Fluorine Effects on NMOS Characteristics and DRAM Refresh

Abstract

Abstract-We observed that in chemical vapor deposition (CVD) tungsten silicide (WSix) poly gate scheme, the gate oxide thickness decreases as gate length is reduced, and it intensifies the roll-off properties of transistor. This is because the fluorine diffuses laterally from WSix to the gate sidewall oxide in addition to its vertical diffusion to the gate oxide during gate re-oxidation process. When the channel length is very small, the gate oxide thickness is further reduced due to a relative increase of the lateral diffusion than the vertical diffusion. In DRAM cells where the channel length is extremely small, we found the thinned gate oxide is a main cause of poor retention time.

Effect of fluorine implantation on recovery characteristics of p-channel MOSFET after negative bias temperature instability stress

“…We can see that the slope reduction corresponds with the C ox reduction, which in turn agrees with the increase in t ox , which shows that the implanted fluorine broke the Si-O bond and created free oxygen, which diffused to the interface and reoxidized there. 22,23) Figure 3 shows change of threshold voltage, ¦V th (%) during NBTI stress and successive recovery with a split of temperature as 100, 125, and 150 °C. Device W/O F I/I shows more degradation than those with F I/I in the same stress field and at the same stress time.…”