Abstract

A two-beam-current method is introduced for e-beam writing in the fabrication of gray-scale masks. Compared with the simpler single-current method, the two-beam-current method offers two important advantages: (a) it can achieve a much larger dynamic range for e-beam exposure; (b) the writing time for a gray-scale mask can be reduced when a large pattern is to be written. Here, the new method is first described in detail and its application to the fabrication of our new gray-scale mask is demonstrated. Then, the improved gray-scale masks were employed to fabricate large dynamic range, high-resolution micro-optical elements of less than a couple of micrometers depth, using deep ultraviolet lithography at 248nm wavelength and an inductively coupled plasma reactive ion etching system.

© 2008 Optical Society of America

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References

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  1. Z. Zhou and S. H. Lee, “Fabrication of an improved gray-scale mask for refractive micro- and meso-optics,” Opt. Lett. 29, 457-458 (2004).
    [CrossRef] [PubMed]
  2. Leica VB Parameter Calculator, http://www.research.ibm.com/people/r/rooks/calc.html
  3. C. Wu, “Method of making high energy beam sensitive glasses,” U.S. patent 5,078,771 (7 January 1992).
  4. S. H. Lee, M. S. Jin, and M. L. Scott, “Method for fabricating continuous space variant attenuating lithography mask for fabrication of devices with three-dimensional structures and microelectronics,” U.S. patent 6,534,221 (18 March 2003).

2004

Jin, M. S.

S. H. Lee, M. S. Jin, and M. L. Scott, “Method for fabricating continuous space variant attenuating lithography mask for fabrication of devices with three-dimensional structures and microelectronics,” U.S. patent 6,534,221 (18 March 2003).

Lee, S. H.

Z. Zhou and S. H. Lee, “Fabrication of an improved gray-scale mask for refractive micro- and meso-optics,” Opt. Lett. 29, 457-458 (2004).
[CrossRef] [PubMed]

S. H. Lee, M. S. Jin, and M. L. Scott, “Method for fabricating continuous space variant attenuating lithography mask for fabrication of devices with three-dimensional structures and microelectronics,” U.S. patent 6,534,221 (18 March 2003).

Scott, M. L.

S. H. Lee, M. S. Jin, and M. L. Scott, “Method for fabricating continuous space variant attenuating lithography mask for fabrication of devices with three-dimensional structures and microelectronics,” U.S. patent 6,534,221 (18 March 2003).

Wu, C.

C. Wu, “Method of making high energy beam sensitive glasses,” U.S. patent 5,078,771 (7 January 1992).

Zhou, Z.

Opt. Lett.

Other

Leica VB Parameter Calculator, http://www.research.ibm.com/people/r/rooks/calc.html

C. Wu, “Method of making high energy beam sensitive glasses,” U.S. patent 5,078,771 (7 January 1992).

S. H. Lee, M. S. Jin, and M. L. Scott, “Method for fabricating continuous space variant attenuating lithography mask for fabrication of devices with three-dimensional structures and microelectronics,” U.S. patent 6,534,221 (18 March 2003).

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Figures (10)

Fig. 1
Fig. 1

Exposure characteristic of the ZEP7000A e-beam resist is shown by the dotted curve. Also shown is a comparison of the dosage dynamic range between a single current I s and two currents I 1 and I 2 .

Fig. 2
Fig. 2

Time saving with the two-beam-current method calculated from the online Parameter Calculator (provided by IBM [2]) for the Leica VB-6HR e-beam system. The slope of the line is approximately 1.3 min / mm 2 .

Fig. 3
Fig. 3

Measured depth profiles of the calibration steps in the e-beam resist. The depths at step # 64 are about 510 and 400 nm for the two-current and single-current methods, respectively.

Fig. 4
Fig. 4

Optical densities of the calibration steps at 248 nm . The maximum optical densities (at step # 64 ) achieved in two-current and single-current methods are 3.02 and 2.30, respectively.

Fig. 5
Fig. 5

Fabrication processes of high-resolution microdevices using our improved gray-scale masks.

Fig. 6
Fig. 6

Exposure characteristic of the PMGI-SF11 resist.

Fig. 7
Fig. 7

SEM picture showing a resolution of 0.2 μm in UV5 by 248 nm lithography.

Fig. 8
Fig. 8

AFM picture of a portion of an off-axis Fresnel lens on quartz

Fig. 9
Fig. 9

AFM picture of a 3-D topographic map on LAF.

Fig. 10
Fig. 10

(a) Microscopic pictures of axicons on the gray-scale mask; (b) the microscopic pattern on PMGI resist (enlarged four times to show the disappearance of the curved line due to stitching error).

Tables (3)

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Table 1 Processing Parameters of a UV5 Resist

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Table 2 Processing Parameters of a PMGI-SF11 Resist

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Table 3 Parameters for Etching PMGI into Quartz

Equations (7)

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D = I / ( f * S ) ,
D max = I s ( f min * S ) = 75 μ C / cm 2 , D min = I s ( f max * S ) = 75 μ C / cm 2 .
D max = I 2 / ( f min * S ) = 125 μ C / cm 2 , D min = I 1 / ( f max * S ) = 5 μ C / cm 2 .
f = I / ( D * S ) ,
T = A / ( S * f ) ,
T s = A / S * f s = 1.2 × 10 7 ( A / S ) ,
T = 0.5 A / ( S * f 1 ) + 0.5 A / ( S * f 2 ) = 0.88 × 10 7 ( A / S ) .

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