Nghiên cứu thiết kế tối ưu mũi dò quét định hướng ứng dụng trong kỹ thuật khắc nano

MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF TECHNOLOGY AND SCIENCE INTERNATIONAL TRAINING INSTITUTE FOR MATERIALS SCIENCE - LE VAN TAM STUDY AND OPTIMIZING DESIGN OF SCANNING PROBES FOR NANOLITHOGRAPHY MASTER THESIS OF MATERIALS SCIENCE Batch ITIMS-2015 SUPERVISOR Dr CHU MANH HOANG Hanoi – 2017 ACKNOWLEDGEMENT I would like to thank my supervisor, Dr Chu Manh Hoang who has supervised and encouraged me during my stay at ITIMS Acknowledgement would be also sent to all the members of optical micro-nano systems and sensors technology Laboratory – International Training Institute for Materials Science (ITIMS) Finally, thanks should also be given to my family and friends, who always supported me in my study I LIST OF PUBLICATIONS Le Van Tam, Dang Van Hieu, Vu Ngoc Hung and Chu Manh Hoang, “Design And Simulation Of Scanning Probe Micro – Cantilever”, National Conference On Applied And Engineering Physics, pp 285-288, 2015, ISBS 978-604-913-232-2 Le Van Tam, Dang Van Hieu, Vu Ngoc Hung and Chu Manh Hoang, “Electrostatic Actuator For Improving Scanning Probe Lithography”, 9th Vietnam National Conference of Solid Physics and Materials Science, pp 393-397, 2015, ISBN 978604-938-722-7 Le Van Tam, Dang Van Hieu, Vu Ngoc Hung and Chu Manh Hoang, “A MicroSuspension Electrostatic Actuator For Improving The Performance Of Scanning Probe Nanolithography”, 3rd International Conference on Advanced Materials and Nanotechnology, pp.285-288, 2016, ISBN 978-604-913-232-2 Dang Van Hieu, Le Van Tam, Nguyen Van Cuong and Chu Manh Hoang, “Design And Simulation Of Serpentine Springs For Scanning Probe”, Workshop on Advanced Nanomaterials & Nanotechnology, pp.221-224, 2017, ISBN 979-604-950298-9 Le Van Tam, Dang Van Hieu, Nguyen Duy Vy, Vu Ngoc Hung and Chu Manh Hoang, “Design And Simulation Analysis Of An Electrostatic Actuator For Improving The Performance Of Scanning Probe Nanolithography”, Vietnam Journal Of Science And Technology, pp.484-493 55, 4, 2017, DOI: 10.15625/25252518/55/4/8803 II STATEMENT OF ORIGINAL AUTHORSHIP I hereby declare that the results presented in the thesis are performed by the author The research contained in this thesis has not been previously submitted to meet requirements for an award at this or any higher education institution Date: Signature: III 28/09/2017 TABLE OF CONTENTS CHAPTER INTRODUCTION 1.1 Scanning probe microscopes (SPMs) 1.1.1 Scanning tunneling microscope (STM) 1.1.2 Atomic force microscope (AFM) 1.2 Scanning probe lithography (SPL) 1.3 Mechanical Scratching 1.4 Cantilever actuator 14 1.4.1 Thermal bimetallic actuation 14 1.4.2 Piezoelectric actuation 15 1.4.3 Electrostatic actuation 16 1.5 Purpose of this thesis 17 CHAPTER DESIGN OF SCANNING PROBE 18 2.1 Single degree of freedom mass spring model for electrostatic actuator 19 2.2 Cantilever structure 24 2.2.1 Operation frequency and stiffness 24 2.2.2 Cantilever probe actuation and sensing 29 2.3 Clamped-clamped probe 32 2.3.1 Operation frequency and stiffness 32 2.3.2 Clamped-clamped actuation and sensing 35 2.4 Micro-suspension based scanning probe 35 2.4.1 Operation frequency and stiffness 36 IV 2.4.2 Micro-suspension probe sensing and actuation 37 2.5 Numerical method 39 CHAPTER RESULTS AND DISCUSSION 42 3.1 Natural frequencies and stiffness 42 3.1.1 Cantilever probe 42 3.1.2 Clamped-clamped probe 44 3.1.3 Micro suspension probe 45 3.2 Static deflection 47 3.3 Dynamic deflection 53 CONCLUSIONS 57 FURTURE WORKS 58 REFERENCES 59 V LIST OF FIGURES Figure 1 The basic configuration of a SPM [2] Figure The basic configuration of AFM [2] Figure Schematic of nanoscale scratching using AFM [17] 10 Figure Schematic of top surface imaging concept, the tip scratching on polymer layer (a); the transfer of the pattern by etching and removing polymer layer (b) [12] 10 Figure AFM image of plowed PMMA groove by silicon tip (a) Profile of the groove (b) [7] 11 Figure SEM image of diamond-coated tip side view and SEM image of tip top view [18] 12 Figure Main steps of the AFM-based trilayer process (a), AFM image of a furrow engraved in polyimide (b) [5] 12 Figure The schematic of AFM tip-based dynamic plowing lithography (a) high scratching velocity (b), medium scratching velocity (c), and low scratching velocity (d) [9] 13 Figure AFM images of an array of pits with a scratching velocity of 400 μm/s [9] 14 Figure 10 Probe array using thermal bimetallic actuator [19] 15 Figure 11 A schematic of the piezoelectric microcantilever array [10] 16 Figure 12 A schematic of electrostatic actuation [6] 16 Figure Single degree of freedom mass-spring for electrostatic actuator 19 Figure 2 Schematic diagram of 2D parallel plate capacitor with fringe field 24 Figure A cantilever probe structure 24 Figure The first natural frequency of cantilever versus dimensions of cantilever 26 Figure The dimensions of probe and forces exert on the tip when probe operating 27 Figure The schematic of unsymmetrical operation mode of the cantilever probe 30 Figure Parallel capacitance depends on the dimensions of beams and the gap 30 Figure Schematic of the clamped-clamped probe 32 Figure The first natural frequency of clamped-clamped probe versus dimensions of clamped-clamped probe 33 Figure 10 The micro-suspension electrostatic actuator 36 Figure 11 Equivalent Lumped-parameter model of the micro-suspension electrostatic actuator 36 Figure 12 The fixed electrode area is equal to the entire back side area of the probe (a) The fixed electrode area is equal to the backside area of the plate (b) 38 Figure 13 Parallel capacitance depends on the length of the plate and the gap 38 Figure 14 Schematic time response of an under damped single degree of freedom system 40 Figure The first three mode shapes and natural frequencies of the cantilever probe 42 Figure The first three mode shapes and natural frequencies of the clampedclamped probe 44 Figure 3 The first three mode shapes and natural frequencies of the micro suspension probe 46 Figure The displacement of tip versus applied voltage 47 Figure The x-displacement versus the z-displacement of tip in the cantilever probe 49 Figure Change in capacitance vs displacement 50 Figure Tip displacements as a function of applied voltage V0 51 Figure Change in capacitance vs displacement 52 Figure Time response of the micro suspension probe with different pressures 53 Figure 10 Quality factor versus ambient pressure 54 Figure 11 The resonant frequency as a function of applied voltage 55 Figure 12 Curves of amplitude (a) and phase (b) versus excitation frequency with Vdc=20V, Vac=2V 55 LIST OF TABLES Table The properties of air and single crystal silicon 19 Table The values of βnL for first three modes 25 Table The dimensions of the cantilever probe 32 Table The values of βnL for first three modes 33 Table The dimensions of the clamped-clamped probe 35 Table The dimensions of the micro suspension probe 39 Table The natural frequencies of the cantilever probe 42 Table The stiffness of the cantilever probe in different vibration directions 43 Table The natural frequencies of the clamped-clamped probe 44 Table 10 The stiffness of the clamped- clamped probe in different vibration directions 45 Table 11 The natural frequencies of the micro suspension probe 46 Table 12 The stiffness of the micro suspension probe in different vibration directions 46 Table 13 Pull-in voltage of probe structures 48 Table 14 Capacitance of scanning probe structures 49 Table 15 The capacitive sensitivity of the probes 50 Table 16 The capacitance of the micro suspension probe 52 probe Kz is larger than the z direction stiffness of two cases above The error between analysis and FEM in this case is higher than in two cases above due to deformation of the plate 3.2 Static deflection Cantilever Clamped-Clamped Micro suspension 1.0 0.9 Displacement (m) 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 50 100 150 200 Applied Voltage (V) Figure The displacement of tip versus applied voltage The displacement of tip under applied DC voltage is shown in figure 3.4 In the case of micro suspension, the fixed electrode area is equal to the entire back-side area of the probe (case 1) The gap between two electrodes in all three scanning probe structures is 3µm, so the maximum displacement of tip is 1µm The displacement of tip depends on stiffness of the probe and the area of the electrode The cantilever and clampedclamped probe have almost same stiffness, but the area of electrode in the clampedclamped probe is larger than in the cantilever probe, so the displacement of tip in the clamped-clamped probe is larger than in the cantilever probe with the same applied voltage The stiffness of micro suspension probe is larger than in cantilever probe, 47 however, the area of the electrode in micro suspension is much larger than in cantilever probe, so the displacement of tip in micro suspension is larger than in cantilever probe The pull-in voltages of probes are shown in table 13 From this result, we can apply the appropriate voltage on the probes In the micro suspension probe, because the higher error in calculating the stiffness of the probe and assuming the displacement of probe depends mainly on electrostatic force acting on the plate, so the error in calculating pull-in voltage in this case is higher Table 13 Pull-in voltage of probe structures Cantilever Clamped- Micro- Clamped suspension Vpull-in [Analysis] (V) 189 121 196 Vpull-in [FEM] (V) 187 122 150 Δ (%) 1.1 0.8 23.4 In the cantilever probe, the approach of tip with surface sample is not perpendicular that can reduce accuracy when fabricating nanostructures In figure 3.5, the xdisplacement of tip increases linearly with the z-displacement of tip, it can reach 60 nm at z displacement of µm This x-displacement can reduce the lithography resolution when fabricating nanostructures 48 0.07 0.06 x (m) 0.05 0.04 0.03 0.02 0.01 0.00 0.0 0.2 0.4 0.6 0.8 1.0 Displacement (m) Figure The x-displacement versus the z-displacement of tip in the cantilever probe Table 14 Capacitance of scanning probe structures Cantilever Clamped-Clamped Micro suspension Cparalell (fF) 103 165 189 Ctotal [Analysis] (fF) 119 188 214 Ctotal [FEM] (fF) 114 181 240 The capacitances of the probe structures are shown in table 11 All structures have parallel capacitance lager than 100 fF From simulation results, in cantilever and clamped-clamped probe, the area of side wall is small, so the fringing capacitance is smaller than 10% of parallel capacitance However, in the micro suspension probe, the area of the side wall is much larger, so the fringing capacitance is equal to 26% of the parallel capacitance 49 Cantilever Clamped-Clamped Micro suspension 70 Capacitance (fF) 60 50 40 30 20 10 0.0 0.2 0.4 0.6 0.8 1.0 Displacement (m) Figure Change in capacitance vs displacement Table 15 The capacitive sensitivity of the probes S (fF/µm) Cantilever Clamped-Clamped Suspension 16 33 57 The changes in capacitance depending on displacement of tip in the probe structures are shown in figure 3.6 The sensitivity of the capacitive sensor in the probes is equal to the slope of the lines with displacement smaller than 0.3µm From this table 12, the micro suspension probe has the highest sensitivity The parallel capacitance of the micro suspension probe is 15% larger than the clamped-clamped probe but the sensitivity of the micro suspension probe is 73% lager than the clamped-clamped probe That is due to the displacement of the plate is parallel to the fixed electrode From the above analysis, the micro suspension has many advantages over the cantilever probe and clamped-clamped probe It can overcome the drawback of the cantilever probe and we also can fabricate a tip array on the probe Therefore, the 50 operational characteristics of the micro suspension will be studied more detail in the following 1.0 Case with fringe field Case without fringe field Case with fringe field Case without fringe field 0.9 Displacement(m) 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 20 40 60 80 100 120 140 160 180 Applied Voltage (V) Figure Tip displacements as a function of applied voltage V0 In order to consider the effect of fringe field and fixed electrode to the operation of the micro suspension scanning probe, we have investigated the two cases of actuation electrodes as shown in figure 2.12 The effect of fixed electrode area on the structure is shown in figure 3.7 In both cases, the dimensions of the beams and plate are fixed In figure 3.7, at the same value of applied voltage, the displacement of tip in case is larger than in case Since the electrostatic force exerting on the probe in case is larger Due to the large sidewall area, effect of the fringe field is significant in case at high applied voltage The displacement of the tip is significantly reduced when no voltage is applied to the side wall of the probe The capacitances of the probe in two cases are shown in table 16 The fringing capacitance in case is much smaller than in case The change in capacitance depending on displacement in both cases is shown in figure 3.8 The sensitivity is obtained from the slopes of the fitting lines in case is 57 fF/µm with standard error 51 Table 16 The capacitance of the micro suspension probe Case Case Cparalell (fF) 189 118 Cfring (fF) 51 Ctotal [FEM] (fF) 240 122 S (fF/µm) 57 41 70 Capacitance (fF) 60 Case Case 50 40 30 20 10 0.0 0.2 0.4 0.6 0.8 1.0 Displacement (m) Figure Change in capacitance vs displacement being 0.68 fF/µm and in case is 41 fF/µm with standard error being 0.42 fF/µm From that the sensitivity in case is larger than in case 2, however, fringing capacitance in case causes a larger nonlinearity between capacitance change and displacement of tip In this thesis, the case is chosen to study in more detail the dynamic characteristics of the micro suspension probe 52 3.3 Dynamic deflection In this section, the dynamic deflection of the micro suspension probe is studied The time response of the arbitrary point at the end of the micro suspension probe with different air pressure obtained from simulation is shown in figure 3.9 At atmospheric pressure, the vibration of the micro suspension probe quickly decays after several periods When decreasing pressure, the micro suspension probe oscillates for a longer time that can reach over several hundred periods at 500 Pa 500 Pa 100 kPa Displacement (m) 0.12 0.10 0.08 0.06 0.04 0.02 0.00 20 40 60 80 Time (m) Figure Time response of the micro suspension probe with different pressures Figure 3.10 presents curves of the quality factor versus pressure that are calculated from theoretical analysis and simulation Both curves have same shape and can be divided into two ranges of pressure At the pressures near atmospheric pressure, the quality factor slowly increases with pressure At lower pressures, the quality factor is more sensitive to pressure and the curves become linear and quality factor is inversely proportional to pressure However, the difference between theoretical analysis and simulation result is very large We found out that the time step in simulation strongly influences the time response of the micro suspension probe So, the time step should be optimized to obtain more accurate results To overcome the adhesion force between the 53 tip and the surface sample, the oscillation amplitude of the probe also should be large enough So, the quality factor of probe should be larger than 100 [22] From this graph, to achieve the quality factor larger than 100, the working pressure should be smaller than 800 Pa with theoretical analysis and 2200 Pa with simulation result Theoretical analysis Simulation Quality Factor 102 101 100 103 104 105 Pressure (Pa) Figure 10 Quality factor versus ambient pressure In figure 3.11, the dependence of resonant frequency on applied voltage in the micro suspension probe (case 1) is calculated by simulation Under the influence of electrostatic spring softening effect, the resonance frequency of the scanning probe decreases when increasing applied voltage When the applied voltage is 104 V, the resonant frequency shift is 10% At low applied voltage, the gap between two electrodes can be assumed to be constant, the resonance frequency shift is small and proportional to the square of the applied voltage At high applied voltage, the gap between two electrodes reduces significantly, the resonant frequency can be smaller than 100 kHz and it can reduce the machining speed Moreover, the quality factor is proportional to the resonant frequency, so the quality factor is also significantly reduced at high applied voltage When applied voltage is equal to pull in voltage, the 54 resonant frequency can be dropped to zero at displacement g/3 From this graph, we can choose the appropriate voltage applied to the probe 104 (V) 140 10% Frequency (kHz) 120 100 80 60 40 20 40 60 80 100 120 140 160 Applied Voltage (V) Figure 11 The resonant frequency as a function of applied voltage 0.30 180 160 140 0.20 Phase (degree) Displacement(m) 0.25 (a) Q=46.2 Q=113.8 Q=222.8 0.15 0.10 0.05 0.00 130 (b) Q=46.2 Q=113.8 Q=222.8 120 100 80 60 40 20 132 134 136 138 130 140 132 134 136 138 140 Frequency (kHz) Frequency (kHz) Figure 12 Curves of amplitude (a) and phase (b) versus excitation frequency with Vdc=20V, Vac=2V The frequency response of micro suspension from simulation is shown in figure 3.12 At same applied voltage, when the quality factor increases, the amplitude of tip increases and the resonant pick is sharper as shown in figure 3.13 a The phase shift 55 between the vibration of the probe and applied force is also shown in figure 3.13 b The slope of the curves is larger when the quality factor increases At the resonant frequency, the phase shift is 90o 56 CONCLUSIONS Scanning probe lithography is recently considered as an emerging technique for lithography at nanoscale This technique can overcome the limit caused by low throughput and high cost from conventional nanofabrication techniques and resolution limited by diffraction phenomenon using conventional photolithography This thesis therefore focuses on proposing and optimally designing scanning probes for aim at pattering nanostructures with high precise The scanning probe is driven by electrostatic actuation Operation characteristics of the scanning probe were investigated using theoretical expresses and FEM simulation The obtained results in this thesis can be summarized as follows: i) A clamped-clamped probe and a micro suspension probe were proposed to overcome lateral deflection drawback using conventional microcantilever scanning probe structure; ii) A design of micro suspension probe for enhancing lithography throughput and actuation force was also proposed; iii) A design guideline of the electrostatically actuated scanning probe using theoretical expresses and FEM simulation has been suggested iv) Operation frequency of the scanning probe is 135.471 kHz, the parallel capacitance of probe is 189 fF, the pull-in voltage is 150 V with the maximum displacement of µm These obtained results are useful for optimizing design of scanning probe for patterning high precise nanostructures 57 FURTURE WORKS • Fabricate the scanning probes by MEMS technology • Setup a control system for scanning probes • Fabricate nanostructures by the scanning probe 58 REFERENCES [1] Bao, M., (2005), Analysis and Design Principles of MEMS Devices, 1st ed Amsterdam: Elsevier B.V [2] Bhushan, B., (2011), Nanotribology and Nanomechanics I, Springer-Verlag Berlin Heidelberg [3] Binnig, G and C F Quate, (1986), “Atomic Force Microscope,” Phys Rev Lett., 56(9), pp 930–933 [4] Binnig, G., H Rohrer, C Gerber, and E Weibel, (1982), “Surface Studies by Scanning Tunneling Microscopy,” Physical Review Letters, 49(1), pp 57–61 [5] Bouchiat, V and D Esteve, “Lift-off lithography using an atomic force microscope,” Appl Phys Lett., vol 69, no 20, p 3098, 1996 [6] Bullen, D and C Liu, “Electrostatically actuated dip pen nanolithography probe arrays,” Sensors Actuators, A Phys., vol 125, no 2, pp 504–511, 2006 [7] Cui, Z., (2009), Nanofabrication: Principles, capabilities and limits, Springer US [8] Gupta, R K., (1998), Electostatic Pull-in Test Structure Design for in-situ Mechanical Property Measurements of Microelectromechanicsl Systems (MEMS) Massachusetts Institute of Technology [9] He, Y., Y Geng, Y Yan, and X Luo, (2017), “Fabrication of Nanoscale Pits with High Throughput on Polymer Thin Film Using AFM Tip-Based Dynamic Plowing Lithography,” Nanoscale Res Lett., 12(1), p 544 [10] Itoh, T., T Ohashi, and T Suga, (1996), “Piezoelectric cantilever array for multiprobe scanning force microscopy,” Proc Ninth Int Work Micro Electromechanical Syst., pp 451–455 [11] Klehn, B and U Kunze, (1999), “Nanolithography with an atomic force microscope by means of vector-scan controlled dynamic plowing, ” J Appl 59 Phys., 85(7), pp 3897–3903 [12] Kunze, U., (2002), “Invited Review Nanoscale devices fabricated by dynamic ploughing with an atomic force microscope,” Superlattices Microstruct., 31(1), pp 3–17 [13] Lobontiu, N and E Garcia, (2005), Mechanics of microelectromechanical systems, Springer US [14] Madou, M J., (2011), Manufacturing techniques for microfabrication and nanotechnology (Vol 2), 3rd ed CRC Press [15] Mol, L., L A Rocha, E Cretu, and R F Wolffenbuttel, (2009), “Squeezed film damping measurements on a parallel-plate MEMS in the free molecule regime,” TRANSDUCERS 2009 - 15th Int Conf Solid-State Sensors, Actuators Microsystems, 74021, pp 1425–1428 [16] Nathanson, H C., W E Newell, R A Wickstrom, and J R Davis, (1967), “The resonant gate transistor,” IEEE Trans Electron Devices, 14(3), pp 117–133 [17] Tseng, A a., (2011), Tip-Based Nanofabrication: Fundamentals and Applications, Springer-Verlag New York [18] Tseng, A a., J Shirakashi, S Nishimura, K Miyashita, and A Notargiacomo, (2009), “Scratching properties of nickel-iron thin film and silicon using atomic force microscopy,” J Appl Phys., 106(4), p 44314 [19] Wang, X F., D A Bullen, J Zou, C Liu, and C A Mirkin, “Thermally actuated probe array for parallel dip-pen nanolithography, (2004), ” J Vac Sci Technol B, 22(6), pp 2563–2567 [20] Weinberg, M S and A Kourepenis, (2006), “Error sources in in-plane silicon tuning-fork MEMS gyroscopes,” J Microelectromechanical Syst., 15(3), pp 479–491 [21] Yan, Y D., Z J Hu, W T Liu, and X S Zhao, (2015), “Effects of scratching parameters on fabrication of polymer nanostructures in atomic force microscope 60 tapping mode,” Procedia CIRP, 28, pp 100–105 [22] Zhong, Q., D Inniss, K Kjoller, and V B Elings, (1993), “Fractured polymer/silica fiber surface studied by tapping mode atomic force microscopy,” Surf Sci., 290, pp L688–L692 61 ... this thesis Scanning probe nanolithography is a low-cost nanoscale patterning technology that can be replaced for expensive photo nanolithography In recent years, nanofabrication by scanning... “Design And Simulation Of Serpentine Springs For Scanning Probe”, Workshop on Advanced Nanomaterials & Nanotechnology, pp.221-224, 2017, ISBN 979-604-950298-9 Le Van Tam, Dang Van Hieu, Nguyen... Electrostatic Actuator For Improving The Performance Of Scanning Probe Nanolithography”, 3rd International Conference on Advanced Materials and Nanotechnology, pp.285-288, 2016, ISBN 978-604-913-232-2 Dang