which fluorine and oxygen radicals appear to interact chemically with materials at a surface when etching is accomplished it will be understood that conventional ion beam etching including ion beam or sputter etching methods using reactive gases such as oxygen and flourocarbons may be successfully substituted in any of the foregoing steps where plasma etching has been prescribed according to the invention it is seen that a novel method is provided for forming microscopic submicron diameter bores in thin insulative films such as employed for example in superconductive and other current control devices the method permits the formation of holes through insulative layers of thickness relatively greater than the diameter of the bore the novel method permits the successful formation of such very small holes in dual component layers by selecting the components of distinct materials one component layer being relatively thick while the other is thinner the upper or thin layer is patterned by use of plasma or ion beam dry etching through an electron beam generated hole in a temporary mask the insulative material of the lower component layer acts as a stop for the dry etching process but is capable of being chemically wet etched the upper component layer is readily dry etched but is resistant to chemical wet etching the upper component layer serves as a permanent mask to define the narrow dimension.