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6589255 
Journal Article 
Reactive ion etching of piezoelectric films for acoustic wave devices 
Wang, JS; Chen, YY; Lakin, KM 
1982 
346-9 vol.1 
INSPEC:2049182 
Reactive ion etching (RIE) which combines some advantages of both plasma etching and sputter etching has been used in processing ZnO/Si and AlN/Si structure for acoustic wave devices. In this study, the etching gases used are CF4, HCl and HI with varying amounts of O2 and Ar. The substrates of interest, which are placed on the cathode electrode of a parallel plate RF reaction chamber, are ZnO, AlN, Al, Si and SiO2. Etching was typically carried out at 50 millitorrs pressure and 75 watts RF power. When using CF4 and 4% O2 gas, Si etch rate was measured as high as 2500 Aring/min. However, the ZnO and AlN etch rates were very low in reactive ion etching or were found unattacked in CF4 plasma etching. By using this high etch selectivity, edge-only supported ZnO and AlN plates were constructed from ZnO/Si or AlN/Si composite structure. When HI gas was used, the etch rate of ZnO was determined to be 2000 Aring/min. The etch selective ratios found here were 40:1 over SiO2 and more than 100:1 over Si and Al. The low Al mask erosion and high stopping ratio for ZnO over Si on Al/ZnO/Si structure is of practical importance for both BAW and SAW devices.