CAREER: Nanolithography Using Ultrashort-Pulsed Laser Processing

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This Faculty Early Career Development (CAREER) Program grant supports basic research in laser-based advanced manufacturing that enables single-step fabrication of nano-scale structures over a large area. Current nanofabrication processes involve multiple steps and are not suitable for fabricating one-of-a-kind or customized nanostructures in a cost-effective manner. In this project, an ultrashort-pulsed laser, which emits flashes of light (pulses) with extremely short duration, is used to drill, cut and pattern materials with nano-scale precision. Because the duration of a pulse is so short (less than one trillionth of a second), the energy of the laser pulse is highly concentrated in the material, creating conditions that are not normally achieved with other processing methods. Ultrashort-pulsed laser processing provides the key advantage of significantly-reducing collateral damage, that is damaging the surrounding material, and thus improving precision in the processing of a variety of materials. This project advances the understanding of ultrashort-pulsed laser processing of dielectric materials, such as glass and diamond, which are commonly used in display panels, microelectronics and cutting tools. Advances resulting from the project benefits society by enabling a new method for nano-scale patterning that reduces manufacturing time and lowers cost, and by supporting an education and outreach program aimed at cultivating a well-trained manufacturing workforce. The project raises public awareness of laser and optical technologies in everyday life, attracts young students to science and technology, and guides college students to pursue a career in advanced manufacturing. The new nanolithography method is based on laser ablation using a sequence of ultrashort laser pulses (a pulse train) that is temporally tuned to create localization of free-carrier population and enhanced absorption of laser energy. Nonlinear interaction between ultrashort laser pulses and wide-bandgap dielectrics is studied and controlled to enhance spatial resolution and improve energy-absorption efficiency. The research generates knowledge of the critical process parameters and relevant nanoscale physics that enable this new nanofabrication method. Three processing modes - drilling, cutting, and projection (using an electronically-controlled spatial light modulator as a customizable photomask) - are explored, and the challenges unique to each mode are studied. Spatial and temporal electron dynamics, which play a key role in laser processing of dielectric materials, are investigated by transient pump-probe microscopy and laser damage threshold measurement. Large-area patterning of arbitrary nanostructures are demonstrated using a system that integrates pulse-train processing with mask-projection lithography. This project enhances the capability of ultrashort-pulsed lasers as a manufacturing tool and opens up new opportunities for studying laser-matter interactions in the above-damage-threshold regime.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.