T. Conard et al., X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry study of the role of Ti and TiN caps on the cobalt/SiO2 interface, J VAC SCI A, 17(4), 1999, pp. 1244-1249
Continuous down scaling of device features and increases in operation frequ
ency of integrated circuit (ICs) requires a low electric resistance of inte
rconnects to transistors. Due to its low resistivity and high thermal stabi
lity, the integration of CoSi2 into ultralarge scale ICs is becoming the ma
in stream. In this study, a 15 or 20 nm Co film was grown on SiO2 and Ti or
TiN top layers were deposited on the Co layer without breaking the vacuum.
The samples were annealed in N-2 ambient and the specimens were analyzed b
y x-ray photoelectron spectroscopy and time-of-flight secondary ion mass sp
ectrometry in depth profile mode. Significantly different depth profiles we
re obtained depending on the nature of the cap layer and on the annealing t
emperature. The multilayer with a top TiN layer presents a profile correspo
nding to sharp interfaces with only a limited diffusion of Ti inside the Co
layer and no differences in chemistry of the interfaces. The Co depth prof
ile has a very symmetrical shape. On the contrary, the presence of a Ti cap
layer induces very strong modification of the interface reactions. An impo
rtant diffusion of the Ti is observed through the Co layer and an accumulat
ion of Ti occurs at the Co/SiO2 interface. At the interface, Ti is observed
in an oxidized form and reduces the top of the SiO2 layer. When the anneal
ing temperature is reduced to 650 degrees C no pile up of Ti is seen at the
interface and the silicon profile is similar to the profile obtained with
the TiN cap layer. (C) 1999 American Vacuum Society. [S0734-2101(99)04104-4
].