Postexposure bake as a process-control parameter for chemically amplified photoresist

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