TITLE:
Characterisation of Thin Films Using a Coherence Scanning Interferometry
AUTHORS:
Yang Yu, Daniel Mansfield
KEYWORDS:
Film Thickness, CCI, Thick Film, HCF
JOURNAL NAME:
Journal of Materials Science and Chemical Engineering,
Vol.3 No.1,
January
20,
2015
ABSTRACT: Accurate measurement of film thickness and
its uniformity are very important to the performance of many coated surfaces
and for many applications are critical. Effective inspection of the film
thickness and uniformity is the key to high performance. Conventionally, film
thickness is meas- ured using a spectrophotometer/reflectometer, ellipsometer
or a physical step measurement; however, these techniques all have limitations.
Coherence Scanning Interferometry (CSI) is an established method to measure
surface topography as this technique offers many advantages such as speed, ease
of use and accuracy. The measurement of “thick” films (exceeding ~1.5 μm) which
gives rise to clearly separate fringe bunches is a well-established CSI
capability. However, a methodology known as the ‘helical complex field’ (HCF) [1]
[2] function allows film thickness to be measured down to ~25 nm. This new
method, combined with Coherence Correlation Interferometry (CCI) [3] offers
film thickness measurements with sub-nanometre vertical resolution and ~1 μm
lateral resolution. It is ideally suited for detailed analysis of coated
optical surfaces. In this paper, the fundamentals of the techniques are
described and some case studies are presented.