Abstract
The on current of MOSFETs can be improved by Ge channel, because its carrier mobility is higher than Si. Thus, an epitaxy Ge buried channel is applied in this thesis. The epitaxy layer is successfully grown by the ultrahigh vacuum chemical molecular epitaxy (UHVCVD) in National Nano Device Laboratories (NDL). However, unstable Ge sub-oxide is easily formed on Ge surface and the epitaxy Ge film has many defects. So in-situ plasma treatments are applied on interfacial layer to improve electrical properties of Ge MOSFETs. In the first part, Ge buries channel is epitaxially grown layer-by-layer on Si SOI to form FinFET. And then, in-situ gas plasma (NH3/CF4/H2) treatments are applied on interfacial layer (IL) in Atomic Layer Deposition (ALD). CF4 plasma may transform some of the high-k from monoclinic to tetragonal, which can improve the k-value. After NH3 plasma treatment, the nitridation of IL can suppress leakage current and achieve smaller EOT. And H2 plasma can psssivate the Ge surface and reduce the dangling bonds at IL/Ge; Results show that electrical characteristics such as on current, Ion/Ioff ratio in CF4 sample are improved, but its leakage current is also increased. Thus, the following task would try to suppress leakage current. In the second part, SOI FinFET with Ge buried channel is also studied, and the serious leakage current caused by CF4 plasma treatment will be resolved. After CF4 plasma treatment, further in-situ H2 or NH3 plasma treatment is applied to passivate the IL damages and reduce interface trap density (Dit). Results show that the CF4+H2 treatment is helpful to obtain better electrical characteristics compared to CF4+NH3 and CF4 sample, in terms of such as drain on current and subthreshold swing.