Abstract: In order to etch an object to be processed, such as a semiconductor wafer, the object to be processed is placed in a vacuum processing chamber, an etching gas is introduced into the vacuum processing chamber, and electrical power is applied to a pair of electrodes within the vacuum processing chamber by a high-frequency electrical power source. A mixed gas of carbon monoxide and a gas which does not contain hydrogen and which contains at least one element from the group IV elements and at least one element from group VII elements is used as the etching gas. A halogenated carbon gas, typically a fluorocarbon such as C.sub.4 F.sub.8, is used as the gas containing elements from the group IV and group VII elements. The concentration of carbon monoxide in the etching gas could be 50% or more. At least approximately 86% of an inert gas, such as argon, xenon, krypton, or N.sub.2 and O.sub.2 could be added to the etching gas.