Simulation of optical microscope images for photomask feature size measurements

Features on photomasks used in the semiconductor industry have steadily decreased in size to fit more elements on a wafer. When the size becomes smaller than the wavelength of the light used in a microscope, simulation becomes an important part of the measurement process because the image does not otherwise yield an accurate value of the dimension being measured. The integral equation form of Maxwell´s equations is used in the simulation process described. We discuss the procedure intended to produce accurate linewidth values using UV light for measurements and integral equations for simulation of the image formation.