Paper TF1-TuM6
Y₂O₃ Atomic Layer Deposition from a Novel Process and its Integration in a Gate First Approach for 0.8 nm Equivalent Oxide Thickness

Tuesday, October 19, 2010, 9:40 am, Room Pecos

A large part of the high-k dielectric stacks investigated for the replacement of the SiO₂ or Si_xO_yN gate oxide in metal-oxide-semiconductor (MOS) field-effect transistors consists of a Hf-based oxide or silicate deposited on top of an ultrathin interfacial SiO₂ layer. We report here the formation of yttrium lanthanum silicate in direct contact with silicon for the fabrication of MOS capacitors with a resulting highly competitive equivalent oxide thickness (EOT) of 0.8nm. Such a low EOT is remarkable as it is obtained with a non Hf-based dielectric and following a high-temperature gate first route. This result is achieved by integrating Y₂O₃ films grown on buffer layers by a novel atomic layer deposition process that combines an original yttrium precursor and an innovative liquid injection source.

The growth of Y₂O₃ thin films by ALD from Y(EtCp)₃ and water precursors will be presented. The yttrium precursor was introduced using a novel delivery scheme consisting of a pulsed injection system from Kemstream®. The control of the growth as a function of various process parameters (precursor supply time, water purging time, temperature) was investigated. Film stoichiometry was determined by Rutherford backscattering spectrometry. The reactivity of Y(EtCp)₃ with water and the frontiers between ALD and CVD regimes will be discussed.

We describe MOS capacitors prepared from ALD-Y₂O₃ thin films deposited onto Si(p-type)/SiO₂(0.8 nm)/La₂O₃ (1 nm) structures. The Y₂O₃ thickness ranges from 1.5 to 3.5 nm. The metal gate electrode consists of 10 nm TiN and implanted polysilicon on top. The complete stack undergoes a high-temperature RTA at 1000˚C for 5 s under N₂ for dopant activation in the poly-Si, which simulates gate first process of CMOS transistor fabrication. Finally, a forming gas anneal is performed at 475˚C. The stack microstructure and composition were studied by transmission electron microscopy, electron loss spectroscopy and energy dispersive x-ray spectrometry. Interdiffusion reactions occur between SiO₂, La₂O₃ and Y₂O₃ layers upon the RTA and result in an yttrium lanthanum silicate film in direct contact with Si. The elemental distribution within the silicate layer will be discussed. C-V and I-V were performed on 10x10 μm² size capacitors in a frequency range of 1 kHz up to 300 kHz. EOTs as low as 0.8 nm were obtained for stacks with initially 3 nm Y₂O₃ deposited films. The leakage current density for such stacks is of 2.1x10^-3 A/cm² at -1V. The formation of silicate enables an appropriate V_FB, which is tunable for nFET and pFET. Results obtained for stacks prepared from different buffer layers such as Al₂O₃ and HfO₂ will also be discussed.