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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 15, Iss. 21 — Oct. 17, 2007
  • pp: 14177–14183
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Localized surface plasmon nanolithography with ultrahigh resolution

Xingzhan Wei, Xiangang Luo, Xiaochun Dong, and Chunlei Du  »View Author Affiliations


Optics Express, Vol. 15, Issue 21, pp. 14177-14183 (2007)
http://dx.doi.org/10.1364/OE.15.014177


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Abstract

A localized surface plasmon nanolithography (LSPN) technique is proposed and demonstrated to produce patterns with a sub-20nm line width. High transmission efficiency is realized by adjusting the period of grating. The well-regulated grating structures in metallic mask are employed to excite surface plasmon polaritons (SPPs) on the illuminated side. The SPP waves propagate toward the tip along the taper surfaces which cause most of energy accumulation at the tip and give rise to high local field enhancements in a near-field region around the tip. The amplitude of local electric field intensity is quite large and the line width can be confined within sub-20nm, at the same time, the contrast and spatial resolution are greatly enhanced, which can facilitate nanolithography efficiently with simple ultraviolet light sources.

© 2007 Optical Society of America

1. Introduction

2. Principle of LSPN

As is well known, in addition to surface plasmon polaritons at a planar dielectric-metal interface, localized surface plasmons can exist in other geometries, such as spheres or cylinders, especially on a surface of small roughness in subwavelength dimension [14

14. A. V. Zayats and I. I.. Smolyaninov, “Near-field photonic: surface plasmon polaritons and locallized surface plasmons,” J. Opt. A: Pure Appl. Opt. 5, S16–S50 (2003). [CrossRef]

]. The magnitude of the electromagnetic field depends significantly on the shape and size of the individual particles, and a very strong electromagnetic field enhancement can be observed at these geometries. Localized surface plasmon contributes to numerous phenomena such as light emission from STM tunnel junctions, enhanced scattering and surface enhanced Raman scattering, and also finds applications in active photonic elements and apertureless scanning near-field microscopy [15

15. D. L. Mills, “Theory of STM-induced enhancement of dynamic dipole moments on crystal surfaces,” Phys. Rev. B 65, 125419/1–11 (2002). [CrossRef]

, 16

16. I. I. Smolyaninov, A. V. Zayats, A. Gungor, and C. C. Davis, “Single-Photon Tunneling via Localized Surface Plasmons,” Phys. Rev. Lett. 88, 187402/1–4 (2002). [CrossRef] [PubMed]

].

Fig. 1. Schematic configuration of simulated LSPN structure which is mainly composed of grooves and tapers.

3. Simulation results and analysis

We numerically demonstrated localized surface plasmon nanolithography with the business software opti-FDTD. In our model, the refractive index used for the photoresist and the quartz are 1.7 and 1.52, respectively. The permittivity of the Al mask is described by the Drude model (εAL(ω) = ε -εP 2/[ω(ω-iVC)]), where the high-frequency bulk permittivity ε = 1, the bulk plasmon frequency εP = 2.4×1016 rad / s, and the electron collision frequency VC =1.1×1015 rad / s. These parameters are obtained by fitting the model to the experimental data taken from the literature [17

17. P. B. Johnson and R. W. Christy, “Optical constants of the noble metals,” Phys. Rev. B 6, 4370–4379 (1972). [CrossRef]

]. A plane-wave, monochromatic illumination source λ = 436nm of transverse magnetic polarization is utilized. For simplicity, two-dimensional simulation is performed in the paper, although it can be extended to the three-dimension.

3.1 Enhancement of the transmission efficiency

As is well known, the corrugated grating-like structures can be used to excite SPPs and modulate the optical transmission [18

18. F. J. Garciá-Vidal, H. J. Lezec, T. W. Ebbesen, and L. Martín-Moreno, “Multiple paths to enhance optical transmission through a single subwavelength slit,” Phys. Rev. Lett. 90, 213901/1–4 (2003). [CrossRef] [PubMed]

,19

19. Z. Li, J. Tian, Z. Liu, W. Zhou, and C. Zhang, “Enhanced light transmission through a single subwavelength aperture in layered films consisting of metal and dielectric,” Opt. Express. 13, 9071–9077 (2005). [CrossRef] [PubMed]

]. In order to consider the modulation function of grooves structure in our scheme, a comparison is made between a single tapered structure and a tapered structure surrounded with a number of ridges as shown in the Fig. 2(a) and Fig. 2(b). Fig. 2(c) shows the enhancement of normalized-to-area transmission efficiency at different ridges number. The parameters are in detail labeled in the Fig. 2 and here take the values of L=320nm, W=15nm, F=20nm, M=50nm, B=100nm, H=2nm and an invariable aspect ratio b/a=2/1 is selected. Here the normalized-to-area transmission efficiency is defined as the numerical value which the energy only emerges from taper tip is normalized by the input energy over the same area.

Fig. 2. (a). Schematic picture of a single tapered structure. (b) Sketch of tapered structure with grooves in the input surface. (c) The enhancement of normalized-to-area transmission efficiency as a function of the number of ridges in input surface (L=320nm, W=15nm, F=20nm, M=50nm, B=100nm, and H=2nm).

3.2 Enhancement of the magnitude of electric field

As indicated earlier, the strongly localized characteristic is important and the amplitude of localized electric field intensity is extremely large, therefore the comparison between the excitation field and localized field will turn essential. As shown in Fig. 3(a), the magnitude of normal component (Ex=3900) and longitudinal component (Ez=2400) at the tip are in the same numerical value scale. Compared with the excitation field (Ex’=376, Ez’=0), they all grow more than ten times, especially the longitudinal component grows much stronger. As for |E|2 (|E|2=|Ex|2+|Ez|2), it grows more than two orders of magnitude (148 times of the excitation field).

Fig. 3. (a). Snapshot of steady fields: Normal component Ex and longitudinal component Ez of the local optical electric field (L=320nm, D=140nm, W=15nm, F=20nm, M=20nm, B=100nm, and H=2nm). (b) Enhancement of |E|2 at the tip for different ridges number (L=320nm, D=300nm, W=15nm, F=20nm, M=50nm, B=100nm, and H=2nm).

It is known from the calculation that the enhancement of |E|2 also depends on the numbers of ridges as shown in Fig. 3(b), where the curve indicates the relationship of |E|2 versus the number of ridges n at the period of surface plasmon resonance condition (D=300nm). It is seen from the curve that the magnitude of |E|2 is gradually enhanced with the increase of n number, and a maximum peak appears at n=20. Subsequently, the electric field intensity will change little with the increase of ridges number.

3.3 Optical resolution

The electric field intensity distribution is given in detail in Fig. 4(a). Excited surface plasmons propagate toward the tip along the tapers surface. Energy is accumulated gradually in the course of SPPs propagation and the amplitude of local electric field increases accordingly. One spatial electric field peak sharply appears just at the tip position. The electric field intensity profile in the photoresist is shown in Fig. 4(b). The line width defined as the full-width at 0.7 maximum is 19.5nm. It is expected that an acceptable nano-photolithography pattern with high spatial resolution and high efficiency can be approached with the profile. Since the technique can breakthrough diffraction-limitation, the line width of several ten nanometers can be achieved by means of the traditional lithography source with such as a wavelength of 436nm by choosing better refractive index matching materials and narrower tip width.

Fig. 4. (a). Light intensity distribution in the mask and the photoresist in the case of surface plasmon excitation and localized surface plasmon accumulation (L=320nm, D=140nm, W=15nm, F=20nm, M=20nm, B=100nm, and H=2nm). (b) Electric field intensity profile in the photoresist at the position of 5nm below the interface of potoresist and tip.

4. Discussion

The decay of |E| amplitude for different tip widths is shown in Fig. 5. When the tip width is 15nm, the electric field magnitude drops exponentially from 1 to 0.042 through longitudinal (Z direction) 30nm distance. In addition, when the electric field intensity decreases to the half of the tip field, the decay length in Z direction is around 3.5nm. However, the decay length is about 8.5nm when the tip width is 30nm. This implies that the smaller tip width creates larger localized electric field at the tip companying with a fast attenuation in the resist. Since the rapid decay of electric field is corresponding to the lower penetration depth in the resist, an optimized design should be done for compromising the lithography resolution and the exposure depth although a very thin photoresist or surface imaging techniques can also be employed properly for solving the conflict [20

20. J. Aizenberg, J. A. Rogers, K. E. Paul, and G. M. Whitesides, “Imaging the irradiance distribution in the optical near field,” Appl. Phys. Lett. 71, 3773–3775 (1997). [CrossRef]

].

Fig. 5. Decay of |E| amplitude along the Z direction for different tip widths.

In our simulation, the line width of 19.5nm is achieved in the photoresist when the tip width is chosen as 15nm. For proving the universality of high spatial resolution which exists in LSPN, we adopt different tip widths. As shown in Fig. 6, the line width is about 20.5nm when the tip width is 15nm; at the same time, the line width is around 37nm for the tip width 30nm. It is obvious that the line widths are just a little bigger than the tip widths (about 5~7nm), so the manufacture of metallic mask with tip structure in small dimension will be the crucial process in LSPN.

Fig. 6. Line width chart at different tip widths

5. Conclusions

In this paper, we put forward a localized surface plasmon nanolithography technique. By adjusting the period of corrugated metallic structures, we can realize photolithography with high transmission efficiency. Our simulation results demonstrate that a line width below 20nm can be realized by the approach of LSPN. By introducing the localized characteristic, the LSPN technique is of the advantages of high efficiency, high spatial resolution, and adapted to the manufacture of flexible patterns, and promising an alternative fabrication for nanometer scale devices.

Acknowledgment

The work was supported by 973 Program of China (No.2006CB302900) and the Chinese Nature Science Grant (60678035) and (60507014). Authors would like to thank Miss Leilei Yang, Ms Qiling Deng for their kind contribution for the work.

References and links

1.

J. Melngailis, “Focused ion beam lithography,” Nucl. Instrum. Methods Phys. Res. B 80, 1271–1280 (1993). [CrossRef]

2.

S. Y. Chou, P. R. Krauss, and P. J. Renstrom, “Imprint lithography with 25-nanometer resolution,” Science 272, 85–87 (1996). [CrossRef]

3.

M. C. McAlpine, R. S. Friedman, and C. M. Lieber, “Nanoimprint Lithography for Hybrid Plastic Electronics,” Nano Lett. 3, 443–445 (2003). [CrossRef]

4.

H. Zhang, S. W. Chung, and C. A. Mirkin, “Fabrication of sub-50 nm Solid-State. Nanostructures Based on Dip-Pen Nanolithography,” Nano Lett. 1, 43–45 (2003). [CrossRef]

5.

M. D. Levenson, “Extending the lifetime of optical lithography technologies with wavefront engineering,” Jpn. J. Appl. Phys. 33, 6765–6773 (1994). [CrossRef]

6.

T. W. Ebbesen, H. J. Lezec, H. F. Ghaemi, T. Thio, and P. A. Wolff, “Extraordinary optical transmission through sub-wavelength hole arrays,” Nature (London) 391, 667–669 (1999). [CrossRef]

7.

X. Luo and T. Ishihara, “Surface plasmon resonant interference nanolithography technique,” Appl. Phys. Lett. 84, 4780–4782 (2004). [CrossRef]

8.

X. Luo and T. Ishihara, “Subwavelength photolithography based on surface-plasmon polariton resonance,” Opt. Express. 12, 3055–3065 (2004). [CrossRef] [PubMed]

9.

W. Srituravanich, N. Fang, C. Sun, Q. Luo, and X. Zhang, “Plasmonic nanolithography,” Nano Lett. 4, 1085–1088 (2004). [CrossRef]

10.

W. Srituravanich, N. Fang, S. Durant, M. Ambati, C. Sun, and X. Zhang, “Sub-100 nm lithography using ultrashort wavelength of surface plasmons,” J. Vac. Sci. Technol. B 22, 3475–3478 (2004). [CrossRef]

11.

Z. W. Liu, Q. H. Wei, and X. Zhang, “Surface plasmon interference nanolithography,” Nano Lett. 5, 957–961 (2005). [CrossRef] [PubMed]

12.

D. B. Shao and S. C. Chen, “Surface-plasmon-assisted nanoscale photolithography by polarized light,” Appl. Phys. Lett. 86, 253107/1–3(2005). [CrossRef]

13.

M. I. Stockman, “Nanofocusing of optical energy in tapered plasmonic waveguides,” Phys. Rev. Lett. 93, 137404/1–4 (2004). [CrossRef] [PubMed]

14.

A. V. Zayats and I. I.. Smolyaninov, “Near-field photonic: surface plasmon polaritons and locallized surface plasmons,” J. Opt. A: Pure Appl. Opt. 5, S16–S50 (2003). [CrossRef]

15.

D. L. Mills, “Theory of STM-induced enhancement of dynamic dipole moments on crystal surfaces,” Phys. Rev. B 65, 125419/1–11 (2002). [CrossRef]

16.

I. I. Smolyaninov, A. V. Zayats, A. Gungor, and C. C. Davis, “Single-Photon Tunneling via Localized Surface Plasmons,” Phys. Rev. Lett. 88, 187402/1–4 (2002). [CrossRef] [PubMed]

17.

P. B. Johnson and R. W. Christy, “Optical constants of the noble metals,” Phys. Rev. B 6, 4370–4379 (1972). [CrossRef]

18.

F. J. Garciá-Vidal, H. J. Lezec, T. W. Ebbesen, and L. Martín-Moreno, “Multiple paths to enhance optical transmission through a single subwavelength slit,” Phys. Rev. Lett. 90, 213901/1–4 (2003). [CrossRef] [PubMed]

19.

Z. Li, J. Tian, Z. Liu, W. Zhou, and C. Zhang, “Enhanced light transmission through a single subwavelength aperture in layered films consisting of metal and dielectric,” Opt. Express. 13, 9071–9077 (2005). [CrossRef] [PubMed]

20.

J. Aizenberg, J. A. Rogers, K. E. Paul, and G. M. Whitesides, “Imaging the irradiance distribution in the optical near field,” Appl. Phys. Lett. 71, 3773–3775 (1997). [CrossRef]

OCIS Codes
(220.3740) Optical design and fabrication : Lithography
(230.7370) Optical devices : Waveguides
(240.6680) Optics at surfaces : Surface plasmons

ToC Category:
Optics at Surfaces

History
Original Manuscript: July 27, 2007
Revised Manuscript: September 22, 2007
Manuscript Accepted: September 22, 2007
Published: October 12, 2007

Citation
Xingzhan Wei, Xiangang Luo, Xiaochun Dong, and Chunlei Du, "Localized surface plasmon nanolithography with ultrahigh resolution," Opt. Express 15, 14177-14183 (2007)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-15-21-14177


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References

  1. J. Melngailis, "Focused ion beam lithography," Nucl. Instrum. Methods Phys. Res. B 80, 1271-1280 (1993). [CrossRef]
  2. S. Y.  Chou, P. R.  Krauss, and P. J.  Renstrom, "Imprint lithography with 25-nanometer resolution," Science  272, 85-87 (1996). [CrossRef]
  3. M. C. McAlpine, R. S. Friedman, and C. M. Lieber, "Nanoimprint Lithography for Hybrid Plastic Electronics," Nano Lett. 3, 443-445 (2003). [CrossRef]
  4. H. Zhang, S. W. Chung, and C. A. Mirkin, "Fabrication of sub-50 nm Solid-State. Nanostructures Based on Dip-Pen Nanolithography," Nano Lett. 1, 43-45 (2003). [CrossRef]
  5. M. D. Levenson, "Extending the lifetime of optical lithography technologies with wavefront engineering," Jpn. J. Appl. Phys. 33, 6765-6773 (1994). [CrossRef]
  6. T. W. Ebbesen, H. J. Lezec, H. F. Ghaemi, T. Thio, and P. A. Wolff, "Extraordinary optical transmission through sub-wavelength hole arrays," Nature (London) 391, 667-669 (1999). [CrossRef]
  7. X. Luo and T. Ishihara, "Surface plasmon resonant interference nanolithography technique," Appl. Phys. Lett. 84, 4780-4782 (2004). [CrossRef]
  8. X. Luo and T. Ishihara, "Subwavelength photolithography based on surface-plasmon polariton resonance," Opt. Express. 12, 3055-3065 (2004). [CrossRef] [PubMed]
  9. W. Srituravanich, N. Fang, C. Sun, Q. Luo, and X. Zhang, "Plasmonic nanolithography," Nano Lett. 4, 1085-1088 (2004). [CrossRef]
  10. W. Srituravanich, N. Fang, S. Durant, M. Ambati, C. Sun, and X. Zhang, "Sub-100 nm lithography using ultrashort wavelength of surface plasmons," J. Vac. Sci. Technol. B 22, 3475-3478 (2004). [CrossRef]
  11. Z. W. Liu, Q. H. Wei, and X. Zhang, "Surface plasmon interference nanolithography," Nano Lett. 5, 957-961 (2005). [CrossRef] [PubMed]
  12. D. B. Shao and S. C. Chen, "Surface-plasmon-assisted nanoscale photolithography by polarized light," Appl. Phys. Lett. 86, 253107/1-3(2005). [CrossRef]
  13. M. I.  Stockman, "Nanofocusing of optical energy in tapered plasmonic waveguides," Phys. Rev. Lett. 93, 137404/1-4 (2004). [CrossRef] [PubMed]
  14. A. V. Zayats and I. I. Smolyaninov, "Near-field photonic: surface plasmon polaritons and locallized surface plasmons," J. Opt. A: Pure Appl. Opt. 5, S16-S50 (2003). [CrossRef]
  15. D. L. Mills, "Theory of STM-induced enhancement of dynamic dipole moments on crystal surfaces," Phys. Rev. B 65, 125419/1-11 (2002). [CrossRef]
  16. I. I. Smolyaninov, A. V. Zayats, A. Gungor, and C. C. Davis, "Single-Photon Tunneling via Localized Surface Plasmons," Phys. Rev. Lett. 88, 187402/1-4 (2002). [CrossRef] [PubMed]
  17. P. B. Johnson and R. W. Christy, "Optical constants of the noble metals," Phys. Rev. B 6, 4370-4379 (1972). [CrossRef]
  18. F. J. Garcýá-Vidal, H. J. Lezec, T. W. Ebbesen, and L. Martín-Moreno, "Multiple paths to enhance optical transmission through a single subwavelength slit," Phys. Rev. Lett. 90, 213901/1-4 (2003). [CrossRef] [PubMed]
  19. Z. Li, J. Tian, Z. Liu, W. Zhou, and C. Zhang, "Enhanced light transmission through a single subwavelength aperture in layered films consisting of metal and dielectric," Opt. Express. 13, 9071-9077 (2005). [CrossRef] [PubMed]
  20. J. Aizenberg, J. A. Rogers, K. E. Paul, and G. M. Whitesides, "Imaging the irradiance distribution in the optical near field," Appl. Phys. Lett. 71, 3773-3775 (1997). [CrossRef]

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