Mechanisms for Enhanced Formation of the C54 Phase of Titanium Silicide

Three methods have recently been developed to enhance the formation of the low-resistivity C54 phase of TiSi₂, the most widely used silicide contact in microelectronic devices. These methods are (1) ion implantation of a transition metal into the silicon prior to Ti deposition, (2) deposition of a thin transition metal interlayer between the Si and the Ti, and (3) codeposition of Ti alloyed with a transition metal. Each of these methods decreases the C54 formation temperature by more than 100°C and improves the probability of phase formation in narrow lines by increasing the nucleation site density. In this paper, we identify the aspects of phase formation which are shared by these three methods, review the methodology by which they were developed, and summarize the applications to silicon devices. Mechanisms responsible for the enhanced formation of C54 TiSi₂ are reviewed, based on a combination of temperature-controlled in situ measurements of resistance, x-ray diffraction and optical scattering, coupled with ex situ studies of phase formation and morphology . The main mechanisms are identified as enhanced nucleation of the C54 phase by a reduction of grain size in the C49 phase and the creation of crystallographic templates of the C40 disilicide phase and the metal-rich Ti₅Si₃ phase.