Journal of the Electrochemical Society vol:155 issue:2 pages:G9-G12
The continuous downscaling of complementary metal oxide semiconductor devices demands the introduction of dielectric layers with a high permittivity kappa. Three-dimensional (3D) transistor structures, such as FinFET devices, require excellent step coverage by the high-kappa material as provided by atomic layer deposition (ALD). In addition, because of the 3D structure, surfaces with different crystallographic orientation need to be covered. Because the initial HfO2 deposition using ALD HfCl4/H2O is governed by the OH surface density, we investigated its dependence on the crystallographic orientation of the silicon substrate. For oxidations in O-3/H2O, a (110) orientated substrate oxidizes faster than silicon (100) up to a thickness of similar to 0.7 nm as measured by X-ray photoelectron spectroscopy. Also, irrespective of the substrate orientation, the HfO2 deposition is found to increase with increasing SiO2 thickness and thus OH coverage of the surface. This implies that, for oxide thicknesses below0.7 nm, the oxidation of silicon (100) results in a thinner oxide and, hence, less HfO2 deposition in comparison to silicon (110). However, these differences are marginal after implementation in transistor devices as is shown by their capacitance and mobility. As a result, for FinFET applications, a conformally deposited HfO2 layer will be independent of the crystallographic substrate orientation.