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Lithography Tools and Capabilities*Chan Kok Wai, Nor Ibrahim, Zhang Shujie, Antonio Castro NetoMicro and Nano Fabrication Facilities, Graphene Research CentreDepartment of Physics, Faculty of Science, National University of Singapore*Contact: kokwai@nus.edu.sg

PhotolithographyElectron Beam Lithography (EBL)The Graphene Research Centre has built a 800 m2 state-of-the-art 1cleanroom facility with Class 1000 and 100 ISO 14644-1 cleanliness standards. It provides sophisticated micro- and nanofabrication facilities for graphene and other research materials. Below we present the lithography tools available in the clean room and their capabilities.

http://graphene.nus.edu.sg/content/clean-roomhttp://www.suss.com/en/products-solutions/products/mask-aligner/mjb4/overview.htmlhttp://microchem.com/pdf/PMMA_Data_Sheet.pdfhttp://www.lesker.com/newweb/Vacuum_systems/deposition_systems_pvd_nano36.cfmhttp://www.microtechweb.com/http://www.microchemicals.com/products/photoresists/azr_1512hs.htmlhttp://microchem.com/PDFs_Dow/S1800.pdfhttp://www.fei.com/products/scanning-electron-microscopes/nova.aspxhttp://www.jcnabity.com/SEM images were obtained using Carl Zeiss Supra FESEM at their Demo Centre in National University of Singapore.ReferencesThe authors thank Ang Han Siong, Dylan, Ryan Woong and Bernard Wong for managing the cleanroom facilities, operation and, health and safety matters. This research centre is supported by National University of Singapore and National Research Foundation Singapore.AcknowledgementsApart from the lithography tools shown here, there are thin film deposition, crystal growth, plasma etcher, annealing furnace, probe station, atomic force microscopy, Raman spectroscopy and etc. tools available in the cleanroom to support world class research activities.

Lithography its an art at the nanoscaleSummaryMask AlignerLaser Writer

Figure 5: FEI nanoSEM230

Figure 1: SUSS MJB4

Figure 3: Microtech LW405B

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2.(a)Figure 2: Microscope images showing the lithography features achieved using the mask aligner. Lithography was done using 3Microchem PMMA resist under DUV exposure, metalized using 4Lesker nano36 thermal evaporator and lifted off. (a) Shows 0.8mm and 1mm linewidths / spacing. (b) Shows 1mm and 1.5mm circles. (c) Shows 2mm fractal patterns.The 2SUSS MJB4 mask aligner is equipped with broadband UV, singlefield or splitfield microscope for fast and accurate alignment, and high resolution printing capability in the submicron range. It is able to support up to 100mm substrate with various contact modes soft, hard and vacuum. Its high resolution (HR) optics (UV250/300/365/400) allows for fast switching between different wavelengths. UV250 optic allows deep UV (DUV) lithography for prints down to 0.5m in vacuum contact.The 5Microtech LW405B system transforms a laser beam into a controlled writing tool for photolithographic mask fabrication or for direct in situ processing on planar substrates. It is equipped with 375nm and 405nm wavelength laser and is able to handle up to 100mm substrate. It has automatic focus function and pads mode for users to design their pattern on the spot and fast lithography. This feature is useful for patterning on crystalline structure at random location on a sample.10mm

2.(b)10mmThe 8FEI Nova nanoSEM 230 is an ultra-high resolution field-emission SEM system configured to get the most information out of the largest selection of samples, down to the nanometer level. It offers ultra-high resolution characterization at low and high voltage in high vacuum (1kV 30kV). Apart from SEM, it is an extensive set of tools for nanoprototyping, with an on-board digital pattern generator and dedicated patterning software (9Nabity - NPGS & designCAD), a high speed electrostatic beam blanker and gas injection systems for direct electron beam writing of nanostructures. With novel technique and acute tuning of the system, we are able to achieve 50nm linewidth features. *There is still room for improvement to push the lithography resolution beyond this limit.1mm0.8mm1mm1.5mm

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40mm6.(b)Figure 4: Microscope images showing the lithography features achieved using the laser writer. Lithography was done using either 6AZ1512HS or 7S1805 photoresists. (a) Test pattern used for dosage trial and stitch test. (b) Shows 0.8mm up to 2mm feature size.Figure 6: Scanning electron microscopy images showing the lithography features achieved using the FEI SEM system.(a) 200nm thick 3950k PMMA A4 was used on Si/SiO2 substrate and metalized with 50nm thick metal. The write was done with 500mC/cm2 dose and 1700x magnification (approx. 100mm x 100mm write field). (b) Shows 40mm in length lines with different linewidths from left; (50nm 500nm). 10(c) Zoom out of the 50nm lines. 10(d) Zoom in of a single 50nm line.

6.(d)50nm

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