By combining conventional silicon microfabrication and direct three-dimensional growth using electron-beam induced carbon contamination, we have developed a scheme for fabricating nanotweezers with a gap of 25 nm. Four silicon oxide cantilevers with a spacing of 1.5 µm extending over an edge of a silicon support chip, were covered with a thin layer of metal. By focusing an electron beam at the ends of the cantilevers, narrow supertips grew from the substrate. Careful alignment of the substrate made the supertips converge to form a nanoscale gap. We demonstrate customization of the shape and size of the tweezer arms, using a simple scheme that allows conveniently fine-tuning of the tip features and the gap to within 5 nm. The supertips can be metallized subsequently, to be made conducting, without significantly affecting the shape of the tweezers. By applying a voltage on the outer electrodes with respect to the inner two electrodes, the gap can be opened and closed. This enables the device to grab and manipulate small particles, with the option of direct electrical measurement on the particle. The advantage of our approach is that no voltage difference is applied between the tweezer arms, making the device ideal for application with such fragile structures as organic objects.

Pattern placement imprecision due to charging of the workpiece is believed to be a significant contribution to the total positional error in electron beam lithography. In an earlier work, Liu et al. [J. Vac. Sci. Technol. B 13, 1979 (1995)] reported that the surface potential of exposed resist could be negative or positive according to the resist thickness and the electron energy. In that work the authors were constrained to use a flood beam. In this study, we report a new independent approach using a Kelvin probe electrometer to measure the surface potential after exposure by a focused beam. There is a qualitative agreement with the earlier work in that the surface potential tends to be less positive at lower electron energies and for thicker resists. We observed positive surface potentials at 10 and 20 keV beam irradiation. This positive charging is much more evident in polybutene sulfone than in UV5.

Electron beam exposure of masks and wafers results in charging of the insulating resist film. This charging results in an electric field which deflects incoming electrons and can be a serious source of pattern placement error in electron-beam lithography. In earlier work (Ingino et al. 1992) the surface potential was found to be positive or even zero under certain conditions. In this study, a model is developed to explain this effect and the surface potential is measured by an independent method, a Kelvin probe non-contacting electrostatic voltmeter. This new study confirms qualitatively the findings of the first study. An area of PBS resist measuring a few square millimeters is exposed using a gaussian focused probe and moved under the Kelvin probe immediately after exposure to measure the surface potential. Thicker resist tended to charge more negatively. The model and experiments confirm early studies that the surface potential is a function of resist thickness, and that there may exist a resist thickness where the surface charge is essentially zero.

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