Paper TF-TuA9
Nucleation and Growth of Conformal and Ultrathin Pt Films on Al₂O₃ and W Substrates Using Plasma Enhanced ALD

Tuesday, October 19, 2010, 4:40 pm, Room Ruidoso

Pt ALD using thermal chemistry has nucleation difficulties and leads to the deposition of Pt nanoclusters. In contrast, Pt ALD using O₂ plasma nucleates much more readily and spectroscopic ellipsometry (SE) studies are consistent with continuous Pt films (H.C.M. Knoops et al., Electrochem. Solid-State Lett. 12, G34 (2009)). However, SE measurements alone were insufficient to characterize the early stages of the Pt ALD process. In this investigation, we have examined Pt ALD with MeCpPtMe₃ and O₂ plasma as the reactants using SE, X-ray reflectivity (XRR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) studies versus the number of ALD cycles. Analysis of the XRR and XPS results indicates that plasma Pt ALD on Al₂O₃ ALD substrates has a short nucleation delay. The nucleation delay is followed by a brief period of rapid Pt ALD film growth of 0.1 nm per cycle that is followed by a slower steady-state Pt ALD film growth of ~0.05 nm per cycle. During the Pt ALD nucleation and growth on the Al₂O₃ ALD substrate, SEM images show that the Pt film morphology evolves from isolated nanoclusters to worm-like nanostructures and finally to a conformal film at a Pt film thickness of approximately 7 nm. Nucleation and growth of Pt ALD on W ALD substrates led to very different results. In this case, a H₂ plasma was used instead of an O₂ plasma to prevent oxidation of the W ALD substrate. XRR and XPS studies revealed that Pt ALD with MeCpPtMe₃ and H₂ plasma as the reactants on W ALD substrates nucleated immediately and a continuous and conformal Pt ALD film was formed at a Pt ALD thickness of less than 5 nm. These results indicate that Pt ALD can be tuned to produce Pt nanoclusters or a continuous and conformal ultrathin Pt film using either thermal or plasma Pt ALD.