Significant Improvement of Copper Dry Etching Property of a High-Pressure Hydrogen-Based Plasma by Nitrogen Gas Addition

The characteristics of copper (Cu) isotropic dry etching using a hydrogen-based plasma generated at 13.3 kPa (100 Torr) were improved dramatically by simply introducing a moderate amount of N2 gas into the process atmosphere. A maximum Cu etch rate of 2.4 μm/min was obtained by nitrogen addition at a H2 mixture ratio (CH2) of 0.9 and an input power of 70 W. The etch rate for the optimally N2-added plasma was 8 times higher than that for the pure H2 plasma. The Cu etch rate increased with increasing input power. The maximum etch rate reached 3.1 μm/min at an input power of 100 W and a CH2 of 0.9. The surface roughness of the etched copper decreased as a result of optimum N2 addition. Furthermore, N2 addition also improved the etch selectivity between Cu and SiO2 such that the selectivity ratio reached 190. Finally, selective etching of a trench-patterned Si wafer with an electroplated Cu layer was demonstrated.