Negative resists chemistry

Both solvent-iaduced swelling and oxygen inhibition ate characteristic of all cross-linking negative resists based on free-radical chemistry. 

The impact on negative-CA resists of airborne base contamination differs qualitatively from their positive tone counterparts. Suppression of acid-catalyzed chemistry at the surface of a negative resist results in some film erosion at the top of the exposed fields and in some cases an apparent loss of photosensitivity, but in general the reUef images formed exhibit the expected cross-sectional profile. This is in sharp contrast with the typical behavior seen with positive-tone CA resists, where suppression of acid-catalyzed chemistry at the surface causes an insoluble surface skin. 

Schematic representation of the chemistry of the cyclized rubber - lns arylazide negative resists.

Besides prinfing and decoration, flexographic, gravure, and lifhographic plates as well as silk screens are used in resist chemistry, which is widely employed in the production of printed circuit boards. A resist is a material that will resist solvent attack. A negative resist is a material that, upon exposure to light cross-links, becomes less soluble in a solvent system that would... 

Both negative and positive acting, oxygen RIE resistnt e-beam resist systems have been prepared through the incorporation of the trimethylsilylmethyl functionality into standard resist chemistry. Resins containing >10 wt% silicon display an RIE resistance more than 10 times greater than conventional photoresists and allow submicron pattern transfer with minimum linewidth loss. 

The radiation chemistry of resist polymers is governed by two main processes, namely, backbone scission and cross-linking. Whether the polymer will act as a positive or negative resist resin under lithographic imaging depends on whether backbone scissioning or the cross-linking process is dominant. ... 

Negative photoresist chemistry. A. Cross-linking of a prolyisoprene rubber by a photoreactive bisazide. B. A radical induced polymerization and cross-linking of an acrylate monomer. C. A single component resist. Electron beam irradiation produces anions that launch a cascade of epoxide ring-opening reactions to cross-link the poljrmer. 

It may be seen from Fig. 7.2 that the gel dose only approximates to a threshold and the degree to which this approaches a sheup threshold is known as the contrast. In a negative resist this is related to the rate of crosslinking and once more is dependent on the resist chemistry and polymeric parameters. It is most conveniently measured from the seune plot of resist thickness with dose. It is usually defined as the gradient of the linear portion of the curve (Fig. 7.3)... 

Figure 25.3 Schematic of block copolymer lithography using a combination of positive- and negative-tone resist chemistry. (Reproduced with permission from Kurt E. Geckeler and Hiroyuki Nishide (eds), Advanced Nanomaterials, VoL 1, Wiley-VCH, Wienheim. 2010.)...

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.

Acid-C t lyzed Chemistry. Acid-catalyzed reactions form the basis for essentially all chemically amplified resist systems for microlithography appHcations (61). These reactions can be generally classified as either cross-linking (photopolymerization) or deprotection reactions. The latter are used to unmask acidic functionality such as phenohc or pendent carboxyhc acid groups, and thus lend themselves to positive tone resist apphcations. Acid-catalyzed polymer cross-linking and photopolymerization reactions, on the other hand, find appHcation in negative tone resist systems. Representative examples of each type of chemistry are Hsted below. 

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