xrf (x-ray fluorescence)

XRF (X-Ray Fluorescence) measures elemental composition and film thickness by detecting characteristic X-rays emitted from atoms excited by an incident X-ray beam. **Principle**: Primary X-ray beam excites core electrons in sample atoms. When outer electrons fill vacancies, characteristic X-rays emitted with energies unique to each element. **Element identification**: Each element produces X-rays at specific energies (K-alpha, L-alpha lines). Energy spectrum identifies elements present. **Quantification**: X-ray intensity proportional to element concentration. Calibrated with standards for quantitative analysis. **Film thickness**: For thin films, X-ray intensity scales linearly with thickness (thin-film approximation). Measures metal film thickness non-destructively. **Applications**: Metal film thickness (Cu, W, Ti, Ta, Co), alloy composition, contamination detection, plating bath monitoring. **Spot size**: Typically 25 um - 2 mm depending on optics. Collimator or polycapillary optics for small spots. **Wafer mapping**: Automated XY stage maps thickness across wafer for uniformity characterization. **Advantages**: Non-destructive, fast (seconds per measurement), multi-element simultaneous detection. No sample preparation needed. **Limitations**: Light elements (Z < 11, Na) difficult to detect. Sensitivity limited to ~0.1% concentration for bulk, ~10^13 atoms/cm² for surface. Not as sensitive as TXRF for trace contamination. **Vendors**: Rigaku, Bruker, Fischer, Malvern Panalytical.