ON THE ACCURACY OF THE QUARTZ-CRYSTAL MICROBALANCE (QCM) IN THIN-FILMDEPOSITIONS

The quartz-crystal microbalance (QCM) is traditionally used as a thin- film deposition monitor. The most commonly used monitor crystal is AT- cut quartz vibrating in its thickness shear mode. The mass of the depo sited film on the quartz crystal's surface is indicated by the change of its resonance frequency. With the introduction of the z-match(TM) t echnique in the 1970s, the accuracy of the QCM dramatically improved. This technique takes into account the mismatch of acoustic impedance b etween the quartz crystal and the deposited thin film. In recent years , new methodologies have been proposed to improve the accuracy of the QCM even further. For many years, we have carefully gathered a vast am ount of data on the deposition of various metals, dielectrics and allo ys on quartz crystals. In this paper, we report results of the compari son of the recently proposed methods with the z-match technique, using the gravimetric measurement of deposited mass on the quartz crystals as the benchmark. We also report an extension formula, which broadens the validity of the z-match technique beyond a normalized frequency sh ift of 50%. (C) 1997 Elsevier Science S.A.