Abstract

We have fabricated refractive sapphire microlenses and characterized their properties for what we believe to be the first time. We use thermally reflown photoresist lenslet patterns as a mask for chlorine-based dry etch of sapphire. Pattern transfer to the mechanically hard and chemically inert sapphire substrate is made possible by an inductively coupled plasma etch system that supplies a high-density plasma gas. Processed sapphire microlenses exhibit properties close to the ideal and operate nearly in the diffraction limit.

© 2001 Optical Society of America

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References

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  1. O. Wada, “Ion beam etching of InP and its application to fabrication of high radiance InGaAsP light emitting diodes,” J. Electrochem. Soc. 131, 2373–2380 (1984).
    [CrossRef]
  2. M. B. Stern, T. R. Jay, “Dry etching for coherent refractive microlens arrays,” Opt. Eng. 33, 3547–3551 (1994).
    [CrossRef]
  3. N. C. Craft, A. Y. Feldblum, “Optical interconnects based on arrays of surface emitting lasers and lenslets,” Appl. Opt. 31, 1735–1739 (1992).
    [CrossRef] [PubMed]
  4. Z. D. Popovic, R. A. Sprague, G. A. N. Connell, “Technique for monolithic fabrication of microlens arrays,” Appl. Opt. 27, 1281–1284 (1988).
    [CrossRef] [PubMed]
  5. S. Haselbeck, H. Schreiber, J. Schwider, N. Streibl, “Microlenses fabricated by melting a photoresist on a base layer,” Opt. Eng. 32, 1322–1324 (1993).
    [CrossRef]
  6. R. W. Cahn, P. Haasen, E. J. Kramer, eds., Materials Science and Technology (VCH, Weinheim, 1993), Chap. 2, pp. 85–101.
  7. See, for example, S. Nakamura, G. Fasol, The Blue Laser Diode (Springer, Berlin, 1997), Chap. 2.
  8. For a general overview see M. A. Lieberman, A. J. Lichtenberg, Principles of Plasma Discharges and Materials Processing (Wiley, New York, 1994), Chap. 12.
  9. H. S. Kim, D. H. Lee, Y. J. Sung, Y. H. Lee, G. Y. Yeom, J. W. Lee, S. H. Chae, T. I. Kim, “Inductively coupled plasma etching of sapphire wafer,” in Proceedings of the 1st UK Nitride Conference (Institute of Physics, Glasgow, 1999), p. 10.
  10. Y. J. Sung, H. S. Kim, Y. H. Lee, J. W. Lee, S. H. Chae, Y. J. Park, G. Y. Yeom, “High rate etching of sapphire wafer using Cl2/BCl3/Ar inductively coupled plasmas,” Mater. Sci. Eng. B 82, 50–52 (2001).
    [CrossRef]
  11. E. D. Palik, ed., Handbook of Optical Constants of Solids II (Academic, San Diego, 1991), Chap. 2, pp. 498–500.

2001 (1)

Y. J. Sung, H. S. Kim, Y. H. Lee, J. W. Lee, S. H. Chae, Y. J. Park, G. Y. Yeom, “High rate etching of sapphire wafer using Cl2/BCl3/Ar inductively coupled plasmas,” Mater. Sci. Eng. B 82, 50–52 (2001).
[CrossRef]

1994 (1)

M. B. Stern, T. R. Jay, “Dry etching for coherent refractive microlens arrays,” Opt. Eng. 33, 3547–3551 (1994).
[CrossRef]

1993 (1)

S. Haselbeck, H. Schreiber, J. Schwider, N. Streibl, “Microlenses fabricated by melting a photoresist on a base layer,” Opt. Eng. 32, 1322–1324 (1993).
[CrossRef]

1992 (1)

1988 (1)

1984 (1)

O. Wada, “Ion beam etching of InP and its application to fabrication of high radiance InGaAsP light emitting diodes,” J. Electrochem. Soc. 131, 2373–2380 (1984).
[CrossRef]

Chae, S. H.

Y. J. Sung, H. S. Kim, Y. H. Lee, J. W. Lee, S. H. Chae, Y. J. Park, G. Y. Yeom, “High rate etching of sapphire wafer using Cl2/BCl3/Ar inductively coupled plasmas,” Mater. Sci. Eng. B 82, 50–52 (2001).
[CrossRef]

H. S. Kim, D. H. Lee, Y. J. Sung, Y. H. Lee, G. Y. Yeom, J. W. Lee, S. H. Chae, T. I. Kim, “Inductively coupled plasma etching of sapphire wafer,” in Proceedings of the 1st UK Nitride Conference (Institute of Physics, Glasgow, 1999), p. 10.

Connell, G. A. N.

Craft, N. C.

Fasol, G.

See, for example, S. Nakamura, G. Fasol, The Blue Laser Diode (Springer, Berlin, 1997), Chap. 2.

Feldblum, A. Y.

Haselbeck, S.

S. Haselbeck, H. Schreiber, J. Schwider, N. Streibl, “Microlenses fabricated by melting a photoresist on a base layer,” Opt. Eng. 32, 1322–1324 (1993).
[CrossRef]

Jay, T. R.

M. B. Stern, T. R. Jay, “Dry etching for coherent refractive microlens arrays,” Opt. Eng. 33, 3547–3551 (1994).
[CrossRef]

Kim, H. S.

Y. J. Sung, H. S. Kim, Y. H. Lee, J. W. Lee, S. H. Chae, Y. J. Park, G. Y. Yeom, “High rate etching of sapphire wafer using Cl2/BCl3/Ar inductively coupled plasmas,” Mater. Sci. Eng. B 82, 50–52 (2001).
[CrossRef]

H. S. Kim, D. H. Lee, Y. J. Sung, Y. H. Lee, G. Y. Yeom, J. W. Lee, S. H. Chae, T. I. Kim, “Inductively coupled plasma etching of sapphire wafer,” in Proceedings of the 1st UK Nitride Conference (Institute of Physics, Glasgow, 1999), p. 10.

Kim, T. I.

H. S. Kim, D. H. Lee, Y. J. Sung, Y. H. Lee, G. Y. Yeom, J. W. Lee, S. H. Chae, T. I. Kim, “Inductively coupled plasma etching of sapphire wafer,” in Proceedings of the 1st UK Nitride Conference (Institute of Physics, Glasgow, 1999), p. 10.

Lee, D. H.

H. S. Kim, D. H. Lee, Y. J. Sung, Y. H. Lee, G. Y. Yeom, J. W. Lee, S. H. Chae, T. I. Kim, “Inductively coupled plasma etching of sapphire wafer,” in Proceedings of the 1st UK Nitride Conference (Institute of Physics, Glasgow, 1999), p. 10.

Lee, J. W.

Y. J. Sung, H. S. Kim, Y. H. Lee, J. W. Lee, S. H. Chae, Y. J. Park, G. Y. Yeom, “High rate etching of sapphire wafer using Cl2/BCl3/Ar inductively coupled plasmas,” Mater. Sci. Eng. B 82, 50–52 (2001).
[CrossRef]

H. S. Kim, D. H. Lee, Y. J. Sung, Y. H. Lee, G. Y. Yeom, J. W. Lee, S. H. Chae, T. I. Kim, “Inductively coupled plasma etching of sapphire wafer,” in Proceedings of the 1st UK Nitride Conference (Institute of Physics, Glasgow, 1999), p. 10.

Lee, Y. H.

Y. J. Sung, H. S. Kim, Y. H. Lee, J. W. Lee, S. H. Chae, Y. J. Park, G. Y. Yeom, “High rate etching of sapphire wafer using Cl2/BCl3/Ar inductively coupled plasmas,” Mater. Sci. Eng. B 82, 50–52 (2001).
[CrossRef]

H. S. Kim, D. H. Lee, Y. J. Sung, Y. H. Lee, G. Y. Yeom, J. W. Lee, S. H. Chae, T. I. Kim, “Inductively coupled plasma etching of sapphire wafer,” in Proceedings of the 1st UK Nitride Conference (Institute of Physics, Glasgow, 1999), p. 10.

Lichtenberg, A. J.

For a general overview see M. A. Lieberman, A. J. Lichtenberg, Principles of Plasma Discharges and Materials Processing (Wiley, New York, 1994), Chap. 12.

Lieberman, M. A.

For a general overview see M. A. Lieberman, A. J. Lichtenberg, Principles of Plasma Discharges and Materials Processing (Wiley, New York, 1994), Chap. 12.

Nakamura, S.

See, for example, S. Nakamura, G. Fasol, The Blue Laser Diode (Springer, Berlin, 1997), Chap. 2.

Park, Y. J.

Y. J. Sung, H. S. Kim, Y. H. Lee, J. W. Lee, S. H. Chae, Y. J. Park, G. Y. Yeom, “High rate etching of sapphire wafer using Cl2/BCl3/Ar inductively coupled plasmas,” Mater. Sci. Eng. B 82, 50–52 (2001).
[CrossRef]

Popovic, Z. D.

Schreiber, H.

S. Haselbeck, H. Schreiber, J. Schwider, N. Streibl, “Microlenses fabricated by melting a photoresist on a base layer,” Opt. Eng. 32, 1322–1324 (1993).
[CrossRef]

Schwider, J.

S. Haselbeck, H. Schreiber, J. Schwider, N. Streibl, “Microlenses fabricated by melting a photoresist on a base layer,” Opt. Eng. 32, 1322–1324 (1993).
[CrossRef]

Sprague, R. A.

Stern, M. B.

M. B. Stern, T. R. Jay, “Dry etching for coherent refractive microlens arrays,” Opt. Eng. 33, 3547–3551 (1994).
[CrossRef]

Streibl, N.

S. Haselbeck, H. Schreiber, J. Schwider, N. Streibl, “Microlenses fabricated by melting a photoresist on a base layer,” Opt. Eng. 32, 1322–1324 (1993).
[CrossRef]

Sung, Y. J.

Y. J. Sung, H. S. Kim, Y. H. Lee, J. W. Lee, S. H. Chae, Y. J. Park, G. Y. Yeom, “High rate etching of sapphire wafer using Cl2/BCl3/Ar inductively coupled plasmas,” Mater. Sci. Eng. B 82, 50–52 (2001).
[CrossRef]

H. S. Kim, D. H. Lee, Y. J. Sung, Y. H. Lee, G. Y. Yeom, J. W. Lee, S. H. Chae, T. I. Kim, “Inductively coupled plasma etching of sapphire wafer,” in Proceedings of the 1st UK Nitride Conference (Institute of Physics, Glasgow, 1999), p. 10.

Wada, O.

O. Wada, “Ion beam etching of InP and its application to fabrication of high radiance InGaAsP light emitting diodes,” J. Electrochem. Soc. 131, 2373–2380 (1984).
[CrossRef]

Yeom, G. Y.

Y. J. Sung, H. S. Kim, Y. H. Lee, J. W. Lee, S. H. Chae, Y. J. Park, G. Y. Yeom, “High rate etching of sapphire wafer using Cl2/BCl3/Ar inductively coupled plasmas,” Mater. Sci. Eng. B 82, 50–52 (2001).
[CrossRef]

H. S. Kim, D. H. Lee, Y. J. Sung, Y. H. Lee, G. Y. Yeom, J. W. Lee, S. H. Chae, T. I. Kim, “Inductively coupled plasma etching of sapphire wafer,” in Proceedings of the 1st UK Nitride Conference (Institute of Physics, Glasgow, 1999), p. 10.

Appl. Opt. (2)

J. Electrochem. Soc. (1)

O. Wada, “Ion beam etching of InP and its application to fabrication of high radiance InGaAsP light emitting diodes,” J. Electrochem. Soc. 131, 2373–2380 (1984).
[CrossRef]

Mater. Sci. Eng. B (1)

Y. J. Sung, H. S. Kim, Y. H. Lee, J. W. Lee, S. H. Chae, Y. J. Park, G. Y. Yeom, “High rate etching of sapphire wafer using Cl2/BCl3/Ar inductively coupled plasmas,” Mater. Sci. Eng. B 82, 50–52 (2001).
[CrossRef]

Opt. Eng. (2)

M. B. Stern, T. R. Jay, “Dry etching for coherent refractive microlens arrays,” Opt. Eng. 33, 3547–3551 (1994).
[CrossRef]

S. Haselbeck, H. Schreiber, J. Schwider, N. Streibl, “Microlenses fabricated by melting a photoresist on a base layer,” Opt. Eng. 32, 1322–1324 (1993).
[CrossRef]

Other (5)

R. W. Cahn, P. Haasen, E. J. Kramer, eds., Materials Science and Technology (VCH, Weinheim, 1993), Chap. 2, pp. 85–101.

See, for example, S. Nakamura, G. Fasol, The Blue Laser Diode (Springer, Berlin, 1997), Chap. 2.

For a general overview see M. A. Lieberman, A. J. Lichtenberg, Principles of Plasma Discharges and Materials Processing (Wiley, New York, 1994), Chap. 12.

H. S. Kim, D. H. Lee, Y. J. Sung, Y. H. Lee, G. Y. Yeom, J. W. Lee, S. H. Chae, T. I. Kim, “Inductively coupled plasma etching of sapphire wafer,” in Proceedings of the 1st UK Nitride Conference (Institute of Physics, Glasgow, 1999), p. 10.

E. D. Palik, ed., Handbook of Optical Constants of Solids II (Academic, San Diego, 1991), Chap. 2, pp. 498–500.

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Figures (7)

Fig. 1
Fig. 1

Schematic diagram of the ICP dry-etch system. The top-loaded rf coil is a planar spiral copper coil with 3.5 turns.

Fig. 2
Fig. 2

Perspective SEM image for a sapphire microlens with lens diameter of 60 µm.

Fig. 3
Fig. 3

Sapphire microlens surface topography imaged by an AFM. The measured rms surface roughness over the scanned area of 1 µm × 1 µm is 0.23 nm.

Fig. 4
Fig. 4

Microlens profiles measured by a stylus profilometer for (a) the photoresist lenslet mask and (b) the processed sapphire microlens after dry etch.

Fig. 5
Fig. 5

Experimental arrangement for focal length and beam profile measurements. The sapphire microlens is mounted on a fine-resolution translational stage so that it can be moved back and forth during the measurements.

Fig. 6
Fig. 6

Relationship between focal length and curvature radius of sapphire microlenses. Different symbols are used to distinguish between different sets of samples, whereas the solid line is based on the theory.

Fig. 7
Fig. 7

Measured intensity distribution of the laser beam at the focal length of a sapphire microlens. The curve drawn over the experimental data is the theoretical Airy pattern for a circular aperture.

Tables (1)

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Table 1 Summary of the Measurements of Focal Length and Beam Spot Size for a Few Sets of Sapphire Microlenses Fabricated under Different Conditionsa

Equations (4)

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Rx=rpk1-1-k2xrp3/2,
Rrp/k.
f=R/n-1,
Ix=I02 J1π xλf/Dπ xλf/D2,

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