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Step-wise Ag thin film patterns fabricated by holographic lithography
Thin Solid Films 517 (2009) 3273–3275
Contents lists available at ScienceDirect
Thin Solid Films j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / t s f
Step-wise Ag thin film patterns fabricated by holographic lithography Hyunkwon Shin a, Hyunjun Kim a, Ki-Soo Lim b, Myeongkyu Lee a,⁎ a b
Department of Materials Science and Engineering, Yonsei University, 134 Shinchon-dong, Seodaemun-ku, Seoul 120-749, Korea Department of Physics, Chungbuk University, 12 Gaesin-dong, Cheongju 361-763, Korea
a r t i c l e
i n f o
Article history: Received 15 April 2008 Received in revised form 24 November 2008 Accepted 2 December 2008 Available online 16 December 2008 PACS: 68.43.Tj 68.60.-p 61.46.Df 68.35.-p
a b s t r a c t A laser-induced thermo-elastic removal was used to pattern nanostructured silver thin films solutiondeposited on the glass substrate. We show that sharp-edged patterns can be fabricated under an interference-generated gradual intensity profile. The etching behavior and the resulting pattern morphology were very sensitive to the cohesion of the film and its adhesion to the substrate, being both modified by the post-deposition annealing process. The fabrication of step-wise one-dimensional (1D) and 2D patterns at the micrometer scales is demonstrated by holographic lithography using an Nd:YAG pulsed laser, along with a discussion on the effect of film cohesion and adhesion. © 2009 Elsevier B.V. All rights reserved.
Keywords: Metal thin film patterning Holographic lithography Nanostructure
1. Introduction Holographic lithography was first suggested by Berger et al. [1] and implemented to fabricate two-dimensional (2D) patterns in a photosensitive polymer, which ultimately served as an etching mask to pattern the underlying semiconductor substrate. The concept was later extended into fabricating 3D photonic crystals with body-centered cubic or face-centered cubic symmetry [2,3]. As holographic lithography is a mask-free process based on the multi-beam interference, a great deal of research has been carried out to develop this method for fabricating 2D and 3D micro/nanostructures [4–8]. However, this technique utilizes a direct interaction between the light and matter and has a limited applicability to nontransparent materials. Therefore, the use of holographic lithography for metals has been mainly focused on the generation of periodic surface structures based on the high-power laserinduced melting, phase transformation, or ablation [9–11]. In the meanwhile, metal thin film patterning is of technological significance because modern electronic and optoelectronic devices commonly require electrode or metallization patterns. Although the fabrication of Au thin film pattern has been reported [12], it actually employs a holography-patterned photoresist layer as an etching mask and thus does not provide an appreciable advantage over the conventional photolithographic process. In a previous work [13], we have reported that Ag nanoparticle Langmuir–Blodgett monolayer can be patterned by ⁎ Corresponding author. Tel.: +82 2 2123 2832; fax: +82 2 312 5375. E-mail address: [email protected] (M. Lee). 0040-6090/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2008.12.019
selectively detaching particles from the substrate using a pulsed laser. Although the fact that the spatial distribution of the nanoparticle can be optically controlled is encouraging, this monolayered film is not suitable for use in electronic device due to a very high resistivity. Here we show that solution-deposited Ag films (up to ~1 µm thickness) can also be directly patterned by holographic lithography using a pulsed Nd:YAG laser. The fabrication of step-wise pattern is demonstrated, with a discussion on the dependence of pattern morphology on the film adhesion and cohesion. 2. Experimental procedure Ag thin films (120 nm to 1 µm thick) were deposited on the glass substrate either by spin-coating or drop-casting using a commercial Ag nano-ink solution (model: NINK-Ag WM2035, ABC Nanotech Inc.). The films were annealed in ambient atmosphere for 30 min in the temperature range of 100 ~ 450 °C. A nanosecond pulsed Nd:YAG laser (λ = 1064 nm, pulse width = 10 ns, repetition rate = 10 Hz) was used for patterning. The interference profile was generated using a single refracting prism made of quartz (refractive index = 1.48). The fact that the beam can be simultaneously split and recombined by a single optical element greatly simplifies the overall optics setup, improving the alignment accuracy and stability [4]. Interfering beams were made incident from the backside of the substrate. Fig. 1(a) is a schematic of the patterning sequence. When the film is exposed to interefering two laser beams, a sinusoidal intensity (i.e., pulse energy density) profile is generated at the substrate-film interface. As the peak energy density
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H. Shin et al. / Thin Solid Films 517 (2009) 3273–3275
Fig. 1. (a) Schematic of the patterning sequence. (b) SEM images of the line patterns fabricated by two-beam interference. All patterns shown have the same period of 8.7 µm.
exceeds a certain level, i.e., a threshold level, the film is locally subject to a thermo-elastic force (bottom, Fig. 1(a)). Fig. 1(b) shows scanning electron microscope (SEM) images of the line patterns fabricated by two-beam interference. All patterns shown have the same period of 8.7 µm. The interference profile was generated by a refracting prism which has an isosceles triangle shape (apex angle = 165°). 3. Results and discussion The patterning mechanism can be explained by the laser-induced thermal response of particles [13–16]. Particles adsorbed to the surface can be ejected when the thermo-elastic force, caused by a rapid thermal expansion of the particle and/or the substrate resulting from pulsed laser irradiation, exceeds the adhesive force (predominantly van der Waals force) between the particle and the substrate [14,15]. The solution-processed film comprises inter-connected nanoparticles. Due to a short penetration depth of the near-infrared wave into the metal, only particles directly adjoining or in close proximity to the substrate will be exposed to the laser light. The thermo-elastic force to detach these particles from the substrate will play a role in pushing out the others on top of them. As illustrated in Fig. 1(b), the pattern morphology was very sensitive to the heat-treament history of the film. For the as-deposited film (just dried without annealing), only a periodic trace was observed with some debris remaining on the
Fig. 2. (a) Film resistivity and threshold pulse energy density measured as a function of the annealing temperature. (b) Estimated temperature dependence of the film cohesion and adhesion.
substrate. This is attributed to the fact that as the film still contains organic additives, its cohesion is too weak. In fact, nanoparticles were easily peeled off the as-deposited film by a sticky tape. When preannealed at 150 °C, the film could be fabricated into a real stripe pattern. However, it revealed a groove-like morphology. In this process, a pattern profile is defined on the substrate-film interface in the form of a thermo-elastic force distribution, not throughout the whole film. Thus it may not be maintained all the way to the top of the film with a vertical uniformity, unless the film has an adequate cohesion. We observed that films annealed at 450 °C can maintain the pattern profile to the film surface with a vertical uniformity, thus giving a step-wise pattern with clear-cut edges (bottom, Fig. 1(b)). An abnormal but interesting observation is that it was impossible to generate a pattern in the film annealed at 250 °C (not shown). Interfering beams resulted in removal of the whole film, instead of causing a periodic detachment. The etching behavior and the resulting pattern morphology are here explained in correlation with the film cohesion and its adhesion to the substrate. If the cohesion is rather strong compared to the adhesion, it would be almost impossible to pattern fine structures because the areas exposed below threshold level would also be detached together. On the contrary, if the cohesion is too weak, a pattern of step-wise morphology would not be obtained as observed in Fig. 1(b) (top and middle images). Fig. 2(a) shows the annealing temperature dependence of film resistivity and threshold pulse energy density. While the film remained almost insulating up to T = 125 °C, the resistivity measured using a 4-probe was suddenly dropped down to ~ 10− 3 Ω cm after annealing at 150 °C. This indicates that the film can be cured around 150 °C, with all organic components removed. Increasing the annealing temperature further lowered the resistivity until it became nearly saturated above 250 °C. This is attributed to the sintering effect. The minimum values obtained were 3–5 times higher than the Ag bulk resistivity of 2.25 × 10− 6 Ω cm. We
Fig. 3. (a) SEM image of a stripe pattern generated by two-beam interference. The inset is a cross-sectional transmission electron microscope image of the film-substrate interface. (b) 2D honeycomb structure fabricated by three-beam interference. The inset shows the surface morphology.
H. Shin et al. / Thin Solid Films 517 (2009) 3273–3275
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patterns. Films of about 800 nm thick, pre-annealed at 450 °C for 30 min were exposed to a single pulse in the patterning process. Wellaligned stripe patterns were obtained by two-beam interference (Fig. 3(a)). The stripe width could be controlled by tuning up the pulse energy. Smooth vertical sidewalls were maintained until the stripe width was scaled down to 1.5 µm, below which the corners of the stripe became rounded. The inset shows a cross-sectional transmission electron microscopic image of the interface. Fig. 3(b) is a 2D honeycomb pattern fabricated by three-beam interference using a prism of trigonal-pyramid shape. Connected honeycomb cells were converted into isolated domains with increased pulse energy. An SEM image of the film surface is given in the inset of Fig. 3(b). Fig. 4 is an optical profiler image showing the step-wise edge in a stripe pattern. The stripe width in the pattern was slightly different from position to position even under fixed pulse energy, which seems to arise from the nonuniform intensity distribution of the laser output. A laser beam with hat-top profile was used in this work and thus a beam homogenizer will be helpful to achieve better pattern uniformity, although a pulsed laser reveals inherent spatial and temporal instability to some extent. 4. Conclusion
Fig. 4. An optical profiler image showing the step-wise edge morphology in a stripe pattern.
found that this photoetching only occurs over a well-defined threshold pulse energy density. It increased with increasing temperature. The measured threshold levels were 0.1–1.8 J/cm2, well below the damage threshold of the substrate (N500 J/cm2). The threshold value was weakly influenced by the film thickness. This implies that the threshold energy density for film patterning is dominantly determined by the adhesion rather than the cohesion. It is thus expected that the adhesion will exhibit a temperature-dependent behavior similar to that of the threshold. In the meanwhile, the variation of cohesion can be estimated from the resistivity data, because they are closely related to each other. The solution-processed film maintains a relatively weak cohesion until the particles begin to be sintered. As the sintering proceeds, the film cohesion increases with a simultaneous drop of the resistivity. That the resisitivity is nearly saturated above 250 °C tells that the cohesion is not much enhanced even though the film is annealed at a higher temperature, while the adhesion continues to increase. The estimated temperature dependences of the cohesion and adhesion are given in Fig. 2(b). It shows that the film annealed at 250 °C has a strong cohesion relative to its adhesion. This may be the reason why the patterning was impossible. For films annealed at 150 °C and as-deposited ones, the absolute magnitude of cohesion is too low. Therefore, a pattern with step-wise morphology is very difficult to generate. It is to be noted that the thermo-elastic force is exerted on the film only when the pulse energy density exceeds the threshold level. While the two-beam interference generates a sinusoidal energy density distribution, the actual driving force for patterning has a different profile. Only the areas exposed above threshold are subject to this force. This makes it possible to fabricate a pattern of step-wise morphology even under a sinusoidal or other gradual interference profile. Fig. 3 shows SEM images of the fabricated
Ag thin films solution-deposited on glass were patterned utilizing a pulsed laser-induced thermo-elastic removal of the material. The etching behavior and the resulting pattern morphology were very sensitive to the cohesion of the film and its adhesion to the substrate, both being modified by the post-deposition annealing process. It was also observed that photoetching only occurs over a well-defined threshold pulse energy density. This made it possible to obtain sharpedged patterns under an interference-generated gradual intensity profile. The fabrication of step-wise 1D and 2D patterns at the micrometer scales has been demonstrated by holographic lithography using a pulsed Nd:YAG laser. In this work, we have used a Nd:YAG laser with a maximum average power of ~ 4 W. This limited the patterned area to several mm2. It is believed that a high-power laser for industrial use will enable patterning over larger area. This holographic method may be applicable to other solution-processed nanoparticulate films if a suitable laser source is used. Acknowledgement This research was supported by the Korea Research Foundation (Grant number: KRF 2006-311-D00586). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16]
V. Berger, O. Gauthier-Lafaye, E. Costard, J. Appl. Phys. 82 (1997) 60. M. Campbell, D. Sharp, M. Harrison, R. Denning, A. Turberfield, Nature 404 (2000) 53. S. Shoji, S. Kawata, Appl. Phys. Lett. 76 (2000) 2668. L. Wu, Y. Zhong, C. Chan, K. Wong, G. Wang, Appl. Phys. Lett. 86 (2005) 241102. Y. Miklyaev, D. Meisel, A. Blanco, G. Feymann, K. Busch, W. Koch, C. Enkrich, M. Deubel, M. Wegener, Appl. Phys. Lett. 82 (2003) 1284. I. Divliansky, T. Mayer, K. Holliday, V. Crespi, Appl. Phys. Lett. 82 (2003) 1667. G. Zhou, F.S. Chau, Appl. Phys. Lett. 90 (2007) 181106. M. Salaun, M. Audier, F. Delyon, M. Duneau, Appl. Surf. Sci. 254 (2007) 830. A. Lasagni, M. D, Alessandria, R. Giovanelli, F. Mucklich, Appl. Surf. Sci. 254 (2007) 930. F. Mucklich, A. Lasagni, C. Daniel, Intermetallics 13 (2004) 437. Y. Nakata, T. Okada, M. Maeda, Appl. Phys. Lett. 81 (2002) 4239. J. Skriniarova, D. Pudis, I. Martincek, J. Kovac, N. Tarjanyi, M. Vesely, I. Turek, Microelectron. J. 38 (2007) 746. H. Kim, H. Shin, J. Ha, M. Lee, K. Lim, J. Appl. Phys. 102 (2007) 083505. M. Arronte, P. Neves, R. Vilar, J. Appl. Phys. 92 (2002) 6973. J. Lee, C. Curran, K. Watkins, Appl. Phys. A 73 (2001) 219. G. Vereecke, E. Röhr, M. Heyns, J. Appl. Phys. 85 (1999) 3837.
Contents lists available at ScienceDirect
Thin Solid Films j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / t s f
Step-wise Ag thin film patterns fabricated by holographic lithography Hyunkwon Shin a, Hyunjun Kim a, Ki-Soo Lim b, Myeongkyu Lee a,⁎ a b
Department of Materials Science and Engineering, Yonsei University, 134 Shinchon-dong, Seodaemun-ku, Seoul 120-749, Korea Department of Physics, Chungbuk University, 12 Gaesin-dong, Cheongju 361-763, Korea
a r t i c l e
i n f o
Article history: Received 15 April 2008 Received in revised form 24 November 2008 Accepted 2 December 2008 Available online 16 December 2008 PACS: 68.43.Tj 68.60.-p 61.46.Df 68.35.-p
a b s t r a c t A laser-induced thermo-elastic removal was used to pattern nanostructured silver thin films solutiondeposited on the glass substrate. We show that sharp-edged patterns can be fabricated under an interference-generated gradual intensity profile. The etching behavior and the resulting pattern morphology were very sensitive to the cohesion of the film and its adhesion to the substrate, being both modified by the post-deposition annealing process. The fabrication of step-wise one-dimensional (1D) and 2D patterns at the micrometer scales is demonstrated by holographic lithography using an Nd:YAG pulsed laser, along with a discussion on the effect of film cohesion and adhesion. © 2009 Elsevier B.V. All rights reserved.
Keywords: Metal thin film patterning Holographic lithography Nanostructure
1. Introduction Holographic lithography was first suggested by Berger et al. [1] and implemented to fabricate two-dimensional (2D) patterns in a photosensitive polymer, which ultimately served as an etching mask to pattern the underlying semiconductor substrate. The concept was later extended into fabricating 3D photonic crystals with body-centered cubic or face-centered cubic symmetry [2,3]. As holographic lithography is a mask-free process based on the multi-beam interference, a great deal of research has been carried out to develop this method for fabricating 2D and 3D micro/nanostructures [4–8]. However, this technique utilizes a direct interaction between the light and matter and has a limited applicability to nontransparent materials. Therefore, the use of holographic lithography for metals has been mainly focused on the generation of periodic surface structures based on the high-power laserinduced melting, phase transformation, or ablation [9–11]. In the meanwhile, metal thin film patterning is of technological significance because modern electronic and optoelectronic devices commonly require electrode or metallization patterns. Although the fabrication of Au thin film pattern has been reported [12], it actually employs a holography-patterned photoresist layer as an etching mask and thus does not provide an appreciable advantage over the conventional photolithographic process. In a previous work [13], we have reported that Ag nanoparticle Langmuir–Blodgett monolayer can be patterned by ⁎ Corresponding author. Tel.: +82 2 2123 2832; fax: +82 2 312 5375. E-mail address: [email protected] (M. Lee). 0040-6090/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2008.12.019
selectively detaching particles from the substrate using a pulsed laser. Although the fact that the spatial distribution of the nanoparticle can be optically controlled is encouraging, this monolayered film is not suitable for use in electronic device due to a very high resistivity. Here we show that solution-deposited Ag films (up to ~1 µm thickness) can also be directly patterned by holographic lithography using a pulsed Nd:YAG laser. The fabrication of step-wise pattern is demonstrated, with a discussion on the dependence of pattern morphology on the film adhesion and cohesion. 2. Experimental procedure Ag thin films (120 nm to 1 µm thick) were deposited on the glass substrate either by spin-coating or drop-casting using a commercial Ag nano-ink solution (model: NINK-Ag WM2035, ABC Nanotech Inc.). The films were annealed in ambient atmosphere for 30 min in the temperature range of 100 ~ 450 °C. A nanosecond pulsed Nd:YAG laser (λ = 1064 nm, pulse width = 10 ns, repetition rate = 10 Hz) was used for patterning. The interference profile was generated using a single refracting prism made of quartz (refractive index = 1.48). The fact that the beam can be simultaneously split and recombined by a single optical element greatly simplifies the overall optics setup, improving the alignment accuracy and stability [4]. Interfering beams were made incident from the backside of the substrate. Fig. 1(a) is a schematic of the patterning sequence. When the film is exposed to interefering two laser beams, a sinusoidal intensity (i.e., pulse energy density) profile is generated at the substrate-film interface. As the peak energy density
3274
H. Shin et al. / Thin Solid Films 517 (2009) 3273–3275
Fig. 1. (a) Schematic of the patterning sequence. (b) SEM images of the line patterns fabricated by two-beam interference. All patterns shown have the same period of 8.7 µm.
exceeds a certain level, i.e., a threshold level, the film is locally subject to a thermo-elastic force (bottom, Fig. 1(a)). Fig. 1(b) shows scanning electron microscope (SEM) images of the line patterns fabricated by two-beam interference. All patterns shown have the same period of 8.7 µm. The interference profile was generated by a refracting prism which has an isosceles triangle shape (apex angle = 165°). 3. Results and discussion The patterning mechanism can be explained by the laser-induced thermal response of particles [13–16]. Particles adsorbed to the surface can be ejected when the thermo-elastic force, caused by a rapid thermal expansion of the particle and/or the substrate resulting from pulsed laser irradiation, exceeds the adhesive force (predominantly van der Waals force) between the particle and the substrate [14,15]. The solution-processed film comprises inter-connected nanoparticles. Due to a short penetration depth of the near-infrared wave into the metal, only particles directly adjoining or in close proximity to the substrate will be exposed to the laser light. The thermo-elastic force to detach these particles from the substrate will play a role in pushing out the others on top of them. As illustrated in Fig. 1(b), the pattern morphology was very sensitive to the heat-treament history of the film. For the as-deposited film (just dried without annealing), only a periodic trace was observed with some debris remaining on the
Fig. 2. (a) Film resistivity and threshold pulse energy density measured as a function of the annealing temperature. (b) Estimated temperature dependence of the film cohesion and adhesion.
substrate. This is attributed to the fact that as the film still contains organic additives, its cohesion is too weak. In fact, nanoparticles were easily peeled off the as-deposited film by a sticky tape. When preannealed at 150 °C, the film could be fabricated into a real stripe pattern. However, it revealed a groove-like morphology. In this process, a pattern profile is defined on the substrate-film interface in the form of a thermo-elastic force distribution, not throughout the whole film. Thus it may not be maintained all the way to the top of the film with a vertical uniformity, unless the film has an adequate cohesion. We observed that films annealed at 450 °C can maintain the pattern profile to the film surface with a vertical uniformity, thus giving a step-wise pattern with clear-cut edges (bottom, Fig. 1(b)). An abnormal but interesting observation is that it was impossible to generate a pattern in the film annealed at 250 °C (not shown). Interfering beams resulted in removal of the whole film, instead of causing a periodic detachment. The etching behavior and the resulting pattern morphology are here explained in correlation with the film cohesion and its adhesion to the substrate. If the cohesion is rather strong compared to the adhesion, it would be almost impossible to pattern fine structures because the areas exposed below threshold level would also be detached together. On the contrary, if the cohesion is too weak, a pattern of step-wise morphology would not be obtained as observed in Fig. 1(b) (top and middle images). Fig. 2(a) shows the annealing temperature dependence of film resistivity and threshold pulse energy density. While the film remained almost insulating up to T = 125 °C, the resistivity measured using a 4-probe was suddenly dropped down to ~ 10− 3 Ω cm after annealing at 150 °C. This indicates that the film can be cured around 150 °C, with all organic components removed. Increasing the annealing temperature further lowered the resistivity until it became nearly saturated above 250 °C. This is attributed to the sintering effect. The minimum values obtained were 3–5 times higher than the Ag bulk resistivity of 2.25 × 10− 6 Ω cm. We
Fig. 3. (a) SEM image of a stripe pattern generated by two-beam interference. The inset is a cross-sectional transmission electron microscope image of the film-substrate interface. (b) 2D honeycomb structure fabricated by three-beam interference. The inset shows the surface morphology.
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patterns. Films of about 800 nm thick, pre-annealed at 450 °C for 30 min were exposed to a single pulse in the patterning process. Wellaligned stripe patterns were obtained by two-beam interference (Fig. 3(a)). The stripe width could be controlled by tuning up the pulse energy. Smooth vertical sidewalls were maintained until the stripe width was scaled down to 1.5 µm, below which the corners of the stripe became rounded. The inset shows a cross-sectional transmission electron microscopic image of the interface. Fig. 3(b) is a 2D honeycomb pattern fabricated by three-beam interference using a prism of trigonal-pyramid shape. Connected honeycomb cells were converted into isolated domains with increased pulse energy. An SEM image of the film surface is given in the inset of Fig. 3(b). Fig. 4 is an optical profiler image showing the step-wise edge in a stripe pattern. The stripe width in the pattern was slightly different from position to position even under fixed pulse energy, which seems to arise from the nonuniform intensity distribution of the laser output. A laser beam with hat-top profile was used in this work and thus a beam homogenizer will be helpful to achieve better pattern uniformity, although a pulsed laser reveals inherent spatial and temporal instability to some extent. 4. Conclusion
Fig. 4. An optical profiler image showing the step-wise edge morphology in a stripe pattern.
found that this photoetching only occurs over a well-defined threshold pulse energy density. It increased with increasing temperature. The measured threshold levels were 0.1–1.8 J/cm2, well below the damage threshold of the substrate (N500 J/cm2). The threshold value was weakly influenced by the film thickness. This implies that the threshold energy density for film patterning is dominantly determined by the adhesion rather than the cohesion. It is thus expected that the adhesion will exhibit a temperature-dependent behavior similar to that of the threshold. In the meanwhile, the variation of cohesion can be estimated from the resistivity data, because they are closely related to each other. The solution-processed film maintains a relatively weak cohesion until the particles begin to be sintered. As the sintering proceeds, the film cohesion increases with a simultaneous drop of the resistivity. That the resisitivity is nearly saturated above 250 °C tells that the cohesion is not much enhanced even though the film is annealed at a higher temperature, while the adhesion continues to increase. The estimated temperature dependences of the cohesion and adhesion are given in Fig. 2(b). It shows that the film annealed at 250 °C has a strong cohesion relative to its adhesion. This may be the reason why the patterning was impossible. For films annealed at 150 °C and as-deposited ones, the absolute magnitude of cohesion is too low. Therefore, a pattern with step-wise morphology is very difficult to generate. It is to be noted that the thermo-elastic force is exerted on the film only when the pulse energy density exceeds the threshold level. While the two-beam interference generates a sinusoidal energy density distribution, the actual driving force for patterning has a different profile. Only the areas exposed above threshold are subject to this force. This makes it possible to fabricate a pattern of step-wise morphology even under a sinusoidal or other gradual interference profile. Fig. 3 shows SEM images of the fabricated
Ag thin films solution-deposited on glass were patterned utilizing a pulsed laser-induced thermo-elastic removal of the material. The etching behavior and the resulting pattern morphology were very sensitive to the cohesion of the film and its adhesion to the substrate, both being modified by the post-deposition annealing process. It was also observed that photoetching only occurs over a well-defined threshold pulse energy density. This made it possible to obtain sharpedged patterns under an interference-generated gradual intensity profile. The fabrication of step-wise 1D and 2D patterns at the micrometer scales has been demonstrated by holographic lithography using a pulsed Nd:YAG laser. In this work, we have used a Nd:YAG laser with a maximum average power of ~ 4 W. This limited the patterned area to several mm2. It is believed that a high-power laser for industrial use will enable patterning over larger area. This holographic method may be applicable to other solution-processed nanoparticulate films if a suitable laser source is used. Acknowledgement This research was supported by the Korea Research Foundation (Grant number: KRF 2006-311-D00586). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16]
V. Berger, O. Gauthier-Lafaye, E. Costard, J. Appl. Phys. 82 (1997) 60. M. Campbell, D. Sharp, M. Harrison, R. Denning, A. Turberfield, Nature 404 (2000) 53. S. Shoji, S. Kawata, Appl. Phys. Lett. 76 (2000) 2668. L. Wu, Y. Zhong, C. Chan, K. Wong, G. Wang, Appl. Phys. Lett. 86 (2005) 241102. Y. Miklyaev, D. Meisel, A. Blanco, G. Feymann, K. Busch, W. Koch, C. Enkrich, M. Deubel, M. Wegener, Appl. Phys. Lett. 82 (2003) 1284. I. Divliansky, T. Mayer, K. Holliday, V. Crespi, Appl. Phys. Lett. 82 (2003) 1667. G. Zhou, F.S. Chau, Appl. Phys. Lett. 90 (2007) 181106. M. Salaun, M. Audier, F. Delyon, M. Duneau, Appl. Surf. Sci. 254 (2007) 830. A. Lasagni, M. D, Alessandria, R. Giovanelli, F. Mucklich, Appl. Surf. Sci. 254 (2007) 930. F. Mucklich, A. Lasagni, C. Daniel, Intermetallics 13 (2004) 437. Y. Nakata, T. Okada, M. Maeda, Appl. Phys. Lett. 81 (2002) 4239. J. Skriniarova, D. Pudis, I. Martincek, J. Kovac, N. Tarjanyi, M. Vesely, I. Turek, Microelectron. J. 38 (2007) 746. H. Kim, H. Shin, J. Ha, M. Lee, K. Lim, J. Appl. Phys. 102 (2007) 083505. M. Arronte, P. Neves, R. Vilar, J. Appl. Phys. 92 (2002) 6973. J. Lee, C. Curran, K. Watkins, Appl. Phys. A 73 (2001) 219. G. Vereecke, E. Röhr, M. Heyns, J. Appl. Phys. 85 (1999) 3837.