Apparatus and method for simultaneous measurement of film thickness and

Abstract

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.