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

A method includes forming an alternating stack of first and second layers, forming a composite hard mask layer over the alternating stack, forming openings in the hard mask, and forming via openings through the alternating stack by performing an anisotropic etch process that transfers a pattern of the openings in the composite hard mask layer through the alternating stack. The compositing hard mask includes a first cladding material layer which has higher etch resistance than upper and lower patterning films of the composite hard mask.