2005 APS March Meeting
Monday–Friday, March 21–25, 2005;
Los Angeles, CA
Session V14: Focus Session: Electronic and Atomic Structure of Interfaces and Gate Stacks I
11:15 AM–2:15 PM,
Thursday, March 24, 2005
LACC
Room: 403B
Sponsoring
Unit:
FIAP
Chair: Alex Demkov, University of Texas-Austin
Abstract ID: BAPS.2005.MAR.V14.4
Abstract: V14.00004 : Metal screening for CMOS application through vacuum and interface work function ab-initio calculations: benefits and limitations
12:15 PM–12:51 PM
Preview Abstract
Abstract
Author:
Leonardo Fonseca
(Freescale Semicondutores Brasil, Ltda)
Future reduction of transistor dimensions in line with historical trends
cannot be achieved with the current SiO$_{2}$/polysilicon technology due to
limited effective oxide thickness (EOT) scalability and excessive power
consumption caused by high gate leakage current. Among the proposed
solutions, the high permissivity dielectric (high-K)/metal combination seems
to be a promising route. While considerable progress has been made towards
identifying a favorable high-K dielectric, with HfO$_{2}$ and its silicates
and nitrides as the leading candidates, n- and p-type metal gates with
appropriate work functions still lack. A rough, ``first order'' metal gate
screening can be performed with considerable confidence through measurement
and calculation of metal vacuum work functions (WFs). However, charge
exchange at metal/dielectric interfaces cause the metal effective WF on a
particular dielectric to differ from its vacuum value, sometimes by as much
as 1 eV [1]. For that reason, metal effective WF \textit{ab-initio} calculations using
interface models are of primary importance if theory is to be used as a
guide for correctly identifying metal gates. In this talk I will discuss the
role of interface states on the pinning of metal Fermi levels and show
results for model HfO$_{2}$/Si and Al$_{2}$O$_{3}$/Si interfaces that
correctly reproduce experimental data with polysilicon as the gate metal
[2]. Next I will describe results of theoretical metal screening for
polysilicon replacement. We have found that while vacuum WF calculations can
be quite accurate, hence useful as a predictive tool, metal/dielectric
interface calculations are severely limited in accuracy by the lack of
experimental information on the atomistic structure of the interfaces and
possibly by an unexpected and still unclear drawback of density functional
theory (DFT) within the local density approximation (LDA) [3]. Improvements
based on empirical scaling of the DFT/LDA calculated metal/dielectric
valence band offset and on bulk GW calculations of the dielectric valence
band edge shift with respect to DFT/LDA results will be discussed. Finally I
will describe experimental difficulties encountered when trying to modulate
metal WFs through interface engineering and how simulations have contributed
to understand why that may be so.
[1] J. K. Schaeffer, L. R. C. Fonseca, S. B. Samavedam, Y. Liang, P. J.
Tobin, and B. E. White, Appl. Phys. Lett. \textbf{85}, 1826 (2004).
[2] C.C. Hobbs \textit{et al.}, \textit{IEEE Trans. Elec. Dev.} \textbf{51}, 971/978 (2004).
[3] L. R. C. Fonseca and A. A. Knizhnik, unpublished.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2005.MAR.V14.4