Roles of F and O radicals and positive ions in a SF 6/0 2 plasma in forming deep via structures

Abstract

The roles of F and O radicals and of various positive ions in forming very high-aspect-ratio anisotropic via structures from Si have been investigated in SF 6/O 2 plasma with the help of analytical techniques using optical emission spectroscopy and X-ray photoelectron spectroscopy. The formation of the sidewall passivation layer was found to be greatly affected by both the horizontal and the vertical etching properties as a limited amount of F radicals was available inside deep via structures. Furthermore, an excessive amount of O radicals in the SF 6/O 2 plasma enhanced the formation of unwanted passivation layers on the bottoms of the vias. We also found that positive ions in the SF 6/O 2 plasma, e.g., SF x +, F + and 0 +, were likely to be responsible for horizontal etching.