Origin of delay times in chemically amplified positive DUV resists

In order to reduce or eliminate post-exposure delay-time effects, it is necessary to remove the extra free volume trapped in the lithographic film during the spin-coating process. Depending on the soft-bake conditions, the Tg of the lithographic film can be lower than that of the resist material. The maximum compaction state can only be reached when the lithographic film is baked at above the Tg temperature of the resist material. This condition cannot be fulfilled when the deprotection mechanism occurs below the Tg of the matrix. This case generally applies to the PHS-tBOC based formulations used in microlithography and explains the delay-time problems encountered with these systems. This approach, based on thermal analysis (DSC), can be generalized to systems with different chemistries and allows the design or selection of delay time-free resists.