Device with patterned wells and method for forming same

A bipolar transistor comprising:

• a semiconductor substrate having top and bottom surfaces;
• a collector well diffused region in the substrate extending from the top surface into the substrate a first depth and having a first surface perimeter defined by a first length and a first width;
• a base diffused region in the substrate and overlapping the collector well diffused region, said base diffused region extending from the top surface into the substrate a second depth and having a second surface perimeter defined by a second length and a second width wherein the length of the base diffused region is enclosed by the well diffused region and the width of the base diffused region is about equal to or greater than the width of the collector well diffused region;
• and
• an emitter diffused region disposed with and surrounded by the based diffused region;
• wherein the collector well diffused region and the base diffused region each has a doping concentration that decreases with depth and with proximity to the respective perimeters, and the doping concentration of the collector well diffused region at the surface intersection of the junction between the collector well diffused region and the corners of the base diffused region is less than the maximum doping concentration of the collector well diffused region at locations of the collector well region that overlap the base diffused region.

In an improved integrated circuit having two or more semiconductor devices electrically isolated from each other, the improvement comprising:

• at least one bipolar transistor comprising:
• a semiconductor substrate having top and bottom surfaces;
• a collector well diffused region in said substrate extending from said top surface into the substrate a first depth and having a first surface perimeter defined by a first length and a first width;
• a base diffused region in said substrate and overlapping said collector well diffused region, said base diffused region extending from said top surface into said substrate a second depth and having a second surface perimeter defined by a second length and a second width, wherein the length of said base diffused region is enclosed by said collector well diffused region and the width of said base diffused region is about equal to or greater than the width of said collector well diffused region;
• and
• an emitter diffused region diffused with and surrounded by said base diffused region;
• wherein said collector well diffused region and said base diffused region each has a doping concentration that decreases with depth and with proximity to the respective perimeters, and the doping concentration of said collector well diffused region at the surface intersection of the junction between said collector well diffused region and the corners of said base diffused region is less than the maximum doping concentration of said collector well diffused region at locations of said collector well region that overlap said base diffused region.

In an improved integrated circuit having two or more semiconductor devices electronically isolated from each other, the improvement comprising:

• at least one semiconductor device comprising a substrate having top and bottom surfaces;
• a collector well diffused region in the substrate having a first surface perimeter and extending from the top surface into the substrate to variable depths such that a plurality of shallower portions are formed between adjacent deeper portions;
• a base diffused region in the substrate, said base diffused region extending from the top surface into the substrate a second depth and having a second surface perimeter lying entirely within said first surface perimeter;
• an emitter diffused region disposed with and surrounded by the base diffused region;
• and
• a collector contact diffusion spaced from the base diffused region and extending from the top surface of the substrate into the collector well diffused region.