Post-processing and performance analysis of BEOL integrated MEMS pressure sensor capacitors in 8-metal 130 nm CMOS

Abstract

Customized post-processing and characterization of MEMS capacitive pressure sensors in an 8-metal back-end-of-line (BEOL) standard 130nm “non-MEMS” CMOS technology is reported in this paper. An optimized foundry compatible etch process customized 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 125μm stiction free etch from opposite sides was performed successfully for the integrated diaphragms. Low power inductive coupled plasma using CHF3 gas along with high RF bias power is utilized to increase lateral etch rate compared to vertical etch rate. Mechanical and electrical characterization indicate a successful etch of the triple layer passivation and the sacrificial silicon dioxide. Sensitivities of the sealed absolute pressure sensors were measured to be 0.07mV/Pa and 0.05mV/Pa for the elliptic and rectangular element respectively. In addition, the linear capacitive transduction dynamic range was found to be 32fF and 23fF respectively for the elliptic and rectangular element (for 80hPa pressure variation).