Phantom Exposure of Chemically Amplified Resist in KrF Excimer Laser Lithography

The phantom exposure of a chemically amplified resist in KrF excimer laser lithography can be attributed to acids generated in the ambient air exposed to KrF excimer laser light. These acids diffuse into the resist film and act as catalytic acids. Phantom exposure expanded to more than 10 mm outside the exposure field, and degrades the patterning characteristics. The critical dimension (CD) uniformity can be improved by using an overcoat to protect the resist from the acid.