Polymethacrylates and Norbornene Polymers for 193 nm Lithography

aromatic polymers are more resistant to dry etching than aliphatic polymers in general and in aliphatic polymers cyclization can reduce the number of hydrogen atoms and therefore N/Nc. As this model showed a poor relationship to chemical structure for etch rates in largely chemical etching, an additional parameter based on polymer structure, called the ring parameter (r) was introduced by Kunz et al. [228], which is defined as 

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. 

Several polymethacrylates, primarily alkyl esters, were compared with a novolac resist in terms of etch rates in CF4 and Ar plasmas. The alkyl groups examined included methyl, terf-butyl, cyclohexyl, norbonyl, adamantyl, and benzyl [226]. The polymerization of alicyclic methacrylates was pioneered by Otsu, who has demonstrated facile polymerization of bulky methacrylates and reported high Tg of this class of polymethacrylates [230]. It has been found that alicyclic polymers exhibit better dry etch resistance than acyclic esters and that the dry etch durability is increased by an increase in the number of rings. Thus, poly(adamantyl methacrylate) is as stable as a novolac resist under dry etch conditions. A 30/70 copolymer of adamantyl methacrylate with ter/-butyl 

Another interesting acrylate polymer for 193 nm lithography is a terpolymer of tricyclo[5.2.1.02 6]decanyl acrylate, tetrahydropyranyl methacrylate, and methacrylic acid (Fig. 58) [237]. In conjunction, new alkylsulfonium salts for use in ArF excimer laser lithography have been synthesized [238]. Methyl-(cyclohexyl)(2-oxocyclohexyl)sulfonium and methyl(2-norbonyl)(2-oxocy-clohexyl)sulfonium triflates are highly transparent with their absorption coefficients of 1125 and 1650 L/mofrcm at 193 nm in sharp contrast with 

Values in parentheses are solubility parameters of hydrolyzed structures (Fig. 62) 

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