haze measurement

**Haze Measurement** is the **quantification of diffuse background light scattering from a wafer surface** — representing the integrated signal from surface microroughness and sub-threshold defects that are too small to resolve individually, serving as a sensitive proxy for surface quality in epitaxial growth monitoring, CMP roughness control, copper contamination detection, and bare wafer incoming inspection. **Haze vs. LPD: Two Distinct Signals** Laser scanning wafer inspection tools simultaneously collect two fundamentally different signals: **LPD (Light Point Defect)**: A discrete, localized intensity spike above the noise floor — a single particle, scratch, or pit large enough to scatter light detectably. Reported as count and coordinates. **Haze**: The broad, spatially varying background intensity across the wafer map — the statistical average scatter from millions of surface features below the LPD detection threshold. Reported in ppm (parts per million of incident light power) averaged over regions or the full wafer. **Physical Origins of Haze** **Surface Microroughness**: The dominant haze source on silicon. RMS roughness (measured independently by AFM) correlates directly with haze — a surface with 0.1 nm RMS roughness produces ~0.05 ppm haze while 0.3 nm RMS may produce 0.5 ppm. CMP processes must achieve Rq < 0.1 nm; haze measurement monitors this without time-consuming AFM. **Epitaxial Surface Defects**: Poor epitaxial growth conditions produce "orange peel" texture — a corrugated surface with periodic undulations at 1–10 µm spatial frequency that elevates haze uniformly while generating few discrete LPDs. Haze maps of epi wafers immediately flag process drift before electrical testing. **Copper Precipitation Hazing**: When copper-contaminated silicon is annealed, copper precipitates form dense arrays of tiny (5–50 nm) CuSi₂ platelets that scatter light but are too small for individual LPD detection. Elevated haze on processed wafers after high-temperature steps signals copper contamination requiring VPD-ICP-MS confirmation. **Stain and Chemical Residue**: Watermarks, acid stains, and cleaning residues produce locally elevated haze in their footprint area, visible as spatial haze non-uniformity even when total particle count is low. **Wafer Map Interpretation** Haze maps are pseudo-colored to reveal spatial patterns: edge-high haze indicates polishing non-uniformity; center-spot elevation suggests cleaning chemistry issue; striated patterns indicate epi reactor rotation non-uniformity; globally elevated haze with no pattern indicates surface roughness from bulk polishing. **Haze Measurement** is **the surface roughness thermometer** — reading the collective scatter of millions of microscopic surface imperfections to detect process problems that individual particle counting completely misses.