TAPERED ALUMINUM INTERCONNECT ETCH

Tapered etching of the aluminum interconnects can assist in planarizat ion of multilevel interconnects by improving step coverage of chemical vapor deposited oxides in tightly spaced arrays. Previously published results have shown that a tapered aluminum profile is formed by addin g small amounts of hydrocarbon gases to Cl2-based etch chemistries [Co burn, Winters, and Chung, J. Appl. Phys. 48, 3532 (1977)]. This proces s relies on the formation of a relatively thick polymer sidewall to ac hieve the tapered profile. While this mechanism is effective, it can b e hard to remove the polymer after etch. A tapered profile was achieve d in a transformer coupled plasma etcher using only additions of N2. T he polymer sidewall formed during the etch was easily removed with the remaining photoresist. Measurements of the metal lines after etch and cross sections with the resist intact showed that the top dimension o f the line was unchanged by the etch while the base of the line was la rger than the base of the photoresist. Even though etch rate results s how a loss of photoresist selectivity, cross sections show no loss in linewidth of the top of the resulting metal line compared to starting resist linewidth indicating that the slope is achieved by increased si dewall passivation rather than by a typical resist erosion mechanism s o the slope of the line is independent of the slope of the resist prio r to etch.