Optical Profiling
Metrology techniques quantify mechanical film stress by measuring changes in substrate radius of curvature caused by thin film deposition or thermal treatment. In semiconductor process monitoring, wafer curvature deflectometry directs parallel laser beams onto a substrate surface and detects position shifts in reflected rays. Multi-beam optical stress monitors track deflection angles to compute surface curvature with sub-kilometer radius resolution.
Non-contact optical measurements prevent mechanical strain artifacts during wafer inspection. Applicability stops when substrate back-surfaces exhibit high optical roughness or low reflectivity.
Stress Calculation
Stoney equation models convert measured changes in substrate curvature into integrated film stress values. In wafer curvature deflectometry, accurate film thickness inputs and substrate elastic constants are required to compute stress magnitudes. Photodiode array detectors record laser spot positions before and after film processing steps.
Differential beam steering isolates genuine substrate curvature from overall sample tilt.
Reflection Mapping
Environmental isolation chambers protect optical laser paths from air turbulence and thermal convection currents. Real-time wafer curvature deflectometry tracks stress evolution during high-temperature thin film deposition cycles. Thermal gradient distortions distort beam paths if chamber window optical quality degrades during process runs.
Calibration Protocol
Certified spherical mirror reference standards calibrate system radius measurement scales across wide curvature ranges. Precision optical target positioning verifies detector spatial linearity prior to production testing. Environmental temperature drift shifts optical bench alignment over extended measurement sequences.
