Improved method of nonintrusive deposition rate monitoring by atomic absorption spectroscopy for physical vapor deposition processes

We have developed a novel optical scheme named COPACT (common optical path for automatic correction of transmission) to improve the long-term stability of monitoring the deposition rate by atomic absorption spectroscopy. In previously developed atomic absorption monitors, the signal changes caused by the vapor flux could not be separated from those caused by viewport coating and minor optical alignment shifts once the deposition process is in progress. The new optical design is capable of measuring the atomic absorption independent of changes in optical system transmission, thus allowing the concentration of atoms in the vapor flux to be unambiguously determined in real-time. Experimental results confirmed the ability of this new optical design to achieve high sensitivity and long-term stability.