In order to repair opaque defects using a focused ion beam instrument that utilizes a Ga ion source, the excess film must be removed by sputter etching. Unfortunately, this method of repairing opaque defects does have several drawbacks. The first and foremost problem is the occurrence of the so called 'river bed', which greatly limits the effectiveness of the FIB mask repair instrument. We have found, however, that by using a new gas assisted etching procedure, the size of river beds can be reduced substantially, while simultaneously producing several other favorable effects. By introducing a new gas, the etching rate for chromium is enhanced 1.26 times, and the etching rate for quartz substrate is reduced 0.28 times. Therefore, the damage to the quartz substrate is reduced by 0.22 times over that found when no gas is used. In addition, the favorable effects make it possible to terminate etching on the quartz substrate, producing a noticeably flat chrome removed surface with little Ga staining. We evaluated the repaired masks using an inspection system, and then examined their printability using an I-line stepper. We obtained highly favorable results on both accounts.