Method of fabricating isolated semiconductor devices in epi-less substrate
View Patent ↗An structure for electrically isolating a semiconductor device is formed by implanting dopant into a semiconductor substrate that does not include an epitaxial layer. Following the implant the structure is exposed to a very limited thermal budget so that dopant does not diffuse significantly. As a result, the dimensions of the isolation structure are limited and defined, thereby allowing a higher packing density than obtainable using conventional processes which include the growth of an epitaxial layer and diffusion of the dopants. In one group of embodiments, the isolation structure includes a deep layer and a sidewall which together form a cup-shaped structure surrounding an enclosed region in which the isolated semiconductor device may be formed. The sidewalls may be formed by a series of pulsed implants at different energies, thereby creating a stack of overlapping implanted regions.
1. A process of fabricating a semiconductor device comprising:
providing a semiconductor substrate of a first conductivity type, the substrate not containing an epitaxial layer;
forming a first mask on a surface of the substrate, said first mask having a first opening, said first opening having a first lateral dimension;
implanting a dopant of a second conductivity type through the first opening to form a first deep layer;
forming a second mask on the surface of the substrate, said second mask having a second opening, said second opening having a second lateral dimension, said second lateral dimension being entirely enclosed within said first lateral dimension; and
implanting dopant of the first conductivity type through the second opening to form a second deep layer, said second deep layer being laterally constrained within said first deep layer,
wherein the straggle of the implant of dopant of the first conductivity type is greater than the straggle of the implant of dopant of the second conductivity type such that the second deep layer overlaps and extends above and below the first deep layer and upper boundaries of said first and second deep layers are located below said surface of said substrate.
2. The process of claim 1 wherein the dopant of the first conductivity type comprises boron and the dopant of the second conductivity type comprises phosphorus.
3. The process of claim 2 wherein the implants of said dopants of the first and second conductivity types have approximately the same range.
4. The process of claim 3 wherein the dose of the dopant of the first conductivity type is lower than the dose of the dopant of the second conductivity type.