Effects of H2 addition on highly selective SiOCN etching using NF3-based plasma

In three-dimensional (3D) stacked logic devices, low dielectric constant (low-k) materials, such as SiOCN, are used as spacer materials and require highly selective isotropic etching. In this study, we investigated the effects of the addition of H2 gas on highly selective SiOCN etching using an NF3/Ar plasma. The etch rate exhibited a peak with increasing H2 flow rate, and the dependence of the etch rate on the H2 flow rate varied depending on the material (SiO2, poly-Si, and SiN). Based on the results of optical emission spectroscopy and x-ray photoelectron spectroscopy analyses, the effects of H2 addition on SiOCN etching were classified into three regions: (i) an increase in the etch rate caused by an increase in the concentration of F radicals, (ii) an increase in the etch rate owing to the formation of an O-depleted reactive layer, and (iii) a decrease in the etch rate owing to the formation of an NHx-containing protective layer. These findings demonstrate that precise control of O- and H-related reactions in both the plasma and materials is essential for achieving highly selective SiOCN etching in advanced 3D stacked logic device integration.