An Evaluation of Silicon Damage Resulting from Ultrasonic Wire Bonding

Ultrasonic wire bonding is a dynamic process which has been found to introduce material damage to improperly protected silicon. Damage is detected through the generation of steam oxidation induced stacking faults in the silicon after the metal and oxides have been removed. Silicon of both (100) and (111) orientations were evaluated with faulting being found predominately on those (111) planes whose lines of interesection with the surface were most nearly perpendicular to the applied direction of ultrasonic motion. Stacking faults predominate at the outer periphery of the bond. In addition to a correlation between the direction of ultrasonic motion and the fault planes observed, different fault planes operate at the toe and heel of the bond. No stacking faults are induced for normal ultrasonic bonding parameters and standard thicknesses of metallization (10 KÃ…) using 2-mil bonding wire. This method of analysis provides a means for evaluating changes in materials and processing to improve bond reliability.