A new approach of ion/atom beam etching is proposed, which utilizes the projectile mass dependence of the sputtering process. As a model experiment, we etch YBa2Cu3O7-delta films using inert gases having different masses. Various etching characteristics are found to depend evidently on the mass of the gases. Substantial improvements such as 2.5-fold increase of the etching selectivity and the reduction of the etching damage of the etched area are demonstrated by using Kr. A primitive semi-empirical extension of Sigmund theory is proposed, which explains the results indeed as a mass effect and suggests the directions of further improvements. The results show a new important factor in plasma and ion/atom beam etching, which can be useful for realizing artificial structures of metal oxides. (C) 2002 Elsevier Science B.V. All rights reserved.