High density fluorocarbon plasma etching of methylsilsesquioxane SiOC(H) low-k material and SiC(H) etch stop layer: surface analyses and investigation of etch mechanisms

Abstract

This paper focuses on plasma etching and XPS surface analyses of new dielectric materials used in integrated circuits. We investigate by XPS surface modifications of methylsilsesquioxane low-k polymer (SiOC(H)) and amorphous hydrogenated silicon carbide (SiC(H)) when exposed to Ar, SF6 and C2F6-based high density plasmas. Ar and SF6 plasmas remove the carbonaceous groups from the surface leading to the formation of fluorinated top layers (SiOF and SiF-like layers) in SF6 plasma. In the case of C2F6-based mixtures, the surface structure fits well with a two-layer model, consisting of a fluorocarbon top layer above a fluorinated interaction layer (SiOF or SiF) on the bulk materials (SiOC(H) or SiC(H)). Determination of top layer thicknesses from XPS data is discussed. We show that material etch rate is not correlated with the total modified thickness, in contrast to the top fluorocarbon layer thickness which is in good correlation with etch rates. Etch yields (etch rates divided by the ion flux) are calculated and are studied in order to draw material etch mechanisms in C2F6 based mixtures. We conclude that for both materials, etching mechanisms in C2F6/H2 mixtures, and to a lesser extent in C2F6/Ar mixtures, are close to those of silicon in fluorocarbon plasmas and different from those of the conventional interlevel dielectric material SiO2. On the contrary etching mechanisms in C2F6/O2 mixtures are similar to those of silicon dioxide in fluorocarbon plasmas.