Method for measuring concentration of dopant within a semiconductor

Abstract

A method is provided for measuring at resolutions which are in some instances less than 20 nanometers the concentration densities within one or more diffusion regions within a semiconductor substrate. The diffusion regions are prepared for measurement by cleaving a cross-sectional surface and polishing that surface to a substantially flat, exposed profile. The profile is purposefully pre-etched to remove oxide abutting the implant area and thereafter dopant-selective etched in accordance with concentration densities within the substrate. Pre-etching of oxide and concentration density etching of doped silicon provides an exposed topological contour measurable by atomic force microscopy (AFM). AFM can detect the entire cross-sectional surface including conductors and dielectrics. The topological height of impurity region profiles of a calibration wafer are correlated to impurity concentrations to form a calibration curve. The calibration curve, in conjunction with topological contour of a target region profile, allows direct and quick measurement of concentration densities along the target region profile at each AFM scan location. The initial scan position is purposefully defined by an oxide pre-etch step to present an easily discernible AFM-read gradient which signals an initial AFM read position.