Abstract
Surface metrology must increasingly contend with submicron films, whose prevalence now extends to products well beyond semiconductor devices. For optical technologies such as coherence-scanning interferometry (CSI), transparent submicron films pose a dual challenge: film effects can distort the measured top surface topography map and metrology requirements may now include three-dimensional maps of film thickness. Yet CSI’s sensitivity also presents an opportunity: modeling film effects can extract surface and thickness information encoded in the distorted signal. Early model-based approaches entailed practical trade-offs between throughput and field of view and restricted the choice of objective magnification. However, more recent advances allow full-field surface films analysis using any objective, with sample-agnostic calibration and throughput comparable to film-free measurements. Beyond transparent films, model-based CSI provides correct topography for any combination of dissimilar materials with known visible-spectrum refractive indices. Results demonstrate single-nm self-consistency between topography and thickness maps.
Highlights
1.1 Surface Metrology with Submicron FilmsSurface metrology must increasingly contend with submicron films, whose prevalence extends to products well beyond semiconductor devices
A surface metrology technology adapted to measure submicron films will retain its performance for topography alone
coherence-scanning interferometry (CSI) determines surface topography from the localized coherence signal produced by interference between reflections from the sample and a reference surface
Summary
Surface metrology must increasingly contend with submicron films, whose prevalence extends to products well beyond semiconductor devices. These films may be incidental, such as oil on a machined part, or of little direct concern to a user interested only in the top surface. The film may be critical, protecting the underlying substrate or providing specific optical characteristics. In any case, adding a submicron film to a component rarely relaxes previous surface metrology requirements. Instead these will generally expand to include film properties, such as thickness, uniformity, and texture
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