Development of super-smooth flat silicon mirror substrates using bowl-feed chemical-mechanical polishing

Abstract

Silicon is one of the important optical substrate materials used for making high reflectivity, high damage threshold mirrors for high power/energy IR lasers and grazing incidence synchrotron X-ray mirrors. These applications require ultra-low roughness or super-smooth substrates that ensure extremely low scattering losses. The present work is an attempt to fabricate super-smooth, flat silicon substrates using the conventional Chemical-Mechanical Polishing (CMP) method with bowl-feed technique. The roughness parameters of the ultra-smooth flat silicon surfaces fabricated using bowl-feed CMP have been measured in Atomic Force Microscope (AFM) and by hard X-Ray Reflectivity (XRR) and are found to be of the order of 5 Å. The surface morphologies of the polished silicon surfaces were also investigated using a Scanning Electron Microscope (SEM). We briefly discuss the bowl-feed CMP process of producing super-smooth, flat silicon substrates and presented the results of surface roughness measurements using various techniques.