CHEMICAL VAPOR DEPOSITION OF THIN FILM MATERIALS FOR ...

pulsed laser deposition [59], nitrogen ion implantation [60] and nitrogen ion beam assisted
evaporation [61] have been reported. However, the poor step coverage which comes intrinsically
with PVD methods makes it not appropriate for certain microelectronic applications.
Comparatively, CVD methods have the advantages of larger area deposition, better step coverage
and better control of morphology and stoichiometry over PVD methods. In the development of
CVD deposition of HfN thin films, the introduction of tetrakis (dialkylamido) hafnium (IV)
complexes [62] as hafnium precursors is an important step. The representative precursors and
their vapor pressures are showed in table 1.
Table 1. Hafnium amide precursors and their properties.[63]
Precursor Chemical formula
Tetrakis (dimethylamido)
hafnium
Tetrakis
(ethylmethylamido)
hafnium
Tetrakis (diethylamido)
hafnium
37
Melting
point (˚C)
Temp
(0.1 torr) (˚C)
Temp (1 torr)
(˚C)
Hf(N(CH3)2)4 30 48 75
Hf(N(CH3)(C2H5))4 liquid 83 113
Hf(N(C2H5)2)4 liquid 96 126
Most of the following studies are based on these metal organic precursors due to their
higher chemical reactivity than hafnium chloride, which needs a very high temperature (>1000˚C)
to react with N2/H2 to form HfN [64]. The CVD reaction of tetrakis (dialkylamido) hafnium (IV)
with ammonia was first studied but resulted in the formation of the insulating phase, Hf3N4,
instead of the conductive phase, HfN [62,65,66]. Highly conformal Hf3N4 films have been
successfully deposited on high aspect ratio surface features, as shown in Fig.14, by ALD method
using tetrakis (dialkylamido) hafnium and ammonia.