Method of forming self-aligned planarization twin-well by using fewer mask counts for cmos transistors

Abstract

The present invention discloses a method of forming CMOS transistors with self-aligned planarization twin-well by using fewer mask counts. After a silicon nitride layer is formed over a first pad oxide layer on a semiconductor substrate, an N-well region is defined by first implanting in the semiconductor substrate. After removing the first photoresist layer, a second ion implantation is performed to define a P-well region. Next, both the silicon nitride layer and the first pad oxide layer are removed. A high temperature long time anneal is done to form a deep twin-well. A plurality of LPD oxide trench isolation regions is formed to define an active area region. A second pad oxide layer is formed on the substrate. Finally, the standard processes can be employed for fabricating the CMOS transistors on the substrate.