High-frequency SAW devices fabricated by reactive ion etch technology

A Reactive Ion Etch (RIE) process selected to fabricate high-frequency SAW devices is presented in this paper. RIE is commonly used in semiconductor IC fabrication to achieve very large scale integration because of its control of metal line width and profile as well as high yield. In this work, BCl₃/Cl₂ chemistry is used to pattern aluminum electrodes on quartz substrates. Various process parameters such as rf power, system pressure, etch time and gas flow are investigated. Finally, an optimized etch process is established for certain critical submicron geometries down to 0.5 μm. The RIE process produces SAW devices having electrodes with steep sidewalls. This increases sidewall reflectivity. The SAW devices are plasma etched to achieve desired center frequency, bandwidth (BW), and insertion loss (IL) with high production yield. An aluminum etch rate of 1000-2000 Å/min. is observed. A controlled etch rate is accomplished at low rf powers (<150 Watts). Higher rf power settings lead to resist damage and reflow. This paper also details a wet etch vs. RIE etch process comparison