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.