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

• Main Authors: Belure, A.R., Biswas, A.K., Raghunathan, D., Rishipal, Bhartiya, S., Singh, Rashmi, Rai, S.K., Pawade, R.S., Kamath, M.P., Benerji, N.S.
• Format: Conference Proceeding
• Language: English
• Subjects: AFM; Bowl-feed method: Super-smooth polishing; Optical fabrication; Roughness; Silicon mirror
• ISSN: 2214-7853; 2214-7853
• DOI: 10.1016/j.matpr.2020.02.490

•Bowl-feed CMP was used to fabricate ultra-low roughness super-smooth Si substrates.•AFM, SEM and X-ray reflectivity were performed to study super-smooth Si surfaces.•Achieved roughness below 5 Å and flatness of λ/10 on the polished Silicon surfaces.•Bowl-feed CMP is proved to be a viable method for super-polishing of Si substrates. 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.