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 (CH_xF_yBr_z, SiBr_x after CF₃Br, and CF_x 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 CF_x 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. [ABSTRACT FROM AUTHOR]