High-rate, scaleable manufacturing at the nanoscale requires a new approach to building workable devices. One of the most significant problems facing high-rate nanomanufacturing is efficient patterning of substrates. To-date, the two next-generation lithography (NGL) technologies that are most likely to be implemented are extreme ultra-violet (EUV) and electron projection lithography (EPL); however, EUV requires a high power EUV source, and EPL has only been able to demonstrate resolution of 60nm. Other nanoscale patterning capabilities require some form of direct-write either by atomic force microscopy (AFM) or e-beam lithography. These techniques have limited application in high-rate, scaleable manufacturing because of the time involved in these serial processes. We are developing a reconfigurable mask that can be customized for a variety of nanoscale patterns through the control of efficient, low-temperature electron emission from an array of carbon nanotubes.
In collaboration with CAMMP, our group is currently optimizing a 5-gas chemical vapor deposition (CVD) CNT growth method to achieve this. The CVD method is easily controlled, scalable and, combined with standard lithographic techniques, allows for easy manipulation of the size and placement of catalyst particles. Carbon nanotubes will be grown from strategically placed Ni nanoparticles to electrically connect pre-fabricated source and drain electrodes in situ.
Fig. 1. SEM image of a carbon nanotube grown by chemical vapor deposition (CVD) on Ni nanoparticle catalysts.
Fig. 2. SEM image of polymethylmethacrylate (PMMA) coated silicon substrate
patterned by electron beam lithography for use as a template for Ni
The controlled pattern of electron emission will stimulate site-specific chemistry on a substrate surface, thus creating a nanoscale pattern in a parallel processing step over a large area. The long-term vision of this effort is high-rate nanomanufacturing using an array of electronically addressable carbon nanotube pillars to pattern a substrate through field emission of electrons. This patterning is illustrated schematically in Figure 3. By individually addressing each nanotube in an array, and being able to control movement of that array at the nanoscale through a standard piezoelectric stage control system, a large number of patterns are achievable with a single mask.
The electron beam produced by the nanotube will either expose a photoresist-type material, activate a chemical reaction between the substrate and absorbed monolayer (e.g. forming Al2O3 from surface oxygen on aluminum1), or selectively desorb molecules or parts of molecules from a surface film. The remaining pattern on the substrate can then be used for selective attachment of antibodies or other molecules, or oxidation, or deposition of metal particles. The intended uses of this masking device include the creation of high-density antibody arrays for rapid chemical sensing, growth and/or placement of carbon nanotubes in the plane of the wafer, and standard IC patterning at the nanoscale.