2.3.1 Hybrid Orientation Technology

An alternative approach yielding mobility improvement in Si exploits the dependence of the carrier mobility in Si inversion layers on the crystal orientation and on the current flow direction. For example, for holes the mobility is 2.5 times higher for (110) surface orientation than for standard (001) orientation depending on the applied effective vertical field. In the hybrid orientation technology (HOT), which is based on wafer bonding techniques and selective epitaxy, the larger carrier mobility of holes for (110) oriented substrate is exploited to enhance the performance of p-channel MOSFETs [Ouyang05,Yang06,Sheraw05]. HOT seems promising because processes are directly compatible with existing CMOS technology and strain engineering.

Figure: Crystallographic directions on the (001) and the (110) substrate. Conventionally, MOSFET channels are aligned along the $\langle110\rangle$ direction on (001) substrate. Highest electron mobility is obtained on (001) substrate, highest hole mobility on (110) substrate with channel direction $\langle110\rangle$.

E. Ungersboeck: Advanced Modelling Aspects of Modern Strained CMOS Technology