Abstract

A two step process has been developed for the fabrication of diffraction limited concave microlens arrays. The process is based on the photoresist filling of melted holes obtained by a preliminary photolithography step. The quality of these microlenses has been tested in a Mach-Zehnder interferometer. The method allows the fabrication of concave microlens arrays with diffraction limited optical performance. Concave microlenses with diameters ranging between 30 µm to 230 µm and numerical apertures up to 0.25 have been demonstrated. As an example, we present the realization of diffusers obtained with random sizes and locations of concave shapes.

© 2008 Optical Society of America

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  1. D. Daly, R. F. Stevens, M. C. Hutley, and N. Davies, "The manufacture of microlenses by melting photoresist," Meas. Sci. Technol. 1, 759-766 (1990).
    [CrossRef]
  2. D. Purdy, "Fabrication of complex micro-optic components using photo-sculpturing through halftone transmission masks," Appl. Opt. 3, 167-175. (1994).
  3. M. T. Gale, G. K. Lang, J. M. Raynor, and H. Schütz, "Fabrication of micro-optical elements by laser beam writing in photoresist," Proc SPIE 1506, 65-70 (1991).
    [CrossRef]
  4. T.-K. Shih, C.-F. Chen, J.-R Ho, and F.-T. Chuang, "Fabrication of PDMS (polydimethylsiloxane) microlens and diffuser using replica molding," Microelectron. Eng. 83, 2499-2503 (2006).
    [CrossRef]
  5. T.-K. Shih, J.-R. Ho, J.-H. Wang, C.-F. Chen, C.-Y. Liu, C.-C. Chen, and W.-T. Whang, "Fabrication of soft reflective microoptical elements using a replication process," Microelectron. Eng. 85, 175-180 (2008).
    [CrossRef]
  6. D. Chandra, S. Yang, and P.-C. Lin, "Strain responsive concave and convex microlens arrays," Appl. Phys. Lett. 91, 251912 (2007).
    [CrossRef]
  7. X. Dong, C. Du, S. Li, C. Wang, and Y. Fu, "Control approach for form accuracy of microlenses with continuous relief," Opt. Express 13, 1353-1360 (2005).
    [CrossRef] [PubMed]
  8. S.-I. Chang and J.-B. Yoon, "Shape-controlled, high fill-factor microlens arrays fabricated by 3D diffuser lithography and plastic replication method," Opt. Express 12, 6366-6371 (2004).
    [CrossRef] [PubMed]
  9. T.-H. Lin, H. Yang, and C.-K. Chao, "Concave microlens array mold fabrication in photoresist using UV proximity printing," Microsyst. Technol.Micro and Nanosystems Information Storage and Processing Systems 13, 1537-1543 (2007).
  10. Y. Xia and G. M. Whitesides, "Soft lithography," Annu. Rev. Mater. Sci. 28, 153-84 (1998).
    [CrossRef]
  11. Ph. Nussbaum, I. Philipoussis, A. Husser and H. P. Herzig, "Simple technique for replication of micro-optical elements," Opt. Eng. 37, 1804-1808 (1998).
    [CrossRef]
  12. A. Schilling, R. Merz, Ch. Ossmann, and H. P. Herzig, "Surface profiles of reflow microlenses under the influence of surface tension and gravity," Opt. Eng 39, 2171-2176 (2000).
    [CrossRef]
  13. D. Malacara and Z. Malacara, Handbook of lens design, (Dekker, New-York, 1994).

2008 (1)

T.-K. Shih, J.-R. Ho, J.-H. Wang, C.-F. Chen, C.-Y. Liu, C.-C. Chen, and W.-T. Whang, "Fabrication of soft reflective microoptical elements using a replication process," Microelectron. Eng. 85, 175-180 (2008).
[CrossRef]

2007 (2)

D. Chandra, S. Yang, and P.-C. Lin, "Strain responsive concave and convex microlens arrays," Appl. Phys. Lett. 91, 251912 (2007).
[CrossRef]

T.-H. Lin, H. Yang, and C.-K. Chao, "Concave microlens array mold fabrication in photoresist using UV proximity printing," Microsyst. Technol.Micro and Nanosystems Information Storage and Processing Systems 13, 1537-1543 (2007).

2006 (1)

T.-K. Shih, C.-F. Chen, J.-R Ho, and F.-T. Chuang, "Fabrication of PDMS (polydimethylsiloxane) microlens and diffuser using replica molding," Microelectron. Eng. 83, 2499-2503 (2006).
[CrossRef]

2005 (1)

2004 (1)

2000 (1)

A. Schilling, R. Merz, Ch. Ossmann, and H. P. Herzig, "Surface profiles of reflow microlenses under the influence of surface tension and gravity," Opt. Eng 39, 2171-2176 (2000).
[CrossRef]

1998 (2)

Y. Xia and G. M. Whitesides, "Soft lithography," Annu. Rev. Mater. Sci. 28, 153-84 (1998).
[CrossRef]

Ph. Nussbaum, I. Philipoussis, A. Husser and H. P. Herzig, "Simple technique for replication of micro-optical elements," Opt. Eng. 37, 1804-1808 (1998).
[CrossRef]

1994 (1)

1991 (1)

M. T. Gale, G. K. Lang, J. M. Raynor, and H. Schütz, "Fabrication of micro-optical elements by laser beam writing in photoresist," Proc SPIE 1506, 65-70 (1991).
[CrossRef]

1990 (1)

D. Daly, R. F. Stevens, M. C. Hutley, and N. Davies, "The manufacture of microlenses by melting photoresist," Meas. Sci. Technol. 1, 759-766 (1990).
[CrossRef]

Chandra, D.

D. Chandra, S. Yang, and P.-C. Lin, "Strain responsive concave and convex microlens arrays," Appl. Phys. Lett. 91, 251912 (2007).
[CrossRef]

Chang, S.-I.

Chao, C.-K.

T.-H. Lin, H. Yang, and C.-K. Chao, "Concave microlens array mold fabrication in photoresist using UV proximity printing," Microsyst. Technol.Micro and Nanosystems Information Storage and Processing Systems 13, 1537-1543 (2007).

Chen, C.-C.

T.-K. Shih, J.-R. Ho, J.-H. Wang, C.-F. Chen, C.-Y. Liu, C.-C. Chen, and W.-T. Whang, "Fabrication of soft reflective microoptical elements using a replication process," Microelectron. Eng. 85, 175-180 (2008).
[CrossRef]

Chen, C.-F.

T.-K. Shih, J.-R. Ho, J.-H. Wang, C.-F. Chen, C.-Y. Liu, C.-C. Chen, and W.-T. Whang, "Fabrication of soft reflective microoptical elements using a replication process," Microelectron. Eng. 85, 175-180 (2008).
[CrossRef]

T.-K. Shih, C.-F. Chen, J.-R Ho, and F.-T. Chuang, "Fabrication of PDMS (polydimethylsiloxane) microlens and diffuser using replica molding," Microelectron. Eng. 83, 2499-2503 (2006).
[CrossRef]

Chuang, F.-T.

T.-K. Shih, C.-F. Chen, J.-R Ho, and F.-T. Chuang, "Fabrication of PDMS (polydimethylsiloxane) microlens and diffuser using replica molding," Microelectron. Eng. 83, 2499-2503 (2006).
[CrossRef]

Daly, D.

D. Daly, R. F. Stevens, M. C. Hutley, and N. Davies, "The manufacture of microlenses by melting photoresist," Meas. Sci. Technol. 1, 759-766 (1990).
[CrossRef]

Davies, N.

D. Daly, R. F. Stevens, M. C. Hutley, and N. Davies, "The manufacture of microlenses by melting photoresist," Meas. Sci. Technol. 1, 759-766 (1990).
[CrossRef]

Dong, X.

Du, C.

Fu, Y.

Gale, M. T.

M. T. Gale, G. K. Lang, J. M. Raynor, and H. Schütz, "Fabrication of micro-optical elements by laser beam writing in photoresist," Proc SPIE 1506, 65-70 (1991).
[CrossRef]

Herzig, H. P.

A. Schilling, R. Merz, Ch. Ossmann, and H. P. Herzig, "Surface profiles of reflow microlenses under the influence of surface tension and gravity," Opt. Eng 39, 2171-2176 (2000).
[CrossRef]

Ph. Nussbaum, I. Philipoussis, A. Husser and H. P. Herzig, "Simple technique for replication of micro-optical elements," Opt. Eng. 37, 1804-1808 (1998).
[CrossRef]

Ho, J.-R

T.-K. Shih, C.-F. Chen, J.-R Ho, and F.-T. Chuang, "Fabrication of PDMS (polydimethylsiloxane) microlens and diffuser using replica molding," Microelectron. Eng. 83, 2499-2503 (2006).
[CrossRef]

Ho, J.-R.

T.-K. Shih, J.-R. Ho, J.-H. Wang, C.-F. Chen, C.-Y. Liu, C.-C. Chen, and W.-T. Whang, "Fabrication of soft reflective microoptical elements using a replication process," Microelectron. Eng. 85, 175-180 (2008).
[CrossRef]

Husser, A.

Ph. Nussbaum, I. Philipoussis, A. Husser and H. P. Herzig, "Simple technique for replication of micro-optical elements," Opt. Eng. 37, 1804-1808 (1998).
[CrossRef]

Hutley, M. C.

D. Daly, R. F. Stevens, M. C. Hutley, and N. Davies, "The manufacture of microlenses by melting photoresist," Meas. Sci. Technol. 1, 759-766 (1990).
[CrossRef]

Lang, G. K.

M. T. Gale, G. K. Lang, J. M. Raynor, and H. Schütz, "Fabrication of micro-optical elements by laser beam writing in photoresist," Proc SPIE 1506, 65-70 (1991).
[CrossRef]

Li, S.

Lin, P.-C.

D. Chandra, S. Yang, and P.-C. Lin, "Strain responsive concave and convex microlens arrays," Appl. Phys. Lett. 91, 251912 (2007).
[CrossRef]

Lin, T.-H.

T.-H. Lin, H. Yang, and C.-K. Chao, "Concave microlens array mold fabrication in photoresist using UV proximity printing," Microsyst. Technol.Micro and Nanosystems Information Storage and Processing Systems 13, 1537-1543 (2007).

Liu, C.-Y.

T.-K. Shih, J.-R. Ho, J.-H. Wang, C.-F. Chen, C.-Y. Liu, C.-C. Chen, and W.-T. Whang, "Fabrication of soft reflective microoptical elements using a replication process," Microelectron. Eng. 85, 175-180 (2008).
[CrossRef]

Merz, R.

A. Schilling, R. Merz, Ch. Ossmann, and H. P. Herzig, "Surface profiles of reflow microlenses under the influence of surface tension and gravity," Opt. Eng 39, 2171-2176 (2000).
[CrossRef]

Nussbaum, Ph.

Ph. Nussbaum, I. Philipoussis, A. Husser and H. P. Herzig, "Simple technique for replication of micro-optical elements," Opt. Eng. 37, 1804-1808 (1998).
[CrossRef]

Ossmann, Ch.

A. Schilling, R. Merz, Ch. Ossmann, and H. P. Herzig, "Surface profiles of reflow microlenses under the influence of surface tension and gravity," Opt. Eng 39, 2171-2176 (2000).
[CrossRef]

Philipoussis, I.

Ph. Nussbaum, I. Philipoussis, A. Husser and H. P. Herzig, "Simple technique for replication of micro-optical elements," Opt. Eng. 37, 1804-1808 (1998).
[CrossRef]

Purdy, D.

Raynor, J. M.

M. T. Gale, G. K. Lang, J. M. Raynor, and H. Schütz, "Fabrication of micro-optical elements by laser beam writing in photoresist," Proc SPIE 1506, 65-70 (1991).
[CrossRef]

Schilling, A.

A. Schilling, R. Merz, Ch. Ossmann, and H. P. Herzig, "Surface profiles of reflow microlenses under the influence of surface tension and gravity," Opt. Eng 39, 2171-2176 (2000).
[CrossRef]

Schütz, H.

M. T. Gale, G. K. Lang, J. M. Raynor, and H. Schütz, "Fabrication of micro-optical elements by laser beam writing in photoresist," Proc SPIE 1506, 65-70 (1991).
[CrossRef]

Shih, T.-K.

T.-K. Shih, J.-R. Ho, J.-H. Wang, C.-F. Chen, C.-Y. Liu, C.-C. Chen, and W.-T. Whang, "Fabrication of soft reflective microoptical elements using a replication process," Microelectron. Eng. 85, 175-180 (2008).
[CrossRef]

T.-K. Shih, C.-F. Chen, J.-R Ho, and F.-T. Chuang, "Fabrication of PDMS (polydimethylsiloxane) microlens and diffuser using replica molding," Microelectron. Eng. 83, 2499-2503 (2006).
[CrossRef]

Stevens, R. F.

D. Daly, R. F. Stevens, M. C. Hutley, and N. Davies, "The manufacture of microlenses by melting photoresist," Meas. Sci. Technol. 1, 759-766 (1990).
[CrossRef]

Wang, C.

Wang, J.-H.

T.-K. Shih, J.-R. Ho, J.-H. Wang, C.-F. Chen, C.-Y. Liu, C.-C. Chen, and W.-T. Whang, "Fabrication of soft reflective microoptical elements using a replication process," Microelectron. Eng. 85, 175-180 (2008).
[CrossRef]

Whang, W.-T.

T.-K. Shih, J.-R. Ho, J.-H. Wang, C.-F. Chen, C.-Y. Liu, C.-C. Chen, and W.-T. Whang, "Fabrication of soft reflective microoptical elements using a replication process," Microelectron. Eng. 85, 175-180 (2008).
[CrossRef]

Whitesides, G. M.

Y. Xia and G. M. Whitesides, "Soft lithography," Annu. Rev. Mater. Sci. 28, 153-84 (1998).
[CrossRef]

Xia, Y.

Y. Xia and G. M. Whitesides, "Soft lithography," Annu. Rev. Mater. Sci. 28, 153-84 (1998).
[CrossRef]

Yang, H.

T.-H. Lin, H. Yang, and C.-K. Chao, "Concave microlens array mold fabrication in photoresist using UV proximity printing," Microsyst. Technol.Micro and Nanosystems Information Storage and Processing Systems 13, 1537-1543 (2007).

Yang, S.

D. Chandra, S. Yang, and P.-C. Lin, "Strain responsive concave and convex microlens arrays," Appl. Phys. Lett. 91, 251912 (2007).
[CrossRef]

Yoon, J.-B.

Annu. Rev. Mater. Sci. (1)

Y. Xia and G. M. Whitesides, "Soft lithography," Annu. Rev. Mater. Sci. 28, 153-84 (1998).
[CrossRef]

Appl. Opt. (1)

Appl. Phys. Lett. (1)

D. Chandra, S. Yang, and P.-C. Lin, "Strain responsive concave and convex microlens arrays," Appl. Phys. Lett. 91, 251912 (2007).
[CrossRef]

Meas. Sci. Technol. (1)

D. Daly, R. F. Stevens, M. C. Hutley, and N. Davies, "The manufacture of microlenses by melting photoresist," Meas. Sci. Technol. 1, 759-766 (1990).
[CrossRef]

Micro and Nanosystems Information Storage and Processing Systems (1)

T.-H. Lin, H. Yang, and C.-K. Chao, "Concave microlens array mold fabrication in photoresist using UV proximity printing," Microsyst. Technol.Micro and Nanosystems Information Storage and Processing Systems 13, 1537-1543 (2007).

Microelectron. Eng. (2)

T.-K. Shih, C.-F. Chen, J.-R Ho, and F.-T. Chuang, "Fabrication of PDMS (polydimethylsiloxane) microlens and diffuser using replica molding," Microelectron. Eng. 83, 2499-2503 (2006).
[CrossRef]

T.-K. Shih, J.-R. Ho, J.-H. Wang, C.-F. Chen, C.-Y. Liu, C.-C. Chen, and W.-T. Whang, "Fabrication of soft reflective microoptical elements using a replication process," Microelectron. Eng. 85, 175-180 (2008).
[CrossRef]

Opt. Eng (1)

A. Schilling, R. Merz, Ch. Ossmann, and H. P. Herzig, "Surface profiles of reflow microlenses under the influence of surface tension and gravity," Opt. Eng 39, 2171-2176 (2000).
[CrossRef]

Opt. Eng. (1)

Ph. Nussbaum, I. Philipoussis, A. Husser and H. P. Herzig, "Simple technique for replication of micro-optical elements," Opt. Eng. 37, 1804-1808 (1998).
[CrossRef]

Opt. Express (2)

Proc SPIE (1)

M. T. Gale, G. K. Lang, J. M. Raynor, and H. Schütz, "Fabrication of micro-optical elements by laser beam writing in photoresist," Proc SPIE 1506, 65-70 (1991).
[CrossRef]

Other (1)

D. Malacara and Z. Malacara, Handbook of lens design, (Dekker, New-York, 1994).

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Figures (13)

Fig. 1.
Fig. 1.

Process flow. The first step shows a crossed section view of cylindrical holes resulting from a conventional photolithography process (spinning of AZ4562 photoresist, UV exposure through a mask with holes and development). During the second step the holes are melted at 150°C for half an hour. In the third step the holes are filled with AZ1518 photoresist during a second spinning step. To finish, the photoresist is dried in an oven at 80°C for 30 minutes. The concave profile obtained by the surface tension is then modified by the solvent removed in the final cure.

Fig. 2.
Fig. 2.

Microscope picture of unmelted (left) and SEM picture of melted (right) hexagonal packed cylindrical holes of diameter Ø=150 µm. The height of the walls (A) between holes depends on the reflow process. Empty spaces (B) have been added to the design to reduce reflow and local photoresist peaks formation during the melting step.

Fig. 3.
Fig. 3.

Illustration of the reflow occurring during the melting step of the first photoresist layer. Using a Mach-Zehnder interferometer two measurements (1) and (2) have been taken. They show interference fringes in the melted walls for two types of photoresist: AZ4562 and AZ9260. While in the first case only one fringe is seen from the lowest to the highest point on the walls more than 3 fringes are distinguished in the second case meaning deformations around 3 times more important.

Fig. 4.
Fig. 4.

Results on the fabrication of concave microlens arrays. The curves show the maximum diameters of diffraction limited microlenses that could be obtained when varying the spin speed of the second layer of AZ1518 photoresist. Over this limit, the Strehl ratio of the concave microlenses drops down to values lower than 80%. The minimum diameters were arbitrary set when only one fringe could be solved on the interference measurements or when homogeneity problems happened. Square (quad) and hexagonal (hexa) packed arrays have been considered.

Fig. 5.
Fig. 5.

Numerical aperture (NA) as function of the microlens diameters (hexagonal packed arrangement) for various spin speed experiments. As an example, in the grey zone corresponding to microlenses with diameters between 70 to 80 microns, NA between 0.07 to 0.14 have been realized by changing the spin speed and/or the dilution of the photoresist.

Fig. 6.
Fig. 6.

Numerical aperture (NA) function of the microlens diameters (square packed arrangement) for various spin speed experiments.

Fig. 7.
Fig. 7.

2D profile deformations from a sphere for increasing microlens diameters from 60 to 110 µm. The arrangement of the array is clearly seen in the deformations which occur at the four cardinals points for square packed array and at both sides of the three axis of symmetry for hexagonal packed microlens array. The first photoresist layer is 17 µm of AZ4562 and the second layer of diluted (4:1) AZ1518 was spin coated at 360 rpm.

Fig. 8.
Fig. 8.

Profile measurements of concave microlenses with Ø=50 µm (white area) obtained at 3 spin speeds of pure AZ1518. The vertical positions are set arbitrary. The anchoring point (i.e., the inflection point of the profile of the microlens) of the meniscus will depend on the filling of the holes. As it can be seen the distances (d1, d2, d3) between the top part of the profile and the starting slope (α1, α2, α3) of the meniscus decrease. At 830 rpm the meniscus starts within the hole and deformations appear at the edges as shown previously in Fig. 7.

Fig. 9.
Fig. 9.

Large scale interference picture and SEM picture of respectively 40 µm pitch and 60 µm pitch concave microlens array showing the homogeneity of the realized samples.

Fig. 10.
Fig. 10.

Pictures of typical defects encountered during the fabrication process. (1) Shadow effect of the structures during spinning of the second layer of photoresist for spin speed higher than 2000 rpm. (2) Local deformation due to local weak adhesion of the first layer. (3) Dust particles. (4) Trapped bubbles. (5) Edge beads formation of photoresist at very low spin speed of the second layer (<400 rpm). (6) Cracks in the second spun layer.

Fig. 11.
Fig. 11.

Illustration of the three patterns of randomly distributed holes. The diameters of the holes were contained in ranges from 100 to 300 µm (RCL 4), 70 to 160 µm (RCL 5) and from 160 to 500 µm (RCL 6).

Fig. 12.
Fig. 12.

2D profiles of three realized diffusers. Because of the reflow occurring during the melting step of the first layer the zones between concave microlenses are no more flat and show a strongly reduced zero order transmission. The first layer is set to 17 microns and the second layer of pure AZ1518 has been spin coated at 200 rpm.

Fig. 13.
Fig. 13.

Measured angular distribution curves of concave microlens diffusers. AZ1518 pure 200 rpm RCL 4 and RCL5 show very nice smooth dispersion while no significant zero order transmission is observable.

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