Atomic flux measurement by diode-laser-based atomic absorption spectroscopy

Diode-laser-based atomic absorption (AA) sensors have been developed for direct measurement of atomic flux, based on both atomic density and velocity information, which is important for in situ monitoring and control of physical vapor deposition processes. Laser beam schemes based on the Doppler shift measurement have been designed for measuring the velocity component normal to the surface of a substrate. Experimental results on electron-beam evaporated barium and yttrium, which are components in YBCO superconductor, demonstrate measurements of true flux instead of simple density in the deposition processes. The flux measurement was confirmed at different pressures showing true flux measurement independent of background pressure. A model-independent flux measurement was achieved by using a cross-beam scheme. In addition, the AA sensor was also used for diagnosing and helping better understand the deposition physics such as sticking coefficient, velocity of the evaporated atoms, and the oxidation of the elements on the substrate. Discussion on practical issues of the AA sensor application is also presented.