High-Ge-Content Si1-xGex Gate Stacks with Low-Temperature Deposited Ultrathin Epitaxial Si: Growth, Structures, Low Interfacial Traps, and Reliability

Si1-xGex with Ge contents higher than x = 0.5 is expected to boost on-current and improve reliability of p-channel metal-oxide-semiconductor (pMOS) devices. However, unavoidable GeOx formation at the high-kappa/Si1-xGex interface with high Ge-contents (HGC) has caused high interfacial trap density, posing a challenge for employing the HGC Si(1-x)Ge(x )as the channel in sub-3 nm complementary MOS technology. In this work, we have deposited epitaxial Si (epi-Si) of six monolayer thickness on Si1-xGex at temperatures of 260-280 degrees C to minimize Ge diffusion and segregation. Si1-xGex layers with a wide range of HGC (0.5 < x <= 0.8) were grown to investigate the effectiveness of the epi-Si on the Si1-xGex To minimize the GeOx formation caused by the oxidation of the segregated Ge on the epi-Si surface, HfO2 was subsequently deposited via e-beam evaporation on the epi-Si. The measurements using reflection high-energy electron diffraction, high-resolution synchrotron radiation X-ray diffraction, and scanning transmission electron microscopy with high-angle annulardark-field imaging have revealed the high crystallinity of the epi-Si, the Si1-xGex layers, and abrupt interfaces of the high-kappa/epi-Si/Si1-xGex layers. The well-controlled interfaces have enabled the achievement of low interfacial trap densities (D-it) of (3-6) x 10(11) eV(-1) cm(-2) in these high-kappa/epi-Si/(HGC)Si1-xGex samples. The minimum D-it values remained at 3 x 10(11) eV(-1) cm(-2) regardless of the Ge content, confirming the effective passivation of the low-temperature deposited epi-Si. By extracting the effective charge sheet densities for the Si1-xGex gate stacks via examination of capacitance-voltage (C-V) hysteresis with decreasing stress voltage in the accumulation region of the MOS capacitors, we have attained very high acceleration factors of 8-12, indicating high reliability of the HfO2/epi-Si/SiGe pMOS gate stacks.

Automated summary

In this study, the deposition of epitaxial Si on Si1-xGex at high temperatures and subsequent deposition of HfO2 on the epi-Si surface have effectively improved the trap density and reliability of pMOS devices with high Ge contents, indicating their potential for sub-3 nm complementary MOS technology.