Characterization of electron-beam deposited tungsten films on sapphire and silicon

Abstract

In this work, the electrical and structural properties of e-beam deposited tungsten films on sapphire are described. Tungsten thin films (200–400 nm) were evaporated on sapphire substrates at different substrate temperature Ts. Film resistivity varied from 95 μΩ cm deposited at room temperature to 5.5 μΩ cm deposited at Tsbetween 440 and 500 °C. The resistivity value of 5.5 μΩ cm is comparable to the bulk resistivity value of 5.50-5.65 μΩ cm. The crystalline structure of these films was characterized by x-ray diffraction and scanning transmission electron microscopy (STEM) (Kikuchi lines). The films show a distinct increase in the degree of crystal orientation as Tsapproaches 400 °C. The films deposited at 400 °C and above shows (100) epitaxial growth on the (1102) plane or r plane of sapphire, which has a distorted fourfold symmetry. Film stresses which vary from tensile (7.3 X 109 dyn/cm2) to compressive (— 4.4X109 dyn/cm2) between 100 and 500 °C were measured by the interference fringe technique. The intrinsic stress was determined to vary from 8.3 X 109 dyn/cm2 at Ts = 100 °C to 2.4X 109 dyn/cm2 at Ts = 500 °C. The observed intrinsic stresses (tensile) in epitaxial films are regarded as produced by the lattice misfit at the film-substrate interface. The minimum total film stress was obtained between Ts= 350 and 400 °C, where tensile intrinsic stress was compensated by the compressive thermal stress. The properties of tungsten films on silicon, silicon oxide, and polysilicon substrates are also discussed. © 1985, American Vacuum Society. All rights reserved.