Optical probe using differential confocal technique for surface profile

A non-contact optical probe for surface profiling with up to 2nm position resolution over 100μm measurement range has been developed, which includes a confocal light path for non-contact position and a capacitance sensor for Z axis displacement measurement. The principle of the optical probe is based on differential confocal technique. The differential light-intensity distribution depends on the confocal axial response (or depth discrimination) properties. Using the diffraction theory, the mathematical analysis of the method has been performed. Validity of the mathematical theory analysis of the differential confocal technique is experimentally verified.