Applications of model-based transparent surface films analysis using coherence-scanning interferometry

Abstract

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.

Characterization of Functional Materials Using Coherence Scanning Interferometry and Environmental Chambers

“…Identification of dissimilar materials and corrections in topography between them are now available on commercial instruments, for example, using model-based signal comparison. 16 The principles of local spectroscopy can then be used in several different applications. For example, areas of different materials can be automatically identified, for example using Otsu's algorithm to binarize the reflectivity map.…”

“…While not significant on deep structures of several μm, in the case of nanometric steps as in this example, when measuring between Au and Al, it is 14.6 nm at a wavelength of 671 nm which has been added to the measured signal, giving the correct depth of 42 ± 0.5 nm in Figure (d), compared with 41 ± 3 nm by AFM. Identification of dissimilar materials and corrections in topography between them are now available on commercial instruments, for example, using model-based signal comparison …”

“…Identification of dissimilar materials and corrections in topography between them are now available on commercial instruments, for example, using model-based signal comparison. 16 …”

Smart optical coordinate and surface metrology

“…• Coherence scanning interferometry (CSI): CSI is a common method for optical measurement of areal surface topography, which uses a type of reflection-mode interference microscopy that builds up a 3D height map of a surface by stacking 2D images along the optical axis of the instrument [52]. Ongoing research in the area focusses on expanding the applications of CSI systems to complex surfaces (for example, those containing high slopes, step-like transitions or thin films [53][54][55][56]), as well as developing new surface reconstruction methods and improving theoretical modelling of CSI systems [57,58]. Development of system calibration and error correction pipelines is also an area of active research [59,60], that ties directly into efforts to improve theoretical models.…”

Does interferometry work? A critical look at the foundations of interferometric surface topography measurement

“…Instruments are available that simultaneously measure flatness, thickness variation and material homogeneity for optical components [4], while other systems based on coherence scanning interferometry (CSI) provide process control for automotive parts [5] and semiconductor devices [6]. Modeling methods have added the ability to analyze surface materials and transparent film structures in addition to surface form and texture [7]. Methods have been developed to acquire data in difficult environments with air turbulence and vibration [8,9].…”