4D-4 Fabrication of FBAR for GHz Band Pass Filter with AlN Film Grown Using MOCVD

Abstract

Film bulk acoustic resonator (FBAR) using AlN film was fabricated. Metal-organic chemical vapor deposition (MOCVD) was used to obtain high oriented AlN (0002) film. The unloaded Q factor (Qscr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ) of fabricated FBAR was improved by reduction of Mo electrode resistance and optimization of cavity etching process. Since Mo nitridation degraded Mo resistance, reaction time between Mo and NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> became shorter than conventional process to suppress the nitridation during AlN deposition. As a result, Mo resistance was improved to be 12.3 muOmegacm from 26.4 muOmegacm. In conventional process using Bosch process to fabricate cavities, insufficient etching selection ratio between Si/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> of 200 brought incomplete structure of cavities. The etching selection ratio between Si/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> was improved to be 650 by change of the etching process. The evaluated Qscr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> of the fabricated FBAR was as high as 1557 at 3.698 GHz. We achieved the high Qscr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> value FBAR using high oriented AlN (0002) film by the MOCVD method