Method of making semiconductor devices by forming an impurity adjusted epitaxial layer over out diffused buried layers having different lateral conductivity types
AssigneeU.S. Philips Corporation
InventorPieter J. W. Jochems
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Abstract
A method of manufacturing a semiconductor device is provided in which semiconductor circuit elements are provided in regions formed by diffusion from one or more buried layers into an epitaxial layer. The diffusion is carried out such that a surface layer having substantially the same doping as the original epitaxial layer is left above the diffused into epitaxial layer above the buried layer. The surface layer serves as a reference doping for insulated gate field effect transistors to be formed. This is of a particular importance for threshold voltage determinations in CMOS circuits having adjoining "twin tub" regions diffused from buried layers of opposite conductivity types.
Claims10
A method of manufacturing a semiconductor device comprising the steps of forming at least a first buried layer of a first conductivity type by introducing a dopant into a surface of a semiconductor substrate, growing onto said substrate an epitaxial layer having a lower overall doping in atoms/cm.sup.2 than said buried layer, forming a region of said first conductivity type in said epitaxial layer by diffusion from said buried layer, and providing surface adjoining semiconductor zones of a semiconductor circuit element in said region,
- wherein the improvement comprises the steps of
- limiting said diffusion into said epitaxial layer to form a surface layer of said epitaxial layer having substantially the same doping concentration as the original epitaxial layer, and
- providing at least one insulated gate field effect transistor in said surface layer.
Dependencies are inferred from the claim text.