A method for forming a contact hole in a silicon oxide layer formed over a silicon nitride layer and a substrate performs an etching process with an etchant, C4F8/Ar or C4F8/C2F6/Ar, on an inductively coupled plasma etcher. The inductively coupled plasma etcher contains a chamber, a ring, and a roof. The etchant used in the etching process is controlled by conditions that include a C4F8 flow of about 10 to 20 sccm, a CO flow of less than about 100 sccm, and an Ar flow of about 50 to 500 sccm. In the meantime, the conditions of the inductively coupled plasma etcher include a roof temperature of about 150 to 300 ° C., a ring temperature of about 150 to 400 ° C., and a pressure within the chamber of about 4 to 50 mtorr. By performing a plasma etching process under the foregoing conditions, a properly profiled contact hole is obtained.