The transport of copper in silicon dioxide thermally grown on single crystalline silicon was studied by capacitance techniques, secondary ion mass spectroscopy (SIMS) analysis, and Rutherford backscattering spectrometry (RBS). Metal/ oxide/silicon (MOS) capacitors were used to study the penetration of copper into the oxide as a function of temperature and applied electric field. The role of a titanium layer between the copper and the oxide was also studied. Bias-thermal stress (BTS) studies of MOS structures were conducted at 150~ to 300~ with an electric field of 1 MV/cm for times ranging between 10 rain and 168 h. It is shown that without bias a relatively small amount of copper reaches the silicon/silicon 17 3

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. Biasthermal 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 lMV/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/Si02 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 f 0.2 eV. Without bias only a small amount of copper pene s th oxide. SIMS analysis shows that for such samples the surface concentration is in the vicinity of l r c m -' and drops exponentially into the oxide. On the other hand, devices stressed under positive electric field, without a titanium barrier can show orders-of-magnitude higher copper concentration in the oxide. If the Ti adhesion layer thickness exceeds about 5nm, the devices are not affected by the BTS, even at 300C.

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