CHEMICAL VAPOR DEPOSITION OF THIN FILM MATERIALS FOR ...

Fig. 14. A cross sectional scanning electron micrograph of uniform Hf3N4 thin film coating by ALD on a high aspect
ratio trench structure (0.17 μm × 0.3 μm × 7.3 μm). Reproduced with permission from [67].
To improve conductivity of the as deposited thin films, the effect of post rapid thermal
annealing [68] and Ar + ion milling [69] have been studied. Both of these methods work to a
certain degree by improving the ratio of Hf to N. To satisfy the oxidation state change of
hafnium element from the precursor (+IV) to the product (+III), utilization of a stronger reducing
agent of N,N-dimethylhydrazine (H2NN(CH3)2) has been proposed and studied [70]. In spite of
the formation of relatively pure HfN thin films, the high reaction temperature (600~800˚C) and
the use of a toxic reactant severely limit its application. By employing hydrogen plasma as
reducing agent, two groups have investigated the atomic layer deposition of HfN thin films with
tetrakis (dimethylamido) hafnium (TDMAH) and tetrakis (ethylmethylamido) hafnium (TEMAH)
respectively [71,72]. In these studies, the hafnium precursors played the role of both a Hf and a
N source. It was found that the incorporation of carbon in the phase of hafnium carbide can
improve the thin film conductivity to a certain degree. In our research, a systematic study on both
CVD and ALD methods by using TDMAH and hydrogen plasma will be carried out. Potential
issues and corresponding reaction mechanisms with these methods will be analyzed and
proposed according to our experimental results.
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