Technique for forming an oxide/nitride layer stack by controlling the nitrogen ion concentration in a nitridation plasma

Abstract

For aggressively scaled field effect transistors, nitrogen is incorporated into a base oxide layer, wherein, at an initial phase of a plasma nitridation process, the nitrogen ion density is maintained at a value so that incorporation of nitrogen into the channel region is minimized. Subsequently, when the thickness of the base oxide layer has increased, due to residual oxygen in the plasma ambient, the nitrogen ion density is increased, thereby increasing the nitridation rate. Preferably, the nitrogen ion density is controlled by varying the pressure of the plasma ambient. Moreover, a system is disclosed that allows control of the nitridation rate in response to an oxide layer thickness.