Design of a positive-tone water-soluble resist

We report the study of a novel class of resists designed to be coated from and developed in pure water, avoiding both the need for the traditional organic solvents and the developers containing organic bases in aqueous solution. We have previously reported on the design of several negative tone resists that operate on the basis of radiation-induced crosslinking. The performance of these negative tone systems meets our fundamental objective of coating from and development in pure water, but their design involving the crosslinking of a matrix polymer limits the resolution that may be achieved because of the swelling that occurs during development. We have now explored novel designs involving positive tone water developable resists that may help alleviate this limitation. For example, water-soluble polymers containing pendant oxazoline units may be insolubilized in situ through their heat-activated reaction with additives containing carboxylic acid groups. Exposure to UV radiation is then used to cleave these solubility modifiers hence restoring solubility to the exposed areas. Analogous materials that involve the addition of divinyl ethers to poly(acrylic acid), followed by photogenerated acid cleavage of the crosslinks have been used generate water-developed positive tone images.