A retrograde p-well for higher density CMOS

A new technique for CMOS p-well (or n-well) formation is described, making use of a deep implant followed by a brief anneal. This results in a retrograde profile, permitting a much shallower well, a large reduction in p-n channel device spacing (5-6 µm versus 10-15 µm), and an opportunity to reduce the risk of latch-up. This technique is more conducive to scaling-with the promise of significantly better performance-than conventional well formation methods. The retrograde p-well has been successfully applied to a linearly shrunk bulk CMOS 4K static RAM, demonstrating its feasibility.