Stress control of sputter-deposited Mo-N films for micromechanical applications

Sputter-deposited metallic thin films are attractive materials for micromechanics but they suffer from large stress variations within the batch or even a single wafer. The origin of such variations is in the microcrystalline structure, and specifically its dependence on sputtering geometry. It might be assumed that getting rid of the long-range atomic order in the deposited film would help in obtaining improved uniformity. The purpose of this study is to amorphise molybdenum films by nitrogen and to characterize the resulting Mo N film properties. A partial cure for the nonuniformity of stress is, indeed, realized since film-plane stress variations are eliminated by nitridation. A vertical gradient still remains, bending relieved micromechanical beams strongly upwards. This behavior is believed to be due to imperfect amorphisation -the existence of columnar nano-scale crystallites.