Bilayer lithography

Semi-Dry Bilayer Lithography (Wet Development/02 RIE Pattern Transfer)... 

The cleavable Si group as described above has been also incorporated in a polymethacrylate resist for 193 nm bilayer lithography (Fig. 151) [422b]. In a similar fashion 1,3-bis(trimethylsilyl)isopropyl methacrylate was terpolymerized with methacrylic acid and methyl methacrylate with AIBN in THF [428]. The COMA system has been modified to be used as a bilayer positive resist by incorporating norbornenes bearing a passive Si group and an acid-cleavable Si group (Fig. 152) [429]. 

LER and resist outgassing during exposure are major issues in bilayer lithography [438, 439]. Si species generated from a bilayer resist during exposure could badly contaminate lenses. Thus, formation of gaseous products must be minimized by proper selection of deprotection chemistry and resist components. 

The very first chemical amplification resist designed for use in bilayer lithography employed Si-containing polyphthalaldehyde as a top layer resin,... 

Fig. 155 All-dry bilayer lithography (thermal development-02 RIE pattern transfer)...

Fig. 158 Acid-catalyzed desilylation for positive bilayer lithography...

While the bilayer lithography can improve the process margin and therefore yield without introducing a new exposure tool, the most serious potential problem is the resist LER after 02 RIE, which is likely to be more devastating as the feature size moves toward <50 nm. 

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