Effects of N2 addition on aluminum alloy etching in inductively coupled plasma source

Addition of N-2 to the plasma activated with Cl-2, BCl3, or their mixtures in an inductively coupled plasma source induces drastic changes in the plasma state. These N-2-related changes in the plasma state sometimes result in abnormal phenomena in aluminum alloy etching, like the wave-like fringes on the sidewalls of patterned metal lines. Optical emission spectroscopy revealed that admixing small amounts of N-2 to the plasma activated with Cl-2, BCl3, or their mixtures generally expedites dissociation processes to increase the density of Cl* radicals within it. On the other hand, N2 addition also accelerates the formation of passivation polymers via carbon species sputtered from patterned photo-resists. The polymers adhere to the sidewalls of patterned metal lines and protect them against the lateral attacks of deflected etchants such as Cl* radicals. Our studies tell that the relative abundance of Cl* radicals within the plasma over the passivation polymers, which is controlled by the amount of N-2 addition, seems to be a critical factor in determining the occurrence of the wave-like fringes on the sidewalls of patterned metal lines.