Fabrication of insulated gate bipolar devices

A method of making a semiconductor device of a type that includes an insulated gate bipolar transistor formed on a semiconductor substrate having dopant of a first conductivity type, the method comprising:

• implanting an upper zone of the substrate with dopant of a second conductivity type;
• growing an epitaxial layer with dopant of the second conductivity type over the semiconductor substrate, the epitaxial layer having an upper zone with a doping concentration less than a doping concentration of the upper zone of the substrate;
• and
• diffusing dopant of the second conductivity type from the upper zone of the substrate into a lower zone of the epitaxial layer, the lower zone of the epitaxial layer having a doping concentration greater than the doping concentration of the upper zone of the epitaxial layer and less than the doping concentration of the upper zone of the substrate.

A method of making a semiconductor device of a type that includes an insulated gate bipolar transistor on a semiconductor substrate having a dopant of a first conductivity type, the method comprising:

• growing a first epitaxial layer having dopant of a second conductivity type over the semiconductor substrate, the first epitaxial layer having a first doping concentration;
• growing a second epitaxial layer having dopant of the second conductivity type over the first epitaxial layer, the second epitaxial layer having a second doping concentration less than the first doping concentration;
• and
• diffusing dopant of the second conductivity type from the first epitaxial layer to a zone between the first and the second epitaxial layers, the zone having a doping concentration between the first and second doping concentrations.

A method of making a semiconductor device of a type that includes an insulated gate bipolar transistor on a semiconductor substrate having dopant of a first conductivity type, the method comprising:

• implanting an upper zone of the substrate with dopant of a second conductivity type;
• growing a first epitaxial layer having dopant of the second conductivity type over the semiconductor substrate, the first epitaxial layer having a first doping concentration;
• growing a second epitaxial layer having dopant of the second conductivity type over the first epitaxial layer, the second epitaxial layer having a second doping concentration less than the first doping concentration;
• and
• diffusing dopant of the second conductivity type from the upper zone of the substrate to a lower zone of the first epitaxial layer, the lower zone of the first epitaxial layer having a doping concentration greater than the first doping concentration in an upper zone of the first epitaxial layer.