RF reactive sputtering AlN thin film at room temperature for CMOS-compatible MEMS application

Abstract

Aluminum nitride (AlN) is widely used in SAW/FBAR devices, energy harvesting, biosensors, and ultrasonic transducers. The preparation of high-quality AlN film plays the key role on the process integration with CMOS circuits. Here, we report an AlN thin film prepared by RF reactive sputtering at room temperature on substrate with different treatments, which is more suitable and economical for CMOS-compatible MEMS fabrication compared with previous works. The AlN thin film was deposited on Si/SiO2/Si3N4 with different surface roughness, which were commonly employed as insulating layers or device layers in CMOS circuits. The morphological characterization by AFM and SEM showed that the AlN thin film was uniform and compact with low roughness and fine grain. The bottom Mo electrode was prepared by DC sputtering at room temperature. In addition, AlN seed layer from the same sputtering process increased the adhesion between the electrode and the substrate, thereby improving the stability of subsequent processes. In summary, we prepared uniform AlN with few defects by a simple and controllable approach. This strategy is potentially applied to CMOS-compatible optical and acoustic devices.