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 N-2 gas into the process atmosphere. A maximum Cu etch rate of 2.4 mu m/min was obtained by nitrogen addition at a H-2 mixture ratio (C-H2) of 0.9 and an input power of 70 W. The etch rate for the optimally N-2-added plasma was 8 times higher than that for the pure H-2 plasma. The Cu etch rate increased with increasing input power. The maximum etch rate reached 3.1 mu m/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 N-2 addition. Furthermore, N-2 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.