Nanometer Lithography by Fast Atom or Ion Beam Milling
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NANOMETER LITHOGRAPHY BY FAST ATOM OR ION BEAM MILLING G. Devaud, J. Fleming, K. Douglas, Department of Physics, University of Colorado, Boulder, CO 80309
ABSTRACT We have produced nanometer scale patterning (nanostructures) by metal shadowing of two-dimensional protein crystals (S-layers), followed by milling with ions or fast atoms. In this parallel process, the metal overlayer is formed into a metal screen consisting of hexagonal arrays of 10 nm size holes with a 20 nm periodicity. We have studied the time evolution of the milling process, and temperature effects. Nanostructure formation may be due to preferential sputtering of the troughs relative to the crests of the metallized S-layer. The effect of temperature on pattern formation indicates that thermal diffusion is also important.
INTRODUCTION The development of nanometer scale technology, i.e. materials and devices structured on a nanometer length scale, is an important scientific and technological goal for applications in electronics, chemistry and optics[1]. Methods of producing nm-scale features have been developed using ion[2], electron[3] and x-ray[41 beams. Scanning tunnelling microscopy has also been used as a tool to fabricate atomic scale structures[5]. Many of these techniques involve the use of complex and expensive equipment. Serial (one-by-one) production is inefficient if a large number of identical features are desirable. There is a need for an inexpensive, parallel (all at once) process which creates large numbers of identical features. Self assembling biological systems can provide a structural framework to build nanostructures in a parallel process. Ion or fast atom bombardment of the metallized S-layer causes the selective removal of metal from the pores of the protein crystal, resulting in nanometer-scale periodic arrays of holes in a metallic overlayer[6]. We have studied the process of pattern formation by looking at the temporal evolution of hole size and shape, and at temperature effects on patterning, in hopes of establishing qualitatively the relative roles of sputtering and thermal diffusion. We conclude that sputtering is likely the dominant process which causes pattern formation, but that thermal diffusion also appears to be required for the formation of well-defined, distinct holes and resultant uniform patterning.
EXPERIMENTAL PROCEDURE Figure 1 shows the procedure used to produce nanostructures in our laboratory. The protein crystal is deposited and dried onto a suitable substrate (Figure la),
Mat. Res. Soc. Symp. Proc. Vol. 236. @1992 Materials Research Society
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metallized (Figure 1b) and milled (Figure 1c). Figure ld shows a plan view of an idealized nanostructure. The protein crystal we use is S-layer, or (a) -sbstrata t surface layer, of S. solfataricus. The isolation procedure has been outlined n Metal shadowing earlier[7]. S-layer sheets (1 j.i average Metal overlayer diameter) were deposited (1 minute Protein C C incubation) onto carbon coated 200 or (b) 400 mesh Cu transmission electron •7 Ion milling micro
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