DEALLOYING KINETICS OF CU1-XTIX ON SIO2 USING IN-SITU X-RAY DIFFRACTION

We study the dealloying of Ti from Cu1-xTix (x similar to 10 atom percent) alloy films on oxidized Si substrates in the temperature range of 375 to 490 degrees C and an estimated O-2 partial pressure of similar to 10(-6) to 10(-5) Torr. Reaction products were determined to be TiO and Ti2O3 and possibly TiO2 at the free surface, and TiO at the SiO2 interface, according to Rutherford backscattering spectrometry and Auger electron spectroscopy. We found that the Cu lattice parameter varies linearly with Ti concentration, and this variation is independent of temperature in this composition range. As a consequence, we were able to study the dealloying kinetics using in situ x-ray diffraction by monitoring the time dependence of the Cu lattice parameter. We observe that the reaction kinetics obey a parabolic rate law, i.e., X(Ti,reacted)(2) = kt, With a Single activation energy of 1.6 +/- 0.1 eV, suggesting that one process governs dealloying kinetics over this temperature range. In addition, we note a pronounced composition dependence, in that the reaction rate increases sharply with increasing Ti concentration. These observations suggest that Ti diffusion in Cu is the rate-limiting kinetic process for the dealloying reactions in this temperature regime. We model the dealloying reaction and in so doing estimate the diffusion coefficient for Ti in these alloy films.