Wyko, Inc.

James D Ayres

Donald K Cohen

Eugene R Cochran

Chris P Brophy

The relative height variation and the thickness of a film of an object are simultaneously measured. A first interference pattern is produced for a calibration surface at a first wavelength and detected. Intensities of the first interference pattern are measured and used to compute a first group of phase values for each pixel. Intensity values of a point of the calibration samples are measured and used to compute a corresponding phase. A second interference pattern for the calibration surface is produced at a second wavelength and detected. Intensities of the second interference pattern are measured and used to compute a second group of phase values for each pixel. Intensity values of the point of the calibration surface are measured and used to compute a corresponding phase. A value for the surface height change .DELTA.h is computed by obtaining a linear combination of the corresponding phase values of the data groups. A drift value is computer by obtaining the difference between the first and second phase values at the point. A corrected surface height change value is computed for the calibration sample by adding the two. This procedure is repeated for a test surface to obtain its corrected surface height change. A corrected relative surface height change value .thrfore.h' is computed by subtracting the corrected surface height change value of the calibration surface from the corrected surface height change value for the test surface for each pixel. Computed .DELTA.h' values are compared to corresponding values from a mathematical model to obtain a best fit value of film thickness t for each pixel and the height error due to phase change is subtracted.

Apparatus and method for simultaneous measurement of film thickness and

Automatic focusing of an interference microscope is accomplished by directly sensing an interference pattern produced by a white light source with an auxiliary point detector. A beamsplitter intercepts part of the interference beam and directs it to the point detector. A narrow band filter filters light passing through the beam splitter on its way to a main detector array. An objective of the interference microscope is rapidly moved to an initial position between a sample surface and a fringe window by operating a position sensor to sense when the objective is a predetermined safe distance from the sample surface and turning off a motor moving the objective. The objective then moves rapidly from the initial position until the presence of fringes is detected by the point detector. Momentum of the microscope causes the objective to overshoot beyond a fringe window. The microscope objective then is moved more slowly through the interference window until fringes again are detected; the lower speed results in substantially reduced overshoot. Intensity measurements from the detector are sensed and stored as the objective moves through the width of the fringe window. The microscope objective then is yet more slowly moved through the fringe window while sensing the intensities produced by the point detector until the objective reaches a point at which the intensity is equal to a preselected percentage of the maximum stored intensity.

Apparatus and method for automatically focusing an interference

Automatic focusing of an interference microscope is accomplished by directly sensing an interference pattern produced by a white light source with an auxiliary point detector. A beamsplitter intercepts part of the interference beam and directs it to the point detector. A narrow band filter filters light passing through the beam splitter on its way to a main detector array. A memory lock position of the microscope objective is manually selected and stored. Initially, the objective moves rapidly from the memory lock position until the presence of fringes is detected by the point detector. Momentum of the microscope causes the objective to overshoot beyond a fringe window. The microscope objective then is moved more slowly through the interference window until fringes again are detected; the lower speed results in substantially reduced overshoot. Intensity measurements from the point detector are sensed and stored as the objective moves through the width of the fringe window. The microscope objective then is yet more slowly moved through the fringe window while sensing the intensities produced by the point detector until the objective reaches a point at which the intensity is equal to a preselected percentage of the maximum stored intensity.

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Tucson, AZ, United States of America

James D Ayres