Quantitative Dopant Profiling by Energy Filtering in the Scanning Electron Microscope

Abstract

Two-dimensional dopant mapping using secondary electrons (SEs) in the scanning electron microscope (SEM) is a technique under intense research and development due to improvements in instrumental resolution and its potential to enable rapid low-cost diagnostics in process optimization for microelectronic and optoelectronic fabrication. However, an initial drawback of the technique is the lack of a complete quantitative model to obtain accurate information on dopant profiles. This paper focuses on detailed studies of dopant profiling quantification on a wide range of doped silicon homojunctions in an SEM under various operating conditions for the first time. Doping type and geometry-dependent effects from the specimen are taken into account, and improved sensitivity, resolution, and quantification accuracy due to energy filtering of the SEs are demonstrated. The resulting SE intensities under varying operating conditions are surveyed with an indication of aspects of the mechanism responsible for doping contrast, including the patch fields, surface band bending, and inelastic mean free path effects in the specimen, as well as the angular velocities of the SEs. Although all samples satisfied the classical logarithmic doping dependence of contrast approximation, some of them required specialized energy-filtering techniques. The theoretical model based on energy filtering to determine the built-in voltage across the $p\!-\!n$ junction that is in the literature does not accurately apply to $n^{+}\!-i-n$ homojunctions. The surface band bending and inelastic mean free path dependence of the SE kinetic energy models have been derived in this paper, which accurately describe the quantitative contrast characteristics from donor distributions, thereby producing more accurate quantification of this technique in semiconductor research and industry.