Novolac-based negative resists

Novolac- or phenolic resin-based resists usually show no pattern deformation induced by swelling during development in aqueous alkaline solution. Examples of such resists are naphtho-quinonediazide/novolac positive photoresists, novolac-based positive electron-beam resist (NPR) (1), and azide/phenolic negative deep-UV resist (MRS) (2). Iwayanagi et al.(2) reported that the development of MRS proceeds in the same manner as the etching process. This resist, consisting of a deep-UV sensitive azide and phenolic resis matrix, is also sensitive to electron-beams. This paper deals with the development mechanism of non-swelling MRS and its electron-beam exposure characteristics. 

In point of fact, the reaction of ketene with the anhydrous base resin has been exploited to produce negative resist images with strongly undercut profiles, which have found applications in lift-off processes (Figure 7.3). Furthermore, Itoh et al. have reported that exposure of a novolac-DNQ positive resist to DUV (250 nm) radiation, to which it is ve absorptive, leads to the creation of a cross-linked crust on the top of the resist. ... 

The use of phenolic polymers in photocrosslinkable systems usually involves multicomponent systems which incorporate polyfunctional low molecular weight crosslinkers. For example, Feely et al. [9] have used hydroxymethyl melamine in combination with a photoactive diazonaphthoquinone which produces an indene carboxylic acid upon irradiation to crosslink a novolac resin. Similarly, Iwayanagi et al. [10] have used photoactive bisazides in combination with poly(p-hydroxy-sty-rene) to afford a negative-tone resist material which does not swell upon development in aqueous base. 

From this result on MRS, we expected that a combination of phenolic-resin-based resist and aqueous alkaline developer would lead to etching-type dissolution and non-swelling resist patterns. In this paper, we report on a new non-swelling negative electron beam resist consisting of an epoxy novolac, azide compound and phenolic resin matrix (EAP) and discuss the radiation chemistry of this resist. 

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