Chlorine contamination can induce corrosion in semiconductor fabs. The contamination sources are some Cl-based gases such as Cl2, HCl and BCl3, or chemicals used in fabrication flows or chemicals in the fabrication environment. Chlorine reacts with some elements immediately and forms the corrosive products. For instance, it is very common that chlorine reacts with Al element by,
Al3+ + 3Cl- = AlCl3 ----------------- 
The AlCl3 is water soluble products.
The most common etchant species of halide gases are Cl2 , IBr, and ICl for etching III nitrides and other compound semiconductor materials in plasma etching processes. On the other hand, I2 and XeF2 had also been used to enhance the etch rate of those materials in FIB .
 I. Chyr and A. J. Steckl, GaN focused ion beam micromachining with gas-assisted etching, J. Vac. Sci. Technol. B 19(6), (2001) 2547.