Direct Focused Ion Beam Writing of Printheads for Pattern Transfer Utilizing Microcontact Printing
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ý.CP is a non-photolithographic technique for printing micron-scale and submicron-scale features and devices. 9-11 It utilizes self-assembled monolayers (SAMs) as an "ink," and polydimethylsiloxane (PDMS) as an elastomeric "stamp." Patterns are cast as molds into PDMS from "masters" (such as traditional photolithography masks, e-beam masks, and now FIB patterned printheads). The PDMS replicas of the original patterns are then coated with SAMs and dried. The PDMS is brought into conformal contact with an Ag-coated single crystal Si substrate, and the SAMs transfer from the PDMS to the Ag film. When the Ag film is etched, it will etch only in regions not patterned by the SAMs, which acts as an etch barrier. Thus, the patterns from the original master are reproduced on the target substrate. (Materials other than Ag have been "printed," such as Al, Au, Cu, Si, etc.)."2 -7 The main advantages of •tCP as a soft-lithographic technique are low cost, ease of reproducibility, and application to both planar and curved surfaces. Conventional lithographic techniques are limited generally to planar surfaces because of small depth of focus; using ý.CP we have been able to print deep sub-micron features on both planar and curved substrates (radius of curvature 3-5 cm), Figure 2. Most results herein are shown for planar surfaces; note that similar results have been realized for experiments on curved surfaces. Whitesides, et al., have also used ItCP for curved surfaces. 18-19 We have developed a new avenue in both ý±CP and FIB fields by fabricating masters for j.CP in the FIB. A main advantage is the rapid prototyping of printhead master patterns in the FIB, enabling a much quicker turnaround time from concept and design to printing. In addition, use of the FIB allows for printhead fabrication on both planar and curved surfaces, which cannot be done easily by conventional lithography. This paper discusses our recent developments in FIB fabrication of masters and applications of pCP.
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Figure 1: (a) FIB micrograph (left) showing 15 patterns out of a 37-pattern printhead. The individual patterns were milled at 1000 pA and 2700 pA beam currents in an FEI 200 FIB. Line patterns are in the top half of the figure, and dot patterns in the bottom half. (b) FIB micrograph (right) showing a magnified view of the lower left dot patterns in (a). Each pattern is 26 x 26 dots.
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Figure 2: (a) FIB micrograph (left) showing pCP surface of a Ag film (1 50nm thick) on a 5cm radius of curvature glass lens. (b) FIB micrograph (right) showing a magnified view of the image in (a). Arrows indicate piCP lines. Experiment Printheads are fabricated in the FIB on single crystal Si (100) wafers. The FIB employed is an FEI Series 200, with a Ga÷ liquid metal ion source, minimum spot size -10 nm, ion energy 30 keV and ion current density -10 A/cm2. The field of view is up to 1 mm2 at 30 keV, and calibrated specimen drift rates are as low as 1.5 nm/min. The depth of focus is of order 200 jtm. Feature sizes less than 0.1 ptm may be fabricated by both mi
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