Avalanche-protected transistors using a bottom breakdown current path and methods of forming the same

A method of forming a field effect transistor, the method comprising:

• providing a semiconductor substrate containing a body semiconductor layer having a doping of a first conductivity type;
• forming a buried first-conductivity-type well within the semiconductor substrate;
• forming a source region and a drain region in an upper portion of the semiconductor substrate, wherein the source region and the drain region have a doping of a second conductivity type that is an opposite of the first conductivity type, and are laterally spaced apart from each other by a channel region, and wherein the buried first-conductivity-type well underlies, and has an areal overlap with, the drain region, is vertically spaced apart from the drain region, and has a higher atomic concentration of dopants of the first conductivity type than the body semiconductor layer;
• forming a doped body contact region in the upper portion of the semiconductor substrate, wherein the doped body contact region has a doping of the first conductivity type, and is spaced from the source region;
• and
• forming a source-side first-conductivity-type well within the semiconductor substrate, wherein the source-side first-conductivity-type well is in direct contact with the source region and has a higher atomic concentration of dopants of the first conductivity type than the body semiconductor layer.

A method of forming a semiconductor structure, comprising:

• providing a semiconductor substrate containing a body semiconductor layer having a doping of a first conductivity type;
• forming a buried first-conductivity-type well within the semiconductor substrate;
• forming a source region and a drain region in an upper portion of the semiconductor substrate, wherein the source region and the drain region have a doping of a second conductivity type that is an opposite of the first conductivity type, and are laterally spaced apart from each other by a channel region;
• forming a doped body contact region in the upper portion of the semiconductor substrate, wherein the doped body contact region has a doping of the first conductivity type, and is spaced from the source region;
• and
• forming a source-side first-conductivity-type well within the semiconductor substrate, wherein the source-side first-conductivity-type well is in direct contact with the source region to provide a first p-n junction having a periphery located entirely within a top surface of the semiconductor substrate, in direct contact with the body semiconductor layer along an interface that extends from the top surface of the semiconductor substrate to a top surface of the buried first-conductivity-type well, and having a higher atomic concentration of dopants of the first conductivity type than the body semiconductor layer.