Liftoff and Undercut in Deposition

TODO

Liftoff is the simplest way to create a pattern using deposition and lithography (sputtered metal in our case).

Patterned and developed photoresist blocks certain areas of the substrate and leaves the rest exposed to deposition. However, sputtering is conformal: it coats all surfaces with a non-zero film thickness, independent of deposition. Thus there would be no way to develop the photoresist as the metal deposition blocks the developer.

Undercut means creating a laterally larger hole in liftoff-resist underneath the photoresist layer. If the LOR layer is thicker than the deposition, it leaves place for the developer to attack the resists.

The developer removes the resists and the metal layer above lifts and floats away, hence the term liftoff.