A Three-Fold Increase in Current Carrying Capability of Al-Cu Metallurgy by Pre-Depositing a Suitable Underlay Material

Abstract

To achieve the desired Cr-Cr202/Al-Cu laminate chip metalization, first Cr is deposited with the evaporation chamber back-filled with water vapor to a partial pressure of 1 to 4 × 10¿3 Pa. This is followed by standard Al Cu evaporation, lift-off or subetch, sinter, and insulation processing. The critical process step of bleeding in water vapor during Cr evaporation has to be maintained at an optimum because too much Cr202 will lead to high contact resistance and too little Cr202 will lead to a loss of diffusion barrier effectiveness. It is during the sintering cycle that 'Cr' diffusion into the Al-Cu metallization structure occurs along with formation of limited amounts of Al2O03 TThe presence of Al and Cr oxides in turn limits the formation of Cr and Al intermetallics. This results in an acceptable sheet resistance of the metallization structure. Accelerated testing of interconnecting stripes and various sizes of metal contacts to resistor and transistor devices at different temperature and current levels has been completed. As for Al-Cu metallization test results for Cr-Cr203/Al-Cu can be represented by tf J¿n exp(¿H ÷ kT) where J is the current density, T is the temperature, k is the Boltzman constant, ¿H is the activation energy and n is the current exponent. Thus at constant temperature J2 = J1 × (tf1 ÷ tf2)1/n and since for Cr-Cr203/Al-Cu metallurgy the testing done supports an improvement in electromigration lifetime of 1OX, an activation energy of 0.