Process for N-well and P-well creation on a silicon substrate using a blanket P-well implant and no N-well steam oxidation step

摘要

An improved process for N-well and P-well creation on a silicon substrate (12). Like the convention process, the improved process begins with the thermal growth of a pad oxide layer (11) on top of the substrate (12). A blanket (unmasked) boron P-well implant creates a boron-bearing P-type layer of substrate (21). Future P-well regions are then masked with photoresist (22). Pad oxide that is not subjacent the photoresist (22) is etched away, as is a portion of the boron-bearing layer (21) beneath the etched pad oxide. These recessed regions, which will become the N-well regions, are then subjected to a phosphorus implant which creates N-well (23). The concentration of the phosphorus implant is high enough to overwhelm any remaining boron atoms in N-well region (23). Following a photoresist strip, a high-temperature drive step in an oxygen ambient is performed, extending the depth of both well regions and creating a thermal oxide layer (24) on top of both P-type layer region (21) and N-well region (23). Growth of the thermal oxide layer (24) heals any imperfections in the silicon crystal structure that were sustained during the silicon etch. The thermal oxide layer (24) is then stripped and a gate oxide layer (25) is grown. This invention significantly reduces the number of steps required to create N-well and P-well regions on a silicon substrate by eliminating the need for a nitride deposition step and a steam oxidation step, both of which are utilized by the conventional process.