Structural and electrical characterization of Al2O3/HfO2/Al2O3 on strained SiGe

The interfacial integrity of a gate stack featuring a polycrystalline SiGe gate, an ultrathin Al2O3/HfO2/Al2O3 nano-laminate and a strained-SiGe surface-channel is examined for full transistor fabrication and characterization. The high-κ dielectric nano-laminate is prepared by means of atomic layer deposition, and the SiGe channel and gate by chemical vapor deposition. After full transistor-processing including a rapid thermal processing step at 930 °C, the 3 nm thick HfO2 film becomes polycrystalline whereas the Al2O3 films about 0.5 nm thick remain in the amorphous state, according to analyses using high-resolution and energy-filtering transmission electron microscopy. No interfacial reaction is observable between the HfO2 film and the SiGe gate or channel, since both interfaces are flat and the two Al2O3 films remain continuous. Well-behaving gate leakage and capacitance characteristics of the transistors are found. An enhanced channel hole mobility compared to the Si universal curve is obtained.