Phase formation and strain relaxation during thermal reaction of Zr and Tiwith strained Si1-x-yGexCy epilayers

Silicides are often used in Si technology for both their ohmic and rectifyi ng properties. In this work, we have compared Zr and Ti germanosilicides as possible metallic contacts on SiGeC alloys in terms of phase formation and stability of the unreacted SiGeC alloy. The germanosilicides are obtained after rapid thermal annealings of Zr or Ti with strained SiGeC layers. The interactions of the metal films with these alloys have been investigated by sheet resistance measurements, x-ray diffraction (XRD), cross-sectional tr ansmission electron microscopy (TEM), and energy dispersive spectroscopy in situ in the TEM. Four crystal x-ray diffraction was performed to measure t he residual strain of the unreacted SiGeC epilayer after reaction. The anal yses indicate that the final compounds are the C49-Zr(SiGe)(2) and C54-Ti(S iGe)(2) phases, respectively: In both cases, the compound is formed by mono crystalline grains with various orientations. Nevertheless, neither XRD, no r sheet resistance measurements give any clear information about the C inco rporation in the phase, when the reaction occurs with a SiGeC layer. We hav e observed that the use of Zr completely avoids Ge segregation with an unif orm layer formed, while in the case of the reaction with Ti, the grains do not form a continuous layer and Ge-segregation is evidenced: A Ge-rich Si1- z-yGez(C-y) alloy is detected in between the metallic grains. In addition, an early strain relaxation of the unreacted SiGe layer is observed after re action, and it is much more important after reaction with Ti. During the re action with nearly compensated SiGeC layers, Zr totally prevents the initia l state of strain, while Ti strongly affects the unreacted SiGeC alloy and destroys its initial state. All these results indicate that Zr may be an in teresting candidate for realizing germanosilicide contacts on IV-IV alloys, due to its good thermal stability. (C) 2000 American Institute of Physics. [S0021-8979(00)08715-6].