Patent ID: 7615752

Claim:
A method of evaluating a parameter of a microstructure on a workpiece, comprising: generating a beam having a wavelength; irradiating a microstructure on a workpiece by passing the beam through an object lens assembly that focuses the beam to a focus area at an object focal plane, wherein the focus area has a dimension not greater than 30 μm, and wherein the beam is focused through at least (a) a 15° range of altitude angles and (b) a 90° range of azimuth angles simultaneously; detecting with a two-dimensional image sensor array a radiation distribution of the return radiation from the beam, which is focused through at least a 15° range of altitude angles, interacting with the microstructure; acquiring a measured selected radiation distribution by reading data from selected pixels in the image sensor array, the selected pixel being less than the total number of illuminated pixels of the image sensor array, the selected pixels being more sensitive to changes in the parameter than non-selected pixels; fitting the measured selected radiation distribution to a simulated selected radiation distribution corresponding to the selected pixels to determine a value of the parameter; and storing the determined value of the parameter.