- Email: [email protected]
Generation of metal patterns by topography-directed deposition
Microelectronic Engineering 87 (2010) 1509–1511
Contents lists available at ScienceDirect
Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee
Generation of metal patterns by topography-directed deposition Dianpeng Qi a, Nan Lu a,*, Bingjie Yang a, Hongbo Xu a, Miaojun Xu a, Lifeng Chi a,b a b
State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012, PR China Physikalisches Institut and Center for Nanotechnology (CeNTech), Westfälische Wilhelms-Universität Münster, D-48149 Münster, Germany
a r t i c l e
i n f o
Article history: Received 7 September 2009 Received in revised form 12 November 2009 Accepted 13 November 2009 Available online 17 November 2009 Keywords: Generation Metal patterns Topography-directed Deposition
a b s t r a c t In this work, we present a method for fabricating high-resolution metal arrays based on the topographymediated electrochemical deposition (ECD) process. By this approach, silver arrays of 200 nm feature size can be obtained with the mediation of microscale patterns on silicon wafer. It should be possible to extend this method to other materials and substrates, which may have applications in sensors, optical and optoelectronic devices. Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction Metal nanoparticle arrays have attracted increasing scientific and technological interests due to their unique properties, such as strong magnetic [1–3], near-field behavior and surface plasmon resonances [4]. Based on these properties, their applications have been extended to the surface plasmon waveguides, surface plasmon nanosensors [5], surface-enhanced Raman scattering [6], metal-enhanced fluorescence, and other devices. To fulfill the expected applications, various approaches have been proposed for the fabrication of metal particle arrays, including electron beam lithography (EBL) [7], microcontact printing, photolithography [8], pulsed laser lithography, scanning probe lithography [9,10], and self-assembly [11]. In these approaches, nanoparticles need to be synthesized previously, and then deposited on the predefined areas to achieve the nanoparticle arrays. As an alternative, template-assisted electrochemical deposition (ECD) has been applied for the generation of metallic nanostructures due to its facile process. Metallic structures have been successfully constructed by ECD on the substrates bearing template structures generated with nanoimprint lithography (NIL) technique, interference lithography, EBL and Langmuir–Blodgett [12–15]. However, for the practical applications, the technique for fabricating metal nanoparticle arrays of high-resolution with high-throughput and low-cost is still a key issue. Herein, we demonstrate how to fabricate highresolution arrays of metal nanoparticles by means of the topography-mediated ECD. By this approach, silver arrays of 200 nm
* Corresponding author. E-mail address: [email protected] (N. Lu). 0167-9317/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2009.11.063
feature size can be obtained with the mediation of microscale patterns, which can decrease the cost efficiently. Furthermore, complex arrays can be achieved with the medication of simple patterns.
2. Generation of metal patterns The fabrication procedure is schematically shown in Fig. 1. Firstly, the SiO2 thin layer was removed with HF and the Si substrates were sonicated consecutively in the bath of acetone, chloroform, ethanol, and water for 5 min, respectively. Secondly, PMMA was spin-coated on the Si substrate followed by baking at 90 °C for 5 min to remove the residual solvent. Thirdly, NIL process was performed at 130 °C, under the pressure of 40 bar for 500 s. After peeling off the stamp from the substrate at 70 °C, the residual polymer was removed by reactive ion etching (RIE, O2) (PVA TePla O-Plasma System 100) at 100 W, 460 mTorr for 1.5 min to achieve the patterned surfaces. Finally, the ECD process was performed by using the patterned Si substrate as working electrode to generate the high-resolution metal arrays [12]. The ECD process was carried out on the BAS100W Electrochemical Analyzer (Bioanalytical Systems, West Lafayette, IN). In order to obtain thin, smooth and more continuous silver nanoparticle arrays. The ECD parameters were optimized firstly. When the ECD process was carried out at 400 and 500 mV for 90 s, some big particles formed in the arrays. The nanoparticles deposited on the terrace with the voltage from 700 to 800 mV for 90 s. The width of the silver nanoparticle wires and rings increased when the deposition duration was prolonged to 120 s. The continuity was not good when decreasing the deposition
1510
D. Qi et al. / Microelectronic Engineering 87 (2010) 1509–1511
electric field Si SiO2 PMMA
Fig. 3. Schematic illustration of the electric-field distribution.
Fig. 1. Schematic illustration of the procedure for creating metal arrays on Si.
Fig. 2. SEM images of the generated silver nanoparticle arrays on Si substrates.
duration to 60 s. So the ECD process was carried out at 600 mV for 90 s after the optimization. Fig. 2 shows the SEM images of the silver nanoparticle arrays of nanowires and nanorings, which were obtained with the mediation of the stripe and square patterns. The width of the nanoparticle line is about 200 nm, which was fabricated with the mediation of 2.5 lm stripes and 5 lm squares. It can be observed that there is a silver dot in the middle of each square, which is caused by the incomplete filling of the stamp cavity. During the imprinting, the resist PMMA was squeezed into the cavity and flowed up the walls of the cavity, and some PMMA was compressed in the center of the cavity [16], which resulted a lower PMMA protrusion existing in the printed recess area. When the RIE process was conducted to remove the residual PMMA layer and oxidize the silicon substrate, the area previously covered by the lower PMMA protrusion cannot be completely oxidized due to the protection. It can still work as a work electrode during the ECD process. Therefore a silver dot formed in the center of each
square after conducting an ECD process. As revealed in Fig. 2, the deposited silver nanowires are not continuous, but if depositing other metals with this method, such as gold, continuous metal nanowires could be achieved [13]. We assume that the Si surface of the valley could be oxidized to SiO2 when RIE process was applied to remove the residual polymer after imprinting, as schematically shown in Fig. 3, the Si substrate covered by the protrusion polymer cannot be oxidized to SiO2. Therefore the thickness of the SiO2 layer along the edges is thinner than that on the center area of the valley. The thinner SiO2 layer along the edges further increased the electrical field strength on the edges [12], which resulted in the selective nucleation of silver along the edges at the initial stage of ECD. The electric-field-assisted fast diffusion of silver ions towards the step edges strongly guided the deposition of the metal nanowires and nanorings [13]. No selectivity can be achieved if the insulating oxide layer in the valleys were removed by a RIE process (Ar and CHF3, at an
Fig. 4. SEM images of Ag nanoparticles patterns on Si substrates without SiO2 layer.
D. Qi et al. / Microelectronic Engineering 87 (2010) 1509–1511
radio-frequency power of 50 W, etching time 30 s), as presented in Fig. 4, the valley areas were filled with high density of silver nanoparticles after removing the oxide layer. 3. Conclusions In summary, a method for fabricating high-resolution metal arrays based on the topography-mediated ECD process has been presented. The combination of NIL and ECD allows for the fabrication of metallic nanowire or nanoring arrays over a wafer-scale area. Silver arrays of 200 nm feature size can be achieved with the mediation of microscale patterns; this technique is cost efficient and high-throughput. It should be possible to extend this method to other materials and substrates, which may have applications in sensor, optical and optoelectronic devices. Acknowledgements This work was supported by the National Natural Science Foundation of China (NSFC 20773052, 20373019), the Program for New Century Excellent Talents in University of China, the National Basic Research Program (2007CB808003, 2009CB939701) and Project 111.
1511
References [1] F.J. Castaño, D. Morecroft, W. Jung, C.A. Ross, Phys. Rev. Lett. 95 (2005) 1372011–137201-4. [2] L.J. Heyderman, M. Klaui, B. Nohammer, C.A.F. Vaz, J.A.C. Bland, C. David, Microelectron. Eng. 780 (2004) 73–74. [3] K.D. Sorge, R. Skomski, M. Daniil, S. Michalski, L. Gao, J. Zhou, M. Yan, Y. Sui, R.D. Kirby, S.H. Liou, D.J. Sellmyer, Scr. Mater. 53 (2005) 457–461. [4] K. Ronse, D. Van Thourhout, S. De Gendt, L. Lagae, G. Vandenberghe, A. Witvrouw, Microelectron. Eng. 73–74 (2004) 312–318. [5] M.A. Schmidt, L.N. Prill Sempere, H.K. Tyagi, C.G. Poulton, P.St.J. Russell, Phys. Rev. B 77 (2008) 033417-1–033417-4. [6] L.S. Zhang, Y. Fang, P.X. Zhang, Chem. Phys. Lett. 451 (2008) 102–105. [7] N. Saitou, Int. J. Jpn. Soc. Prec. Eng. 30 (1996) 107–11. [8] G.F. Cardinale, C.C. Henderson, J.E.M. Goldsmith, P.J.S. Mangat, J. Cobb, S.D. Hector, J. Vac. Sci. Technol. B 17 (1999) 2970–2974. [9] B. Fay, Microelectron. Eng. 11 (2002) 61–62. [10] H.D. Fonseca Filho, R. Prioli, Vac. Sci. Technol. B 27 (2009) 134–138. [11] C.Y. Huang, B. Dong, N. Lv, B.J. Yang, L.G. Gao, L. Tian, D.P. Qi, Q. Wu, L.F. Chi, Small 5 (2009) 583–586. [12] B.J. Yang, N. Lu, C.Y. Huang, D.P. Qi, G. Shi, H.B. Xu, X.D. Chen, B. Dong, W. Song, B. Zhao, L.F. Chi, Langmuir 25 (2009) 55–58. [13] R. Ji, W. Lee, R. Scholz, U. Gösele, K. Nielsch, Adv. Mater. 18 (2006) 2593–2596. [14] E.J. Menke, M.A. Thompson, C. Xiang, L.C. Yang, R.M. Penner, Nat. Mater. 5 (2006) 914–919. [15] M.Z. Zhang, S. Lenhert, M. Wang, L.F. Chi, N. Lu, H. Fuchs, N.B. Ming, Adv. Mater. 16 (2004) 409–413. [16] H. Schift, L.J. Heyderman, M. Auf der Maur, J. Gobrecht, Nanotechnology 12 (2001) 173–177.
Contents lists available at ScienceDirect
Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee
Generation of metal patterns by topography-directed deposition Dianpeng Qi a, Nan Lu a,*, Bingjie Yang a, Hongbo Xu a, Miaojun Xu a, Lifeng Chi a,b a b
State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012, PR China Physikalisches Institut and Center for Nanotechnology (CeNTech), Westfälische Wilhelms-Universität Münster, D-48149 Münster, Germany
a r t i c l e
i n f o
Article history: Received 7 September 2009 Received in revised form 12 November 2009 Accepted 13 November 2009 Available online 17 November 2009 Keywords: Generation Metal patterns Topography-directed Deposition
a b s t r a c t In this work, we present a method for fabricating high-resolution metal arrays based on the topographymediated electrochemical deposition (ECD) process. By this approach, silver arrays of 200 nm feature size can be obtained with the mediation of microscale patterns on silicon wafer. It should be possible to extend this method to other materials and substrates, which may have applications in sensors, optical and optoelectronic devices. Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction Metal nanoparticle arrays have attracted increasing scientific and technological interests due to their unique properties, such as strong magnetic [1–3], near-field behavior and surface plasmon resonances [4]. Based on these properties, their applications have been extended to the surface plasmon waveguides, surface plasmon nanosensors [5], surface-enhanced Raman scattering [6], metal-enhanced fluorescence, and other devices. To fulfill the expected applications, various approaches have been proposed for the fabrication of metal particle arrays, including electron beam lithography (EBL) [7], microcontact printing, photolithography [8], pulsed laser lithography, scanning probe lithography [9,10], and self-assembly [11]. In these approaches, nanoparticles need to be synthesized previously, and then deposited on the predefined areas to achieve the nanoparticle arrays. As an alternative, template-assisted electrochemical deposition (ECD) has been applied for the generation of metallic nanostructures due to its facile process. Metallic structures have been successfully constructed by ECD on the substrates bearing template structures generated with nanoimprint lithography (NIL) technique, interference lithography, EBL and Langmuir–Blodgett [12–15]. However, for the practical applications, the technique for fabricating metal nanoparticle arrays of high-resolution with high-throughput and low-cost is still a key issue. Herein, we demonstrate how to fabricate highresolution arrays of metal nanoparticles by means of the topography-mediated ECD. By this approach, silver arrays of 200 nm
* Corresponding author. E-mail address: [email protected] (N. Lu). 0167-9317/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2009.11.063
feature size can be obtained with the mediation of microscale patterns, which can decrease the cost efficiently. Furthermore, complex arrays can be achieved with the medication of simple patterns.
2. Generation of metal patterns The fabrication procedure is schematically shown in Fig. 1. Firstly, the SiO2 thin layer was removed with HF and the Si substrates were sonicated consecutively in the bath of acetone, chloroform, ethanol, and water for 5 min, respectively. Secondly, PMMA was spin-coated on the Si substrate followed by baking at 90 °C for 5 min to remove the residual solvent. Thirdly, NIL process was performed at 130 °C, under the pressure of 40 bar for 500 s. After peeling off the stamp from the substrate at 70 °C, the residual polymer was removed by reactive ion etching (RIE, O2) (PVA TePla O-Plasma System 100) at 100 W, 460 mTorr for 1.5 min to achieve the patterned surfaces. Finally, the ECD process was performed by using the patterned Si substrate as working electrode to generate the high-resolution metal arrays [12]. The ECD process was carried out on the BAS100W Electrochemical Analyzer (Bioanalytical Systems, West Lafayette, IN). In order to obtain thin, smooth and more continuous silver nanoparticle arrays. The ECD parameters were optimized firstly. When the ECD process was carried out at 400 and 500 mV for 90 s, some big particles formed in the arrays. The nanoparticles deposited on the terrace with the voltage from 700 to 800 mV for 90 s. The width of the silver nanoparticle wires and rings increased when the deposition duration was prolonged to 120 s. The continuity was not good when decreasing the deposition
1510
D. Qi et al. / Microelectronic Engineering 87 (2010) 1509–1511
electric field Si SiO2 PMMA
Fig. 3. Schematic illustration of the electric-field distribution.
Fig. 1. Schematic illustration of the procedure for creating metal arrays on Si.
Fig. 2. SEM images of the generated silver nanoparticle arrays on Si substrates.
duration to 60 s. So the ECD process was carried out at 600 mV for 90 s after the optimization. Fig. 2 shows the SEM images of the silver nanoparticle arrays of nanowires and nanorings, which were obtained with the mediation of the stripe and square patterns. The width of the nanoparticle line is about 200 nm, which was fabricated with the mediation of 2.5 lm stripes and 5 lm squares. It can be observed that there is a silver dot in the middle of each square, which is caused by the incomplete filling of the stamp cavity. During the imprinting, the resist PMMA was squeezed into the cavity and flowed up the walls of the cavity, and some PMMA was compressed in the center of the cavity [16], which resulted a lower PMMA protrusion existing in the printed recess area. When the RIE process was conducted to remove the residual PMMA layer and oxidize the silicon substrate, the area previously covered by the lower PMMA protrusion cannot be completely oxidized due to the protection. It can still work as a work electrode during the ECD process. Therefore a silver dot formed in the center of each
square after conducting an ECD process. As revealed in Fig. 2, the deposited silver nanowires are not continuous, but if depositing other metals with this method, such as gold, continuous metal nanowires could be achieved [13]. We assume that the Si surface of the valley could be oxidized to SiO2 when RIE process was applied to remove the residual polymer after imprinting, as schematically shown in Fig. 3, the Si substrate covered by the protrusion polymer cannot be oxidized to SiO2. Therefore the thickness of the SiO2 layer along the edges is thinner than that on the center area of the valley. The thinner SiO2 layer along the edges further increased the electrical field strength on the edges [12], which resulted in the selective nucleation of silver along the edges at the initial stage of ECD. The electric-field-assisted fast diffusion of silver ions towards the step edges strongly guided the deposition of the metal nanowires and nanorings [13]. No selectivity can be achieved if the insulating oxide layer in the valleys were removed by a RIE process (Ar and CHF3, at an
Fig. 4. SEM images of Ag nanoparticles patterns on Si substrates without SiO2 layer.
D. Qi et al. / Microelectronic Engineering 87 (2010) 1509–1511
radio-frequency power of 50 W, etching time 30 s), as presented in Fig. 4, the valley areas were filled with high density of silver nanoparticles after removing the oxide layer. 3. Conclusions In summary, a method for fabricating high-resolution metal arrays based on the topography-mediated ECD process has been presented. The combination of NIL and ECD allows for the fabrication of metallic nanowire or nanoring arrays over a wafer-scale area. Silver arrays of 200 nm feature size can be achieved with the mediation of microscale patterns; this technique is cost efficient and high-throughput. It should be possible to extend this method to other materials and substrates, which may have applications in sensor, optical and optoelectronic devices. Acknowledgements This work was supported by the National Natural Science Foundation of China (NSFC 20773052, 20373019), the Program for New Century Excellent Talents in University of China, the National Basic Research Program (2007CB808003, 2009CB939701) and Project 111.
1511
References [1] F.J. Castaño, D. Morecroft, W. Jung, C.A. Ross, Phys. Rev. Lett. 95 (2005) 1372011–137201-4. [2] L.J. Heyderman, M. Klaui, B. Nohammer, C.A.F. Vaz, J.A.C. Bland, C. David, Microelectron. Eng. 780 (2004) 73–74. [3] K.D. Sorge, R. Skomski, M. Daniil, S. Michalski, L. Gao, J. Zhou, M. Yan, Y. Sui, R.D. Kirby, S.H. Liou, D.J. Sellmyer, Scr. Mater. 53 (2005) 457–461. [4] K. Ronse, D. Van Thourhout, S. De Gendt, L. Lagae, G. Vandenberghe, A. Witvrouw, Microelectron. Eng. 73–74 (2004) 312–318. [5] M.A. Schmidt, L.N. Prill Sempere, H.K. Tyagi, C.G. Poulton, P.St.J. Russell, Phys. Rev. B 77 (2008) 033417-1–033417-4. [6] L.S. Zhang, Y. Fang, P.X. Zhang, Chem. Phys. Lett. 451 (2008) 102–105. [7] N. Saitou, Int. J. Jpn. Soc. Prec. Eng. 30 (1996) 107–11. [8] G.F. Cardinale, C.C. Henderson, J.E.M. Goldsmith, P.J.S. Mangat, J. Cobb, S.D. Hector, J. Vac. Sci. Technol. B 17 (1999) 2970–2974. [9] B. Fay, Microelectron. Eng. 11 (2002) 61–62. [10] H.D. Fonseca Filho, R. Prioli, Vac. Sci. Technol. B 27 (2009) 134–138. [11] C.Y. Huang, B. Dong, N. Lv, B.J. Yang, L.G. Gao, L. Tian, D.P. Qi, Q. Wu, L.F. Chi, Small 5 (2009) 583–586. [12] B.J. Yang, N. Lu, C.Y. Huang, D.P. Qi, G. Shi, H.B. Xu, X.D. Chen, B. Dong, W. Song, B. Zhao, L.F. Chi, Langmuir 25 (2009) 55–58. [13] R. Ji, W. Lee, R. Scholz, U. Gösele, K. Nielsch, Adv. Mater. 18 (2006) 2593–2596. [14] E.J. Menke, M.A. Thompson, C. Xiang, L.C. Yang, R.M. Penner, Nat. Mater. 5 (2006) 914–919. [15] M.Z. Zhang, S. Lenhert, M. Wang, L.F. Chi, N. Lu, H. Fuchs, N.B. Ming, Adv. Mater. 16 (2004) 409–413. [16] H. Schift, L.J. Heyderman, M. Auf der Maur, J. Gobrecht, Nanotechnology 12 (2001) 173–177.