Quenching of electron temperature and electron density in ionized physical vapor deposition

Abstract

The addition of sputtered metal atoms to a high density plasma results in the ionization of the metal species. The ionized physical vapor deposition technique allows the deposition of metal films from ionic species and is a potential method for the fabrication of integrated circuits with high aspect ratio interconnect features. Maximizing the temperature and density of the plasma electrons is important to optimizing the ionization of metal. The present work reports that the electron temperature and electron density of the plasma decrease with increasing metal density. Direct measurement of electron temperature quenching using a rf compensated Langmuir probe demonstrates a ∼20% decrease in electron temperature due to metal additions of ∼10 12 atoms/cm 3 . The electron density is determined using microwave interferometry and decreases by ∼15% as metal atoms are added to the discharge. A fixed temperature global model, however, indicates that thermalized metal atoms should increase the electron density. Gas heating due to energetic sputtered neutrals is shown to be responsible for the observed decrease in electron density.