MOSI2 DIFFUSION BARRIER FOR THE PASSIVATION OF COPPER AT ELEVATED-TEMPERATURES

Sputter deposited MoSi2 coatings (200 and 400 nm thick) on copper have been studied in an attempt to prevent or at least reduce the oxidatio n of copper. Samples were exposed to an air ambient at temperatures ra nging from 600-850 degrees C for up to 15 min. Sputter-deposited MoSi2 was amorphous upon deposition and crystallized on annealing. Silicon from the MoSi2 was found to diffuse into the copper causing the MoSi2 to transform to lower silicides. The primary oxidation product for MoS i2-coated samples was CuO (with small amounts of Cu2O), which is in co ntrast to uncoated copper where Cu2O is the main oxidation product. Th e amount of copper consumed by oxidation, for a 200 nm MoSi2 barrier r elative to uncoated copper, was reduced by approximate to 140 times at 600 degrees C and approximate to 30 times at 800 degrees C. A 400 nm MoSi2 coating yielded an improvement of approximate to 420 times at 60 0 degrees C, and approximate to 200 times at 850 degrees C. For the 40 0 nm barrier exposed to air for 15 min, this corresponds to a 35 nm Cu O layer at 600 degrees C and a 300 nm thick oxide layer at 850 degrees C.