Abstract

A new method for fabrication of diffractive structures, which we call quasi-direct writing, is illustrated. The diffractive structures can be generated by changing the pixel spacing along the direction of the cross scan (with zero overlap) and keeping the pixel spacing constant along the other scan direction, with a normal overlap of 50%–60%, while the substrate surface is scanned with a focused ion beam (FIB). Quasi-direct writing is a method for achieving special customer designs when the milling machine has no computer programming function. Diffractive structures with various periods and depths can be derived by controlling the parameters of pixel spacing, beam current, ion incidence angle, and the scan time or ion dose. The method is not restricted to any one material and can be used for metals, insulators, and semiconductors.

© 2004 Optical Society of America

Full Article  |  PDF Article

References

  • View by:
  • |

  1. Andrei Y. Smuk and Nabil M. Lawandy, �??Direct laser writing diffractive optics in glass,�?? Opt. Lett. 22, 1030 (1997).
    [CrossRef] [PubMed]
  2. Michael T.Gale, Markus Rossi, Jorn Pedersen, and Helmut Schutz, �??Fabrication of continuous-relief micro-optical elements by direct laser writing in photoresists,�?? Opt. Eng. 33, 3556 (1994).
    [CrossRef]
  3. T. Fujita, H. Nishihara, and J. Koyama, �??Fabrication of microlenses using electron-beam lithography,�?? Opt. Lett. 6, 613 (1981).
    [CrossRef] [PubMed]
  4. Fu Yong-Qi and Ngoi Kok Ann Bryan, �??Diffractive optical elements with continuous relief fabricated by focused ion beam for monomode fiber coupling,�?? Opt. Express 7, 141-147 (2000). <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-7-3-141.">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-7-3-141.</a>
    [CrossRef] [PubMed]
  5. Yongqi Fu and Ngoi Kok Ann Bryan, �??Hybrid micro-diffractive-refractive optical element with continuous relief fabricated by focused ion beam for single-mode coupling,�?? Appl. Opt. 40, 5872 (2001).
    [CrossRef]
  6. Yongqi Fu and Ngoi Kok Ann Bryan, �??Self-organized formation of a blaze grating like structure on Si(100) induced by focused ion beam scanning,�?? Opt. Express 12, 227 (2004). <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-12-2-227">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-12-2-227</a>
    [CrossRef] [PubMed]

Cited By

OSA participates in CrossRef's Cited-By Linking service. Citing articles from OSA journals and other participating publishers are listed here.

Alert me when this article is cited.


Figures (7)

Fig. 1.
Fig. 1.

Schematic of FIB digital scanning steps and sizes in the defined scan area of L × W. Overlap (h) in both the X and the Y direction can be controlled by varying the X- and Y-direction pixel spacing. (a) Overlap of 50%–60% in both the X and the Y scan direction for FIB direct writing; (b) overlap of 50%–60% in the X direction and zero in the Y direction for quasi-direct writing.

Fig. 2.
Fig. 2.

Ion beam current versus lateral dimension and depth of the diffractive structures measured with an AFM in a 15 μm × 15 μm area. Scanning was carried out with an ion energy of 40 keV, an ion incidence angle of 0°, ion dose of 1.5 nC/μm2, and beam current of 569 pA. X and Y pixel spaces are 0.02 and 0.6 μm, respectively. The inset FIB images are for beam currents of 99 pA and 2 nA. The substrate material is Si (111).

Fig. 3.
Fig. 3.

Ion energy versus lateral dimension and depth of the diffractive structures measured with an AFM in a 15 μm × 15 μm area. Scanning was carried out with an ion incidence angle of 0° and beam current of 569 pA. X and Y pixel spaces are 0.02 and 0.8 μm, respectively. The ion dose is 1.5 nC/μm2. The substrate material is Si (111). The dotted line indicates that no ripples are observed for ion energies below 25 keV.

Fig. 4.
Fig. 4.

Ion incidence angles versus lateral dimension and depth of the diffractive structures measured with an AFM in a 15 μm × 15 μm area. The scanning was carried out with ion energy of 40 keV, a scan time of 64 min, and a beam current of 569 pA. X and Y pixel spaces are 0.02 and 0.6 μm, respectively. The inset AFM images are for ion incidence angles of 0° and 70°. The substrate material is Si (111).

Fig. 5.
Fig. 5.

Y pixel spaces versus lateral dimension and depth of the diffractive structures measured with an AFM in a 15 μm × 15 μm area. X pixel spaces were fixed at 0.02 μm. The scanning was carried out with an ion energy of 40 keV, an ion dose of 1.5 nC/μm2, ion incidence angles of 0° 45°, and 80°, and a beam current of 569 pA. The inset FIB images correspond to Y pixel spaces of 0.1 and 2 μm, indicated by the arrows. The white arrows in the FIB images show the projection direction of the ion beam and scan path. The substrate material is Si (111).

Fig. 6
Fig. 6

Ion-beam scanning time versus lateral dimension and depth of the diffractive structures measured with an AFM in the scanned 15 μm × 15 μm area. The scanning was carried out with ion energy of 40 keV and beam current of 569 pA. X and Y pixel spaces are 0.02 and 0.6 μm, respectively. The inset AFM images correspond to scanning times of 4 and 64 min, indicated by the arrows. The diffractive structures changed from sinusoidal to blazelike topographies. The substrate material is Si (111).

Fig. 7.
Fig. 7.

Diffractive structure change for various process parameters with quasi-direct FIB writing on quartz, measured with an AFM. (a) Three-dimensional (3D) image of the grating with a line density of 787 lines/mm, milled with scan time 8 min, beam current 569 pA, and incidence angle 15°. (b) 2D profile with depth 24.4 nm and width 1270 nm. (c) 3D image of the grating with a line density of 900 lines/mm, milled with scan time 32 min, , beam current 569 pA, and incidence angle 60°. (d) 2D profile with depth 439 nm and width 1110 nm.

Metrics