Impact on off-state leakage current in PMOS device by metallic contamination

The impact of metallic contaminations on off-state leakage current in pMOS device is intensively studied in sub-micron CMOS technology. It is found that anomalous high Ioff leakage of pMOS device (nMOS not affected) shows the strong correlations to high frequent use of control wafer in a wet bench for pre-cleaning process prior to spacer oxide deposition as well as long queue (Q)-time between after pre-cleaning and before spacer oxide deposition. I-V analysis has proved that this off leakage of pMOS is mainly due to p-n (drain-well) junction leakage in reverse bias mode. Further examination for both nMOS and pMOS Ioff leakage behaviors seems to show metallic contamination which can efficiently act as recombination centers with deep level by pairing metallic impurity-boron in the p-type doped silicon, resulting in affecting the reverse bias p-n junction leakage of pMOS transistor only. A new approach to reduce this Ioff leakage by introducing rapid thermal annealing (RTA) before pre-cleaning process is recommended to prevent metallic impurity from diffusing through the screen oxide layer.