Ultra‐large‐scale integration patterning with less than 0.25‐μm precision requires the optimization of electron cyclotron resonance (ECR) plasma discharge. This is because ion motion and etching results are affected by magnetohydrodynamic plasma instability and charge accumulation on the substrate in nonuniform plasma. Microloading and unusual notching at the boundary pattern between dense patterns and open spaces are both caused duringn+poly‐Si etching in nonuniform plasma. To prevent these problems, optimally uniform ECR plasma generation is necessary. This is accomplished by optimizing both the magnetic field profile and the introduction of microwaves.