Two-step codeposition process for enhanced C54–TiSi2 formation in the Ti–Si binary system

Abstract

This work demonstrates the possibility of decreasing the C54–TiSi2 formation temperature during rapid thermal annealing (RTA) by more than 50 °C using a two-step binary Ti–Si codeposition process on Si (100) substrates. This process is based on codepositing a particular double-layer microstructure. The first layer is an amorphous Ti–Si alloy codeposited on Si (100) with a composition close to Ti5Si3. After crystallizing this first layer at temperatures near 600 °C, a second layer is formed by room-temperature codeposition of an amorphous capping layer with a composition close to TiSi2. Analyses by Rutherford backscattering spectrometry and film-thickness measurements by transmission electron microscopy on samples constructed according to this method show a structure of 20 nm TiSi1.3/45 nm Ti3.7Si3/Si. On rapid thermal annealing (3 °C/s to 710 °C), C49–TiSi2 formation occurs at the silicide/silicon interface keeping Ti5Si3 as an intermediate layer, and the capping layer is transformed to C54–TiSi2. This microstructure is fundamentally different from that developed after RTA of Ti/Si bilayers in which C49–TiSi2 forms and subsequently transforms to C54 at temperatures ∼800 °C. The two-step process studied here places hexagonal Ti5Si3 in close contact with the amorphous capping layer. This layer acts as a catalyst for the formation of C54–TiSi2 by decreasing the energy barrier for C54 nucleation. The present experiments also suggest that the transformation from C49 to C54 can be mediated by a layer of Ti5Si3 in much the same fashion as metal-mediated crystallization processes. The enhanced formation of C54–TiSi2 using the two-step silicidation of binary Ti–Si alloys is an attractive alternative to other methods which lower the C54 formation temperature by introducing a third element. Such a third element can produce thermodynamically stable high-resistivity silicides that may decrease device performance.