High-density etching plasma excitation by slot type and coaxial line type of microwave antennas

Microwave radiation by slot antennas is used to generate large-diameter high-density plasmas where transverse magnetic (TM) mode of surface waves is excited along the plasma-quartz interface. When fluorine-rich etching plasma is produced in CF4/O2 at 40 Pa, anomalous erosion (many deep microholes) of quartz surface is observed after 40 h. This serious erosion limits the throughput of etching process. In order to overcome this problem, a coaxial line antenna is newly introduced and its performance is compared with the slot antenna excitation. In the same discharge conditions, the coaxial line antenna does not give rise to anomalous erosion of quartz surface. This different result is explained by simplified analysis of cylindrical transmission electron microscope mode and planar TM mode. In addition, the coaxial line antenna has a great advantage of no need of large-area thick quartz window, no density jump, higher power efficiency, and better density uniformity