Physical Mechanism of Threshold Voltage Modulation by Ge Channel Ion Implantation in the TiN/HfO₂ Gate Stack Systems

We extensively investigated the physical origin of the threshold voltage V_TH modulation by the Ge channel ion implantation (I/I) in HfO₂/TiN/polycrystalline Si gate stack systems. The possible V_TH modulation factors were carefully distinguished from each other by changing the channel dopant concentration and the thickness of the gate dielectric films. It was found that the changes in energy-band offset and dopant concentration in the channel region are minor factors of the V_TH modulation. However, it was also found that ΔV_TH is sensitive to the oxidation condition of the interfacial oxide layer; a longer oxidation induces a larger ΔV_TH. From the X-ray spectroscopy, we found that a Ge pile-up at the interfacial layer/channel interface occurs, and that the V_TH modulation range correlates well with the amount of piled-up Ge.