Wyko, Inc.

Paul J Caber

Donald K Cohen

Chris P Brophy

Bryan W Guenther

John B Hayes

Chiayu Ai

Interferometric apparatus that combines white-light VSI and single-wavelength PSI capabilities to improve the accuracy of height measurements in steep regions and in areas with large inter-pixel steps on the test surface. The technique consists of performing VSI measurements to obtain a relatively coarse profile of the test surface and to identify regions separated by a large step. Then PSI measurements are carried out over the test surface to obtain a relatively fine profile. Offsets between VSI and PSI measurements are calculated to correct for misalignments and phase shifts that may have occurred between the two sets of measurements. Finally, the fine PSI data are integrated to within one quarter wavelength of the coarse VSI data. The resulting quality of the height data in each of the step regions is thus improved to within the resolution of the PSI measurements.

Combination of white-light scanning and phase-shifting interferometry

A scanning interferometer that utilizes a DC gear motor instead of a PZT translator in closed-loop configuration with an LVTD position sensor. The DC motor is connected to the scanning mechanism so that a rotational motion of the motor shaft produces a translation along the optical axis of either the sample or the objective of the interferometer. During scanning, the motor is driven by the input of a ramp signal into the system. The closed-loop configuration is such that a constant, or nearly constant voltage is applied to the DC motor to produce a constant-speed scan in response to the ramp input. Any non-linearity in the speed of motion is corrected by an adjustment to the motor voltage. At the completion of the scan, the ramp input is removed and the motor is automatically returned to the starting position to satisfy the closed-loop condition. In order to maintain the image in focus on the sensor over the wide range of scanning, a pair of relay lenses is inserted in the optical path between the interferometer and the light detector.

Combination of motorized and piezoelectric translation for long-range

A method of profiling a rough surface of an object includes moving the object along a z axis so that a highest point of the rough surface is optically aligned with and outside of the focus range of a solid-state imaging array. An interferogram of the rough surface then is produced by means of a two beam interferometer. The solid-state imaging array is operated to scan the rough surface along x and y axes to produce intensity data for each pixel of the solid-state imaging array for a plurality of frames each shifted from the other by a preselected phase difference. The modulation for each pixel is computed from the intensity data. The most recently computed modulation of each pixel is compared with a stored prior value of modulation of that pixel. The prior value is replaced with the most recently computed value if the most recently computed value is greater. The object is incrementally moved a selected distance along the z axis, and the foregoing procedure is repeated until maximum values of modulation and corresponding relative height of the rough surface are obtained and stored for each pixel.

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Tucson, AZ, United States of America

Paul J Caber