Patent ID: 7700492

Claim:
A method for performing a plasma etching on a silicon oxide film through an amorphous carbon mask, the method comprising: performing the plasma etching by using a first etching gas containing a fluorocarbon gas, an oxygen gas, a helium gas and at least one of an argon gas, a krypton gas and a xenon gas, wherein the fluorocarbon gas is C 4 F 6 , C 4 F 8 , or C 5 F 8 , wherein after completing the plasma etching by using the first etching gas, a plasma etching using a second etching gas is performed, and the second etching gas is obtained by removing the helium gas from the first etching gas, wherein the plasma etching using the second etching gas is an overetching process, wherein, in the first etching gas, a ratio of a flow rate of the helium gas to a flow rate of at least one of the argon gas, the krypton gas and the xenon gas is 5 to 50% and the ratio of the etching rate of the silicon oxide to the etching rate of the amorphous carbon mask is about 21.