Hole transport in strained SiGe-channel MOSFETs : velocity in scaled devices and mobility under applied mechanical strain

Since the 90 nm CMOS technology node, geometric scaling of CMOS has been supplemented with strain to boost transistor drive current. Future CMOS technology nodes (i.e. beyond the 32 nm node) will require more significant changes to continue improvements in transistor performance. Novel CMOS channel materials and device architectures are one option for enhancing carrier transport and increasing device performance. In this work strained SiGe and Ge are examined as a means of increasing the drive current in deeply scaled CMOS. As part of this work a novel high mobility strained-Ge on-insulator substrate has been developed, and the hole transport characteristics of short channel and asymmetrically strained-SiGe channel p-MOSFETs have been explored. A thin-body biaxial compressive strained-Si/strained-Ge heterostructure on-insulator (HOI) substrate has been developed, which combines the electrostatic benefits of the thin-body architecture with the transport benefits of biaxial compressive strain. A novel Germanium on Silicon growth method and a low temperature bond and etch-back process have been developed to enable Ge HOI fabrication. P-MOSFETs were also fabricated using these substrates and the hole mobility characteristics were studied. The hole mobility and velocity characteristics of short channel biaxial compressive strained-Si 45 Geo.55 p-MOSFETs on-insulator have also been examined. Devices with gate lengths down to 65 nm were fabricated. The short channel mobility characteristics were extracted and a 2.4x hole mobility enhancement relative to relaxed-Si was observed. The measured hole velocity enhancement is more modest at about 1.2x. Band structure and ballistic velocity simulations suggest that a more substantial velocity improvement can be expected with the incorporation of added longitudinal uniaxial compressive strain in the SiGe channel. The hole mobility characteristics of biaxial strained SiGe and Ge p-MOSFETs with applied uniaxial strain are also studied. The hole mobility in biaxial compressive strained SiGe is already enhanced relative to relaxed Si. It is observed that this mobility enhancement increases further with the application of <110> longitudinal uniaxial compressive strain. Since hole mobility and velocity are correlated through their dependence on the hole effective mass, a mass driven increase in mobility with applied uniaxial strain should result in an increase in velocity. Simulations have also been performed to estimate the hole effective mass change in asymmetric strained SiGe. Finally the piezo resistance coefficients of strained SiGe are extracted and found to be larger than in Si.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2010

Author dc:creator

• Gomez, Leonardo, Ph. D. Massachusetts Institute of Technology

Advisor dc:contributor.advisor

• Judy L. Hoyt.

• Electrical Engineering and Computer Science.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/60144

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/60144