Patent ID: 7615164

Claim:
A plasma etching method comprising: positioning a substrate over a plasma generating electrode, the electrode powerable at different first and second frequencies, wherein a surface of the substrate comprises an outermost portion over an innermost portion, the outermost portion being at least five times the thickness of the innermost portion; generating one plasma over the substrate to expose at least a portion of the innermost portion, the plasma being generated with the electrode from a first applied power at the first frequency and a second applied power at the second frequency, a ratio of the first applied power to the second applied power being from 0.26 to 5.9; and after exposing the portion of the innermost portion, generating another plasma over the substrate to remove at least some of the innermost portion, the plasma being generated with the electrode from a third applied power at the first frequency and a fourth applied power at the second frequency, a ratio of the third applied power to the fourth applied power being from 0 to 0.25 or at least 6.0, wherein the outermost portion is removed at a higher rate than the innermost portion.