Negative tone materials

A separate group of negative tone materials based on the thermal polymerization of benzocyclobutenes (BCB) has been developed by the Dow Chemical Co. (50,51) and have been used as SBCs (52). The chemistry is based on the in situ generation of reactive, ortho-quinodimethane dienes that undergo facile polymerization to form a thermoset network (Fig. 17). The physical properties of the materials can be tailored by modification of the connecting group X. One such modified... 

Both negative and positive tone aqueous developable materials have been introduced. Negative tone materials have been derived from tbe covalent-type polyamic ester precursors through the use of additives that enhance solubility of the unexposed film in aqueous developers (53). Positive tone materials are based on either polyamic ester precursors containing carboxylic acid (54) or phenolic oxygen substituents (55,56) or on aromatic poly(ortho-hydroxyamides) as precursors to polybenzoxazoles (57,58), a class of high temperature stable, heterocyclic polymers with thermal and mechanical film properties similar to polyimides (Fig. 18). In both approaches, the acid-base reaction of the phenolic or carboxylic... 

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. 

C The Epoxy Resists. The first negative tone electron beam resist materials with useful sensitivity were based on utilizing the radiation chemistry of the oxirane or epoxy moiety. The most widely used of these materials, COP (Figure 32) is a copolymer of glycidyl methacrylate and ethyl acrylate and was developed at Bell Laboratories (43,44). COP has found wide applicability in the manufacturing of photomasks. The active element... 

In 1979, Smith and co-workers described the development of a system they called PDF (which presumably stands for Plasma Developable Photoresist) that is based on the use of a material, the structure of which has not yet been divulged 61). In this process the resist is coated in the usual fashion and exposed optically. The exposed film is then subjected to a baking cycle that produces a relief image of negative-tone that is, depressions are generated in unexposed areas (Figure 45). This relief structure is... 

Note 3 In a positive-tone resist, also called a positive resist, the material in the irradiated area not covered by a mask is removed, which results in an image with a pattern identical with that on the mask. In a negative-tone resist, also called a negative resist, the non-irradiated area is subsequently removed, which results in an image with a pattern that is the complement of that on the mask. 

These results confirm the potential of poly (p-formyloxystyrene) as a useful resist material combining such interesting properties as ability to be imaged in both positive or negative tone, ease of preparation, and activity in the deep UV, with a moderate sensitivity and good contrast. 

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