Chemical modification of subcritical water for the dissolution of Si3N4 layer in the fabrication of microelectronic devices

Subcritical water was used to selectively remove Si3N4 layers in the 3D NAND fabrication. Various fluorine compounds were added to subcritical water. When sulfonyl fluoride-based additives were added to subcritical water, the dissolution of Si3N4 was accelerated by F-, and the Si3N4-to-SiO2 removal selectivity increased owing to the high [F-]/[HF2-] ratio and low OH- concentration. Furthermore, the addition of H2SiO3 to the subcritical water resulted in selective and uniform Si3N4 removal without the loss of SiO2 layers in the 128-layer Si3N4/SiO2 stack structure. However, the addition of ammonium fluoride compounds to subcritical water could not achieve selective removal of Si3N4. The addition of HCl to the ammonium fluoride-containing subcritical water suppressed the dissolution of Si and SiO2. Further addition of H2SiO3 and optimization of the additive concentrations led to selective and uniform Si3N4 removal in the 128-layer Si3N4/SiO2 stack structure without the loss of the Si substrate and SiO2 layers. [Display omitted] •Subcritical water was used to remove Si3N4 layers in microelectronic devices.•Addition of various fluorine additives improved Si3N4 dissolution.•Si3N4 removal selectivity improved by control of [F-]/[HF2-] ratio at different pH.•Addition of H2SiO3 with fluorine compound further improved removal selectivity.