Abstract
In this thesis, high density plasma induced charging damage on submicron MOSFETs reliability is studied. First of all, the effects of gate oxide scaling on charging damage are investigated. Next, the possibility of reducing plasma charging damage by process optimization has been discussed. In chapter 3, effects of gate oxide scaling on the plasma charging damage are investigated. F-N tunneling, direct tunneling reliability and hot carrier reliability were studied and these techniques were employed to characterize the devices. We found that the tunneling properties of ultra-thin oxides have changed dramatically. The consequence is that the mechanisms of plasma charging, F-N, direct tunneling current stressing and hot carrier injection have also changed. The electrical characteristics of MOSFETs are greatly improved as the gate oxide continues to scale down. However, the large gate leakage current is still a big problem. Antenna-structure-sensitive charging effects have also been investigated. Only the correlation between antenna peripheral length and hot carrier reliability was found. After that, the characterization of F-N, direct tunneling reliability and hot carrier reliability was performed. It was shown that as the length of antenna structure is increased, the F-N and direct tunneling current stressing induced Gm, Vth and Idsat degradation increased, too. And then it’s shown that F-N and direct tunneling current stressing induced degradation is less for thinner oxides. However, the 25A gate oxide still can not avoid to be damaged by plasma charging effect. On the other hand, the LDD structure was found to greatly improve the hot carrier reliability. And next the F-N, direct tunneling current stressing and hot carrier stressing techniques are also compared. We suggest that F-N and direct tunneling current stressing technique are employed first to reveal the minor charging damage. And then the hot carrier stressing is used to simulate the charging effects on real device operation. Finally, the issue of plasma non-uniformity induced reliability degradation has been discussed. We conclude that the charging damage due to positive charging affects the hot carrier reliability minimally. An inverse argument was made that the negative charging affects the hot carrier reliability severely. In chapter 4 the possibility of reducing plasma charging damage by process optimization was discussed. The F-N stressing induced Gm and Idsat degradation is alleviated by N2O RTN process. This improvement could be attributed to the nitrogen piled-up at the Si/SiO2 interface and repaired unperfected Si bonds with robust Si-N bonds. The location dependent charging damage has also been suppressed using N2O RTN process. Finally, the charging model during the overetching stage is discussed. It is shown that if the overetching percentage was reduced from 40% to 25%, the hot carrier stressing induced Gm degradation and Vth shift of antenna devices could be lowered. Besides, the TCP etcher still performs well even with such a high overetching percentage ( 50% ). These results are consistent with our earlier reports.