In Vacuo XPS Study on Pt Growth by Atomic Layer Deposition Using MeCpPtMe3 and N2/NH3 Plasma

Abstract

Atomic layer deposition (ALD) has been an attractive tool in the fabrication of Pt thin layers and nanoparticles. In this work, the surface chemistry of Pt ALD through the MeCpPtMe₃/N₂-plasma (N₂*) and the MeCpPtMe₃/NH₃-plasma (NH₃*) processes at 300 °C have been investigated in detail using in vacuo X-ray photoelectron spectroscopy (XPS) during the ALD process, so that the evolution of surface species at each step of the ALD cycle can be studied under growth relevant conditions. In particular, the nature of the N-containing surface species and their role in the surface reactions during nucleation and steady growth are carefully scrutinized. Both processes are completely O-free. Persistent surface N and/or C species are detected, which are, however, not built into the film. Remarkably, the common N-species seen in other metal ALD processes by N-based plasmas, such as metal-NH_x groups or N adatoms, are not present on the growth surface. For the MeCpPtMe₃/N₂* process, −CN-H_x is identified as the main N-containing species engaged in surface reactions. On the other hand, N-containing species seem to play an insignificant role in the NH₃* process. It is revealed that the surface species and reaction pathways of the MeCpPtMe₃/N₂* and the MeCpPtMe₃/NH₃* processes are not only different to those of the O-based processes but also differ from each other. On the basis of surface species quantification results, a growth mechanism is proposed for the N₂* and the NH₃*-based processes, respectively. Our results show that N-based plasmas are a promising alternative to O-based reactants in Pt ALD growth.