Abstract: The present invention provides a method and apparatus for high-speed autofocus and tilt of an inspection surface in a microscope system. The method and apparatus herein described projects an array of spots, lines, circles, grids or other shapes on the surface to be adjusted. The superposition of the array on the surface is imaged by a CCD camera and captured for subsequent analysis. Analysis of the captured image determines both the distance and angle through which the surface must be adjusted to bring it into the focal plane of the optical system. Focus and tilt error is estimated by comparing image dilation and distortion with calibrated data.

Abstract: The present invention provides a method and apparatus for high precision image metrology. A feature dimension from the image is determined by measuring corresponding features in the Fourier power spectrum of the image with substantially improved precision due to immunity from noise and system response. Operationally, a digital image of the sample is acquired at sufficient resolution to capture the feature of interest. A sample widow is chosen which substantially isolates the feature of interest. The feature window is then piecewise extended to a predetermined window size for effective Fourier Transform interpolation. A Fourier Power Spectrum of the sample widow is generated at high sample density such that the loci of extremal points indicative of a feature dimension is identified with high precision. The relative spacing of the extremal points is measured and related to the desired feature dimension.