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12 December 2006


IMEC reports record-performance Ge pMOS FETs using Si-compatible processing

At the IEEE International Electron Devices Meeting (IEDM 2006) in San Francisco, CA, USA, IMEC has reported high-performance germanium pMOS devices using a silicon-compatible process flow.

Ge is being investigated as a promising high-mobility channel material for future nanoscale pMOS devices, showing higher potential than strained silicon. But until now Ge results have been limited to either long-channel or ring-shaped devices. Now, without using enhancement techniques such as strain, IMEC has reported both excellent hole mobility for long-channel devices (up to 2.7 times higher than the universal hole mobility for silicon) and high drive currents for short-channel devices with the shortest gate length reported (125nm), claims IMEC.
A peak mobility of 315cm2/Vs was achieved for a typical 10 micron by 10 micron device. The effective oxide thickness (EOT) is about 1.2nm, with gate leakage of less than 0.01 A/cm2. Record Ge pMOS drain current of 670µA/micron was obtained for a gate length of 190nm and Vd of -1.5V.

The pMOS devices were fabricated in a Si-compatible process flow using 200mm Ge-on-Si wafers from ASM. The Ge top layer of the wafers was grown epitaxially directly on silicon. The gate deposition sequence started with Ge surface passivation, consisting of an ultra-thin (~0.6nm) epitaxial Si layer which was partially oxidized after growth. To avoid further oxidation, the Si passivation layer was immediately capped by a 4nm atomic-layer deposited HfO2 gate dielectric from an ASM Pulsar 2000 reactor followed by 10nm TaN and 80nm TiN deposited using physical vapor deposition.

Future research aims to further improve the devices by implementing strain, optimizing the ion implantation conditions, and scaling the gate length further.

The results were obtained within IMEC's core program on (sub-)32nm CMOS, which joins forces from nine IC manufacturers and foundries (Infineon, Intel, Micron, NXP, Panasonic, Samsung, STMicroelectronics, Texas Instruments and TSMC).