Release etching and characterization of MEMS capacitive pressure sensors integrated on a standard 8-metal 130 nm CMOS process
Abstract Monolithic post-processing and characterization of CMOS MEMS capacitive absolute pressure sensors co-integrated on an 8-metal BEOL (back-end-of-line) 130 nm CMOS device is reported in this paper. An optimized foundry compatible etch process for an IBM CMOS fabricated top triple layered passivation is discussed. A mixture of wet and plasma dry etch process is proposed for both an elliptic and a rectangular structured pressure sensor capacitor. Lateral 125 μm stiction free etch from opposite sides was performed successfully for the monolithically integrated diaphragms on the 130 nm CMOS platform. Low power inductive coupled plasma using CHF 3 gas along with high RF bias power is utilized to increase lateral etch rate compared to vertical etch rate. Mechanical and electrical characterization results indicate a successful etch of the triple layer passivation and the sacrificial oxide. Sensitivities of the fluorosilicate sealed absolute pressure sensors were measured to be 0.07 mV/Pa and 0.05 mV/Pa for the elliptic and rectangular element, respectively. In addition, the linear capacitive transduction dynamic range was found to be 0.32 pF and 0.23 pF, respectively, for the elliptic and rectangular element (for 80 hPa pressure variation).