Photomask edge roughness characterization using an atomic force microscope

Photomask edge roughness metrology has historically been performed using optical techniques. However, current optical techniques fail to provide the necessary resolution to meet the requirements for reduced mask edge roughness driven by improved resolution of advanced wafer lithography systems. Atomic force microscopy (AFM) has demonstrated the capability to provide the required physical characterization of printed mask features. At the macroscopic level, the critical dimensions (CDs) of linewidth, sidewall angle, and chrome thickness are measured using an attractive mode, critical dimension scanning algorithm with flared silicon tips. For localized examination of the line edge roughness, the system is operated with sharp conical tips (10-30 nm radius) scanned parallel to the profile edge. This new technique provides 10-30 nm resolution. In addition, Fourier analysis of the line edge roughness data can be used to identify periodic error signatures in the mask pattern generation.