We have investigated the compatibility of Cl2/BCl3/IBr3etch gas mixtures with a cryo‐pumped ultrahigh vacuum chemically assisted ion‐beam etching system. The machine was designed for the fabrication of ultrahigh‐quality laser facets in monolithically integrated GaAs‐ and InP‐based optoelectronic integrated circuits. The chemical composition of etch byproducts deposited in the vacuum chambers and the pumping system has been examined in particular detail. After 70 h of process time, samples of such deposits were scraped from the chamber walls and the various stages of the cryo‐pump and roughing pump; these samples were analyzed using energy‐dispersive x‐ray measurements. Automated overnight regeneration of the cryopump, the use of integrated external bakeout heaters, and the implementation of a cryo‐pumped load‐lock chamber allow the deposition of reactive Cl‐containing residues to be confined to surfaces and components which can be cleaned or replaced during routinely scheduled yearly maintenance.