Varactor structure and method

A method for forming a varactor diode, comprising:

• providing a semiconductor substrate having an outer surface, then in any order:
• forming a first doped region of a first conductivity type beneath the surface, having a first peak dopant concentration located a first distance beneath the surface;
• forming a second doped region of a second, opposite, conductivity type beneath the surface, having a second peak dopant concentration located a second distance beneath the surface;
• and
• forming a third doped region of the second, opposite, conductivity type at or beneath the surface, having a third peak dopant concentration such that the second doped region forms a retrograde doping profile extending away from the third doped region at least partly toward the first doped region.

A method for forming a varactor, comprising:

• providing a substrate having an outer surface, then in any order:
• forming a first N-type doped region in the substrate having a first peak doping concentration located a first distance beneath the surface;
• forming a second N-type doped region in the substrate having a second peak dopant concentration located a second distance beneath the surface less than the first distance;
• forming a third P-type doped region in the substrate having a third peak dopant concentration located a third distance beneath the surface less than the second distance;
• and
• forming a fourth P-type doped region having a fourth peak dopant concentration greater than the third peak dopant concentration and closer to the surface than the third distance.