Measuring submicrometer structures near the limit of resolution of opticalmicroscopy

Simple structures, such as lines and grooves, on chromium photomasks and si licon wafers, whose widths are in the range of the classical resolution lim it of light microscopy or slightly below it, are imaged in the microscope u sing a special object scanning meth od The measurement results are compared with model calculations based on the transmission cross coefficient. The d ependence of the image on the spatial coherence of the illumination is inve stigated. The results are discussed by comparing them with different resolu tion criteria. They show that the classical resolution limits are no sharpl y defined limits. Even limes, slits, and grooves whose widths are smaller t han half the wavelength can be clearly imaged and their dimensions can be m easured. The higher the spatial coherence of the illumination, the higher i n contrast are the formed images of these structures.