Low Damage Cryogenic Etching of Porous Organosilicate Low-k Materials Using SF6/O2/SiF4

Abstract

Low temperature plasma etching of porous organosilicate low-k films is studied, in an ICP chamber with cryo-cooled substrate holder, using Fluorine-based plasma discharges. It is demonstrated that plasma-induced damage is significantly reduced when the base temperature is below a threshold Tc that depends on pore size of low-k materials. For T < Tc, almost no carbon depletion is observed and the k-value degradation is negligible. It is shown that protection occurs mainly through the condensation of the etch by-products and their ability to seal the open pores against radical diffusion. By addition of SiF4 and O2 into the gas discharge, plasma-induced damage is further reduced, as a result of SiOxFy deposition. Vertical trench profiles are obtained in patterned structures, using an inorganic hard mask. The damage reduction mechanism is discussed and a protection model is proposed.