III-N nanowire atomic force cantilevers for ultra-vertical-wall scanning-probe, scanning-tunneling, and near-field microscopy (Conference Presentation)

Abstract

The steady advance of nanotechnology from investigation to application and to manufacturing is increasing the demands on nanoscale metrology and lithography. As dimensions shrink to the nano-scale, the available metrologies, necessary for any advanced manufacturing process, become limited. Optical metrology faces resolution limits associated with the large size of the photon relative to the nanostructure. Interference techniques offer sub-wavelength resolution, but at the expense of experimental and signal processing complexity. Electron and ion microscopies (SEM, TEM, FIB, etc.) offer resolution but require high vacuum and are generally unavailable for in-line manufacturing applications. Scanning probe techniques such as atomic force microscopy (AFM), scanning tunneling microscopy (STM), and near-field scanning optical microscopy (NSOM) are very attractive, yet, still unreliable to produce ideal results. For example, AFM, commercial tips are often pyramidal, resulting in significant artifacts requiring complex and uncertain deconvolution of the data. For STM and STL (scanning-tunneling lithography), amorphous/polycrystalline metal tips are the dominant commercial technology but are subject to erosion and wear. For NSOM, metal tips require a complex alignment - optical fibers offer an alternative but are difficult to combine with AFM and STM functionality. To overcome to the above-mentioned problems, we have developed a single nanowire probe systems, based on single crystal III-N semiconductors. Uniform GaN nanowire arrays, formed thought a combination of wet and dry etch of MOCVD GaN films, were achieved over a large area (>105 μm2) with an aspect ratio as large as 50, a radius as small as 17 nm, and atomic-scale sidewall roughness (<1 nm), allowing metrology of vertical structures with no artifact correction. Doping, during MOCVD film growth, controlled the conductivity of the GaN. Studies of the etching mechanism for different doping level are also reported. Optical emission properties of the 65 nm radius and 2 micron length GaN, mounted on an AFM tip shows a lasing at 365 nm with a line width of 0.15 nm and a Q-factor of 1139-2443. Our results show that fabrication of high-quality GaN nanowire arrays with adaptable aspect ratio and large-area uniformity is feasible through a top-down approach using interferometric lithography and is promising for fabrication of III-nitride-based nanophotonic devices (radial/axial) on the original substrate. Indeed we will also present the state of the art results of these nanowires in AFM and STM metrology as well in field emission and scanning tunneling lithography and NSOM and demonstrate as, such a single wide-bandgap tip technology offers the functionality and versatility of several incumbent technologies in one single, universal, system.