Analysis of an ONO gate film effect on n- and p-MOSFET mobilities

The effect of the nitrogen atoms in the gate oxide and why gate oxide nitridation acts oppositely on the n- and p-MOSFET mobilities were studied. It was found that the mobility changes for the oxide/nitride/oxide (ONO) gate MOSFETs are not caused by the high-temperature process during the rapid thermal process (RTP), but rather are caused by the involvement of the nitrogen atoms in the gate oxide. The interfacial structures were observed by TEM. Although some interfacial structure difference was observed, there was no major difference in surface roughness between `PO' and `NO' samples. The opposite effect of the ONO gate films on the n- and p-MOSFET mobilities cannot be explained completely by a donor layer formation by the nitrogen diffusion into the substrate. The effect might be explained by the residual mechanical stress caused by the involvement of the nitrogen atoms in the gate oxide