A technique used in processing semiconductor devices or wafers to produce a required metallization pattern (see metallizing). The wafer is covered with resist, which is then exposed and developed to produce the desired pattern. Metal is then applied, usually by evaporation, and deposited on top of the resist as well as the substrate. The resist is dissolved using a suitable solvent and the metal on the resist is removed or ‘lifted off’ with it, leaving the desired pattern on the substrate. This technique contrasts with the etch processes, where metal is applied to the wafer first. The metal is covered with resist, which is exposed and developed to produce a protective layer for the desired pattern. The metal is then etched away before the remaining resist is dissolved. These two processes, contrasting gallium arsenide and silicon, are shown in the diagram. For lift-off to be facilitated a small protruding lip at the top edge of the resist is desirable. Assisted lift-off is a multilevel resist technique used to produce such a protruding lip. Other methods of edge profile modification include baking the wafer after development of the resist, which produces a crust on the resist with a suitable lip. The resist may be soaked in chlorobenzene to remove residual solvents from the upper layers of the resist film. This retards development of the resist in the upper layer and produces a suitable undercut edge.

Comparison of lift-off (right) with etch process (left)