Reverse short and narrow channel effects in n and p transistors: quantification of the enhanced diffusion and the gate oxide thickness increase

Abstract

The threshold voltage (VT) of CMOS 6 IBM technology n and p transistors function of their length L was investigated. A reverse short channel effect (RSCE) was observed simultaneously on the n inverted and p buried channel transistors, i.e. a VT n( L) increase and a correlated VT p( L) decrease when L was decreased. The same effect was observed for narrower channels. After correction of the standard short channel effect, the correlation between VT n( L) and VT p( L) was explained by two components: first a boron oxidation enhanced diffusion in the channel during the sidewall polysilicon gate oxidation; second, an increase of the gate oxide electrical thickness inversely proportional to the gate conductor width. This thickness increase was interpreted as due to a contaminant diffusion from the gate stack sidewall during the sidewall oxidation, either oxygen producing a physical thickness increase, or fluorine reducing the oxide dielectric constant.