We developed a measurement method for linewidth patterns of photomasks, and started a calibration service of the
photomask linewidth measurement. For the photomask standards, high-quality of chromium film patterns, typical
thickness of about 80 nm, sharp edges (edge angles more than 85 degree) and smooth side walls on a quart glass
substrate were used. Two kinds of microscopes, an atomic force microscope (AFM) and a scanning electron microscope
(SEM), were employed to calibrate the linewidth.
At the first, the surface profile of line structures were inspected using the AFM, so that the distance between the left and
the right side walls at the edge positions were geometrically-determined. Before the each measurement of photomask
patterns by the AFM tips, each of the tip shape was checked using a needle artifact. Then AFM profiles of the photomask
patterns were corrected using the tip shape data. The linewidth was calculated using the corrected profiles under a
definition of the edge positions, a 10 % level from the top film surface. At the next, the linewidth bias between SEM and
AFM were evaluated using the AFM data. Using this method, an uncertainty of the linewidth measurement was
evaluated at 60 nm for a linewidth range of 0.5 μm-10 μm.