Selective Etching of SiO2 by Radical Recombination through NF3/H2 Pulsed RF Plasma

The structure of semiconductor devices is changing from a two-dimensional (2D) structure to a three-dimensional (3D) structure. For the processing of these 3D devices, the development of selective isotropic etching techniques is required. In this study, the isotropic cyclic dry etching of SiO 2 using NF 3 /H 2 plasma for HF generation and NH 3 gas as a solvent has been investigated. Especially, the effects of pulsed radio frequency (RF) plasma on the control of the etch species and the etch characteristics of SiO 2, such as the etch rate and selectivity over SiN x, have been investigated. The application of pulsed plasma with a duty ratio of 50% improved the SiO 2 etch depth per cycle (EPC) to ∼20% and improved the etch selectivity over SiN x from ∼35 to ∼50 compared to continuous wave (CW) plasma. The improvement of the SiO 2 etch rate and the selectivity of SiO 2 over SiN x through the application of pulsed plasma is attributed to the recombination of species during the RF-off period. During the RF-off period, HF reacts with NH 3 introduced into the process chamber to produce NH 4 F. Additionally, the improved etch selectivity over SiN x is due to the removal of F radicals during the RF-off period, achieved by the recombination of F with H and subsequent reaction with NH 3 . Thus, the application of pulsed plasma not only increases SiO 2 etching but also enhances the etch selectivity over SiN x .