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

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 TiSi_1.3/45 nm Ti_3.7Si₃/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. © 2001 American Institute of Physics.