Diode-laser-based atomic absorption monitor using frequency-modulation spectroscopy for physical vapor deposition process control

We have developed an atomic monitoring system for physical vapor deposition process control based on a frequency-modulation (FM) spectroscopy scheme using a 670 nm external cavity diode laser. FM detection made it possible to measure absorption as low as 10−6. For electron-beam evaporated yttrium, deposition rate control with a relative accuracy better than 1% at a rate of 3.5 Å/s has been realized, corresponding to a deposition rate resolution of 0.03 Å/s. Variations in Doppler shifts due to the velocity distribution of the atomic vapor within the deposition chamber have been measured, demonstrating the possibility of velocity mapping of evaporated atoms in the deposition process.