(The) effect of hydrogen and fluoring in the $Si-SiO_2$ system and Si surface

Abstract

The effects of hydrogen plasma exposure on the characteristics of Metal Oxide Semiconductor(MOS) devices have been studied. The hydrogen plasma was generated by Remote Plasma CVD system to reduce the plasma damage. Helium Plasma was exposed to the MOS device to compare with the hydrogen plasma. The helium plasma give rise to parallel threshold voltage shift, and no changes in maximum transconductance and subthreshold slope, while the hydrogen plasma degrades the maximum transconductance and make subthreshold swing increase in n-channel MOSFET. These results indicate that the interface traps are generated by the diffusion of excess atomic hydrogen. But at temperatures above $400^\circ C$, nearly no hydrogenation effects was observed. Also, these effects were confirmed by quasi-static capacitance-voltage(C-V) analysis. After excess atomic hydrogen diffusion, the defect level of $E_\nu+0.3eV$ and $E_\nu+0.8eV$ in the silicon band gap were observed. These defect levels are known as the silicon dangling bond which act as amphoteric depending on the charge state. And the decrease of interface trap density near the band edge was observed after atomic hydrogen diffusion. A model is proposed to explain these experimental results and possible interpretation is discussed on the basis of our results as well as others. Also, the effect of fluorine on the Si-SiO$_2$ interfaces have been investigated. The fluorine is introduced by the ion implantation after polysilicon deposition. The fluorinated oxide shows a hot carrier injection hardness which is explained by the bond strain gradient (BSG) relaxation. Combinational effects of fluorinated and PDSN (Planma Deposited Silicon Nitride) passivation layer on the device parameter also have been studied. The hydregenation effect for the fluorinated device was investigated. A possible mechanism of interface trap generation and annealing is proposed based on these experimental results.