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 80 Å, 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 Total Reflection X-ray Fluorescence

Metallic surface contamination on semiconductor wafers

Strengths

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