Whitney Longsine's research while affiliated with Texas A&M University and other places

Advances in inkjet technology is facilitating fabrication processes across a wide range of technology, including 3D printing, electronic circuit printing, solar cell, and sensors. A major area for potential growth of inkjet technology exists in the semiconductor market for lithographic patterning. The most basic form of nanoimprint lithography (NIL) requires a 1X mask, imprint fluid, and a substrate. This chapter provides a general description of the two prominent types of NIL: thermal and UV-NIL, a discussion of the inkjet technology used and requirements, and the review of successful applications using NIL with inkjet printheads. For the UV-NIL process, it focuses on jet and flash imprint lithography (J-FIL) as it utilizes the advantages of inkjet printheads for its process. The most widely discussed applications for J-FIL are semiconductor devices. J-FIL nanoimprint lithography is currently the only imprint technology making the transition from research to high-volume manufacturing in the semiconductor industry.

Nanoimprint lithography (NIL), a molding process, can replicate features <10 nm over large areas with long-range order. We describe the early development and fundamental principles underlying the two most commonly used types of NIL, thermal and UV, and contrast them with conventional photolithography methods used in the semiconductor industry. We then describe current advances toward full commercial industrialization of UV curable NIL (UV-NIL) technology for integrated circuit production. We conclude with brief overviews of some emerging areas of research, from photonics to biotechnology, in which the ability of NIL to fabricate structures of arbitrary geometry is providing new paths for development. As with previous innovations, the increasing availability of tools and techniques from the semiconductor industry is poised to provide a path to bring these innovations from the lab to everyday life. Expected final online publication date for the Annual Review of Chemical and Biomolecular Engineering Volume 7 is June 07, 2016. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.

Imprint lithography has been shown to be an effective technique for replication of nano-scale features. Jet and Flash Imprint Lithography (J-FIL) involves the field-by-field deposition and exposure of a low viscosity resist deposited by jetting technology onto the substrate. The patterned mask is lowered into the fluid which then quickly flows into the relief patterns in the mask by capillary action. Following this filling step, the resist is crosslinked under UV radiation, and then the mask is removed, leaving a patterned resist on the substrate. Non-fill defectivity must always be considered within the context of process throughput. Processing steps such as resist exposure time and mask/wafer separation are well understood, and typical times for the steps are on the order of 0.10 to 0.20 seconds. To achieve a total process throughput of 20 wafers per hour (wph), it is necessary to complete the fluid fill step in 1.0 seconds, making it the key limiting step in an imprint process. Recently, defect densities of less than 1.0/cm2 have been achieved at a fill time of 1.2 seconds by reducing resist drop size and optimizing the drop pattern. There are several parameters that can impact resist filling. Key parameters include resist drop volume (smaller is better), system controls (which address drop spreading after jetting), Design for Imprint or DFI (to accelerate drop spreading) and material engineering (to promote wetting between the resist and underlying adhesion layer). In addition, it is mandatory to maintain fast filling, even for edge field imprinting. This paper addresses the improvements made with reduced drop volume and enhanced surface wetting to demonstrate that fast filling can be achieved for both full fields and edge fields. By incorporating the changes to the process noted above, we are now attaining fill times of 1 second with non-fill defectivity of ~ 0.1 defects/cm2.

Imprint lithography is an effective technique for replication of nanoscale features. Jet and Flash™ Imprint Lithography (J-FIL™) uses field-by-field deposition and exposure of a low viscosity resist deposited by inkjet printing onto the substrate. The patterned mask is lowered into the fluid, where capillary action assists to flow the fluid into the relief patterns. Following the filling step, the resist is UV cured, the mask is removed, and a patterned resist is left on the substrate. J-FIL™ is a technique, where the imprint technology provides the nanoscale pattern resolution while the inkjet technology contributes the throughput that is required for industrial applications. The drop volume and drop placement accuracy of the inkjet-printed resist is critical, allowing the volume to be distributed appropriately across the substrate surface to achieve a uniform target thickness and preventing non-filling of the relief patterns. With J-FIL™, it is possible to resolve 28 run structures with residual layer thickness of 13 and 20 nm on 300 mm and 450 mm Si-wafers. In this study, improvements during the filling step are explored for low droplet volumes at high ejection frequencies when using standard printheads with jetting performance of 12 kHz, <3pL and modified printheads with jetting performance of 28 kHz, <2pL.

Ultrasound is emerging as an attractive alternative modality to standard x-ray and CT methods for bone assessment applications. As of today, however, there is a lack of systematic studies that investigate the performance of diagnostic ultrasound techniques in bone imaging applications. This study aims at understanding the performance limitations of new ultrasound techniques for imaging bones in controlled experiments in vitro. Experiments are performed on samples of mammalian and non-mammalian bones with controlled defects with size ranging from 400 microm to 5 mm. Ultrasound findings are statistically compared with those obtained from the same samples using standard x-ray imaging modalities and optical microscopy. The results of this study demonstrate that it is feasible to use diagnostic ultrasound imaging techniques to assess sub-millimeter bone defects in real time and with high accuracy and precision. These results also demonstrate that ultrasound imaging techniques perform comparably better than x-ray imaging and optical imaging methods, in the assessment of a wide range of controlled defects both in mammalian and non-mammalian bones. In the future, ultrasound imaging techniques might provide a cost-effective, real-time, safe and portable diagnostic tool for bone imaging applications.