Formation Mechanism and Crystallographic Relationship of Epitaxy Ti and Al Thin Films in Ionized Metal Plasma Deposition

Abstract

Ti thin film is widely used as a diffusion barrier to impede the Al/Cu migrating to the Si substrate in the applications requiring high temperature processes such as high temperature sputtering and reflow developed for via-filling. To improve the bottom coverage without losing the excellent diffusion blockage and other electronic properties, the ionized metal plasma (IMP) deposition technique has been developed. This method has better control of the angular distribution on the substrate, and thus has been used to deposit Ti as diffusion barriers for the subquarter micron device applications. However, the formation mechanism of the epitaxy Ti thin film deposited by ionic metal plasma deposition is not clear. In this work, the epitaxy Ti thin film has been characterized by the transmission electron microscope. The mechanism of the epitaxy Ti thin film formation and also the crystallographic relationship between the Ti and Al thin films in the IMP deposition have been analyzed in detail. The results show that the lattice image of the Ti layer in the sample as deposited has a square-block-like structure with the c axis perpendicular to the interfaces. This structure has anisotropic diffusion properties that can retard the diffusion of Al across the Ti layer in the initial stage of the high temperature Al sputtering or reflow processes.