Recently, superlens imaging lithography below the diffraction limit has been experimentally verified. However, the short exposure depth owing to the near-field attribute of this method restricts its practical application. A tri-layer resist process, which increases the pattern depth through two-step dry etching, can overcome this drawback. In this paper, we investigated the scheme of superlens imaging lithography employing a tri-layer resist process and analysed the effect of the air gap between the object and the photosensitive layer on the exposure depth by finite-difference time-domain analyses. Through optimising the three layer resist thicknesses and dry-etching parameters of the tri-layer resist process, we patterned a high aspect ratio structure with half pitch of 110 nm and depth of 400 nm in our experiment. (C) 2013 Elsevier B.V. All rights reserved.