Method of forming and etching a resist protect oxide layer including end-point etch

Abstract

The present invention provides a method for forming and etching a resist protect oxide layer, of which provides improved etch selectivity to a shallow trench isolation and an increased pre-metal dip processing window. The process begins by forming a shallow trench isolation on a semiconductor substrate. The semiconductor substrate has a first area and a second area separated by the shallow trench isolation. A gate is formed on the semiconductor substrate in the first area, adjacent to the shallow trench isolation. In a key step, a resist protect oxide layer comprising a thin silicon oxide layer and an overlying thin nitrogen containing layer, is deposited over the semiconductor substrate, the gate, and the shallow trench isolation. The thin nitrogen containing layer can be composed of silicon nitride or silicon oxynitride. Alternatively, if the notrogen containing layer is composed of silicon oxynitride, the oxide layer can be omitted because oxynitride's stress is less than nitrogen, so the oxynitride could use a native oxide layer as the buffer oxide. The resist protect oxide layer is patterned in an RPO etch step; thereby exposing the first area, including the source and drain regions. A key advantage of the invention is that the RPO etch step can be performed in an endpoint mode where the endpoint is detected by the nitrogen content of the etch chamber ambient. Silicide regions can then be formed on the source and drain regions. A second key advantage of the invention is that the nitrogen containing layer of the resist protect oxide layer has a slower etch rate during pre-metal dip than a resist protect oxide layer composed of only oxide.