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. <EOS>