Optical Sensor Methodology for Measuring Shift, Thickness, Refractive Index and Tilt Angle of Thin Films

We propose a simple optical method and device design for the non-contact determination of small shift, thickness, refractive index, tilt angle thin films. The proposed sensor consists laser light source, third- or two-order spiral amplitude zone plate with high numerical aperture, CCD camera connected to computer. It is shown that third-order transforms incident Gaussian beam into three-petal rotating beam. By measuring rotation intensity distribution, one can measure following: minimum shift along axis about 7 nm (the wavelength 532 nm), change in thickness by 3 nm, 0.1 degrees, index 0.01.