Visual and Electric Ohmic Metal Degradation From Later Process Steps
Ohmic metal degradation caused wafers to fail at wafer final test due to high contact resistance. A change in the morphology of the ohmic metal near first interconnect metal was associated with the increase in contact resistance. It was found that previously good Ohmic contacts were ruined by overheating in O2 plasma tools near the end of the fab process. Reducing time in plasma at that step solved the problem without compromising the quality of the plasma clean.