Two-dimensional impurity diffusion studies: Process models and test structures for low concentration boron diffusion

The continuing trend toward the reduction of lateral surface dimensions has resulted in highly two dimensional structures in modern silicon integrated circuits. New analytical 2D process models for ion implantation and impurity diffusion were developed, and they include detailed considerations of the geometry and ambient effects. An approximate expression is derived to model the 2D diffusion of low concentration impurities under local oxidation conditions, and these models are in the 2D device analyses of several small geometry MOS transistors. A technique developed to measure the surface impurity profiles of laterally diffused regions is applied to a number of test structures to determine the lateral distribution of 2D impurity profiles. Diffusion of boron in the nonoxidized area is enhanced by neighboring oxidized regions and this enhancement is a sensitive function of lateral distance.