By Jason Tiffany, Infineon Technologies, Richmond, Virginia, Barney Cohen, SensArray Corp., Fremont, California

As linewidths approach 90nm node in volume production, post exposure bake (PEB) uniformity becomes a much larger component of the across-wafer critical dimension uniformity (CDU). In production, the need for PEB plate matching has led to novel solutions such as plate-specific dose offsets. However, this type of correction does not help across-wafer CDU. A different approach using an in situ wireless RTD wafer is explored.

Due to unequal activation energies of critical PEB processes, any thermal history difference can result in a corresponding CD variation – differences that become more pronounced as the industry moves to manufacturing at the 90nm node. The rise time of the resist to the target temperature has been shown to affect CD, with the most critical time being the first 5-7 sec. A typical PEB plate has multizone thermal control with one thermal sensor per zone….