Patent ID: 7943524

Claim:
An etching method comprising: feeding a processing gas into an airtight processing chamber to generate therein a plasma of the processing gas; and selectively etching a silicon oxide film against a silicon nitride film, the silicon oxide film being formed on an object to be processed disposed in the processing chamber, wherein the processing gas is a gaseous mixture including a C 4 F 6 gas, an oxygen gas, a nitrogen gas and an inert gas, and wherein an etching selectivity of the silicon oxide film to the silicon nitride film is controlled by adjusting a ratio of a total flow rate of the oxygen gas and the nitrogen gas to a flow rate of the C 4 F 6 gas, and a ratio of a flow rate of the nitrogen gas to the flow rate of the C 4 F 6 gas, wherein the ratio of the flow rate of the nitrogen gas to the flow rate of the C 4 F 6 gas is greater than or equal to 25/8 and less than or equal to 85/8, and the ratio of the total flow rate of the oxygen gas and the nitrogen gas to the flow rate of the C 4 F 6 gas is controlled greater than or equal to 15/4 and less than or equal to 45/4, and wherein the etching selectivity of the silicon oxide film layer to the silicon nitride film is greater than or equal to about 20.