Fabrication of high-aspect-ratio silicon nanostructures using near-field scanning optical lithography and silicon anisotropic wet-etching processOutlineIntroductionSlide 4The Near-field scanning optical lithography (NSOL) systemFabrication processResults: After PR DevelopmentResult: After KOH wet etchingSummaryEE235 Class Presentation on Lithography (Spring 2007)Fabrication of high-aspect-ratio siliconFabrication of high-aspect-ratio siliconnanostructures using near-field scanningnanostructures using near-field scanningoptical lithography and silicon anisotropicoptical lithography and silicon anisotropicwet-etching processwet-etching processby S. J. Kwon, Y. M. Jeong, and S. H. Jeong by S. J. Kwon, Y. M. Jeong, and S. H. Jeong Gwangju Institute of Science and Technology (Korea)Gwangju Institute of Science and Technology (Korea)Applied Phys. A – Material Science and Processing, vol. 86, Applied Phys. A – Material Science and Processing, vol. 86, pp. 11-18, 2007)pp. 11-18, 2007)Presented by Darsen Lu (3/19/2007)Presented by Darsen Lu (3/19/2007)EE235 Class Presentation on Lithography (Spring 2007)UC Berkeley - 2OutlineOutlineIntroductionIntroductionDescription of the tools and experimental Description of the tools and experimental setupsetupFabrication ResultsFabrication ResultsConclusionConclusionEE235 Class Presentation on Lithography (Spring 2007)UC Berkeley - 3IntroductionIntroductionScanning probe lithography (SPL)Scanning probe lithography (SPL)SPL is a nanopatterning technique based on scanning probe miSPL is a nanopatterning technique based on scanning probe microscope technologiescroscope technologiesVarious forms of SPL techniques includeVarious forms of SPL techniques includeAtomic Force Microscope (AFM) LithographyAtomic Force Microscope (AFM) LithographyDip-pen lithographyDip-pen lithographyNear Field Scanning Optical lithographyNear Field Scanning Optical lithography(NSOL)(NSOL)As opposed to the electron beam (e-beam) lithography, SPLs cAs opposed to the electron beam (e-beam) lithography, SPLs can be exercised under ambient conditionsan be exercised under ambient conditionsThis PaperThis PaperThe The NSOLNSOL is used to pattern is used to pattern nanochannelnanochannels with high aspect r with high aspect ratioatioEE235 Class Presentation on Lithography (Spring 2007)UC Berkeley - 4Dip Pen NanolithographyIn near field scanning optical microscopy (NSOM) a very small light source very close to the sample is scanned. Light passes through a sub-wavelength diameter aperture and illuminates a sample that is placed within its near field, at a distance much less than the wavelength of the light. The resolution achieved is far better than that which is attainable in conventional optical microscopes. Atomic Force MicroscopeNear Field Scanning Optical Microscopyhttp://stm2.nrl.navy.mil/how-afm/how-afm.html http://www.nanoink.net/WhatisDPN.htm http://en.wikipedia.org/wiki/Near-field_scanning_optical_microscope IntroductionIntroductionEE235 Class Presentation on Lithography (Spring 2007)UC Berkeley - 5The Near-field scanning optical The Near-field scanning optical lithography (NSOL) systemlithography (NSOL) system442nm, 130mW, He-Cd Laser SourceShutterPosition Feedback SystemApertured Cantilever NanoprobePower MeterND FilterFiberWafer + PRLight goes througLight goes through the apertured ch the apertured cantilever nanoproantilever nanoprobe and expose thbe and expose the photoresist (PR)e photoresist (PR)..The nanoprobe mThe nanoprobe moves along a trajeoves along a trajectory to pattern tctory to pattern the PRhe PRMotorized StageEE235 Class Presentation on Lithography (Spring 2007)UC Berkeley - 6Fabrication process Fabrication process Goal: fabricate high-aspect-ratio (HAR) nanochGoal: fabricate high-aspect-ratio (HAR) nanochannelsannelsProcedure:Procedure:1. Start with a 110 wafer2. Deposit 10nm nitride using LPCVD3. A commercial photoresist is deposited on the wafer4. The 111 direction of the wafer is aligned precisely to the y-axis of the microscope5. The NSOL scans through the programmed trajectory6. PR Development7. RIE etch of PR and nitride in CF4/O2 Plasma8. KOH wet etchEE235 Class Presentation on Lithography (Spring 2007)UC Berkeley - 7Results: After PR DevelopmentResults: After PR DevelopmentGood linewidth uniformity is achieved (Fig. 1, 2)Good linewidth uniformity is achieved (Fig. 1, 2)Reproducibility over the same sample has been Reproducibility over the same sample has been proved (Fig. 3)proved (Fig. 3)Fig. 2 Fig. 4Fig. 1Fig. 3Reproducibility between different Reproducibility between different samples requires further study (Fig. 4)samples requires further study (Fig. 4)Solid lines: first sampleSolid lines: first sampleDotted lines: second sampleDotted lines: second sample13%7.7%EE235 Class Presentation on Lithography (Spring 2007)UC Berkeley - 8Result: After KOH wet etchingResult: After KOH wet etchingWet Etching ResultWet Etching Result1. Width 200nm / Depth 800nm1. Width 200nm / Depth 800nm2. Width 230nm / Depth 1560nm2. Width 230nm / Depth 1560nmCompare with theoretical KOH Compare with theoretical KOH selectivityselectivityReason for width increase: Reason for width increase: Nonzero etching in the Nonzero etching in the {111} plane{111} planeThinning of SiThinning of Si33NN44 at the at the edge of the channel during edge of the channel during the dry-etchingthe dry-etchingThe. {111} : {110} = 1 : 600The. {111} : {110} = 1 : 600Exp. {111} : {110} = 1 : 26Exp. {111} : {110} = 1 : 26NSOL effect was proven by NSOL effect was proven by closing the shutter during the closing the shutter during the scanning process (see right scanning process (see right figure)figure)EE235 Class Presentation on Lithography (Spring 2007)UC Berkeley - 9SummarySummaryAn NSOL system has been set up for nanofabricationAn NSOL system has been set up for nanofabricationLines have been patterned and good linewidth uniformitLines have been patterned and good linewidth uniformity has been demonstrated. However, further study is ney has been demonstrated. However, further study is needed to improve the reproducibility over different sampleded to improve the reproducibility over different samples.es.Nanochannel has been produced after wet etching. A liNanochannel has been produced after wet etching. A linewidth of ~200nm and an aspect ratio of 1:6.8 has beenewidth of ~200nm and
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