Valarie Welsh

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The motivation for the creation of PIT metal gate PMOS process transistors was to investigate and prove the work function of molybdenum can be changed through reactive sputtering and thermal processing. The existing PIT metal gate PMOS process was adapted to form Molybdenum and Molybdenum-Nitride PMOS transistors. Processing of the molybdenum films affected the final composition of the gate electrode and ultimately its work function. Through theoretical and real analysis, the work functions of Mo and MoN gates were extracted and compared with one another as well as to Al. Examination of the extracted work functions revealed the presence of other phenomena accountable for 1.5-2.0V shift in Vt from one gate type to another. While no single mechanism is identified as the source of extra charge, contamination of the Mo/SiO2 interface, oxidation of the Mo, work function difference, or some combination of all three are likely to explain the shifts in threshold voltages.

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