Influence of Al Surface Modification on Selectivity in Via-Hole Etching Employing CHF3 Plasma

The Al etching characteristics in CHF3 plasma have been studied. The etching rate increased drastically with decreasing pressure. Analysis of the surface exposed to CHF3 plasma revealed that the Al surface was not covered with a fluorocarbon film, but was fluorinated. It has become evident that Al fluoride is sputtered much faster than Al. That is, fluorination of the surface results in the high etching rate of Al in a CHF3 plasma. Furthermore, the surface analyses of Si, Al, W and Ni exposed to CHF3 plasma made it clear that fluorocarbon films are formed on the materials whose etching products have high vapor pressure, and are not formed on the materials whose vapor pressure for the etching products is very low. The continuous fluorine consumption which is caused by evaporation of etching products through the fluorocarbon film, leads to formation of fluorocarbon film.