Bleachable absorbance

The synthesis and characterization of a novel class of diazoketones that function in a manner analogous to the diazoquinones but have bleachable absorbance maxima in the DUV region have been described (Figure 2.9). These systems are reported to function with photosensitivity comparable to that of the DQN systems, but their utihty still appears to be limited by the feet that they are employed in conjuction with a novolac resin, which has a substantial, unbleachable absorbance in the DUV region. This undesirable resin absorbance leads to reduced contrast 24, 25). 

Two interesting attempts to redesign the dissolution-inhibitor-matrix-resin systems have been reported. Grant et al. (37) proposed an alternative inhibitor for novolac resins. They found that 5-diazo-Meldrum s acid (structure 3.5) exhibits an intense, bleachable absorbance at 254 nm with a sharp... 

When it was observed that the DNQ/novolac resists in use at the time became more transparent on exposure (i.e., they bleached). Dill used this change in optical absorbance as a way of monitoring the kinetics of exposure. He developed a first-order model of exposure consisting of three parameters A, B, and C, now called the Dill model, which accurately fit the experimental measurement results of the transmittance of a resist coating on an optically matched glass wafer as a function of exposure dose. The Dill parameters A, B, and C, describe bleachable absorbance, nonbleachable absorbance, and exposure rate constant, respectively." ... 

An effective contrast-enhancing layer must possess certain essential characteristics It must be thermally stable, soluble in solvents that permit casting on photoresist layers with no mixing at the interface, strongly absorbing in the desired spectral region, and bleachable upon exposure. In addition, removal of this layer from the exposed photoresist prior to image development is desirable. 

The spectral properties of wines were measured with a Varian 300 UV/Vis spectrophotometer, and wine colour density (absorbance [420 nm + S20 nm]), hue (absorbance [420 nm / 520 nm]), and non-bleachable pigments (absorbance 520 nm in presence of SO2) were determined as described by Somers and Evans... 

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