Additive mobility enhancement and off-state current reduction in SiGe channel pMOSFETs with optimized Si Cap and high-k metal gate stacks

We have demonstrated high mobility pMOSFETs on high quality epitaxial SiGe films selectively grown on Si (100) substrates. With a Si cap processed on SiGe channels, HfSiO₂ high-k gate dielectrics exhibited low C-V hysteresis (<10 mV), interface trap density (7.5times10¹⁰), and gate leakage current (~10^-2 A/cm² at an EOT of 13.4 Aring), which are comparable to gate stack on Si channels. The mobility enhancement afforded intrinsically by the SiGe channel (60%) is further increased by a Si cap (40%) process, resulting in a combined ~100% enhancement over Si channels. The Si cap process also mitigates the low potential barrier issues of SiGe channels, which are major causes of the high off-state current of small bandgap energy SiGe pMOSFETs, by improving gate control over the channel.