Title page for ETD etd-01192005-172005

Type of Document

Dissertation

Author

Lazar, Heather Rebecca,

Author's Email Address

hrlazar@ncsu.edu

URN

etd-01192005-172005

Title

Mobility Degradation of Advanced CMOS Devices

Degree

PhD

Graduate Program

Electrical Engineering

Advisory Committee

Advisor Name	Title
Dr. Veena Misra	Committee Chair
Dr. Eric Vogel	Committee Member
Dr. Gerry Lucovsky	Committee Member
Dr. Griff Bilbro	Committee Member
Dr. Jayant Baliga	Committee Member

Keywords

MOSFET
high k dielectrics
metal gate electrodes
bulk trapping
interface traps
interfaces
charge pumping
mobility

Date of Defense

2005-01-31

Availability

unrestricted

Abstract

As alternative materials are being pursued for CMOS gate dielectric scaling to
below 1 nm, challenges arise that warrant investigation for greater understanding.
Mobility values, in particular, of ultra thin SiO2 and high k MOSFET devices have
been reported to be low and the reason behind this degradation is still unclear.
Furthermore, a study on the effects of implementation of candidate metal gate
electrodes on mobility values has not yet been performed. Since many of the
properties of these materials are still under scrutiny, accurate determination of their
electrical and analytical characteristics is needed.
In this work, an investigation of the mobility of several candidate metal gate
electrodes on high k dielectrics was performed and compared with that of SiO2 and
polysilicon. This work was separated into two components. The first study
compared three metal gate electrodes on HfO2 with that of SiO2 in the 2 nm EOT
range fabricated at North Carolina State University. Standard and advanced
electrical characterization, including Dit and bulk trapping characteristics, was
performed including two and three level charge pumping and other pulsed methods.
It was found that mobility values were very similar for the metal gate electrodes both
on high k and SiO2. The second study analyzed the mobility values for aggressively
scaled EOT (< 2nm) devices with a metal and polysilicon gate electrode indicating a severely degraded mobility. Both the interface and the bulk trapping behavior of
these devices were also analyzed and used to correct the mobilities. However,
corrections to mobility for both trapping and interface trap density did not recover the
mobility of these devices. The mechanism responsible for mobility degradation
beyond trapping in these aggressively scaled MOSFETs will be discussed. Finally,
steps necessary to enhance mobility will be presented.

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