DNS-novolac positive photoresist

FIGURE 5.45 Schematic of image reversal process of DNS-novolac positive photoresist. 

A DNS-based positive photoresist can be used for deep-UV exposures if the binder resin in the photoresist itself does not absorb. Since novolacs made fi-om the condensation of formaldehyde with pure p-cresol (instead of commercial cresol mixtures) are found to have very transparent windows at about 250 nm, a DNS/p-cresol novolac-based photoresist gives a positive image after deep-UV exposure and development with aqueous base. A copolymer of styrene and maleimide is also used in place of novolac as a binder for DNS-based deep-UV positive resists. 

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