Wafer-scale fabrication of nanoapertures using corner lithography

Abstract

Several submicron probe technologies require the use of apertures to serve as electrical, optical or fluidic probes; for example, writing precisely using an atomic force microscope or near-field sensing of light reflecting from a biological surface. Controlling the size of such apertures below 100 nm is a challenge in fabrication. One way to accomplish this scale is to use high resolution tools such as deep UV or e-beam. However, these tools are wafer-scale and expensive, or only provide series fabrication. For this reason, in this study a versatile method adapted from conventional micromachining is investigated to fabricate protruding apertures on wafer-scale. This approach is called corner lithography and offers control of the size of the aperture with diameter less than 50 nm using a low-budget lithography tool. For example, by tuning the process parameters, an estimated mean size of 44.5 nm and an estimated standard deviation of 2.3 nm are found. The technique is demonstrated-based on a theoretical foundation including a statistical analysis-with the nanofabrication of apertures at the apexes of micromachined pyramids. Besides apertures, the technique enables the construction of wires, slits and dots into versatile three-dimensional structures.

3D Nanofabrication of fluidic components by corner lithography

“…Corner lithography is a method to fabricate 3D nanostructures smaller than resolution of photolithography (Burouni et al, 2011(Burouni et al, , 2013Berenschot et al, 2012;Sarajlic et al, 2005;Burouni et al, 2011). This method is compatible with scaling down the size of the nanostructure, which agrees with the primary design size expectations.…”

“…) 2 − 1, which a is the final width in the apex, t is the deposited layer thickness, α is the angle of corner, and r is the relative isotropic etch distance (Burouni et al, 2013). In order to make two different aperture sizes as first opening, the structures were conformally coated by a Si 3 N 4 layer of 324 and 168 nm to make 200 and 100 nm aperture size for devices A and B, respectively.…”

“…The procedure was followed by isotropically thinning down in 85% H 3 PO 4 , leaving the nano-dots in sharp concave corners. The etching factor was defined as 1.35 (Burouni et al, 2011(Burouni et al, , 2013. In this case, all the nanowires in the four oblique ribs of the pyramid were removed by the etchant and a nano-dot was left at the end to use as an inversion mask.…”

“…When the over-etch factor of the layer in corner lithography is in the range of 1.0t to 1.22t, the nanowires will remain in the ribs of a pyramidal mold that is etched in the substrate. The 25 nm of Si 3 N 4 layer is isotropically etched regarding the etching factor of 1.00t to result 29 nm nanowires thickness (Burouni et al, 2013). The formed nitride layer is used as an etch-mask in the LOCOS step.…”

“…This method can be used to fabricate 3D nano-apertures (Burouni et al, 2011(Burouni et al, , 2013, 3D nanowires, and silicon oxide pyramids containing nanoscale metal tips Sarajlic et al, 2005;Burouni et al, 2011). It can be employed to fabricate a conductive nanowire, which is applicable in Scanning Thermal Microscopy (SThM), and as thermal sensor.…”