Process monitoring techniques using acoustic waves

The authors outline the limitations of current film thickness technology and propose two novel methods for nondestructive, in-situ film thickness process monitoring: acoustic time domain reflectometry (TDR) and acoustic reflection coefficient phase measurements. Theoretical calculations and experimental measurements of different metal films are used to demonstrate the viability of these techniques. An experimental system has been built and preliminary results on gold films show promise for using acoustic TDR as a postdeposition process monitor. An experimental system based on acoustic reflection coefficient phase measurements has been built and shows good preliminary results in gold and aluminum films