Paper TF+EM+MI-WeA8
Atomic Layer Deposition of Stoichiometric TaSi₂ on Si(001)

Wednesday, November 9, 2016, 4:40 pm, Room 105A

Transition metal disilicides are of great interest in Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETs) due to their ability to tune the work function at the metal contact in the source/drain regions. Various kinds of transition metal silicides such as TiSi₂, NiSi₂ and WSi₂ have been studied in previous decades, however, nanoscale studies of TaSi₂ are relatively scarce. Previously, Lemonds et al. successfully demonstrated atomic layer deposition (ALD) of tantalum silicide (TaSi_x) on SiO₂ using TaF₅ and Si₂H₆. In this work, it is demonstrated that using similar reaction conditions TaSi₂ can be grown by ALD process on oxide-free clean Si(001). The growth rate of TaSi₂ on Si(001) was monitored in-situ using a Quartz Crystal Microbalance (QCM) during the deposition. This enabled optimization of the TaF₅ and Si₂H₆ dosing to avoid chemical vapor deposition (CVD) components. Scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), scanning tunneling spectroscopy (STS) and atomic force microscopy (AFM) have been used to investigate the atomic and electronic structure of Si(001) surface after TaSi₂ thin film deposition. HF cleaned Si(001) was used for the substrate. The chemical composition was determined by XPS after ALD to be that of a stoichiometric TaSi₂ film formed on the Si substrate. The key variables in forming stoichiometric TaSi₂ are the ratio of the precursors and the surface temperatures. In the ALD process, a 100x fold excess of Si₂H₆ is required to prevent formation of TaOx; in addition, the surface temperature must be above 240C. These requirements for excess Si₂H₆ and a high surface temperature are likely due to high activation barrier to break the residual Ta-F bonds on the surface after the TaF₄ half pulse since the Ta-F bonds are stronger than the Si-H bonds.