Nitrogen-doped amorphous carbon coating on copper pads for direct wire bonding with a long-term humidity reliability

To improve the long-term reliability of copper (Cu) pads used in LSIs, nitrogen-doped amorphous carbon (a-C:N) coating is applied to the Cu pads with direct wire-bonding to prevent Cu oxidation in humidity. To obtain a thin barrier, the thickness optimization of a-C:N layer was carried out under temperature humidity storage (THS) testing at the conditions of 85 °C/85% relative humidity. Cu pad chains coated with the optimized a-C:N film were fabricated by direct bonding with aluminum (Al) wires. The electrical connection up to 210 bonds was obtained with the 10 and 15 nm thick a-C:N coated Cu pads. The reliability test of the pad-chains under the THS was carried out, and a 15 nm thick a-C:N can preserve the electrical connection along 100 h of the THS test. The a-C:N coating is expected to improve the humidity reliability of Cu pads with direct wire-bonding for long-term data storage.