Measurement and control of a residual oxide layer on TiSi2 films employed in ohmic contact structures

An inadvertent oxide layer is formed on a titanium disilicide (TiSi₂) film following various wet and dry processes in a manufacturing environment. The use of H₂SO₄:H₂O₂:H₂O (1:1:5) as a wet etch for excess Ti metal, prior to the high temperature anneal used to form a subsequent TiSi₂ layer, is identified as the source of the undesired oxide via multiwavelength spectroscopic ellipsometry and Auger electron spectrometry studies. This inadvertent oxide layer on TiSi₂ is shown to form bad electrical contacts and is a contributing source to large standby currents in polysilicon gate shunts. Spectroscopic ellipsometry is shown herein as a unique analytical tool to determine both the thickness and structure of this poorly structured oxide during process development. A single wavelength ellipsometer monitoring scheme for both the appearance as well as the thickness of this inadvertent oxide layer is proposed for use in high-volume manufacturing