Highly regioselective PACs for i-line resist design: synthetic reaction model, dissolution kinetics and lithographic response

Abstract

Most positive diazonaphthoquinone/novolak resists use mixtures of various DNQ-esters and positional isomers as the photoactive compounds (PACs). Compared to using a single compound, PAC mixtures often offer formulation advantages in terms of optimizing the lithographic response and improving storage stability. We have investigated a broad class of PACs for which the condensation reaction of diazonaphthoquinone sulphonyl chloride with the polyhydroxylated ballast group is highly regioselective; this produces mixtures which strongly favor either even-numbered isomers (tetraesters, hexaesters and octaesters) or odd-numbered isomers (triesters and pentaesters). In this paper we describe observed PAC DNQ-ester distributions as a function of the ballast molecular structure and the DNQ:ballast mole ratio. A synthetic reaction model is offered to explain the origins of these unusual DNQ-ester distributions. The effects of these distributions on resist performance is explored through dissolution kinetics (Rmin, Rmax and qeffective) and lithography.