Impact of nitrogen implantation into polysilicon followed by drive-in process on gate oxide integrity

A nitridation technique involving shallow implantation of nitrogen into the polysilicon gate followed by thermal drive-in process was studied. Success ful incorporation of nitrogen into the gate oxide/polysilicon interface has been achieved; and thereby the reliability of gate oxide has been improved due to the reduced boron diffusion into the gate oxide in p(+) polysilicon gate metal oxide semiconductor devices. An amount of nitrogen segregated i n the oxide was found to be independent of the nitrogen implantation dose b ut to depend only on the drive-in thermal budget. Therefore, a high thermal budget in the drive-in process with a low nitrogen implantation dose is a promising direction for this process to have a high nitrogen concentration in the oxide and a low nitrogen concentration in the polysilicon to avoid a serious poly-depletion problem. However, it also has been found that when the amount of nitrogen incorporation in the oxide exceeds a certain limit, gate oxide reliability is degraded due to enhanced electron trapping. (C) 1 999 The Electrochemical Society. S0013-4651(99)01-055-1. All rights reserve d.