Analysis of plasma etch defects utilizing a comb test structure

Abstract

Three metal compositions are patterned via plasma etching into comb structures. The comb structures have pitches of 4 μm, 5 μm, 7 μm and 12 μm, with a line width of 2 μm, on a field oxide of 8,000 Angstroms thickness, using <111> p-type substrates. These comb test structures have been used to determine the number of bridges, and thus the yield, of the metal compositions: pure aluminum, silicon(2%)-aluminum, and copper(0.5%)-silicon(2%)-aluminum. Bridge failures are photographed and classified according to the source of the defect. The defects due to plasma particles are used to determine a yield model for this etch process. Through the use of yield model and test structure data the etch process is evaluated for the different metal systems. This allows a quantitative comparison of the systems in terms of defect clustering, defect density and defect size distribution, and hence projections for the best yielding process via the yield model.