Thin film metrology using modal wavefront sensing

Presented here is a novel non-contact method of film thickness measurement based on wavefront sensing. We describe a simplified measurement technique based on the measurement of the spatial separation of reflections from each of the film interfaces. Effectively we are measuring a single aberration, tilt. We present some analysis to show how the technique works, and describe the experimental set-up and procedure used to capture the results. We then present some of our results to date, and discuss how the system may be calibrated to give an absolute measure of film thickness. Finally we describe some of the future work to be carried out to encompass full wavefront sensing and allow not only film thickness to be measured but also information on surface roughness, surface profile and refractive index to be gathered. © 2005 IOP Publishing Ltd.