Abstract: A method of measuring thin film thickness, especially on semiconductor substrates, in which the substrate is illuminated with ultraviolet light of a fixed wavelength corresponding to a persistent spectral line and the amount of light reflected from the substrate is detected and measured. The ultraviolet light preferably has a wavelength in the range from 240 nm to 300 nm, and the 253.6 nm spectral line of mercury is considered best. Comparing the measured amount of light from the substrate to a known amount of light detected from a standard calibration substrate with known reflectivity, the reflectivity of the test substrate is computed. The thickness of a thin film on the substrate is determined from the computed reflectivity using Fresnel's equation or a lookup table derived from the same.

Abstract: A confocal measuring microscope including a spectrometer and autofocus system sharing common optical elements in which the intensity of light entering the spectrometer from a particular spot on a workpiece is used to determine a focus condition for the same spot. The microscope includes at least one light source, an illumination field stop, and a microscope objective that images the stop onto a workpiece supported by a movable platform. The objective also forms an image of the illuminated portion of the object. An aperture in a second stop and intersecting the image plane passes light from part of the image to the spectrometer, while viewing optics are used to view the image. In one embodiment, a detector is placed at the zero order position, while in another embodiment a laser is placed at the zero order position. In the later embodiment an integrator circuit connected to the detector array replaces the zero order detector for measuring the total intensity of light entering the spectrometer.