A method for forming a memory device having a stair step structure, comprising: forming a first mask over a stack comprising alternating conductive materials and insulating materials to define a first exposed area having a non-square rectangle shape including a length and a width perpendicular to the length; forming a second mask centered over the first exposed area to define second exposed areas of equal area non-contiguous with one another due to the second mask, the second exposed areas being at opposite ends of the first exposed area, the second mask comprising: an initial length less than the length of the first exposed area; and an initial width extending beyond the width of the first exposed area to overlap parts of the first mask, the initial width of the second mask equal to at least the width of the first exposed area plus a product of a number of stair steps in one of the stair step structures times an amount by which the initial width of the second mask is resized to form one stair step; removing portions of a first conductive material of the stack exposed within the second exposed areas; trimming the second mask to reduce a size of the second mask; and removing another portion of the first conductive material and a portion of a second conductive material thereunder after trimming the second mask to form the stair step structures, each of the stair step structures comprising a 3D structure having a plurality of stair steps at different elevations extending to different distances in the lateral dimension. forming a first mask over a stack comprising alternating conductive materials and insulating materials to define a first exposed area having a non-square rectangle shape including a length and a width perpendicular to the length; forming a second mask centered over the first exposed area to define second exposed areas of equal area non-contiguous with one another due to the second mask, the second exposed areas being at opposite ends of the first exposed area, the second mask comprising: an initial length less than the length of the first exposed area; and an initial width extending beyond the width of the first exposed area to overlap parts of the first mask, the initial width of the second mask equal to at least the width of the first exposed area plus a product of a number of stair steps in one of the stair step structures times an amount by which the initial width of the second mask is resized to form one stair step; an initial length less than the length of the first exposed area; and an initial width extending beyond the width of the first exposed area to overlap parts of the first mask, the initial width of the second mask equal to at least the width of the first exposed area plus a product of a number of stair steps in one of the stair step structures times an amount by which the initial width of the second mask is resized to form one stair step; removing portions of a first conductive material of the stack exposed within the second exposed areas; trimming the second mask to reduce a size of the second mask; and removing another portion of the first conductive material and a portion of a second conductive material thereunder after trimming the second mask to form the stair step structures, each of the stair step structures comprising a 3D structure having a plurality of stair steps at different elevations extending to different distances in the lateral dimension.