FIELD

This disclosure relates to the field of integrated circuits. More particularly, this disclosure relates to extended drain metal oxide semiconductor (MOS) transistors in integrated circuits.

BACKGROUND

Some integrated circuits include extended drain metal oxide semiconductor (MOS) transistors with drains having the same conductivity type as the underlying substrate. The drains must be isolated from the substrate, which involves added process complexity or increased component area, or both. Providing the isolation without degrading the performance and reliability parameters of the transistor, such as on-state current, off-state current, threshold, and hot carrier reliability, has proven to be challenging.

SUMMARY

The present disclosure introduces an integrated circuit including an extended drain metal oxide semiconductor (MOS) transistor, located over a lower layer in a substrate of the integrated circuit. A drain well of the extended drain MOS transistor and the lower layer both have a first conductivity type. The drain well is separated from the lower layer by a drain isolation well having a second conductivity type, opposite from the first conductivity type. A source region of the extended drain MOS transistor is separated from the lower layer by a body well having the second conductivity type. Both the drain isolation well and the body well contact the lower layer. An average dopant density of the second conductivity type in the drain isolation well is less than an average dopant density of the second conductivity type in the body well.

