Negative-acting resists

Fig. 4. Chemistry of poly(vinyl cinnamate) negative-acting resist. Initial light absorption by the photosensitizer is followed by energy transfer to produce a pendant cinnamate group in a triplet electronic state. This combines with a second cinnamate on another polymer chain, forming a polymer—polymer...

Fig. 5. Chemistry of cyclized mbbei—bis-a2ide negative acting resist, (a) Preparation of cyclized mbber resin from polyisoprene (b) photochemistry of aromatic bis-a2ide sensiti2ers. The primary photoproduct is a highly reactive nitrene which may combine with molecular oxygen to form oxygenated products, or may react with the resin matrix by addition or insertion to form polymer—polymer linkages.

We report here a novel technique used to measure the cross-linking and scission yields for negative acting resist systems. The three systems investigated were polyfglycidyl methacrylate-co-3-chlorostyrene) (GMC), poly(3-chloro-styrene) (PCLS), and polystyrene (PS). The technique requires generating an... 

However, the important considerations are sensitivity and tone (positive or negative). When covalent bonds are formed, the increase in molecular weight results in negative-acting resists. A molecular weight decrease because of polymeric backbone scissions produces positive-acting resists. 

The origin of these effects lies in the different radiation susceptibilities of the two copolymer components. PDMS is a negative-acting resist whose sensitivity has been reported to be for a molecular weight of 71,800 (5). PMMA, on the other hand, is positive... 

By general convention, the sensitivity, S, is related to the thickness, d, of the resist layer measured after exposure and development, and is obtained from exposure characteristic curves, as are illustrated in Fig. 9.3. In the case of positively functioning resists, S = corresponds to the exposure light dose required to completely remove the irradiated polymer from the substrate, i.e. the dose at which the normalized thickness of the resist layer is equal to zero, dirr/do=0. In the case of negatively acting resists, the sensitivity is reported as S = or... 

Positive-acting resists are subject to the same problems as are negative-acting resists, although they may be easier to remove cleanly, after exposure, from areas to be etched or plated. Problems related to plating photoresist-coated boards are reviewed in Chap. 29. 

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