Incorporation of chlorine during chlorine reactive ion beam etching of aluminum–copper alloys

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Abstract
Reactive ion etching of aluminum–copper thin films, used for interconnects on semiconductor devices, is complicated by implantation of reactive gases in the film during etching. Incorporation of chlorine in aluminum–copper thin films during reactive ion beam etching with chlorine ions was studied. Unannealed thin films of aluminum-4% copper alloys were etched with 500 and 1000 eV chlorine ions at current densities that ranged from 0.01 to 0.5 mA/cm2. Copper, oxygen, and chlorine concentrations as a function of position were determined using Auger sputter depth profiling, scanning electron microscopy with x-ray fluorescence spectroscopy and Rutherford backscattering spectroscopy. The amount of chlorine incorporated in the film was measured as a function of ion energy, current density, and angle of incidence. If chlorine was not removed from the near surface layer before exposure to air, numerous mounds formed on about 30% of the surface; these were composed primarily of aluminum, oxygen, and chlorine. The chlorine was observed to be completely confined to these mounds and the oxide layer that forms on the surface of the film after etching and upon contact to air. Implications for developing reactive ion etching techniques in which no chlorine remains in the near surface layer will be discussed.

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