Abstract
We present an evaluation of the thermal stability for various elemental metals and binary/ternary conducting compounds on gate dielectrics. The continued scaling of polysilicon gated complementary metal oxide semiconductor (CMOS) devices may face limitations such as polydepletion, incompatibility with some high-k dielectrics, high series resistance, and boron penetration. In this study, 24 different elemental metals and metallic compounds with work functions ranging from 4.0 to 5.2 eV covering n-type field effect transistor (nFET), midgap, and pFET gate electrodes were examined. The films were characterized during rapid thermal annealing in a forming gas ambient up to 1000°C. Three techniques, in situ X-ray diffraction, resistance, and elastic light scattering analysis were used simultaneously during annealing. It was found that many of the elemental materials, especially those with nFET work functions, undergo reactions with the SiO2 and Al2O3, gate dielectrics, while others became unstable because of melting (Al) or agglomeration (Co, Ni, Pd and CoSi2). Two binary compounds, W 2N and RuO2, underwent dissociation in the hydrogen-containing ambient Materials stable above 700°C include Mo, W, Re, Ru, Co, Rh, Ir, Pd, Pt, W2N, TaN, TaSiN, and CoSi2, making them possible choices for integration involving higher temperature processing. © 2004 The Electrochemical Society. All rights reserved.