(658g) Mocvd Heterostructures of Tio2 and Al2o3 Using Cycling of Tdeat, Tma and O2

The demand for faster
integrated circuit performance continues to lead to shrinking transistor
feature sizes. The technology roadmaps predict that the thickness of the SiO₂
gate dielectric needs to be scaled down to sub-2 nm for sub-0.1 mm complementary metal oxide semiconductors. Therefore, the concerns
regarding high tunneling leakage current and low gate capacitance of ultrathin
SiO₂ lead to the exploration of alternative dielectric materials
with higher permittivity. Among these candidates, aluminum oxide (Al₂O₃)
and Titanium oxide (TiO₂) films have attracted attention due to
their higher dielectric constants, around 9 and 80, respectively.

In this study, tetrakis(diethylamino)titanium
(TDEAT) and trimethyl aluminum (TMA) were used for TiO₂ and Al₂O₃
film chemical vapor deposition (CVD). Oxygen was used as oxidant.  TMA has been
widely studied for Al₂O₃ film deposition using H₂O
as co-reactant. It is a good Al-containing precursor and its characteristics
are well known. However the Al₂O₃ film properties using O₂
as co-reactant have not been studied much. TDEAT, as an amino-based titanium
precursor for titanium oxides deposition, is also scarcely explored even though
it has had a long history in the industry of TiN deposition. Amino-based metal
precursors are very promising due to their high reactivity and less impurity
incorporation. The addition of NH₃ as a catalyst has also been studied.

Thin films of TiO₂
and Al₂O₃ were deposited on H-passivated Si(100)
substrate through cycling of the source gases. The depositions were carried out in a low pressure
chemical vapor deposition chamber. The reaction pressure was 0.7 torr and the
reaction temperature was 100-300^oC. The film thickness was probed
using spectroellipsometry. The surface morphology and roughness of both
as-deposited and annealed films were analyzed with atomic force microscopy
(AFM). Rutherford backscattering spectroscopy (RBS) was utilized for compositional
analyses. Atomic compositions, interface reaction and annealing effects were also
studied using x-ray photoelectron spectroscopy (XPS).

It
was found that the growth rate of both Al₂O₃ and TiO₂
films deposited using NH₃ is higher than that of films deposited
without NH₃. AFM analysis reveals that the surface of Al₂O₃
films is much smoother than that of TiO₂ films. The image roughness of
as-deposited Al₂O₃ is 0.1 nm while TiO₂ is 1
nm. Even though the roughness of TiO₂ is a few times higher than
that of Al₂O₃, it is still better than that of TiO₂
deposited by titanium tetra-isopropoxide (TTIP). The roughness of both Al₂O₃
and TiO₂ films increases with deposition temperature and post-deposition
annealing temperature. In the absence of NH₃, there is no detectable
formation of SiO₂ in the as-deposited Al₂O₃ film,
while a thin layer of silicon suboxide formed in the as-deposited TiO₂
film based on XPS analysis. With the addition of NH₃, both as-deposited
Al₂O₃ and TiO₂ have no SiO₂
formation, which manifested itself only after annealing of the films. The carbon
absence in the RBS analyses indicates that the carbon detected by XPS is surface
contamination of the sample.