LOW STRESS TaN THIN FILM DEVELOPMENT FOR MEMS/SENSOR ELECTRODE APPLICATION

Abstract

TaN \ Ta is the excellent material against copper diffusion, and is widely used as Cu diffusion barrier in Complementary Metal-Oxide-Semiconductor (CMOS) Back End of Line ( Cu -BEOL) process. Due to its good electrical and thermal property, TaN is also evaluated as electrode material for Micro-Electro-Mechanical Systems (MEMS)/sensor application. In this work, CMOS compatible MEMS based bolometer process with post-interconnect CMOS-MEMS single chip integration scheme was developed on 200 mm standard CMOS Cu BEOL, and TaN thin film was used as key electrode material in micro-bridge structure. The micro-bridge structure, with sensing resistor on surface of the micro-bridge, forms a resonant cavity for IR absorption. There are only several layers of thin film on the micro-bridge, and stress of the electrode layer play very important role to determine the performance of the micro-bridge. Additionally sheet resistance of TaN electrode should be controlled at around 377 Ohm/SQ to match the free space impedance, which is much higher than CMOS baseline process. Low stress and high resistivity TaN film was developed with thickness of 200 Å and compressive stress of about 900 MPa as best condition. From the electrical and physical data, the optimized TaN film process can well match this application.