Provided is a substrate processing method that may prevent the non-uniformity of the thickness of landing pads deposited on each step in a vertical NAND device having a stepped structure. The substrate processing method includes stacking, a plurality of times, a stack structure including an insulating layer and a sacrificial layer and etching the stack structure to form a stepped structure having an upper surface, a lower surface, and a side surface connecting the upper surface and the lower surface. The method also includes forming a barrier layer on the stepped structure, forming a mask layer on the barrier layer and exposing at least a portion of the barrier layer by etching at least a portion of the mask layer with a first etching solution The method further includes etching the exposed barrier layer with a second etching solution and etching the mask layer with a third etching solution.