Gas-assisted etching (GAE) in FIB is a technique that enhances the etching effects on selected regions by introducing reactive chemical precursors. The etching effects include:
i) Enhancement of the FIB etch rate.
ii) Reduction of unwanted doping from primary ion species (e.g. Ga+ ions in most FIB systems) into the substrate.
iii) Reduction of redeposition, and consequent reduction of Ga contamination.
iv) Selectivity on multiple layer structures.
With proper ion beam scan conditions, such as beam current, beam dwell time (e.g. 1 µs), beam overlap (e.g. 0 - 50%), frame time, and gas flux, this technique has many applications to etch rate enhancements:
i) Cl2 for etching GaAs, Si, and InP. [2,3]
ii) XeF2 for etching SiO2, W, diamond , and semiconductors.
iii) H2O for etching PMMA , photoresists , carbon, and other carbonaceous materials.
iv) Etch rate enhancements of 63× to 93× and 23× to 33× faster by I2 at 35 °C and XeF2 at 25 °C, respectively, on GaN. 
The schematic illustration in Figure 2473 presents the locations of the gas source, the focused ion beam, the sample surface, and the volatilized and sputtered species. By selecting the gas source and beam scan conditions, deposition of materials may occur (see page2546) or material removal can be enhanced.
Figure 2473. The schematic illustration presenting the locations of the gas source, the focused ion beam, the sample surface, and the volatilized and sputtered species.
 I. Chyr and A. J. Steckl, GaN focused ion beam micromachining with gas-assisted etching, J. Vac. Sci. Technol. B 19(6), (2001) 2547.
 R. J. Young, J. R. Cleaver, and H. Ahmed, Microelectron. Eng. 11, 409 (1990).
 R. J. Young, J. R. Cleaver, and H. Ahmed, J. Vac. Sci. Technol. B 11, 234 (1993).
 L. R. Harriott, Jpn. J. Appl. Phys., Part 1 33, 7094 (1995).
 P. E. Russell, T. J. Stark, D. P. Griffis, J. R. Phillips, and K. K. Jarausch,
J. Vac. Sci. Technol. B 16, 2494 (1998).
 T. J. Stark, G. M. Shedd, J. Vitarelli, D. P. Griffis, and P. E. Russell, J.
Vac. Sci. Technol. B 13, 2565 (1995).
 T. J. Stark, D. P. Griffis, and P. E. Russell, J. Vac. Sci. Technol. B 14,