Study of forming a p+ poly-Si gate by inductively coupled nitrogen plasma nitridation of the stacked poly-Si layers

Abstract

Formation of a p+ poly-Si gate by using the stacked poly-Si layers that are nitridized by using inductively coupled nitrogen plasma (ICNP) has been studied. The stacked poly-Si gate structure consists of three poly-Si layers with thickness of 50, 50, and 100 nm, respectively. As for the control samples that do not receive nitrogen plasma nitridation, when they are annealed at 900 °C, the gate oxide integrity is significantly degraded and the flat-band voltage (Vfb) shift is large, attributable to considerable boron penetration through gate oxide. If the ICNP treatment is directly done with respect to the gate oxide layer, the Vfb shift can be considerably reduced, but the resultant gate oxide integrity is even much worse than that for the control samples. However, for the specimens that sustain ICNP treatment immediately after the deposition of the first poly-Si layer, the degradation of gate oxide integrity and the Vfb shift are significantly alleviated even at 900 °C. Hence, the process scheme that employs the stacked poly-Si gate nitridized by the ICNP treatment is highly available for forming a p+ poly-Si gate.