PROCEEDINGS ARTICLE | April 1, 2009
Proc. SPIE. 7273, Advances in Resist Materials and Processing Technology XXVI
KEYWORDS: Polymethylmethacrylate, Quartz, Polymers, Crystals, Silicon, Manufacturing, Polymerization, Line width roughness, Line edge roughness, Semiconducting wafers
Classical electron-beam resists such as poly(methyl methacrylate) (PMMA) and Nippon Zeon's ZEP function as high
resolution and low roughness positive resists on the basis of radiation induced main chain scission to reduce the
molecular weight while chemical amplification resists utilized in device manufacturing function on the basis of acidcatalyzed
deprotection to change the polarity. In an attempt to increase the resolution and reduce the line roughness of
chemical amplification resists, we prepared copolymers that undergo radiation induced main chain scission and acidcatalyzed
deprotection. In another word, we wanted to increase the sensitivity of the PMMA resist by incorporating the
acid-catalyzed deprotection mechanism in polymers that undergo main chain scission, maintaining the high resolution
and low roughness of PMMA. To synthesize such hybrid resist polymers, we selected α-substituted acrylates and α-
substituted styrenes. The former included methyl methacrylate (MMA), t-butyl methacrylate (TBMA), methyl α-
fluoroacrylate (MFA), t-butyl α-fluoroacrylate (TBFA), and t-butyl α-trifluoromethylacrylate (TBTFMA) and the latter
α-methylstyrene (αMEST), α-methyleneindane (αMEIN), and α-methylenetetralin (αMETL). The α-substituted tbutyl
acrylic esters were copolymerized with the methyl esters and also with α-substituted styrenic monomers using 2,
2'-azobis(isobutyronitrile) (AIBN). Hybrid resists were formulated by adding a photochemical acid generator and a
base quencher to the copolymers and developers were selected by studying the dissolution behavior of unexposed and
254 nm exposed resist films using a quartz crystal microbalance (QCM). In addition to the difference in the imaging
mechanism, PMMA and ZEP differ from the chemical amplification resists in developers; organic solvent vs. aqueous
base. We were interested in looking also into the influence of the developer on the lithographic performance.
Contrast curves were generated by exposing the resist films to 100 keV electron beams and by changing the
postexposure bake temperature (PEB) on a thermal gradient hot plate (TGP). The resists were imaged on our Leica 100
keV electron-beam system and line roughness was measured.
