Abstract

We describe a promising approach to the processing of micro-optical components, where CO2 laser irradiation in raster scan is used to generate localized surface melting of binary or multilevel structures on silica, fabricated by conventional reactive-ion etching. The technique is shown to provide well-controlled local smoothing of step features by viscous flow under surface tension forces, relaxing the scale length of etch steps controllably between 1 and 30μm. Uniform treatment of extended areas is obtained by raster scanning with a power stabilized, Gaussian beam profile in the 0.5 to 1mm diameter range. For step heights of 1μm or less, the laser-induced relaxation is symmetric, giving softening of just the upper and lower corners at a threshold power of 4.7W, extending to symmetric long scale relaxation at 7.9W, with the upper limit set by the onset of significant vaporization. Some asymmetry of the relaxation is observed for 3μm high steps. Also, undercut steps or troughs produced by photolithography and etching of a deep 64 level multistep surface are found to have a polarization-dependent distortion after laser smoothing. The laser reflow process may be useful for improving the diffraction efficiency by suppressing high orders in binary diffractive optical elements, or for converting multilevel etched structures in fused silica into smoothed refractive surfaces in, for example, custom microlens arrays.

© 2010 Optical Society of America

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References

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    [CrossRef]
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    [CrossRef]
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    [CrossRef]
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    [CrossRef]
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2009 (1)

2008 (1)

Y. Chen, A. Y. Yi, D. Yao, F. Klocke, and G. Pongs, “A reflow process for glass microlens array fabrication by use of precision compression molding,” J. Micromech. Microeng. 18, 055022 (2008).
[CrossRef]

2007 (2)

C. Vass, K. Osvay, M. Csete, and B. Hopp, “Fabrication of 550 nm gratings in fused silica by laser induced backside wet etching technique,” Appl. Surf. Sci. 253, 8059-8063(2007).
[CrossRef]

G. Kopitkovas, T. Lippert, J. Venturini, C. David, and A. Wokaun, “Laser induced backside wet etching: mechanisms and fabrication of micro-optical elements,” J. Phys. Conf. Ser. 59, 526-532 (2007).
[CrossRef]

2006 (3)

2005 (1)

K. Zimmer and R. Bohme, “Precise etching of fused silica for refractive and diffractive micro-optical applications,” Opt. Lasers Eng. 43, 1349-1360 (2005).
[CrossRef]

2003 (1)

M. Mansuripur, A. R. Zakharian, and J. V. Moloney, “Interaction of light with subwavelength structures,” Opt. Photonics News 14(3), 56-61 (2003).

2002 (2)

1998 (1)

F. Vega, N. Lupon, J. A. Cebrian, and F. Laguarta, “Laser application for optical glass polishing,” Opt. Eng. 37, 272-279 (1998).
[CrossRef]

1995 (2)

M. Kuittinen, H. P. Herzig, and P. Ehbets, “Improvements in diffraction efficiency of gratings and microlenses with continuous relief surfaces,” Opt. Commun. 120, pp. 230-234(1995).
[CrossRef]

M. G. Moharam, E. B. Grann, and D. A. Pommet, “Formulation for stable and efficient implementation of the rigorous coupled-wave analysis of binary gratings,” J. Opt. Soc. Am. A 12, 1068-1076 (1995).
[CrossRef]

1994 (1)

1987 (1)

1982 (1)

Armengol, J.

Baker, H. J.

Bohme, R.

K. Zimmer and R. Bohme, “Precise etching of fused silica for refractive and diffractive micro-optical applications,” Opt. Lasers Eng. 43, 1349-1360 (2005).
[CrossRef]

Cebrian, J. A.

F. Vega, N. Lupon, J. A. Cebrian, and F. Laguarta, “Laser application for optical glass polishing,” Opt. Eng. 37, 272-279 (1998).
[CrossRef]

Chen, Y.

Y. Chen, A. Y. Yi, D. Yao, F. Klocke, and G. Pongs, “A reflow process for glass microlens array fabrication by use of precision compression molding,” J. Micromech. Microeng. 18, 055022 (2008).
[CrossRef]

Csete, M.

C. Vass, K. Osvay, M. Csete, and B. Hopp, “Fabrication of 550 nm gratings in fused silica by laser induced backside wet etching technique,” Appl. Surf. Sci. 253, 8059-8063(2007).
[CrossRef]

David, C.

G. Kopitkovas, T. Lippert, J. Venturini, C. David, and A. Wokaun, “Laser induced backside wet etching: mechanisms and fabrication of micro-optical elements,” J. Phys. Conf. Ser. 59, 526-532 (2007).
[CrossRef]

Doremaus, R. H.

R. H. Doremaus, “Viscosity of silica,” J. Appl. Phys. 92, 7619-7629 (2002).
[CrossRef]

Driggers, R. G.

R. G. Driggers, “Diffractive optics fabrication,” in Encyclopedia of Optical Engineering: Vol. 1 (Marcel Dekker, 2003), pp. 374-388.

Ehbets, P.

M. Kuittinen, H. P. Herzig, and P. Ehbets, “Improvements in diffraction efficiency of gratings and microlenses with continuous relief surfaces,” Opt. Commun. 120, pp. 230-234(1995).
[CrossRef]

Grann, E. B.

Guyon, E.

E. Guyon, J. Hulin, L. Petit, and C. Mitescu, “The physics of fluids,” in Physical Hydrodynamics (Oxford U. Press, 2001), pp. 31-40.

Hall, D. R.

Herzig, H. P.

M. Kuittinen, H. P. Herzig, and P. Ehbets, “Improvements in diffraction efficiency of gratings and microlenses with continuous relief surfaces,” Opt. Commun. 120, pp. 230-234(1995).
[CrossRef]

Hopp, B.

C. Vass, K. Osvay, M. Csete, and B. Hopp, “Fabrication of 550 nm gratings in fused silica by laser induced backside wet etching technique,” Appl. Surf. Sci. 253, 8059-8063(2007).
[CrossRef]

Hulin, J.

E. Guyon, J. Hulin, L. Petit, and C. Mitescu, “The physics of fluids,” in Physical Hydrodynamics (Oxford U. Press, 2001), pp. 31-40.

Jahns, J.

S. Sinzinger and J. Jahns, “Fabrication of diffractive optics,” in Microoptics (Wiley-VCH, 1999), pp. 129-179.

Klocke, F.

Y. Chen, A. Y. Yi, D. Yao, F. Klocke, and G. Pongs, “A reflow process for glass microlens array fabrication by use of precision compression molding,” J. Micromech. Microeng. 18, 055022 (2008).
[CrossRef]

Kopitkovas, G.

G. Kopitkovas, T. Lippert, J. Venturini, C. David, and A. Wokaun, “Laser induced backside wet etching: mechanisms and fabrication of micro-optical elements,” J. Phys. Conf. Ser. 59, 526-532 (2007).
[CrossRef]

Kuittinen, M.

M. Kuittinen, H. P. Herzig, and P. Ehbets, “Improvements in diffraction efficiency of gratings and microlenses with continuous relief surfaces,” Opt. Commun. 120, pp. 230-234(1995).
[CrossRef]

Laguarta, F.

F. Vega, N. Lupon, J. A. Cebrian, and F. Laguarta, “Laser application for optical glass polishing,” Opt. Eng. 37, 272-279 (1998).
[CrossRef]

F. Laguarta, N. Lupon, and J. Armengol, “Optical glass polishing by controlled laser surface-heat treatment,” Appl. Opt. 33, 6508-6512 (1994).
[CrossRef] [PubMed]

Lippert, T.

G. Kopitkovas, T. Lippert, J. Venturini, C. David, and A. Wokaun, “Laser induced backside wet etching: mechanisms and fabrication of micro-optical elements,” J. Phys. Conf. Ser. 59, 526-532 (2007).
[CrossRef]

Lowdermilk, W. H.

Lupon, N.

F. Vega, N. Lupon, J. A. Cebrian, and F. Laguarta, “Laser application for optical glass polishing,” Opt. Eng. 37, 272-279 (1998).
[CrossRef]

F. Laguarta, N. Lupon, and J. Armengol, “Optical glass polishing by controlled laser surface-heat treatment,” Appl. Opt. 33, 6508-6512 (1994).
[CrossRef] [PubMed]

Mansuripur, M.

M. Mansuripur, A. R. Zakharian, and J. V. Moloney, “Interaction of light with subwavelength structures,” Opt. Photonics News 14(3), 56-61 (2003).

Markillie, G. A. J.

McLachlan, A. D.

Mendez, E.

Meyer, F. P.

Milam, D.

Mitescu, C.

E. Guyon, J. Hulin, L. Petit, and C. Mitescu, “The physics of fluids,” in Physical Hydrodynamics (Oxford U. Press, 2001), pp. 31-40.

Moharam, M. G.

Moloney, J. V.

M. Mansuripur, A. R. Zakharian, and J. V. Moloney, “Interaction of light with subwavelength structures,” Opt. Photonics News 14(3), 56-61 (2003).

Monjardin, J. F.

Nowak, K. M.

Nowak, M.

Osvay, K.

C. Vass, K. Osvay, M. Csete, and B. Hopp, “Fabrication of 550 nm gratings in fused silica by laser induced backside wet etching technique,” Appl. Surf. Sci. 253, 8059-8063(2007).
[CrossRef]

Petit, L.

E. Guyon, J. Hulin, L. Petit, and C. Mitescu, “The physics of fluids,” in Physical Hydrodynamics (Oxford U. Press, 2001), pp. 31-40.

Philipp, H. R.

H. R. Philipp, “Silicon dioxide SiO2 (glass),” in Handbook of Optical Constants of Solids, E.D.Palik, ed. (Academic, 1985), pp. 749-763.

Pommet, D. A.

Pongs, G.

Y. Chen, A. Y. Yi, D. Yao, F. Klocke, and G. Pongs, “A reflow process for glass microlens array fabrication by use of precision compression molding,” J. Micromech. Microeng. 18, 055022 (2008).
[CrossRef]

Sinzinger, S.

S. Sinzinger and J. Jahns, “Fabrication of diffractive optics,” in Microoptics (Wiley-VCH, 1999), pp. 129-179.

Temple, P. A.

Trela, N.

Vass, C.

C. Vass, K. Osvay, M. Csete, and B. Hopp, “Fabrication of 550 nm gratings in fused silica by laser induced backside wet etching technique,” Appl. Surf. Sci. 253, 8059-8063(2007).
[CrossRef]

Vega, F.

F. Vega, N. Lupon, J. A. Cebrian, and F. Laguarta, “Laser application for optical glass polishing,” Opt. Eng. 37, 272-279 (1998).
[CrossRef]

Venturini, J.

G. Kopitkovas, T. Lippert, J. Venturini, C. David, and A. Wokaun, “Laser induced backside wet etching: mechanisms and fabrication of micro-optical elements,” J. Phys. Conf. Ser. 59, 526-532 (2007).
[CrossRef]

Villarreal, F. J.

Wendland, J. J.

Wokaun, A.

G. Kopitkovas, T. Lippert, J. Venturini, C. David, and A. Wokaun, “Laser induced backside wet etching: mechanisms and fabrication of micro-optical elements,” J. Phys. Conf. Ser. 59, 526-532 (2007).
[CrossRef]

Yao, D.

Y. Chen, A. Y. Yi, D. Yao, F. Klocke, and G. Pongs, “A reflow process for glass microlens array fabrication by use of precision compression molding,” J. Micromech. Microeng. 18, 055022 (2008).
[CrossRef]

Yi, A. Y.

Y. Chen, A. Y. Yi, D. Yao, F. Klocke, and G. Pongs, “A reflow process for glass microlens array fabrication by use of precision compression molding,” J. Micromech. Microeng. 18, 055022 (2008).
[CrossRef]

Zakharian, A. R.

M. Mansuripur, A. R. Zakharian, and J. V. Moloney, “Interaction of light with subwavelength structures,” Opt. Photonics News 14(3), 56-61 (2003).

Zimmer, K.

K. Zimmer and R. Bohme, “Precise etching of fused silica for refractive and diffractive micro-optical applications,” Opt. Lasers Eng. 43, 1349-1360 (2005).
[CrossRef]

Appl. Opt. (6)

Appl. Surf. Sci. (1)

C. Vass, K. Osvay, M. Csete, and B. Hopp, “Fabrication of 550 nm gratings in fused silica by laser induced backside wet etching technique,” Appl. Surf. Sci. 253, 8059-8063(2007).
[CrossRef]

J. Appl. Phys. (1)

R. H. Doremaus, “Viscosity of silica,” J. Appl. Phys. 92, 7619-7629 (2002).
[CrossRef]

J. Micromech. Microeng. (1)

Y. Chen, A. Y. Yi, D. Yao, F. Klocke, and G. Pongs, “A reflow process for glass microlens array fabrication by use of precision compression molding,” J. Micromech. Microeng. 18, 055022 (2008).
[CrossRef]

J. Opt. Soc. Am. A (1)

J. Phys. Conf. Ser. (1)

G. Kopitkovas, T. Lippert, J. Venturini, C. David, and A. Wokaun, “Laser induced backside wet etching: mechanisms and fabrication of micro-optical elements,” J. Phys. Conf. Ser. 59, 526-532 (2007).
[CrossRef]

Opt. Commun. (1)

M. Kuittinen, H. P. Herzig, and P. Ehbets, “Improvements in diffraction efficiency of gratings and microlenses with continuous relief surfaces,” Opt. Commun. 120, pp. 230-234(1995).
[CrossRef]

Opt. Eng. (1)

F. Vega, N. Lupon, J. A. Cebrian, and F. Laguarta, “Laser application for optical glass polishing,” Opt. Eng. 37, 272-279 (1998).
[CrossRef]

Opt. Express (2)

Opt. Lasers Eng. (1)

K. Zimmer and R. Bohme, “Precise etching of fused silica for refractive and diffractive micro-optical applications,” Opt. Lasers Eng. 43, 1349-1360 (2005).
[CrossRef]

Opt. Photonics News (1)

M. Mansuripur, A. R. Zakharian, and J. V. Moloney, “Interaction of light with subwavelength structures,” Opt. Photonics News 14(3), 56-61 (2003).

Other (4)

H. R. Philipp, “Silicon dioxide SiO2 (glass),” in Handbook of Optical Constants of Solids, E.D.Palik, ed. (Academic, 1985), pp. 749-763.

E. Guyon, J. Hulin, L. Petit, and C. Mitescu, “The physics of fluids,” in Physical Hydrodynamics (Oxford U. Press, 2001), pp. 31-40.

S. Sinzinger and J. Jahns, “Fabrication of diffractive optics,” in Microoptics (Wiley-VCH, 1999), pp. 129-179.

R. G. Driggers, “Diffractive optics fabrication,” in Encyclopedia of Optical Engineering: Vol. 1 (Marcel Dekker, 2003), pp. 374-388.

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Figures (9)

Fig. 1
Fig. 1

Surface relaxation of the etched structure by CO 2 laser irradiation. Solid arrows indicate the significant pressure acting on the molten edges, whereas dotted arrows indicate the liquid flow.

Fig. 2
Fig. 2

(a) Illustration of the binary grating with spatial period of 22.6 μm and step height of 1 μm . (b) Micrographs of the structure after laser treatment with N = 10 unidirectional scans in the direction shown, for laser power of 7.35 W , 7.85 W , and 9.00 W , respectively.

Fig. 3
Fig. 3

Evolution of the step profile of the binary grating as a function of laser line scans, N, with fixed laser power, P = 7.35 W . The diameter of the laser beam was 1 mm .

Fig. 4
Fig. 4

AFM surface profile of laser-treated binary samples with (a)  0.8 μm initial step height and (b)  3 μm initial step height. Dotted line indicates ideal shape of a binary grating before laser smoothing. The diameter of the laser beam used was 550 μm .

Fig. 5
Fig. 5

Light scatter distribution versus diffraction order at different raster scan laser treatment conditions of the binary grating with step height of 0.8 μm .

Fig. 6
Fig. 6

Microscope image of (a) the untreated multilevel etched structure, with visible zigzag steps and a groove in the middle, and (b) the same sample after laser treatment at laser power of 7.6 W .

Fig. 7
Fig. 7

Laser smoothing effect of “normal etched” steps, marked as the A area in Fig. 6a, at different laser powers. Each profile is offset by 0.2 μm .

Fig. 8
Fig. 8

Laser smoothing effect of the misregistered region, marked as the B area in Fig. 6a, at different laser power. Each profile is offset by 0.5 μm .

Fig. 9
Fig. 9

Misregistered etch steps oriented perpendicular to the scan direction (a) before and (b) after laser treatment with laser power of 7.6 W .

Equations (2)

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P = γ R .
N π · d m 4 · Δ x ,

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