Reduction of effects of rarefaction in ionized physical vapour deposition discharges

Ionized physical vapour deposition (IPVD) is of current interest to the sem iconductor industry for the deposition of thin metal films as diffusion bar riers and seed layers in high aspect ratio features. One of the aims of IPV D is to collimate depositing particle fluxes by ionizing a significant frac tion of the incident metal vapour and applying an electric potential bias t o the substrate. A system consisting of a de-powered, 15 cm diameter copper sputter source and a RF induction plasma powered by a single-turn, 36 cm d iameter, loop antenna internal to the vacuum chamber has been examined. Mea surements made with a biased quartz crystal microbalance in an argon backgr ound of 10-90 mTorr demonstrate that, at low magnetron sputtering levels of 100 W, ionized metal flux fractions (IMFFs) as high as 90% can be observed . However, further measurements of the IMFFs and plasma density indicate ra refaction of the background argon gas as the metal flux to the plasma incre ases. Results are presented from an experimental investigation of methods t o reduce the gas rarefaction. These include the modulation of the metal Bur on the timescale of the process gas residence time and increasing the targ et-to-substrate height.