The introduction of hafnium oxide-based gate dielectrics for the 45-nm CMOS technology node made by leading semiconductor device manufacturers was a necessary instrument in downscaling of transistor dimensions in order to match consumer demand for increased computing power without additional cost. For future nodes, the ITRS roadmap predicts the need for equivalent oxide thicknesses (EOT’s) down to 5Å which will only be possible using materials with even higher κ-values (κ >30), while at the same time sufficiently large band offsets will be needed to control gate leakage. New dielectric materials based on doped ZrO₂ and HfO₂; or lanthanide oxides have been considered as potential candidates in this respect. In order to deposit these materials via ALD a key requirement is the availability of precursors with appropriate deposition characteristics. This requires the molecular design of ALD precursors tailored to optimise process parameters such as evaporation temperature, oxide deposition temperature, layer purity and uniformity. For example, careful selection and design of ligands in complexes such as [(RCp)₂MMe(OR)] (R = alkyl, Cp = cyclopentadienyl, M = Zr, Hf) leads to precursors with improved physical properties and significantly enhanced ALD performance. Even with careful precursor selection and design it can be difficult to obtain precursors with the desired properties, which has led to the increased use of liquid injection ALD techniques. Using this approach, a precursor is held at room temperature in solution until required at “point of use” in the ALD process allowing the use of higher evaporation temperatures while minimising precursor decomposition. In this paper, we describe the deposition of gate dielectric thin films by liquid injection ALD using the precursors [(MeCp)₂MR(OR’)] (M = Zr, Hf; R,R’ = alkyl) combined with lanthanum and titanium Cp-based precursors.

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