Tapered etching of aluminum with CHF[sub 3]/Cl[sub 2]/BCl[sub 3] and its impact on step coverage of plasma-deposited silicon oxide from tetraethoxysilane

The tapered etching of aluminum CHF3/Cl2/BCl3 gas mixtures in a hexode reactive ion etching reactor is reported. The process involves sidewall polymer deposition during etching; Auger analysis of the deposit showed mainly carbon and chlorine. The metal sidewall angle (taper angle) was studied as a function of processing conditions, the spacing between Al lines, and photoresist thickness. The extent of taper increased with increasing CHF3 flow rates, saturating at high flow rates, and decreased with increasing Cl2 flow rates. The extent of taper increased with bias in the range –190 to –230 V, and decreased in the range –230 to –260 V. In addition, the extent of taper increased with increasing spacing and with decreasing photoresist thickness. The taper angle for a given spacing can be tailored in the range 60°–90° by adjusting processing conditions. As expected, the step coverage of plasma-enhanced TEOS oxide on taper-etched aluminum lines showed a marked improvement over that of vertical aluminum lines.