Effect of initial Al contamination on ultrathin gate oxides

As the feature size of ultralarge scale integrated circuits shrinks, the th ickness of gate oxide decreases and its control becomes important. We have investigated the effect of Al contamination on the oxidation kinetics and t he dielectric breakdown for ultrathin oxides. The presence of as little as 10(11)similar to 10(13) atom/cm(2) of Al at silicon wafer surfaces accelera tes the growth rate of thin (<30 Angstrom) oxides. The increase in the oxid ation rate in the presence of Al results from the decrease in activation en ergy for the surface reaction constant. It is suggested that the enhanced s urface reactivity is due to the spontaneous oxidation and autocatalytic eff ect of Al. We conclude that retardation of the oxidation rate for thick oxi des is due to the decrease in diffusion of oxygen through the Al-residing o xide, since Al mainly exists in the top layer of the. oxide. Dielectric bre akdown characteristics were performed on metaloxide-semiconductor capacitor s as a function of Al concentration in NH4OH/H2O2/H2O prediffusion clean so lution. Dielectric breakdown fields of the ultrathin oxides were large in s pite of Al contamination, and we could not observe any significant differen ces among the Al-contaminated wafers. (C) 2000 The Electrochemical Society. S0013-4651(99)08-085-4. All rights reserved.