Mechanical and electrical properties of RF magnetron sputter deposited amorphous silicon-rich silicon nitride thin films

Abstract

Amorphous silicon nitride thin films in a thickness range of 40 to 500nm are deposited onto (100) silicon wafers using radio frequency magnetron sputter deposition. Analysis of variance techniques are used to determine which deposition parameter has a significant impact on the film properties. The biaxial stress of the layers is found to be compressive independent of the plasma chamber pressure levels and to increase with increasing plasma power. The chemical composition of the films is silicon-rich, resulting in an index of refraction (IOR) of 2.55 independent of deposition conditions. Both IOR and X-ray photoelectron spectroscopy measurements indicate a nitrogen to silicon ratio in the range of 0.71–0.85. The etch rates for HF wet chemical etching and for CF4:O2 reactive ion etching are found to be much higher compared to direct current sputter deposited silicon nitride films with only a weak dependency on the deposition conditions. Temperature dependent leakage current measurements using Au/Cr/SiNx/Si structures between 25 and 300°C show two dominating leakage current mechanisms: ohmic conduction dominates at low applied electric field values below 0.1 MV/cm and Poole–Frenkel type conduction above 0.3MV/cm. The extracted electrical parameters such as the activation energy or the barrier height are found to be nearly unaffected by the deposition parameters.