Using absorption spectroscopy to determine the ionization fraction of copper in an ionized physical vapor deposition discharge

Abstract

Summary form only given. Accompanying the steady increase in the number of components on a given integrated circuit is the increase in the aspect ratio of the features associated with such components. Conventional physical vapor deposition techniques are not suitable to fill such high aspect ratio trenches and vias. Ionized physical vapor deposition (IPVD) offers a promising alternative to traditional physical vapor deposition techniques. Maturation of this technique is important for continued advances in microelectronics technology. This technique entails allowing metal vapor introduced via a sputter source to diffuse through a high density, secondary plasma. The metal ions formed as they pass through the secondary plasma are collected anisotropically under the influence of the electric field present in the sheath of the biased substrate. An important parameter characterizing ionized physical vapor deposition systems is the ionization fraction of the metal vapor. The variations in the copper ionization fraction in a Cu/Ar IPVD plasma has been measured using absorption spectroscopy. The ionization fraction is inferred by determining the changes in the copper neutral concentration at fixed magnetron sputter powers as a function of RF power at 10, 20, 30 and 40 mTorr. It is observed that for a range of RF powers, the maximum ionization fraction occurs at the condition of highest pressure. The effect of antenna sputtering for antennas made of material identical to the magnetron sputter target was also investigated. It was found that significant antenna sputtering can reduce the total copper ionization fraction.