The disclosure relates to a method for forming a nanoscale structure by forming a pattern on a selectively etched layer located on top of a substrate using lithography, wherein the pattern results a gap having sidewalls, performing RIE on the gap having sidewalls, wherein RIE results in the formation of a self-aligned mask on the bottom wall of the gap with unprotected regions on the bottom wall of the gap near the junctions with the sidewalls, and wet etching the gap having a self-aligned mask and unprotected regions to remove the substrate under the unprotected regions to form a nanoscale structure in the substrate. The disclosure also relates to a nanoscale structure array including a plurality of nanotrenches, nanochannels or nanofins having a width of 50 nm or less and an average variation in width of 5% or less along the entire length of each nanotrench, nanochannel or nanofin.