Coherence scanning interferometry

Coherence scanning interferometry (CSI) is any of a class of optical surface measurement methods wherein the localization of interference fringes during a scan of optical path length provides a means to determine surface characteristics such as topography, transparent film structure, and optical properties. CSI is currently the most common interference microscopy technique for areal surface topography measurement.^[1] The term "CSI" was adopted by the International Organization for Standardization (ISO).^[2]

Characteristic CSI signal

The technique encompasses but is not limited to instruments that use spectrally broadband, visible sources (white light) to achieve interference fringe localization. CSI uses either fringe localization alone or in combination with interference fringe phase, depending on the surface type, desired surface topography repeatability and software capabilities. The table below compiles alternative terms that conform at least in part to the above definition.

Applications in Optical Metrology

Coherence Scanning Interferometry (CSI) is widely used in optical surface metrology for non-contact, three-dimensional surface characterization.^[3] Due to its ability to measure surfaces with significant height variations, including steep slopes and discontinuities, CSI is particularly suitable for applications in precision manufacturing, microelectromechanical systems (MEMS), semiconductor inspection, and optical component analysis.^[4]

In these contexts, CSI provides high-resolution areal surface measurements without requiring surface contact or sample preparation. The technique is standardized under the ISO 25178 norm, which defines areal surface texture parameters for metrological evaluation.^[5] Modern commercial profilometers often integrate CSI alongside other measurement modes such as confocal microscopy and Ai Focus Variation to enhance versatility and accuracy in surface inspection.^[6]

Acronym	Term	Reference
CSI	Coherence scanning interferometry	[7]
CPM	Coherence probe microscope	[8]
CSM	Coherence scanning microscope	[9]
CR	Coherence radar	[10]
CCI	Coherence correlation interferometry	[11]
MCM	Mirau correlation microscope	[12]
WLI	White light interferometry	[13]
WLSI	White light scanning interferometry	[14]
SWLI	Scanning white light interferometry	[15]
WLS	White Light Scanner
WLPSI	White light phase shifting interferometry	[16]
VSI	Vertical scanning interferometry	[17]
RSP	Rough surface profiler	[18]
IRS	Infrared scanning	[19]
OCT	Full-field optical coherence tomography	[20]