Mobility and performance enhancement in compressively strained SiGe channel PMOSFETs

Abstract

We report that drive current enhancement and higher mobilities than the universal mobility in compressively strained Si 1− x Ge x on Si surface-channel p-type metal-oxide–semiconductor field-effect-transistors (PMOSFETs) with HfO 2 gate dielectric, for gate lengths ( L G) down to 180 nm. 36% drive current enhancement was achieved for Si 0.8Ge 0.2 channel PMOSFETs compared to Si with HfO 2 gate dielectric. We demonstrate that using SiGe in the channel may be one way to recover the mobility degradation due to the use of HfO 2. Buried-channel PMOSFETs with a Si cap layer and SiO 2 gate dielectrics were also studied. 41% peak mobility enhancement in Si 1− x Ge x channel PMOSFETs was observed compared to Si channel PMOSFETs. 17% drive current enhancement was achieved for 70 nm channel length ( L G) Si 0.9Ge 0.1 PMOSFETs with SiO 2 gate dielectric. This shows the impact of increased hole mobility even for ultra-small geometry of MOSFETs and modest Ge mole fractions. Comparable short channel effects (SCE) were achieved for the buried-channel Si 1− x Ge x devices with L G=70 nm, by controlling Si cap thickness, compared to the Si channel devices. Drive current enhancement without significant SCE and leakage current degradation was observed in this work.