Temperature-Corrected Quartz-Crystal Microbalance for Real-Time Film Thickness Monitoring in Vacuum Evaporation

For a quartz-crystal microbalance system without thermocouples for monitoring thin film thickness, a computational method which corrects for the temperature variation in the quartz crystal is presented. This correction method eliminates the need for pipes and electrical wires, simplifying the conventional system. To avoid the use of electrical wires, both a laser diode and a microlens were used to transmit the signal of the change of resonant frequency of the quartz crystal. Using a 4.2 MHz resonant AT-cut quartz-crystal plate, the error in the measurement of Ti film thickness was <3.0% under the conditions of deposition time <230 s and the quartz-crystal temperature <160° C.