Total Reflection X-ray Fluorescence (TXRF)
Total reflection X-ray fluorescence (TXRF) is a surface elemental analysis technique often used for the ultra-trace analysis of particles, residues, and impurities on smooth surfaces. It is currently an important tool for wafer surface contamination control in semiconductor chip manufacturing.
TXRF is basically an energy dispersive XRF technique in a special geometry. An incident beam impinges upon a sample at angles below the critical angle of external total reflection for X-rays resulting in reflection of almost 100% of the excitation beam photons. Due to its unique configuration, the main advantage of TXRF over conventional XRF is reduced measurement background contributions by elimination of sample scattering resulting in increased elemental measurement sensitivity.
a) Conventional XRF geometry. The angle of incidence is greater than the critical angle and the primary radiation penetrates into the sample.
b) Conventional TXRF geometry. The angle of incident X-rays is less than the critical angle and the primary radiation is reflected off of the sample surface.
One of the major drawbacks of conventional TXRF is that localized sample information is difficult to obtain due to the large excitation beam size (typically 1 cm in diameter). Doubly curved crystal optics can be used to focus X-rays to small spots for localized TXRF elemental analysis. A slit is used to restrict beam divergence in the scattering plane to less than the critical angle in order to meet the total reflection requirement. The flux density on the reflection surface is several orders of magnitude higher than that of conventional TXRF systems yielding high elemental sensitivity.