Abstract: A plasma etching method, wherein less particles is produced, for forming trenches in a substrate is provided. The method includes performing a first etching step on a substrate using a first etching condition and then performing a second etching step on the substrate using a second etching condition. Between the first and the second etching step, a transition step is carried out in which the variation of each reaction chamber parameters is adjusted below a specific percentage, such as, 15%. By so doing, the number of particles is substantially reduced. An oxygen plasma-cleaning operation is also performed at a pressure between 40 mTorr to 80 mTorr inside the reaction chamber to reduce the number of defects.