Study for phosphorus contamination to high voltage transistors

Threshold voltage (V
TH
) needs to be well controlled to determine the switching point of the transistors. However V
TH
variation was observed on high voltage transistor during development phase. Investigations show that the V
TH
variation was caused by phosphorus contamination from wafer backside. Various wet chemical cleaning methods were evaluated to understand the effectiveness for the phosphorus decontamination. Good V
TH
result was achieved with improved cleaning solution.