Tantalum metallization and properties of silicon MOS structures under stress

Stresses at the surface of a silicon wafer and at the Si-SiO₂ interface were induced by the sputter deposition of tantalum films. The sputtering of tantalum produced deformation of the silicon wafers by bending, and the radius of curvature was a function of the tantalum sputtering voltage and the tantalum film thickness. The magnitude of the stress induced at the silicon surface was determined from automatic Bragg angle control measurements of the radius of curvature. The surface distribution of the strain field and its distribution in the bulk of the silicon wafer were observed by the use of X-ray transmission topography. The electrical properties of the MOS capacitor were studied as a function of the induced stress. It was found that the largest changes with induced stress occur in the values of recombination time and capture cross section, while the surface state charge density Q_ss and the surface state density N_ss are not significantly affected. Auger electron spectroscopy showed that implanted tantalum atoms diffuse through the SiO₂ and reach the silicon surface.