Elsevier

Optics & Laser Technology

Volume 44, Issue 6, September 2012, Pages 1649-1653
Optics & Laser Technology

Fabrication of high aspect ratio subwavelength gratings based on X-ray lithography and electron beam lithography

https://doi.org/10.1016/j.optlastec.2011.11.051Get rights and content

Abstract

In this paper, we present two nano-fabrication technologies that provide effective approaches for low-cost, large-scale manufacturing of nano-gratings. One grating is fabricated on polymethylmethacrylate (PMMA) with the pitch of 500 nm, and height of 2000 nm, and the other is fabricated on silicon wafer with the pitch of 666 nm, and height of 200 nm. High aspect ratio PMMA nanostructures which use X-ray lithography and electron beam lithography (EBL) are reported in this paper. These gratings can be used as molds, making it possible for industrial nano-imprinting technology to significantly cut cost and shorten process time.

Highlights

► Two kinds of high aspect ratio subwavelength gratings are manufactured. ► These gratings can be used as mold for nano-imprinting technology. ► Fast atom beam (FAB) etching is used for effective fabrication. ► A coupling layer is introduced to keep the gratings from conglutination

Introduction

So far, there are a number of reported techniques for fabrication of diffractive optical elements (DOE), yet the height of those gratings is not sufficient [1], [2], [3]. Grating is a very important optical component that has been widely used in optical measurement, integrated optics, optical information processing, sensors, lab-on-chip, filters and other areas [4], [5]. A single fiber Bragg grating, 1.5 cm in length, embedded on a cantilever, is capable of simultaneously measuring and discriminating strain and temperature over wide ranges with sensitivities of 3.38 pm/μm and 19.05 pm/°C, respectively [6]. For photodetectors, nanoscale diffraction gratings in active region can trap light, significantly modifying their optical absorption, reflectance and transmission properties and thus resulting in enhanced photoresponse [7]. A high-contrast subwavelength grating is integrated into a surface emitting laser instead of conventional Bragg-reflectors [8]. Subwavelength gratings can operate as waveguide couplers, subwavelength antireflection structures, resonance structures, gratings can be used in distributed-feedback and distributed-Bragg-reflector laser configurations, and wavelength-division multiplexing [9], [10], [11], [12], [13].

Nowadays, there is a growing need for a class of optical components integrated with diffraction gratings [14], [15]. And the grating period is required to be not more than1 μm, such as X-ray transmission gratings (TGs) [16]. Subwavelength phenomenon has been exploited for many years in free-space optics. A broad-band mirror with reflectivity more than 98.5% has been achieved by Mateus et al. [17]. And recently, it has been found that surface plasmons can concentrate and channel light with subwavelength grating, leading to miniaturized photonic circuits [18].

Section snippets

Nano-manufacturing of subwavelength gratings

These years great interest is focused on laser based nano-manufacturing technologies [19]. Scanning Near-field Photolithography (SNP) using laser coupled Near-field Scanning Optical Microscopy (NSOM) can achieve 20–55 nm resolution in surface patterning and the laser etched depth is 20–100 nm [20], [21]. Immersion laser interference lithography is developed at Max-Planck Institute of Microstructure Physics, Germany [22]. Line patterns with a period less than 100 nm and width of 45 nm are

Experimental work

A schematic of the X-ray lithography fabrication process is shown in Fig. 1. It starts from the coupling layer which is the interlayer between PMMA and Si substrate, spin-coated to the silicon substrate, 300 nm in thickness (Fig. 1(b)). Since, the coupling layer is very important, we tried several kinds of interlayer materials, and NUC APZ6633 has the best performance. It can keep gratings from conglutination. Secondly, PMMA is spin-coated to the interlayer, 2300 nm in thickness (Fig. 1(c)). And

Results and analysis

The SEM micrograph of PMMA nano-gratings obtained by the processes is shown in Fig. 4; the inset is a magnified view of the gratings. It's easy to see that the side walls are very flat and straight. The structure is line gratings, 250 nm in width, 2000 nm in depth, and 500 nm in period. It is area is 2 mm2, and aspect ratio is about 8, which has not been achieved before. A schematic of the test equipment is shown in Fig. 5. After the TM light beam is diffracted by the sample, it is diffracted into

Conclusions

In summary, two subwavelength grating's fabrication methods are successfully developed. One subwavelength grating is directly fabricated on PMMA photoresist using X-ray lithography, obtaining a high aspect ratio which is approximately 8. Especially, the introduction of interlayer eliminates the phenomenon of conglutination. The other one is prepared using EBL and FAB techniques on Si (100) substrates. Their uniformities of grating pitches and shapes are confirmed. Both of them can be directly

Acknowledgment

The authors acknowledge financial support by “Shanghai Pujiang Talent Plan” Sponsorship (no. 09PJ1406200) and International Cooperation Project from Ministry of Science and Technology of China (2009DFB10330).

References (28)

  • C. Thirstrup et al.

    Sensors and Actuators B

    (2004)
  • Y. Lin et al.

    Sensors and Actuators

    (2007)
  • Hiroyuki Tsukamoto et al.

    Japanese Journal of Applied Physics

    (2006)
  • Mats Peter Björnängen et al.

    Proceedings of SPIE—The International Society for Optical Engineering

    (2004)
  • J Zhao et al.

    IEEE Electron Device Letters

    (1997)
  • A.S. Jugessur et al.

    Journal of Vacuum Science and Technology B

    (2010)
  • P.S. Reddy

    Microwave and Optical Technology Letters

    (2011)
  • A.K. Sharma et al.

    IEEE-Nanotechnology

    (2001)
  • Huang Michael C.Y., Zhou Ye, Chang-Hasnain Connie J. IEEE 20th International Semiconductor Laser Conference...
  • J. Zhao et al.

    IEEE Transactions on Electron Devices

    (1997)
  • Z. Yu et al.

    Applied Physics Letters

    (2000)
  • Y. Kanamori et al.

    Japanese Journal of Applied Physics

    (2003)
  • M.A. Green et al.

    IEEE Transactions on Electron Devices

    (1990)
  • Y. Toma Y et al.

    Japanese Journal of Applied Physics

    (1997)
  • Cited by (22)

    • Investigation into the effect of distinct nanostructures on silicon reflectivity for solar cells

      2022, Materials Today: Proceedings
      Citation Excerpt :

      Table 2 shows the comparision between simulation and experimental results obstained for optimized rectangular cross-sectioned nanograting. The reason for this reduction is given by Fresnels theory [12,13]. According to this theory whenever a ray of light travelled between two optic mediums with different value of refractive index, there is change in the refractive index at the interface of two optic medium.

    • Laser heat-mode lithography characteristics and mechanism of ZnS-SiO<inf>2</inf> thin films

      2018, Materials Chemistry and Physics
      Citation Excerpt :

      Up until now, X-ray lithography and electron beam lithography have been the primary methods of nanoscale pattern structure fabrication. However, these methods are disadvantaged by the high vacuum environment, diffraction limit, and complex operations required [8,9]. Fortunately, laser heat-mode lithography has been found to be an alternative.

    • Fabrication of sub-micron surface structures on copper, stainless steel and titanium using picosecond laser interference patterning

      2016, Applied Surface Science
      Citation Excerpt :

      Grooves, dimples and pillar-like structures can be generated with different technologies. Besides lithographic methods such as photolithography [1], interference lithography [2,3], nanoimprint lithography [4,5] and deep X-ray lithography [6], short (nanosecond and sub-nanosecond) and ultrashort pulsed (pico- and femtosecond) laser-based techniques have been established to fabricate well-defined surface micro pattern over the last decades [7–10]. The effect of such micro structures improves, for example, the anti-adhesive properties of cutting tools [11], reduces friction of automotive components [12,13], generates hydrophobic or superhydrophobic surfaces [14–16], enhances cell proliferation on biomaterials [17–19], boosts solar cell efficiency [20] and promotes adhesive bonding [21].

    • High resolution spin-on electron beam lithography resist with exceptional dry etching resistance

      2015, Applied Materials Today
      Citation Excerpt :

      The trend of ever decreasing feature sizes in subsequent lithography generations runs parallel to the need for higher performance resists, in terms of resolution, contrast and etch resistance during pattern transfer [2–5]. In particular, a range of applications, including X-ray Fresnel lenses [6,7], NEMS [8–10], photonic metamaterials [11–13], polarizers [14–16], and biomolecules sorting devices [17,18] require the ability of fabricating high-resolution high-aspect-ratio structures. However, this usually entails a trade-off between the best performing conditions for attaining the highest resolution by electron beam lithography (EBL), i.e. with very thin resists, and the need to produce etching masks withstanding prolonged pattern transfer processes by dry etching techniques.

    • Control of γ lamella precipitation in Ti-39 at.% Al single crystals by nanogroove-induced dislocation bands

      2015, Acta Materialia
      Citation Excerpt :

      Focused ion beam (FIB) etching presents an alternative mask-less process, whereby nanometer-scale gratings can be directly fabricated on very hard materials such as silicon [10], and has achieved high aspect ratio gratings with a pitch of 500 nm and depth of 2 μm on poly-methyl-methacrylate. Silicon gratings with a period of 666 nm and depth of 200 nm have also been produced by X-ray lithography and electron beam lithography (EBL) combined with fast atom beam etching (FAB) [11]. Despite the success achieved with existing techniques, there is a demand for new processes that are productive and less costly than lithography based methods.

    View all citing articles on Scopus
    View full text