Metal Electrodes Work Function Measurement at Deca-Nanometer Scale using Kelvin Probe Force Microscope: a Step Forward t
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0917-E12-04
Metal Electrodes Work Function Measurement at Deca-Nanometer Scale using Kelvin Probe Force Microscope: a Step Forward to the Comprehension of Deposition Techniques Impact on Devices Electrical Properties Nicolas Gaillard1,2, Denis Mariolle3, Francois Bertin3, Mickael Gros-Jean1, and Ahmad Bsiesy2,4 1 STMicroelectronics, 850, rue Jean Monnet, Crolles, 38926, France 2 CEA-DRFMC, Spintec Laboratory, 17 rue des martyrs, Grenoble, 38054, France 3 CEA-DRT-LETI, CEA/GRE, 17 rue des martyrs, Grenoble, 38054, France 4 Université Joseph Fourier, Grenoble, 38041, France
ABSTRACT In this letter, we report on Work Function (WF) measurements performed at decananometer scale on various metals using Kelvin probe Force Microscope (KFM). We first demonstrated the relationship between the WF value and the grain crystallographic orientation by combining KFM and Electron Back Scattered Diffraction (EBSD) performed over the same Cu area. Once this relationship was established, KFM was used to provide, in addition to WF values, crystallographic properties of TiN PVD films grown on various substrates. Finally we characterized the effect of N2/H2 plasma treatment on the WF of TiN grown by CVD. In the latter case, the modification of the bulk chemical potential by post-treatment was proposed. INTRODUCTION To address polysilicon high resistance and depletion issues, advanced researches are currently focused on metals deposition processes [1] as well as Work Function (WF) engineering [2]. Electrode WF is a key parameter since it governs major devices electrical characteristics such as MOSFETs threshold voltage (Vth) and Metal/Insulator/Metal (MIM) capacitors leakage currents. Thus, the understanding of deposition processes impact on metal WF value and variation within film becomes an important issue in sub-0.1 µm technologies [3]. Based on charges transfer annulations between a metal coated AFM tip and the sample connected as a capacitor, KFM is a spatially resolved technique well suited to characterize local WF variations on metal layers with a noise level less than 5 meV. We report in this letter Contact Difference Potential (CPD) mappings, i.e. WF mappings, of various metal layers used in Front End (FEOL) and Back End Of the Line (BEOL) applications. As KFM is sensitive to environment artifacts when operated in air [4], we first calibrate the experiment by measuring the modification of the CPD with the air hygrometry. Then, we demonstrate the KFM accuracy through characterizations of polycrystalline samples such as aluminum and copper BEOL layers. A one to one correspondence between the grain WF and crystallographic orientation is demonstrated thanks to a comparison of the potential mapping obtained with KFM and Electron Back Scattered Diffraction (EBSD) analysis performed over the same Cu area. Finally, WF measurements of TiN layers deposited by PVD and CVD techniques are discussed.
ORIGIN OF METAL WORK FUNCTION The WF, defined as the minimum amount of energy required to extract a particle from the bulk to local vacuum lev
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