Although Scanning Tunneling Microscopy (STM) was initially developed, with tremendous success, as a surface analysis instrument, its potential for surface and material modification is now being exploited for nanofabrication. For example, STM can be used for additive nanofabrication by depositing material from a gas precursor (a localized chemical vapor deposition technique) or from an electrolyte (localized electro-deposition). In contrast, material can also be removed from the substrate by (1) mechanical means like contacting the tip against the sample as in atomic force microscopy (AFM), and (2) by electrical pulses. Other approaches like localized etching of the surface with a gas or electrolyte also fall under the second category where material is removed from the substrate. While these techniques are expected to be critical in the development and manufacture of future second order (less than 10nm) and third order (less than 1nm) nano-devices, STM can also be incorporated into immediate practical fabrication -- to expose resists. On high-resolution poly-methyl methacrylate (PMMA) resists, 100 nm linewidths (with pattern transfer) have already been demonstrated while in other resists linewidths in the tens of nanometers are also possible. Note that the major advantage of STM-based approach is that it is the least expensive tool able to produce structures with dimensions below 100 nm. Thus, it has the potential to make nanotechnology economically viable and is poised to play a significant role in future technological progress, especially, when manufacturing processes in electronics, optics, and precision machining begin to require nanometer-scale control over feature sizes.
Unfortunately, STM-based nanofabrication lacks sufficient throughput at present -- note that throughput is a critical factor in the cost-of-ownership equation. Several approaches have been proposed to increase the throughput in STM-based nanofabrication techniques. For example, micro-fabrication techniques, developed in Japan and in Stanford University, have dramatically increased the number of parallel piezo-scanners on a probe and thereby increased the speed of STM processes. However, the estimated writing speeds are still too high. Other approaches to increasing throughput include increasing processing speed and increasing scanning speeds of STMs. Towards the goal of identifying critical parameters the design of nanofabrication equipment, this paper quantifies equipment requirements necessary to achieve a desired throughputs in terms of equipment and process parameters like parallelism, processing speed, access-speeds, and spot size.
The article develops a methodology, which can be used to identify and design sub-systems and components of nanofabrication equipment. For example, the methodology can be used to study the sensitivity of key equipment parameters and therefore identify key design modifications needed to achieve a desired throughput in the system. In addition to the generic theoretical developments, this work will also consider the specific problem of high-speed high-density nano-storage. In particular, the proposed methodology will be studied for the nano-ablation-based data-storage in HPOG graphite samples.
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