Lift-off (microtechnology) - Disadvantages

Disadvantages

There are 3 major problems with lift-off:

Retention

This is the worst problem for liftoff processes. If this problem occurs, unwanted parts of the metal layer will remain on the wafer. This can be caused by different situations. The resist below the parts that should have been lifted off could not have dissolved properly. Also, it is possible that the metal has adhered so well to the parts that should remain that it prevents lift-off.

Ears

When the metal is deposited, and it covers the sidewalls of the resist, "ears" can be formed. These are made of the metal along the sidewall which will be standing upwards from the surface. Also, it is possible that these ears will fall over on the surface, causing an unwanted shape on the substrate.

If the ears remain on the surface, the risk remains that these ears will go through different layers put on top of the wafer and they might cause unwanted connections.

Redeposition

During the liftoff process it is possible that particles of metal will become reattached to the surface, at a random location. It is very difficult to remove these particles after the wafer has dried.