In Situ Characterization of Anodic Silicon Oxide Films by AC Impedance Measurements

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Journal titleJournal of The Electrochemical Society
Pages17051712; # of pages: 8
Subjectanodised layers; dielectric thin films; electric impedance; electrical conductivity; electrochemistry; semiconductor-insulator boundaries; surface topography
AbstractAnodic oxide films grown on Si in an aqueous NH4OH solution have been characterized by in situ ac impedancetechniques, and their behavior compared to thermal SiO2 oxides. Mott-Schottky analysis of oxide-free p- and n-type Sileads to doping concentrations which are in excellent agreement with independent data of conductivity measurements. Thegrowth of anodic oxides can be monitored with in situ impedance measurements. Anodic oxide films exhibit a nonidealcapacitive behavior and hence a constant-phase element has to be introduced for the evaluation of the experimental resultsin terms of an equivalent circuit. For oxides thicker than 50 Å the roughness factor for the oxide surface can bedetermined by a comparison of the capacitance results with the film thickness obtained from x-ray photoelectron spectroscopy(XPS) measurements. For thinner oxides the space-charge capacitance in the Si and the effect of the surfaceroughness have to be considered to obtain a good agreement of impedance and XPS data. A comparison of impedancespectra of anodic and thermal oxides shows that anodic oxides not only exhibit less ideal capacitive behavior but also showa drastically lower charge-transfer resistance indicating a relatively high mobility of ions in the anodic oxide film. Thenonideality of the anodic oxides is also evident from cyclic capacitance-voltage (C-V) measurements in which a stronghysteresis is observed in contrast to thermal oxides for the anodic oxide films. Furthermore, the dielectric constant of theanodic oxides is higher than for ideal SiO2 films, which can most probably be attributed to the presence of hydroxides inthe film. The quality of the anodic oxide films can be significantly improved by annealing. The imperfect nature of theas-grown anodic oxide films is also reflected in a lower chemical resistance to etching in NH4OH solutions compared tothermal oxides. By postoxidation annealing also the chemical resistance of anodic oxides is greatly improved.
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AffiliationNational Research Council Canada; NRC Institute for Microstructural Sciences
Peer reviewedNo
NPARC number12338056
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Record identifierf2db6047-1e8b-4f50-b1cf-9c1b099cf8d6
Record created2009-09-10
Record modified2016-05-09
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