Total Reflection X-ray Fluorescence (TXRF)

Total Reflection X-ray Fluorescence (TXRF) utilizes extremely low-angle X-ray excitation of a polished wafer surface to obtain the concentration of surface metallic contaminants.

The incident angle of the x-ray beam (typically 0.05-0.5°) is below the critical angle for the substrate and limits excitation to the outermost surface of the sample (~ top 80Å, depending on the material). The fluorescence signal emitted from the sample is characteristic of the elemental contaminants present.

A highly surface-sensitive technique, TXRF is optimized for analyzing surface metal contamination on semiconductor wafers such as Si, SiC, GaAs or sapphire.

Ideal uses of TXRF

Metallic surface contamination on semiconductor wafers

Strengths of TXRF

Trace element analysis
Survey analysis
Quantitative
Non-destructive
Automated analysis
Whole wafer analysis (up to 300 mm)
Can analyze many substrates, e.g. Si, SiC, GaAs, InP, sapphire, glass

Limitations

Cannot detect low-Z elements (below Na on periodic chart)
Polished surface required for best detection limits

TXRF Technical Specifications

Signal Detected: Fluorescent x-rays from wafer surface
Elements Detected: Na-U
Detection Limits: 10⁹ – 10¹² at/cm²
Depth Resolution: 30 – 80 Å (Sampling Depth)
Imaging/Mapping: Optional
Lateral Resolution/Probe Size: ~10 mm