Particle
Diameter, distribution, morphology, refractive index, absorption and surface coating.
Optical response is a system property
Particle, medium, wavelength and instrument must be evaluated together.
A particle does not have one universal scattering strength. Response changes with diameter, shape, refractive index, absorption, surrounding medium, wavelength, polarization, angle, substrate and detector geometry.
Environment
Air, water, solvent, polymer matrix or wafer substrate changes optical contrast.
Illumination
Wavelength, polarization, coherence and incidence angle define the interaction regime.
Instrument
Collection angle, numerical aperture, detector, algorithms and threshold define reported response.
Size regime
Use the appropriate scattering model.
When particles are much smaller than the wavelength, a Rayleigh-type approximation may provide intuition, including the strong dependence of scattering on particle size. As particle size becomes comparable to wavelength, Mie or more application-specific models are needed. Deposited particles on a wafer introduce substrate interactions that a simple free-space sphere model may not represent.
Response = f(diameter, wavelength, particle index, medium index, shape, geometry, instrument)UV/DUV relevance
Shorter wavelengths do not eliminate material-response differences.
Semiconductor inspection systems can operate at ultraviolet or deep-ultraviolet wavelengths and use highly specific optical geometries. Silica is often evaluated because the desired response may differ from PSL or because the contaminant model itself is silica. The tool model, wavelength, wafer, deposition pattern and acceptance criterion must be documented.
Procurement evidence
Ask for the fields that control optical comparability.
- Nominal and measured diameter with method
- Distribution width and evidence of aggregation state
- Material and surface treatment
- Medium and concentration
- Wavelength or instrument context for any optical-response claim
- Lot-specific certificate and uncertainty
- Representative application or tool verification when required
Questions engineers ask
Frequently asked questions
Is silica always easier to detect than PSL?
No. Detectability depends on particle size, wavelength, surrounding medium, refractive-index contrast, geometry and instrument design.
Can I use a refractive-index value from one wavelength at another wavelength?
Only with an appropriate dispersion model or verified data. Refractive index varies with wavelength.
Sources and verification
Technical basis
- NIST measurement protocols — Supports defining the optical measurand and conditions.
- Applied Physics UV-Vis silica particles — Current commercial UV-Vis-oriented silica pathway.
- Applied Physics wafer standards — Commercial wafer-metrology pathway.
Commercial specifications should be confirmed against the current Applied Physics quotation, certificate, lot documentation and product page before purchase or protocol use.
Continue the research
Related technical guidance
UV/DUV inspection
Apply optical principles to wafer inspection.
Silica vs. PSL
Compare material response without universal rankings.
Optical instrument calibration
Build instrument-specific evidence.
Applied Physics technical pathway
Need a particle specification reviewed?
Send the target size, medium, concentration, application, certificate requirements and shipping destination. Applied Physics can evaluate the appropriate silica family or custom pathway.