A SPECIAL CASE OF USING ELLIPSOMETRY TO MEASURE THE THICKNESS OF OXIDE ON POLYSILICON .1. THEORETICAL CONSIDERATIONS

Ellipsometry is used routinely to measure the thickness of silicon dioxide thermally grown on single-crystal silicon. Single wavelength ellipsometry is not used routinely to measure the thickness of thermally grown oxide on polysilicon because of the multilayer nature of the structure and uncertainty in the thicknesses of underlying layers. There is a special case when single-wavelength ellipsometry can be readily used for this measurement. If the oxide layer which separates the single-crystal silicon from the polysilicon is thin, i.e., 100Å or less, a simplifying assumption can be made in the calculations. Estimates of the thickness of the oxide on the polysilicon can be obtained with an accuracy of the order of the thickness of the lower separating oxide. This method is particularly appropriate for test wafers where the thickness of the lower oxide can be chosen to optimize the measurement technique while still giving a representative polysilicon layer. © 1990, The Electrochemical Society, Inc. All rights reserved.