Addressing challenges in lithography using sub-millisecond post exposure bake of chemically amplified resists

摘要

Chemically amplified photoresists require a post exposure bake (PEB), typically on a hot plate at 90-150°C for 30-120 seconds, to catalytically deprotect the polymer backbone. During PEB, excessive diffusion of the photo-generated acid results in loss of line edge definition, blurring of latent images and changes in the line edge roughness. Both acid diffusion and deprotection are thermally activated processes, with the relative rates affected by the time/temperature profile of the PEB. In this work, we introduce an alternate PEB method involving millisecond time frame heating over a temperature range of 300°C to 420°C using a continuous wave CO2 laser. A methodology is developed for characterizing the resist deprotection and acid diffusion kinetics under laser PEB (/-PEB) and comparing the behavior with conventional hot plate PEB. Results show that the deprotection rate sensitivity with temperature is smaller for /-PEB compared to that of hot plate PEB, suggesting a possible change in the deprotection mechanism. Acid diffusivity under /-PEB is reduced by a factor of 102-103 compared to values extrapolated from the hot plate PEB data. Under EUV exposure, patterns formed using /-PEB show significantly smoother surface roughness while requiring less than half the dose required for hot plate PEB - a direct consequence of enhanced deprotection at high PEB temperature and reduced acid diffusion in the millisecond time frame.