A chemically assisted ion beam etching system has been developed which performs high quality, highly anisotropic etching of AlGaAs/GaAs at relatively low ion energies (200 eV). The use of three grid ion optics in a Kaufman ion source allows etching at low energies with reasonable rates without loss of profile verticality. All ultrahigh vacuum etching chamber construction with a high throughput turbomolecular pump and high vacuum loadlock provide routine high quality etching of AlGaAs without the use of etch chamber cryo panels or cryo pumps. Low ion energy and a clean vacuum environment permit the use of a single level, non hard baked photoresist mask. Benefits include high pattern resolution and fidelity, low mask erosion rate, good dimensional control, and easy, complete mask stripping as well as reduced substrate damage.