Silicon Orientation Effects in the Atomic Layer Deposition of Hafnium Oxide

Abstract

The continuous downscaling of complementary metal oxide semiconductor devices demands the introduction of dielectric layers with a high permittivity κ. Three-dimensional (3D) transistor structures, such as FinFET devices, require excellent step coverage by the high-κ 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 HfO2deposition using ALDHfCl4∕H2Ois governed by the OH surface density, we investigated its dependence on the crystallographic orientation of the silicon substrate. For oxidations inO3∕H2O, a (110) orientated substrate oxidizes faster than silicon (100) up to a thickness of∼0.7nmas measured by X-ray photoelectron spectroscopy. Also, irrespective of the substrate orientation, theHfO2deposition is found to increase with increasingSiO2thickness and thus OH coverage of the surface. This implies that, for oxide thicknesses below0.7nm, the oxidation of silicon (100) results in a thinner oxide and, hence, lessHfO2deposition 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 depositedHfO2layer will be independent of the crystallographic substrate orientation.