Reliability of copper metallization on silicon-dioxide

The reliability of copper metallization on silicon-dioxide over single crystalline silicon was studied by capacitance techniques, secondary-ion-mass spectroscopy analysis and Rutherford back scattering. The metallization was either evaporated copper or electroless copper deposited in an alkali-free process. The barrier role of a titanium adhesion layer between the copper and the oxide has also been studied. Bias-thermal stress (BTS) studies of MOS structures were conducted at 150°C, 250°C, 275°C and 300°C. The biased samples were stressed at electric field of 1 MV/cm for a time ranging between 10 minutes for the higher temperatures up to 168 hours at the lower temperatures. The high-frequency capacitance versus voltage (CV) characteristics of the MOS devices change drastically when the copper reaches the Si/SiO₂ interface. The penetration time of copper through the oxide was characterized as a function of the temperature and was found to increase exponentially with temperature with an activation energy of about 0.85±0.2 eV. Without bias only a small amount of copper penetrates the oxide