Lithography via electrospun fibers with quantitative morphology analysis

Electrospun fibers have been used to enhance material properties, as drug delivery devices, and for physical filtration systems. However, the use of electrospinning as a viable method for lithographic patterning and subsequent pattern transfer has not been demonstrated. As with traditional lithography methods, feature position and size are critical to the performance and repeatability of resultant structures. The placement of electrospun fibers is driven by the electrostatic field strength. In the present research, the electrostatic field strength between the spinneret (capillary) and the substrate (collection electrode) is controlled by modifying the voltage applied to two electrodes on or adjacent to the substrate. Such manipulation modifies the applied electrostatic field, creating a stronger field strength directed at one electrode as compared to the other. The fiber will preferentially be directed to the electrode along the path of highest field strength, resulting in deposition to the desired electrode. Two methods to control the voltage applied to the two electrodes during electrospinning are presented: (1) electronic control of the applied electrode voltage and (2) electromechanical control of the applied electrode voltage. The use of an electromechanical commutator resulted in an increase in deposition (and associated lithographic write) speed. Both methods of voltage control result in the deposition of aligned fibers onto the substrate. Additional studies examine the relationship between shape of the electrodes and subsequent alignment achieved. Image analysis quantifying image analysis via fast Fourier transform is used to quantify fiber alignment. Resultant fibers are used to transfer the fiber pattern into an underlying silicon substrate via lift-off and subsequent plasma etching. Results demonstrate the potential of electrospun fiber masks for future use in the economical fabrication of electronic and optical devices where nanoscale features over large areas are suitable. (C) 2016 American Vacuum Society.