Autocatalytic Fragmentation of Acetoacetate Derivatives as Acid Amplifiers to Proliferate Acid Molecules

A novel concept of acid proliferation to improve the photosensitivity of chemically amplified photoresist materials is described by presenting the autocatalytic fragmentation of acetoacetates having a (sulfonyloxy)methyl residue to liberate the corresponding sulfonic acid. 2-Methyl-2-((methane- or p -toluenesulfonyloxy)methyl)acetoacetates were designed to be subjected to the acid-catalyzed fragmentation through the corresponding acetoacetic acids which are readily decarboxylated and undergo the subsequent β-elimination to give a sulfonic acid which can act as the autocatalyst to lead to the increment of acid concentration in geometric progression. Among the acetoacetates tested, tert -butyl 2-methyl-2-(( p- toluenesulfonyloxy)methyl)acetoacetate was the most suitable reagent for the present purpose because of its reasonable thermal stability. A nonlinear generation of the sulfonic acid was confirmed in the acidolytic transformation of the acetoacetate in nonpolar solvents and in a film of poly[4-(( tert -butoxycarbonyl)oxy)styrene] (PBOCSt), respectively. It was found that the addition of the acetoacetate to a film of PBOCSt doped with a photoacid generator enhances the photosensitivity characteristics.