Abstract An integrated circuit having a substrate of a first conductivity type, a first layer of opposite conductivity type thereon and a second layer of said first conductivity type inversely graded on said first layer and including a heavily doped region adjacent the surface opposite said first layer. A ring of said opposite conductivity type extends through said second layer and partially into said first layer and a diffused region of said opposite conductivity type is in the surface of said second layer. The method of fabrication includes epitaxially forming said first layer on said substrate, expitaxially forming said second layer on said first layer having a decreasing impurity concentration from the P-N junction to the surface, forming said ring, nonselectively diffusing to increase the impurity concentration at the area adjacent the surface of said second layer and selectively diffusing to form said diffused surface region.
A method of fabricating an integrated circuit comprising: epitaxially forming on a substrate of a first conductivity type, a first layer of opposite conductivity type; epitaxially forming on said first layer a graded second layer of said first conductivity type of decreasing impurity concentration; forming a ring of said opposite conductivity type through said second layer and partially into said first layer; nonselectively diffusing impurities of said first conductivity type into the surface of said second layer; and selectively diffusing impurities of said opposite conductivity type into said second layer to form a surface region within said ring.
Claim 2
Independent Claim
98 words
A method of fabricating an integrated circuit comprising: epitaxially forming on a substrate of a first conductivity type, a first layer of opposite conductivity type; epitaxially forming on said first layer a graded second layer of said first conductivity type of decreasing impurity concentration; forming a ring of said opposite conductivity type through said second layer and partially into said first layer; nonselectively diffusing impurities of said first conductivity type into the surface of said second layer; and selectively diffusing impurities of said opposite conductivity type into said second layer to form a surface region within said ring.
Claim 3
Dependent Claim
49 words
The method of claim 1 wherein said second epitaxial step is performed to produce a substantially linear gradient from approximately 5 × 10 15 atoms per cubic centimeter at the boundary with said first layer to approximately 1 × 10 15 atoms per cubic centimeter at its opposite surface.
Claim 4
Dependent Claim
18 words
The method of claim 2 wherein said second epitaxial step is performed in a plurality of discrete steps.
Claim 5
Dependent Claim
17 words
The method of claim 2 wherein said second epitaxial step is performed using continuously varying impurity concentration.
Claim 6
Dependent Claim
31 words
The method of claim 2 wherein said nonselective diffusion is performed to produce a surface area having impurities in the range of 10 18 to 10 19 atoms per cubic centimeter.
Claim 7
Dependent Claim
40 words
The method of claim 1 wherein said first epitaxial layer has an impurity concentration less than said substrate and greater than said second epitaxial layer and said ring and surface region have impurity concentration greater than said first epitaxial layer.