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 suicide/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 suicides that may decrease device performance. © 2001 American Institute of Physics.