Acceleration Factors for IC Leakage Current in a Steam Environment

Leakage current measurements were made across the surface of silicon test chips up to a temperature of 130°C (403°K) and 70% relative humidity (RH) to develop a more accelerated temperature-humidity-bias corrosion test. Several equations were fitted to the data in order to extrapolate the surface conductivity data to operating conditions. A smooth transistion from atmospheric pressure into the pressurized steam region was observed. The leakage current acceleration factor is the same at 130°C/60%RH and 85°C/85%RH for bare gold electrodes. For nitride-covered aluminum conductors the equlvalent conditions are 130°C/65%RH or 85°C/85%RH. The advantage in the steam region is a larger temperature differential between the sample and saturation; approximately 15°C as opposed to 4°C for the 85°C/85%RH. This makes the steam test easier to control, but might raise the temperature beyond the decomposition limits for organic packaging materials. For inorganic systems with nitride-covered aluminum electrodes, an acceleration by a factor of three compared to 85°%C/85%RH can be obtained at 140°C/70%RH or 17°C/60%RH. Coefficients were determined by multiple regression analysis for three forms of equations which express the surface conductivity in terms of reciprocal absolute temperature and RH. The acceleration factors determined by a power law are consistently lower than those determined by two forms of an exponential equation.