Abstract
Accurate characterization of thin films and geometric features including the cavities during and after the fabrication process is crucial for proper CMUT operation, reliability, consistent array operation, and improved yield. Three different optical profilometry techniques: white light interferometry, laser confocal microscopy, and structural grid illumination microscopy have been reviewed in this paper with a focus on characterization of various thin films and geometric features during different CMUT fabrication stages and post processing. The relative merits of each technique have been investigated experimentally in the context of CMUT fabrication for better characterization and process development. The surface roughness and diaphragm deformation results have also been compared with AFM data. From the review, it appears that characterization needs of CMUTs are unique and a combination of complex diversified characterization tools is necessary to generate sufficient data for design verification and functional optimization.
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References
Adam Puche (2005) Independent Resolution Testing of OptiGrid® Device. http://www.qioptiq.com/download/OptiGrid%20Resolution%20Comp.pdf. Accessed 17 Apr 2018
Bakhtazad A, Manwar R, Chowdhury S (2014) Cavity formation in bonded silicon wafers using partially cured dry etch bisbenzo-cyclobutene (BCB). In: Proc. of 2014 IEEE 5th Latin American Symp. on Circuits and Systems (LASCAS), Santiago, Chile, pp 1–4
Biggs DSC (2010) 3D deconvolution microscopy. Curr Protoc Cytom 52(1):12–19
Brennan JC et al (2015) Flexible conformable hydrophobized surfaces for turbulent flow drag reduction. Sci Rep. https://doi.org/10.1038/srep10267
Bruker (2018) Through transmissive media module. https://www.bruker.com/products/surface-and-dimensional-analysis/3d-optical-microscopes/accessories/through-transmissive-media-ttm-module.html. Accessed Apr 2018
Cianci E et al (2002) Fabrication of capacitive ultrasonic transducers by a low temperature and fully surface-micromachined process. Precis Eng 26(4):347–354
Claxton NS, Fellers TJ, Davidson MW (2006) Laser scanning confocal microscopy. Department of optical microscopy and digital imaging, Florida State University, Tallahassee. https://www.researchgate.net/publication/265074777_LASER_SCANNING_CONFOCAL_MICROSCOPY. Accessed Apr 2018
Cole RW, Jinadasa T, Brown CM (2011) Measuring and interpreting point spread functions to determine confocal microscope resolution and ensure quality control. Nat Protoc 6(12):1929
ContourGT-K (2018) 3D Optical Microscope. https://www.bruker.com/products/surface-and-dimensional-analysis/3d-optical-microscopes/contourgt-k/overview.html. Accessed 23 Aug 2018
Cox I, Sheppard C, Wilson T (1996) Super-resolution by confocal fluorescent microscopy. SPIE Milest Ser MS 131:178–181
de Groot P (2015) Principles of interference microscopy for the measurement of surface topography. Adv Opt Photon 7(1):1–65
de Groot PJ, de Lega XC, Fay MF (2008) Transparent film profiling and analysis by interference microscopy. In: Interferometry XIV: applications, 70640I, San Diego, California, US. https://doi.org/10.1117/12.794936
Delica S, Blanca CM (2007) Wide-field depth-sectioning fluorescence microscopy using projector-generated patterned illumination. Appl Opt 46(29):7237
Duparre A et al (2002) Surface characterization techniques for determining the root-mean-square roughness and power spectral densities of optical components. Appl Opt 41(1):154–171
Erguri AS et al (2005) Capacitive micromachined ultrasonic transducers: fabrication technology. IEEE Trans Ultrason Ferroelectr Freq Control 52(12):2242–2258
Flex-Axiom (2018) AFM for materials research. https://www.nanosurf.com/en/products/flex-axiom-afm-for-materials-research. Accessed 27 Sep 2018
Guo S, Gustafsson G, Hagel OJ, Arwin H (1996) Determination of refractive index and thickness of thick transparent films by variable-angle spectroscopic ellipsometry: application to benzocyclobutene films. Appl Opt 35(10):1693–1699
Hernandez J, Zure T, Chowdhury S (2013) Capacitance measurements of an SOI based CMUT. In: Proc. of 2013 IEEE Fourth Latin American Symposium on Circuits and Systems (LASCAS). Cuzco, Peru, pp 1–4
Kossivas F, Doumanidis C, Kyprianou A (2012) Thickness measurement of photoresist thin films using interferometry. In: Padron I (ed) Interferometry-research and applications in science and technology, IntechOpen, pp 361–376. https://doi.org/10.5772/34983. https://www.intechopen.com/books/interferometry-research-and-applications-in-science-and-technology/thickness-measurement-of-photoresist-thin-films-using-interferometry. Accessed Feb 2018
Kulik EA, Calahan P (1997) Laser profilometry of polymeric materials. Cells and Materials 7(2):3
Leach R (2011) Optical measurement of surface topography. Springer, New York
Li Z et al (2016) Fabrication of capacitive micromachined ultrasonic transducers based on adhesive wafer bonding technique. J Micromech Microeng 26(11):115019
Logan AS, Wong LLP, Yeow JTW (2011) A 1-D capacitive micromachined ultrasonic transducer imaging array fabricated with a silicon-nitride-based fusion process. IEEE/ASME Trans Mechatr 16(5):861–865
Manwar R, Simpson T, Bakhtazad A, Chowdhury S (2017) Fabrication and characterization of a high frequency and high coupling coefficient CMUT array. Microsyst Technol 23(10):4965–4977
Modafe A, Ghalichechian N, Powers M, Khbeis M, Ghodssi R (2005) Embedded benzocyclobutene in silicon: an integrated fabrication process for electrical and thermal isolation in MEMS. Microelectron Eng 82(2):154–167
Neil MA, Juškaitis R, Wilson T (1997) Method of obtaining optical sectioning by using structured light in a conventional microscope. Opt Lett 22(24):1905
Oralkan O et al (2002) Capacitive micromachined ultrasonic transducers: next-generation arrays for acoustic imaging? IEEE Trans Ultrason Ferroelectr Freq Control 49(11):1596–1610
Park M-C, Kim S-W (2001) Compensation of phase change on reflection in white-light interferometry for step height measurement. Opt Lett 26(7):420–422
Sakai T, Sakuyama S, Mizukoshi M (2008) A new flip-chip bonding method using ultra-precision cutting of metal/adhesive layers. J Jpn Inst Electr Pack 11(3):217–222
Saxena M, Eluru G, Gorthi SS (2015) Structured illumination microscopy. Adv Opt Photon 7(2):241
Scanning Probe Microscope AFM5500M (2018) https://www.hitachi-hightech.com/global/science/products/microscopes/afm/units/afm5500m.html
Schmit J, Creath K, Wyant JC (2007) Surface profilers, multiple wavelength, and white light interferometry. In: Malacara D (ed) Optical Shop Testing, 3rd edn. Wiley, pp 667–755
VK-X260 K (2018) Technical Guides| VK-X series| KEYENCE America. https://www.keyence.com/products/measure-sys/3d-measure/vk-x100_x200/models/vk-x260k/index.jsp. Accessed 27 Sep 2018
Wilson T (2011) Resolution and optical sectioning in the confocal microscope. J Microsc 244(2):113–121
Yahya NAM et al (2011) Curing methods yield multiple refractive index of benzocyclobutene polymer film. Int J Mat Metallurgic Eng World Acad Sci Eng Technol 5(2):163–165
Yamaner FY, Zhang X, Oralkan Ö (2014) Fabrication of anodically bonded capacitive micromachined ultrasonic transducers with vacuum-sealed cavities. In: Proc. of 2014 IEEE International Ultras. Symposium (IUS), Chicago, IL, USA, pp 604–607
Yang G-R, Zhao Y-P, Neirynck JM, Murarka SP, Gutmann RJ (1997) Chemical-mechanical polishing of parylene N and benzocyclobutene films. J Electrochem Soc 144(9):3249–3255
ZETA-20 (2018) true color 3d non-contact optical profiler with multi mode optics technology. https://www.zeta-inst.com/products/true-color-3D-optical-profiler. Accessed 27 Sep 2018
Zhuang X et al (2009) Wafer-bonded 2-D CMUT arrays incorporating through-wafer trench-isolated interconnects with a supporting frame. IEEE Trans Ultrason Ferroelectr Freq Control 56(1):182–192
Zure T, Chowdhury S (2012) Fabrication and measurements of dynamic response of an SOI based non-planar CMUT array. Microsyst Technol 18(5):629–638
Zure T, Hernandez J, Chowdhury S (2012) Dynamic analysis of an SOI based CMUT. In: Proc. of 2012 IEEE International Conference on Industrial Technology (ICIT), Athens, Greece, pp 539–544
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Bakhtazad, A., Chowdhury, S. An evaluation of optical profilometry techniques for CMUT characterization. Microsyst Technol 25, 3627–3642 (2019). https://doi.org/10.1007/s00542-019-04377-4
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DOI: https://doi.org/10.1007/s00542-019-04377-4