Plasma (dry) etch
Beginner
Carving away material with a glowing, electrically charged gas that cuts straight down instead of eating sideways.
Novice
Etching with ions and reactive gas fragments in a low-pressure plasma. Unlike a liquid etch, which eats in every direction, ions accelerated toward the wafer etch mostly downward, so the shape in the resist transfers with vertical walls.
Expert
Reactive ion etching balances physical sputtering (directional, unselective) against chemical attack by radicals (selective, isotropic). Pressure, ion energy and gas mix set anisotropy, selectivity to the layer underneath, and damage.