Described herein is a technology related to a method for generating a high density plasma ionization on a plasma processing system. Particularly, the high density plasma ionization may include an electron cyclotron resonant (ECR) plasma that is utilized for semiconductor fabrication such as an etching of a substrate. The ECR plasma may be generated by a combination of electromagnetic fields from a resonant structure, radiated microwave energy from a radio frequency (RF) microwave source, and presence of a low-pressure plasma region (e.g., about 1 mTorr or less) on the plasma processing system.