Acid amplified imaging

A terpolymer of ter/-butyl methacrylate (TBMA), methyl methacrylate (MMA), and methacrylic acid (MAA) was initially developed as a chemically amplified thick laser resist for circuit board fabrication [ 180]. The terpolymer containing 1 wt% of di(ferf-butylphenyl)iodonium trifluoromethanesulfonate (triflate) has demonstrated excellent imaging at 193 nm when developed with a dilute (0.01 N) TMAH aqueous solution [181]. This terpolymer single layer resist was employed for exposure tool testing. 

A change of a polarity from a polar to nonpolar state (reverse polarity change) can be accomplished by the pinacol-pinacolone rearrangement and has been exploited in chemically amplified lithographic imaging [151, 348-350]. The pinacol rearrangement involves conversion of vie-diols to ketones or aldehydes with an acid as a catalyst (Fig. 115). 

H. Ito, Chemical amplification resists for microlithography, Adv. Polym. Set, 172, 149 (2005). Ito, Y. Maekawa, R. Sooriyakumaran, and E.A. Mash, Acid catalyzed dehydration A new mechanism for chemically amplified lithographic imaging, Polymers for Microelectronics, ACS Symp. Series 537, L.F. Thompson, C.G. Willson, and S. Tagawa, Eds., p. 64, American Chemical Society, Washington, DC. (1994). 

In a positive-tone resist, the areas that are exposed to the radiation develop away into the solvent faster than unexposed areas, resulting in a positive-tone image of the mask. The majority of commercial, positive-tone, nonchemically amplified resists used today are variations of the well-known, two-component, diazonaphthoquinone-novolac resist [5]. Novolac is a name generally given to acid-catalyzed phenol formaldehyde condensation polymers of the type shown in Fig. 2. 

Acid Proliferation Reactions and Their Application to Chemically Amplified Lithographic Imaging... 

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