Abstract
A systematic experimental evaluation of the thermal stability of Ru metal gate electrodes in direct contact with
Si
O
2
and Hf-based dielectric layers was performed and correlated with electrical device measurements. The distinctly different interfacial reactions in the
Ru
∕
Si
O
2
,
Ru
∕
Hf
O
2
, and
Ru
∕
Hf
Si
O
x
film systems were observed through cross-sectional high-resolution transmission electron microscopy, high angle annular dark field scanning transmission electron microscopy with electron-energy-loss spectra, and energy dispersive x-ray spectra analysis. Ru interacted with
Si
O
2
, but remained stable on
Hf
O
2
at
1000
°
C
. The onset of
Ru
∕
Si
O
2
interfacial interactions is identified via silicon substrate pitting possibly from Ru diffusion into the dielectric in samples exposed to a
900
°
C
∕
10
-
s
anneal. The dependence of capacitor device degradation with decreasing
Si
O
2
thickness suggests Ru diffuses through
Si
O
2
, followed by an abrupt, rapid, nonuniform interaction of ruthenium silicide as Ru contacts the Si substrate. Local interdiffusion detected on
Ru
∕
Hf
Si
O
x
samples may be due to phase separation of
Hf
Si
O
x
into
Hf
O
2
grains within a
Si
O
2
matrix, suggesting that
Si
O
2
provides a diffusion pathway for Ru. Detailed evidence consistent with a dual reaction mechanism for the
Ru
∕
Si
O
2
system at
1000
°
C
is presented.