METHOD OF MAKING A THREE-DIMENSIONAL MEMORY DEVICE USING COMPOSITE HARD MASKS FOR FORMATION OF DEEP VIA OPENINGS

An alternating stack of first material layers and second material layers is formed over a substrate. A hard mask layer is formed over the alternating stack and cavities are formed in the hard mask layer. A cladding liner is formed on sidewalls of the cavities in the hard mask layer. Via openings are formed through each layer within the alternating stack by performing an anisotropic etch process that transfers a pattern of the cavities through the alternating stack.