Reciprocity failure in novolak/diazoquinone photoresist with 364-nm exposure

Intensity-independent photobleaching (reciprocity failure) was observed when a film of novolak/diazoquinone photoresist was exposed at 364 and 351 nm in the intensity range 1 to 400 mW/cm². It was found that a dark reaction can be observed for short times after turning off the light during a bleach. It is postulated that these effects are a result of the absorbance of the intermediate ketene, which may decay on the same time scale as the exposure time and hence introduce a nonphotochemical time-dependent bleaching that couples with the photochemical bleaching to give reciprocity failure. The magnitude of the reciprocity failure is sufficient to have a significant detrimental effect on resolution and process control. Thus it is important not only to reduce the absorbance of the final product but also that of the intermediates