Journal of the Electrochemical Society vol:158 issue:7 pages:H687-H692
High mobility channels are currently being explored to replace the silicon channel in future CMOS technology nodes. However, until now the promising bulk properties are very difficult to translate into high transconductance due to a poor passivation of the interface between the gate dielectric and the channel. We have studied the S-passivation of the germanium surface combined with various high-permittivity dielectric gate stacks. (NH4)(2)S is used to achieve a S-terminated Ge surface. We found that the Ge/S/ Al2O3 interface is superior to both the Ge/S/ZrO2 and Ge/S/HfO2 interfaces. Bi-layer stacks consisting of Ge/S/Al2O3/HfO2 or Ge/ S/Al2O3/ZrO2 were built to achieve a gate stack with low EOT (Equivalent Oxide Thickness). In these bi-layer stacks, the Al2O3 thickness is reduced to a minimum without degradation of the interface properties. Rather thick Al2O3 interlayers (similar to 2 nm) are needed due to island growth on S-terminated Ge surface. A pMOSFET was built using a bi-layer gate stack (Ge/S/Al2O3/HfO2). The peak mobility of this device is > 200 cm(2)/Vs at an EOT of 1.5 nm. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3582524] All rights reserved.