Ultrapure Water-Related Problems and Waterless Cleaning Challenges

Abstract

Ultrapure water can cause several serious problems in modern semiconductor manufacturing. With device geometry shrinking and becoming more complex, conventional aqueous cleaning and subsequent drying tends to collapse high aspect-ratio nano-structures due to the high surface tension of water. The high resistivity of water can cause flow electrification during wafer rinsing and the high reactivity of water with oxygen and silicon forms watermarks on silicon surfaces. Furthermore, in the FEOL, some high-k gate capping materials dissolve in water while, in the BEOL, Cu is corroded in water during rinsing. If high-permittivity water remains in porous low-k interlayers after aqueous treatments, the k-value of the film increases. The solutions to all of these problems will be discussed. Finally, as the ultimate solutions, waterless cleaning techniques are described and discussed, which include HF vapor cleaning, cryogenic nitrogen aerosol cleaning, supercritical carbon-dioxide cleaning, and pinpoint cleaning such as nano-tweezer pickup.