||This study is to develop the manufacturing processes of thin film bulk acoustic device by MEMS technology, including lithography, wet etching, dry etching and rf Magnetron sputtering.LPCVD is used to deposit SiNx as the membranes and mask for etching of silicon wafer. The electrodes of molybdenum metal (Mo) and piezoelectric layer of aluminum nitride (AlN) on top side are prepared by dc and rf sputtering,respectively. The acoustic cavity on back side is achieved by 30%wt 100℃ KOH solution and reactive ion etching (RIE).|
In this study, the crystallography of the coated films was analyzed by X-ray diffraction. The surface and cross-sectional morphologies of AlN films were investigated by electron microscope. The piezoelectric layer of AlN thin film prepared by rf magnetron sputtering shows the highly c-axis preferred orientation and fine morphology under the optimal sputtering parameters of rf power of 200W, sputtering pressure of 3 mTorr, substrate temperature of 400℃ and nitrogen concentration of 25%. The frequency responses of fabricated FBAR devices are evaluated using the Hewlett-Packard 8720-ET network analyzer.
Moreover, the optimal thickness of 1500Å SiNx film prepared by LPCVD revealed the excellent masking effect and non-stress for membrane. The yield for the fabrication of acoustic cavity is maximum of 85% can be achieved by using the combined etching steps of wet and dry etching.