Plasma etching method

摘要

A plasma etching apparatus has a lower electrode (24) for supporting a semiconductor wafer (W) in a processing room (14a), an upper electrode (40) opposite to the lower electrode, and an RF power supply (28) for applying an RF power across the upper and lower electrodes. An SiN layer (5) as an underlayer having a shoulder portion (5a), and an SiO2 layer (6) covering the SiN layer are disposed on the wafer. A contact hole (8) is formed in the SiO2 layer by etching so as to expose the shoulder portion of the SiN layer. A processing gas contains C4F8 and CO. To set the etching selection ratio of SiO2/SiN, the discharge duration of each part of the processing gas is used as a parameter. The progress of dissociation of C4F8 is controlled by selecting the discharge duration. The discharge duration is determined by the residence time of each part of the processing gas and the application time of an RF power. <IMAGE> <IMAGE>