Enhancement of resist resolution and sensitivity via applied electric field

This article presents a methodology for enhancing the resist sensitivity and resolution based on confining the photoacid drift/diffusion by external electric field. An alternating electric field applied to the resist film during postexposure bake can enhance the photoacid drift in the vertical direction, reduce the bake time, and thereby confine the lateral acid diffusion. A mathematical model is presented and a rigorous solution is obtained in the case of Fickean diffusion and constant electric field. The experiments were conducted on UVIIHS resist with a JEOL electron-beam exposure tool. The scanning electron microscope pictures show that electric-field enhanced postexposure bake (PEB) can reduce the FEB time requirement by 30%, and at the same time, improve the sharpness of two-dimensional corners and increase the verticality of resist sidewalls. Electric-field-enhanced FEB also significantly improves the tolerance of overexposure and provides better critical dimension control. It is estimated that it reduces the lateral acid diffusion length by about 70 nm, or 50%. (C) 2000 American Vacuum Society. [S0734-211X(00)17606-1].