Optical Metrology Calibration Limits for Micro Machined Aluminum Components
Optical metrology of micro-machined aluminum requires phase-filtering algorithms, reflection polarization, and exact 20°C thermal drift corrections.
Coherence Scanning Interferometry
Meaning
Non-contact optical method for measuring surface topography provides sub-nanometer vertical resolution for industrial components. Height information is extracted through coherence scanning interferometry by observing the interference patterns produced when a reference light beam meets a beam reflected from the specimen. The technique operates by scanning the optical path length and identifying the peak of the interference envelope at each pixel.
It stops applying when the surface gradient exceeds the numerical aperture of the objective lens or when the material is excessively transparent.
Resolution Capacity
Spatial measurements depend on the wavelength of the light source and the precision of the mechanical vertical drive. Because coherence scanning interferometry uses a broadband source, the short coherence length allows for the unambiguous identification of surface features. High precision is achieved even on complex geometries.
This enables the inspection of semiconductor wafers and micro-electromechanical systems.
Signal Analysis
Algorithms process the resulting fringe patterns to determine the exact position of every point on the surface. Modern coherence scanning interferometry systems utilize frequency domain analysis to improve speed and reduce sensitivity to environmental vibrations. A single scan can capture millions of data points in seconds.
This allows for high-density mapping of surface roughness and height.
Surface Validation
Manufacturing environments rely on this method to verify that components meet design tolerances. Engineers use coherence scanning interferometry to inspect fuel injector nozzles and optical lenses. The process ensures that surface finish requirements are met.
Correct calibration against a certified step height standard is required for valid results.