Sidewall effect of photomask by scanning electron microscope and optical critical dimension metrology

Sidewall effects on critical dimensions (CD) of photomasks are studied. CDs of patterns are measured by a scanning electron microscope (SEM) and a deep-UV microscope. CDs of the patterns are also calculated by an aerial image simulation. The sidewall effects on the measured CDs are compared with effects on the calculated CD. The results indicate that the sidewall effect on CDs by SEM differs from the effect on the aerial image, and that the effect on CDs by a deep-UV microscope corresponds to the effect on the aerial image. The factor of the sidewall effect on an aerial image is studied using an electric field calculation simulator. The result reveals that the factor is transmissivity. SEMs have no information about transmission, and therefore the effects differ from each other. A deep-UV microscope employs transmitted light just like a wafer aligner, and therefore the effects correspond to each other. (c) 2005 Society of Photo-Optical Instrumentation Engineers.