High slope surface measurement based on an information-rich approach using coherence scanning interferometry
Start: December 2016
Student: Matthew Thomas
Supervisors: Richard Leach, Rong Su
Industrial supervisor: Peter de Groot
Coherence scanning interferometry (CSI) is one of the most accurate optical metrology techniques that determines a sample’s surface topography by localisation of low-coherence interference fringes during a scan along the optical axis of the system. Current commercial CSI systems are able to measure surface topography with sub-nanometre precision. However, CSI has some limitations; one being its limited detectability of high surface slopes due to the limited numerical aperture of its objective optics.
This project involves the development of a computational method for high-precision surface metrology from first principles, based on an information-rich approach using CSI. The aim is to extend CSI to be capable of handling high slope surfaces, by fully considering the 3D linear systems theory for CSI and the signal response of the system in the non-linear regime (e.g. multiple reflection and scattering signals). This project will include optical modelling, including analytical and numerical solutions of Maxwell’s equations. The novelty of the project lies with the combination of instrument modelling with a priori manufacturing data to significantly increase the bandwidth of the measurement, allowing for the measurement of high slope surfaces.
Typical CSI fringes of a sinusoidal surface, with high slope sections visibly weaker in contrast, possibly increasing the measurement uncertainty in this area.