Post-exposure bake as a process-control parameter for chemically-amplffied photoresist

A new method is described for the real-time in-line control of critical dimensions forpositive-tone chemically amplified resist systems. The technique relies on the generation of adiffraction grating in the resist film when a latent image appears during the post-exposure bake. Asimple optical illumination/collection arrangement allows the diffracted signal to be measuredduring the post-exposure bake. This signal can be correlated to linewidths when measured by anon-destructive SEM. The result is a post-exposure bake time that can be used to correct forexposure-and-bake temperature variations to conveniently provide overall process control.Results generated by a prototype system are presented for a variety of 0.5-.tm mask levels andprocess conditions.