Effects of N2 Addition on Aluminum Alloy Etching in Inductively Coupled Plasma Source

Abstract

Addition of N2 to the plasma activated with Cl2, BCl3, or their mixtures in an inductively coupled plasma source induces drastic changes in the plasma state. These N2-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 N2 to the plasma activated with Cl2, 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 N2 addition, seems to be a critical factor in determining the occurrence of the wave-like fringes on the sidewalls of patterned metal lines.