nanoTrek®-Quantum Tunneling Linear Encoder for Sub-nanometer Positional Metrology with Centimeters Range

Realisation of the first working linear encoder based on quantum tunneling between arrays of nanowires is presented. The sensing element consists of 12,000 nanowires, each 90 nm wide and 5 mm long, on an area of 5 x 4.3 mm. The sensing element was fabricated using phase shift mask lithography and dry etch processes followed by CMP; characterisation was carried with SEM and AFM. Finally transduction mechanism, showing linear encoder performance was demonstrated with electrical testing using independent nanopositioner. Strong signals in µA range are obtained on scans from several hundred nm to several mm range. nanoTrek® may address problems of dimensional metrology and alignment at the next technology nodes in micro-fabrication, nano-positioning and nano-imprinting. K e y w o r d s : quantum tunneling, NEMS, positional metrology, linear encoder, tunneling sensors 1 MOTIVATION Sub-nanometer dimensional metrology is critical to advance microelectronic manufacturing below the 100 nm critical dimensions limit, and then on to the next nodes defined by Sematech International: 65 nm and 45 nm. Metrology tools to reach those next nodes are not well developed. New sub-nanometer metrology solutions and new technology is required [1]. Quantum-π proprietary technology [2,3] is well suited to offer those solutions and to provide the necessary metrology tools. Nanometer and sub-nanometer scale positional metrology is also critical to advancements in nanotechnology, in general. 2 nanoTrek® CONCEPT Quantum-π technology utilizes physical phenomenon of electron tunneling. Quantum electron tunneling occurs when two electrical conductors are placed in a very close proximity to each other and are separated by an insulating layer. When small bias potential is applied between conductors, electric current flows between them despite no apparent "presence or availablity" of electric carriers in the gap region. Quantum tunneling is an exceedingly sensitive probe of inter-electrode separation, electrode area, the type of electrode material and the nature of intervening insulator. Quantum-π technology is based on variable overlap area of the electrodes. A generic Quantum-π nanoTrek® device is composed of two plates separated by a very thin layer of soft-matter spacer insulator. Several hundred to several thousand nanowires are fabricated on each substrate. The nanowires on the two surfaces facing each other and aligned with each other form elongated electrodes in the tunneling process. Substrates are allowed to slide past each other while their normal separation remains constant-this makes our device distinctly different from any previously built tunneling sensors where cantilevers and tips were critical elements and it was variable inter-electrode separation that produced transduction signal. Any lateral shift of substrates with nanowires will induce change in alignment and that in turn will result in measurable changes of electrical current flowing between the plates. This effect is demonstrated on Figures 1 and 2. Figure 1: Idealised device showing strips of conductors perfectly overlapping each other (top projection at left panel, cross section at middle panel, max current-right panel). Figure 2: Idealised device showing strips of conductors in offset position (top projection at left panel, cross section at middle panel, results in no current-right panel).