Ran Cheng

Demonstration of ultra-thin buried oxide germanium-on-insulator MOSFETs by direct wafer bonding and polishing techniques

The ultra-thin body and ultra-thin buried-oxide (UTBB) Germanium-on-Insulator (GeOI) substrates have been fabricated by direct wafer bonding and polishing techniques. The Ge and BOX layer thicknesses are as thin as 9 and 13 nm, respectively. The UTBB GeOI substrates exhibit superior crystal quality (similar to the bulk single crystalline Ge) and sufficiently reduced surface roughness. As a result, the Hall hole mobility of UTBB GeOI reaches 1330 cm2/V s with a carrier concentration of 2 × 1016 cm−3. The inversion mode UTBB GeOI nMOSFETs have also been demonstrated with suppressed mobility degradation during Ge layer thinning, indicating the feasibility of this GeOI substrate formation technique in future CMOS technologies.

Ultrafast pulse characterization of hot carrier injection effects on ballistic carrier transport for sub-100 nm MOSFETs

In this work, we investigate the effect of hot carrier injection (HCI) on the ballistic transport characteristics of SOI MOSFETs for the first time. Ballistic efficiency is an important indicator of device performance for nanoscale transistors. In the process of HCI stress, the traps and defects generated in the transistor channel would increase the carrier scattering and therefore degrade the ballistic efficiency. The effect of this degradation changes with gate length. In addition, due to low thermal conductivity of the oxide layer and high on-state current for nanoscale transistors, the SOI MOSFETs suffer from severe self-heating effect (SHE) which would affect the accurate evaluation of HCI effects on the ballistic carrier transport. Ultrafast pulse measurement were employed in this study to exempt the SHE from the characterization process, yielding more realistic results for the reliability estimation on device ballisticity.

A systematic study on dry etching process of germanium for Ge 3D-FETs applications

In this study, reactive-ion etching (RIE) of Ge in different ambient was systematically investigated. Several dominant parameters (applied power, gas flow rate and gas compositions) during the etching were considered to improve the profile of 3D Ge structures. Besides, it was experimentally confirmed that to obtain Ge sidewalls with small roughness and a large angle, adding O2 and an appropriate masking material are important. Finally, by optimizing the process parameters, Ge sidewalls with an angle near 80° and smooth surfaces were successfully achieved.