Cryogenic etching of porous low-k dielectrics in CF3Br and CF4 plasmas
Low temperature etching of organosilicate low-k dielectrics in CF3Br and CF4 plasmas is studied. The chemical composition of pristine and etched low-k films was measured by Fourier transform infrared spectroscopy. Reduction of plasma-induced damage at low process temperature is observed. It is shown that the plasma damage reduction is related to protective effects of accumulated reaction products (CHxFyBrz, SiBrx after CF3Br, and CFx polymers after CF4 plasma). The reaction products could then be removed by thermal annealing for the pores to become empty. In the case of CF4 plasma, the thickness of CFx polymer increases with the temperature reduction, which is measured by ellipsometry. This polymer layer leads to a strong decrease in the diffusion rate of fluorine atoms and, as a consequence, to reduction of plasma-induced damage. Bromine containing reaction products are less efficient for low-k surface protection against the plasma damage.
