Plasma etching method

A plasma etching method is performed by plasma etching an SiN layer through a mask layer to form a first wiring portion and a second wiring portion, the first and the second wiring portions having different wiring densities in the etched SiN layer, the mask having two pattern portions respectively corresponding to the first and the second wiring portions. In the plasma etching step, by using an etching gas including fluorocarbon and C₂H₂F₄, the line width variation between the first and the second wiring portions is restrained.