Submillisecond post-exposure bake of chemically amplified resists by CO₂ laser spike annealing

Pattern formation in a chemically amplified photoresist requires a post-exposure bake (PEB) to catalytically deprotect the polymer. Excessive diffusion of the photogenerated acid results in the loss of line edge definition, blurring of latent images, and changes in the line edge roughness. To optimize the process, the authors have explored submillisecond PEB using a CO₂ laser-based scanned annealing system [M. Chandhok (private communication)]. Several polymer and photoacid generator resist systems were studied under 800 μs laser spike annealing at estimated temperatures between 200 and 400 °C. All the resist systems exhibit remarkable stability in this time/temperature regime, with the maximum useful temperature limited by thermal deprotection and/or decomposition of the polymer backbone. At lower temperatures, high resolution patterns with sub- 100-nm features are formed, comparable to hotplate reference samples. Resist sensitivity is improved significantly for several resist systems (dose to clear is lowered), while other systems exhibit little change in photosensitivity.