Image-reversal process flood exposure

Figure 2.3. The base-catalyzed image-reversal process involves a patternwise exposure that converts the diazoquinone to the corresponding indenecarboxylic acid, follotved by a bake step that causes base-catalyzed decarboxylation that produces the nonphotosensitive indene derivative. Subsequent flood exposure converts the diazoquinone in the previously unexposed areas of the film into the indenecarboxylic acid. Development then yields a negative image of the mask because the originally patterned areas containing the lipophilic indene derivative are less soluble in base than those containing the...

Although DNQ sensitizers react with X-rays, very little ICA is formed. This observation was made even when exposure was conducted under ambient conditions in which water vapor was present. The net result is that the irradiated areas of the resist have very poor solubility in aqueous base. In fact, if a UV flood exposure is used after imagewise X-ray irradiation, the areas exposed only to the UV can be selectively removed with a developer, a process that leads to an image-reversal scheme. 

---