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-degrees-C to 300-degrees-C with an electric field of 1 MV/cm for times ranging between 10 min and 168 h. It is shown that without bias a relatively small amount of copper reaches the silicon/silicon dioxide interface, with a maximum surface concentration of about 10(17) cm-3 that drops exponentially with depth in the oxide. The high-frequency (100 kHz) capacitance vs. voltage (CV) characteristics of the MOS devices changed drastically when a positive bias was applied to the gate and copper reached the silicon/silicon-dioxide interface. The penetration time for copper through the oxide was characterized as a function of the temperature. The copper drift velocity, mobility and diffusivity in the oxide were determined and the copper profiles in the capacitors were characterized b SIMS. The activation energy for the diffusivity and mobility models was found to be 0.93 +/- 0.2 eV Devices without a barrier layer, which were stressed under a positive electric field, showed high copper concentration in the oxide, up to 10(21) cm-3. At high temperatures and long stress times a significant amount of copper was also found in the silicon substrate. A titanium layer thicker than 5 run acted as effective barrier even after 30 h of BTS at 300-degrees-C.
