A Reliable Release Method for A Back-End-Of-Line Nems Switch of A Monolithic Three-Dimensional Integrated Cmos-Nems Circuit

Abstract

This paper reports a reliable release method for an aluminum (Al) back-end-of-line (BEOL) NEMS switch of a monolithic three-dimensional (M3D) integrated CMOS-NEMS circuit. We examined the causes of Al damage during the etching process of sacrificial silicon dioxide (SiO2) when using a hydrofluoric acid (HF solution) and determined that water (H2O) in the HF solution is the main cause of the Al damage. Therefore, by adding sulfuric acid (H2SO4) with strong hygroscopicity to the HF solution, we developed a reliable release method that achieves superb selectivity (> 105) of SiO2 over Al. Using the proposed method, we successfully released Al BEOL NEMS switches and demonstrated an M3D CMOS-NEMS circuit with a demultiplexer (DEMUX) function.