Structural properties and stability of Zr and Ti germanosilicides formed by rapid thermal annealing

Because of their good ohmic and rectifying properties, silicides are routinely used in Si technology. This approach has been recently extended to the novel devices produced using Si1-xGex alloys. Here, we study the Zr and Ti germanosilicides produced in the low thermal budget contact formation during Si/Si1-xGex heterodevice processing. Phase formation was monitored by combining a range of spectrometries with electron microscopy and x-ray diffraction techniques, while sheet resistance measurements allowed correlation of phase formation with film conductance. After completion of the reaction, the final crystalline phase was either C49-Zr(Si1-yGey)(2) in the entire Ge composition (x) range, or C54-Ti(Si1-yGey)(2) in the Ge composition range 0-0.47. In the Zr-Si-Ge system, the C49-Zr(Si1-yGey)(2) formation temperature (T-f) decreases as x increases, and films formed at this temperature are continuous. Excess heating (above T-f) produces islanded films with embedded grains. A most significant feature of the results was that no Ge segregation was detected at any annealing temperature and that the Ge content in the C49 phase (y) remained equal to x for all x. This is in contrast to results on the C54-Ti(Si1-yGey)(2) films, which were discontinuous when x>0.10, and in which Ge segregation occurred in the form of Ge-rich SiGe decorations separating the germanosilicide grains. The Ge content in the final C54 phase (y) was always lower than the value of x in the initial SiGe alloy, and the measured sheet resistance of the corresponding contacts was large. Our results indicate that the alloys formed between Zr and Si1-xGex are good candidates as stable contacts on Si1-xGex, and hence that Zr should be preferred for contacting in Ge-rich SiGe-based applications. (C) 2002 American Institute of Physics.