Conductance transient comparative analysis of ECR-PECVD deposited SiN x , SiO 2 /SiN x and SiO x N y dielectric films on
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E3.12.1
Conductance transient comparative analysis of ECR-PECVD deposited SiNx, SiO2/SiNx and SiOxNy dielectric films on silicon substrates H. Castán, S. Dueñas, J. Barbolla, A. Del Prado1, E. San Andrés1, I. Mártil1 and G. GonzálezDíaz1 Departamento de Electricidad y Electrónica, E.T.S.I. Telecomunicación, Campus “Miguel Delibes”, Universidad de Valladolid, 47011 Valladolid. Spain. 1 Departamento de Física Aplicada III (Electricidad y Electrónica), Facultad de Ciencias Físicas, Universidad Complutense, 28040 Madrid. Spain.
ABSTRACT A study of metal-insulator-semiconductor (MIS) structures based on SiNx, SiO2/SiNx and SiOxNy films deposited on silicon by electron cyclotron resonance plasma-enhanced chemical vapour deposition (ECR-PECVD) is presented. Interface trap densities measured by deep level transient spectroscopy (DLTS) are higher for silicon oxynitride-based MIS capacitors than for silicon nitride and silicon oxide-silicon nitride-based ones. However, conductance transient analysis demonstrated that Al/SiNx/Si devices exhibit the highest disordered-induced gap states (DIGS) density, whereas the lowest one corresponds to Al/SiNx/SiO2/Si, and silicon oynitridebased MIS capacitors show an intermediate behaviour. In addition, thermal treatments applied to Al/SiOxNy/Si samples reduce DIGS densities to values even lower than those corresponding to Al/SiNx/SiO2/Si devices. INTRODUCTION As the scale of integration increases and the thickness of the dielectric is reduced, the performance of SiO2 is degraded due to tunnelling currents and permeability to boron and alkali ion diffusion. SiNx shows better impermeability properties than SiO2, as well as a higher dielectric constant which allows physically thicker dielectrics with the same capacitance-voltage performance [1]. On the other hand, silicon oxynitride shows some advantages with respect to SiNx, such as lower stress and higher band gap [2]. The electron-cyclotron resonance plasma-enhanced chemical vapor deposition (ECRPECVD) is one of the most suitable deposition procedures to obtain insulator thin films because it is a low cost thermal process and the substrate is placed outside the plasma region, reducing the damage induced by ion bombardment [3]. Device quality SiNx, SiO2 and SiOxNy have been deposited at a low substrate temperature with this technique. This work is aimed to carry out a comparative electrical characterization of MIS structures fabricated from ECR-PECVD deposited SiNx, SiO2/SiNx and SiOxNy dielectric films. The electrical characteristics of the dielectric films are related to the amount of defects and charge trapping centers in the dielectric bulk and the interface between dielectric and semiconducting substrate. The densities of interface states and defects inside the dielectric have been measured by using deep level transient spectroscopy (DLTS) and conductance transient analysis, respectively. EXPERIMENTAL DETAILS Substrates used were n-Si (5 Ω cm, orientation), on which we have previously deposited Al back electrodes by thermal evaporat
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