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 formatio n temperature during rapid thermal annealing (RTA) by more than 50 degreesC using a two-step binary Ti-Si codeposition process on Si (100) substrates. This process is based on codepositing a particular double-layer microstruc ture. The first layer is an amorphous Ti-Si alloy codeposited on Si (100) w ith a composition close to Ti5Si3. After crystallizing this first layer at temperatures near 600 degreesC, a second layer is formed by room-temperatur e codeposition of an amorphous capping layer with a composition close to Ti Si2. Analyses by Rutherford backscattering spectrometry and film-thickness measurements by transmission electron microscopy on samples constructed acc ording to this method show a structure of 20 nm TiSi1.3/45 nm Ti3.7Si3/Si. On rapid thermal annealing (3 degreesC/s to 710 degreesC), C49-TiSi2 format ion occurs at the silicide/silicon interface keeping Ti5Si3 as an intermedi ate layer, and the capping layer is transformed to C54-TiSi2. This microstr ucture is fundamentally different from that developed after RTA of Ti/Si bi layers in which C49-TiSi2 forms and subsequently transforms to C54 at tempe ratures similar to 800 degreesC. The two-step process studied here places h exagonal Ti5Si3 in close contact with the amorphous capping layer. This lay er acts as a catalyst for the formation of C54-TiSi2 by decreasing the ener gy barrier for C54 nucleation. The present experiments also suggest that th e transformation from C49 to C54 can be mediated by a layer of Ti5Si3 in mu ch the same fashion as metal-mediated crystallization processes. The enhanc ed formation of C54-TiSi2 using the two-step silicidation of binary Ti-Si a lloys is an attractive alternative to other methods which lower the C54 for mation temperature by introducing a third element. Such a third element can produce thermodynamically stable high-resistivity silicides that may decre ase device performance. (C) 2001 American Institute of Physics.