Method for fabricating a multilayer epitaxial structure

摘要

An all epitaxial process performed entirely in a CVD reactor is employed to grow heavily doped layer on lightly doped layer on a heavily doped substrate, eliminating the need for separate diffusion, even for high impurity concentrations. The process starts with a heavily doped silicon substrate of carrier concentration typically greater than 1x1019 per cm3. To minimize outdiffusion, the substrate is "capped" by growing very thin and heavily doped silicon layers which are depleted by hydrogen purges. A first epitaxial layer is grown over the "capped" substrate. This layer is relatively lightly doped, having a resistivity of more than 200 ohm.cm. A second epitaxial layer is then grown over the first epitaxial layer. The second epitaxial layer has a polarity opposite to that of the substrate and is heavily doped to a resistivity of less than 0.005 ohm cm.