive approach to dramatically increasing radiation sensitivities of resist systems for use in short wavelength lithographic technologies (deep U V < 300 nm, electron beams, and x-ray radiations). Acid-catalyzed deprotection (deesterification) of polymer pendant groups to change a polarity of repeat units and the solubility of polymer has been successfully employed in the design of the tBOC dual tone resist (2), which allowed manufacture of 1-megabit dynamic random access memory devices by deep U V lithography (3). The polarity change from a nonpolar to a polar state as embodied in the tBOC resist provides positive imaging with aqueous base or alcohol or swelling-free negative imaging with nonpolar organic solvents (Scheme I). Such an acid-catalyzed deprotection mechanism to photochemically generate a base-soluble functionality has at tracted a great deal of attention and is currently pursued by many research groups for the design of aqueous base developable, positive resist systems for replacement of novolac/diazoquinone resists (4). A polarity reversal has been also utilized in the chemical amplification scheme (Scheme I). One such system employs thermal deesterification and acid-catalyzed rearrangement of poly(2-cyclopropyl-2-propyl 4-vinylbenzoate)(5). Current address: Department of Chemistry, University of Wisconsin, Madison, WI 53706 Current address: IBM General Technology Division, East Fishkill Facilities, Hopewell Junction, NY 12533 Current address: Department of Chemistry, University of Arizona, Tucson, AZ 85721
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0097-6156/94/0537-0064$07.00/0 © 1994 American Chemical Society Thompson et al.; Polymers for Microelectronics ACS Symposium Series; American Chemical Society: Washington, DC, 1993.
Downloaded by GEORGE MASON UNIV on June 4, 2016 | http://pubs.acs.org Publication Date: November 23, 1993 | doi: 10.1021/bk-1994-0537.ch005
5. ITO ET AL.
Acid-Catalyzed Dehydration
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We have been also interested in inducing a reverse polarity change from a polar to a nonpolar state for lithographic imaging (Scheme I) and reported that pinacol rearrangement, which is acid-catalyzed, of pendant wc-diol to ketone (Scheme II) cleanly and facilely occurs in polymeric films (6, 7). Pinacol rearrangement of small wc-diols to ketones or aldehydes in phenolic resins provides aqueous base developable, negative, chemical amplification resists with high sensitivity and high resolution (6-8). Other examples of the reverse polarity change that have been reported include photochemical transformation of pyridinium ylides to 1,2-diazepines (9), acid-catalyzed condensation of dissolutionpromoting silanol to dissolution-inhibiting siloxane in a novolac resin (10), photochemically-induced partial etherification and esterification of poly(4-hydroxystyrene) (11-13). We believe that polarity alteration through clean structural transformation could offer high resist contrasts, swelling-free development in a negative mode, and some versatile applications. Therefore, we have continued to exploit the reverse polarity change in the resist design and report in this paper sensitive resist systems based on acid-catalyzed dehydration of pendant alcohol to olefin (Scheme III) as well as a different pathway in dehydration of pendant secondary alcohol. EXPERIMENTAL Materials 4-(2-Hydroxy-2-propyl)styrene [4-vinylphenyl dimethyl carbinol, a,adimethyl(4-vinyl)benzyl alcohol] and 4-(l-hydroxyethyl)styrene [4-vinylphenyl methyl carbinol,
