WSi Schottky diodes: effect of sputtering deposition conditions on the barrier height

Tungsten thin films were deposited on silicon substrates by DC magnetron sputtering in argon and xenon. The effects of the sputter deposition conditions were studied. X-ray diffraction was used to examine the structure and the lattice parameters while the stress was determined from the measurement of the substrate curvature after metallization by using a profilometer. The resistivity was measured by using a four-point probe. The barrier heights (ΦB) for WSi Schottky diodes were determined from I-V and C-V measurements. A compressive-to-tensile stress transition is observed as the working gas pressure is increased. The transition occurs at higher pressure for the lighter gas (argon) and coincides with a significant increase of the W-film resistivity. We show that the change in stress and resistivity, which is frequently observed, is only associated with the transformation of the α-W-phase into the β-W-phase for films prepared with argon. The films deposited in xenon always exhibit the α-W-structure. In addition, a change (ΔΦB≈50 meV) in the Schottky barrier height on n-type is observed at the critical pressure. On the other hand, the barrier height on the p-type remains constant under all the experimental conditions investigated. These last results indicate that the Fermi level at the interface is pinned with respect to the valence band edge.