Two-dimensional low concentration boron profiles: Modeling and measurement

To model small devices successfully and to establish valid design rules for VLSI technology, two-dimensional (2-D) impurity profiles must be characterized. New analytical 2-D process models for ion implantation and impurity diffusion have been developed, and they include detailed considerations of the geometry and ambient effects. An approximate expression is derived to model the diffusion of low-concentration impurities under local-oxidation conditions, which can be conveniently used in the 2-D device analyses of small-geometry semiconductor devices. Measured results for the NMOST channel-stop (CS) diffusions show good agreement with the analytical calculations, and applications of the models to optimize 2-D profiles in NMOST are discussed.