| 摘要 |
A positive acting photoresist system including a hydrophobic blocked polymer can be made to function in a negative sense (or tone) in what is known as an "image reversal" process, which may be summarized as follows: (1) After being exposed to UV radiation through a mask pattern to produce photogenerated acid, a photoresist coated wafer is treated with a gaseous base such as ammonia. The base reacts with photogenerated acid to produce a salt, effectively preventing deblocking of the polymer. (2) The wafer then is exposed to a vacuum to remove any excess base. (3) The wafer is then flood-exposed (i.e., no mask is used) with UV light. This produces acid in the previously masked-over areas. The sensitizer has already been largely destroyed in the original image area and so little acid is produced there. (4) The wafer is then baked to deblock the polymer in the area not exposed in step (1) and developed in aqueous alkali. The resulting image is the inverse of the original mask pattern. That is, those areas that received irradiation through the mask remain, and those areas that were flood-exposed are removed by the developer.
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