Superjunction structures for power devices and methods of manufacture

A power device comprising:

• a first N-type epitaxial layer disposed on a substrate;
• a second N-type epitaxial layer disposed on the first N-type epitaxial layer;
• a first trench extending through the second N-type epitaxial layer and terminating within the first N-type epitaxial layer;
• a second trench extending through the second N-type epitaxial layer and terminating within the first N-type epitaxial layer;
• and
• a mesa disposed between the first trench and the second trench, the mesa defining an N-type pillar from the first N-type epitaxial layer and the second N-type epitaxial layer,
• the first trench including a first P-type pillar,
• the second trench including a second P-type pillar,
• the first P-type pillar and the second P-type pillar forming pillars of alternating conductivity type with the N-type pillar,
• each P-type pillar including:
• a first trench epitaxial layer disposed on a trench sidewall and a trench bottom surface;
• and
• a second trench epitaxial layer disposed on the first trench epitaxial layer, the first trench epitaxial layer including an N-type epitaxial layer having a doping concentration that is lower than a doping concentration of the second trench epitaxial layer, the second trench epitaxial layer including a P-type epitaxial layer.

A power device comprising:

• a first N-type epitaxial layer disposed on a substrate;
• a second N-type epitaxial layer disposed on the first N-type epitaxial layer;
• a first trench extending through the second N-type epitaxial layer and terminating within the first N-type epitaxial layer;
• a second trench extending through the second N-type epitaxial layer and terminating within the first N-type epitaxial layer;
• and
• a mesa disposed between the first trench and the second trench, the mesa defining an N-type pillar from the first N-type epitaxial layer and the second N-type epitaxial layer,
• the first trench including a first P-type pillar,
• the second trench including a second P-type pillar,
• the first P-type pillar and the second P-type pillar forming pillars of alternating conductivity type with the N-type pillar, and
• the N-type pillar including an upper N-region, a middle N-region and a lower N-region, the upper N-region having a doping concentration that is lower than a doping concentration of the middle N-region, and the doping concentration of the middle N-region being lower than a doping concentration of the lower N-region.