Study on Influence of O 2 Concentration in Wafer Cleaning Ambient for Smoothness of Silicon (110) Surface Appearing at Sidewall of Three-Dimensional Transistors

We investigated the influence of O 2 concentration in ultra pure water (UPW) on the Si(110) surface roughness during the immersion of Si into UPW. The suppressing of O 2 concentration in UPW is very effective to suppress the increase of microroughness of Si(110) surface. The O 2 concentration in UPW can be controlled by the ambient O 2 concentration. Si(110) surface cannot be roughened when the O 2 concentration is suppressed to less than 100 ppm in ambient (4 ppb in UPW) and the immersion time is less than 1 hour. It can be expected that the Si(110) surface flatness is maintained, and this surface is mainly used for the channel of FinFET. Furthermore, we demonstrated that the O 2 concentration in a prototype 200-mm single-wafer cleaning chamber can be decreased to less than 100 ppm within 1 minute by an N 2 purge of 200 l/min.