Limitations of the calibration curve method for determining dopant profiles from scanning capacitance microscope measurements

Abstract
The calibration or conversion curve method (CCM) refers here to using a database of calculations of the capacitance done for a matrix set of model parameters, such as oxide thickness, uniform dopant density, etc., as one method for interpreting scanning capacitance microscope (SCM) measurements. The method was originally intended to help analyze SCM data for slowly varying dopant profiles, where the condition of quasi charge neutrality could be suitably maintained during SCM measurement. However, when the dopant gradient becomes sufficiently large, the quasi charge neutrality condition becomes less satisfied, and the CCM becomes less accurate (unless the gradient is taken into account in some manner). To help evaluate the limitations of the CCM (without gradient correction) in extracting two-dimensional dopant profiles from simulated SCM data, we analyze two representative ion-implanted steep-gradient dopant profiles currently used in device fabrication. The dopant profiles are derived from Monte Carlo simulation, not from secondary ion mass spectroscopy (SIMS) data. Depending upon the magnitude of the dopant gradient, the CCM results show the dopant profile peak to be both underestimated and displaced. The error in estimating the dopant concentration could be as large as 50% for these representative profiles. The calculations are done for two dimensions.

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