Metal etch selectively removes portions of an aluminum layer to leave conductive circuit paths on a device. The process must precisely eliminate the metal left exposed by the photoresist pattern and avoid undercutting the sides of the remaining circuits.
A wafer is placed into the etch tool's processing chamber and given a negative electrical charge. The chamber is heated to 200°F (100°C) and brought to a vacuum level of 10 millitorrs, then filled with a positively charged plasma (usually a mix of nitrogen, chlorine and boron trichloride). The opposing electrical charges cause the rapidly moving plasma molecules to align themselves in a vertical direction, forming a microscopic chemical and physical "sandblasting" action which removes the exposed aluminum.