Analysis of sidewall cleans relating to titanium salicide filaments

An empirical correlation was reported of the occurrence of titanium salicide sidewall filaments to the type of wafer cleans that are used prior to titanium deposition, particularly those cleans that follow the etching of the sidewall spacers on the polysilicon gate. This paper demonstrates that the occurrence of the filaments favors a high ratio of polysilicon area to perimeter and/or a low ratio of sidewall nitride to oxide area. The surface concentration of aluminum is reduced by changing the sidewall cleans from room temperature SC-1 to a combination of piranha and hot SC-1, based on ToF SIMS analysis. However, etch rates on test wafers do not support aluminum as being the root cause of the filaments. Alternately, the behavior of the filaments partially can be correlated to the concentrations of chlorine or fluorine.