Mohamed Rinzan, INFICON, East Syracuse, NY
Thin film thickness rate monitors use the Z-match equation to translate a change in resonance frequency of a Quartz crystal microbalance to change in film thickness. The Z-match equation accounts for the acoustic impedance of the thin film layer being deposited, but neglects the acoustic impedances of the thin film layers deposited on the microbalance prior to the current layer. For a small electrode mass load on the microbalance this means a single film layer can be measured with low error in layer thickness. However, for a microbalance with multiple layers, errors in deposition thickness accumulate due to mathematical exclusion of acoustic impedance of all preceding layers. We present our recently patented Multi-Z method, which incorporates the acoustic impedance of all the layers. Unlike Z-match’s aggregate approach Multi-Z treats the multiple layers as a distributed system. The Multi-Z translation of resonance frequency change to thickness shows reduced layer thickness error for several material systems with different acoustic impedances. This method provides an excellent advantage in applications where Quartz crystal microbalance is used to monitor multiple layers with low layer thickness error.