Meaning
Topographical interference patterns observed at sharp steps during white light interferometry create false height spikes along edge boundaries. This measurement artifact, known as the optical batwing effect, occurs when light diffracted from high and low sides of a step feature recombines and distorts fringe analysis. The phenomenon impacts non contact surface height calculations on micromachined optical moulds and microfluidic cavity steps.
The effect is strictly an optical measurement error restricted to step boundaries exceeding coherence length, leaving the physical tool steel unperturbed.
Diffraction Behavior
Light waves reflected from adjacent horizontal surfaces interfere destructively near sharp vertical steps. Interference fringes generated across the step boundary shift phase, causing white light interferometers to calculate localized height spikes that do not exist on the steel cavity. Lowering spatial coherence or utilizing coherence scanning algorithms mitigates phase errors along micro channel edges.
Adjusting objective numerical aperture changes the light acceptance angle, reducing the amplitude of false edge peaks. Film thickness measuring tools and surface profilers must filter edge data to prevent false step height reporting. Accurate determination of channel step depth depends on isolating diffraction noise from real mould geometry.
Measurement Error
False height spikes recorded along cavity edges skew maximum peak height parameters on tool datasheets. Uncorrected edge data suggests micro cracks or burrs on steel features where actual surfaces are smooth. Quality technicians identify batwing signatures by comparing optical profiles with contact stylus scans.
Edge Reconstruction
Data processing algorithms detect characteristic batwing signals and trim false elevation spikes from profile scans. Slope adaptive signal processing calculates true edge position without altering surrounding surface roughness values. Validated edge filtering ensures optical profiler scans accurately represent tool cavity dimensions.
