Redeposition of sputtered atoms may occur in FIB milling. Redeposition depends on the solid angle for the escape of secondary products and will cause the actual milling depth to be less than the designed depth. The redeposition trend increases in the following cases:
i) FIB milling is performed in a confined trench.
ii) FIB milling is performed in a high-aspect-ratio trench.
iii) Higher ion beam currents are used.
Furthermore, since ex-situ lift-out specimens are prepared to electron transparency within a trench, redeposition artifacts may readily build up. However, there are less redeposited materials in the TEM specimens prepared by in-situ lift-out method since any sputtered material may easily be removed by the FIB vacuum system.
Note that GAE (gas-assisted etching) in FIB milling can significantly reduce the redeposition artifacts, and thus reduce Ga contamination.