Interferometric Method for Step Height Measurements on Surfaces with Variable Tilts
Original Publication Date: 1980-Sep-01
Included in the Prior Art Database: 2005-Feb-13
Testing and analysis of surfaces often require accurate measurements of small steps or gradients. For such purposes, optical methods have been used which are based on measuring the phase difference of two laser beams reflected from two spots with an unknown vertical distance. The values obtained by these methods are accurate to some nanometers, if the surface is maintained in a horizontal position or at a constant tilt angle. A time-varying tilt, however, introduces an additional phase difference and impairs the accuracy.