Stress relaxation in tungsten films by ion irradiation

Abstract

Tungsten films, grown by plasma-enhanced chemical vapor deposition for very large scale integration interconnect applications, suffer from a high internal tensile stress that leads to contact failure. We show with wafer curvature measurements that the stress can be relaxed via viscous flow at room temperature by irradiating the films with energetic ions after deposition. Transmission electron microscopy does not indicate significant structural changes in the W films during irradiation. We varied the irradiation conditions (from 140 keV B ions to 400 keV P ions) and find that the flow rate scales with the nuclear stopping power. Similarities and differences with beam-induced mixing and diffusion are discussed.