Deep trench etching in silicon with fluorine containing plasmas

Single crystal silicon was etched with mixtures of SF6, CBrF3, Ar and O2, using different electrode materials to obtain deep trenches. The etch rates, both vertically and horizontally increase when the relative flow of SF6 increases. When using aluminium or stainless steel electrodes, the amount of SF6 has to be limited to 10% of the total flow of fluorine containing gases to obtain wall profiles with an angle of over 80°. However, in all these cases considerable surface roughness is observed. A solution to this problem is the use of a graphite electrode, which permits the use of SF6 as the sole halogen containing gas to obtain vertical walls. Depending on the Ar addition, processes with good anisotropy and without surface roughness can be obtained.