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Optical lithography onto inside surfaces of small-diameter pipes
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Microelectronic Engineering 85 (2008) 1043–1046 www.elsevier.com/locate/mee
Optical lithography onto inside surfaces of small-diameter pipes Toshiyuki Horiuchi *, Masahiro Katayama, Yuusuke Watanabe, Katsuyuki Fujita 1, Takashi Yasuda 2 Tokyo Denki University, 2-2 Kanda-Nishiki-cho, Chiyoda-ku, Tokyo 101-8457, Japan Received 21 September 2007; received in revised form 17 December 2007; accepted 23 January 2008 Available online 7 February 2008
Abstract Lithography onto inside surfaces of small-diameter pipes was investigated. Two types of exposure rod for inserting into the pipes were developed. One has a chip of light emitting diode (LED) at the rod end, and the other transmits the exposure light through an optical fiber. In the latter case, LED was used as a source, too. Aluminum pipes with an inner diameter of 5 mm were coated with a positive resist PMER P-AR900. The resist thickness was controlled to be approximately 10 lm, and the pipes were exposed to the light beam from the inserted exposure rods. The exposure light beams were narrowed using handmade pinholes with hole-sizes of 170 lm and 100 lm. Patterns were delineated rotating and moving the pipes. As a result, space patterns with a width of less than 200 lm were printed. Not only simple linear patterns but also helicoids and character patterns were successfully printed. The novel ‘‘inside lithography’’ is feasible and will be useful for carving various fine grooves onto the inside surfaces of small-diameter pipes and cylinders. Ó 2008 Elsevier B.V. All rights reserved. Keywords: Inside lithography; Small-diameter pipe; Exposure rod; Light emitting diode; Optical fiber
1. Introduction Lithographic patterning technology onto the outer surfaces of shafts and pipes has been developed and it enabled to fabricate various useful micro-mechanical components such as micro-screws, splines, springs, coils and others [1– 5]. On the other hand, patterning technology onto inner surfaces of small-diameter pipes has not been considered yet. Inner surface patterning may also be one of the most difficult processes for other micro-fabrication methods. For example, precise cutting and laser abrasion patterning are not convenient because the cutting tools and laser heads are hard to access to the narrow recesses. However, fine fluid bearing grooves, minute screw nuts, spline nuts and other micro components will be precisely carved if the resist-coated inner surfaces were arbitrarily patterned by applying lithography. For this reason, feasibility of the *
1 2
Corresponding author. Tel.: +81 3 5280 3407; fax: +81 3 5280 3571. E-mail address: [email protected] (T. Horiuchi). Present address: Canon Semiconductor Equipment Inc. Present address: Sayama Precision Co., Ltd.
0167-9317/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2008.01.084
‘‘inside lithography’’ is investigated [6]. Immediate targets are the inner diameter of less than 5 mm and the pattern width of less than 200 lm, considering the practical use.
2. Exposure principle for ‘‘inside lithography’’ It seemed difficult how to coat a resist in the pipes and to expose the resist for arbitrarily sensitizing it. However, the ‘‘draw-up method’’ which had been already developed to coat a resist on outside surfaces of shafts [3] was also effective for coating the resist on the inside surfaces. For this reason, deliberation was mainly concentrated on the exposure schemes. As an ordinary but a certain procedure, we decided to insert an exposure rod into the specimen pipes. Figs. 1 and 2 show the two ideas. In Fig. 1, an exposure rod that had a blue light emitting diode (LED) chip was used. Electric power was supplied through a copper ribbon tape pasted on the acrylic rod with a rectangular cross section. The central wavelength of the LED light was 428 nm depending on the availability of the LED-chip. The lighting size was approximately 0.45 mm by 0.6 mm.
1044
T. Horiuchi et al. / Microelectronic Engineering 85 (2008) 1043–1046
Exposure rod (Acrylic bar)
Pinhole
Exposure light
Rotation
Exposure rod
Specimen pipe coated with a resist
Automatic rotation stage
Linear motion Resist
LED
Aluminum specimen pipe
Fig. 1. Exposure rod with a light emitting diode chip.
Exposure rod (Aluminum pipe) Optical fiber
Pinhole
Rotation
Manual Y, Z-stage Linear motion Lens LED
Resist
Manual X-stage
Automatic X-stage
Fig. 3. Developed exposure system.
Aluminum specimen pipe
Fig. 2. Exposure rod using an optical fiber.
In Fig. 2, an optical fiber was used for supplying the exposure light. Since the light source was placed at the outside of the specimen pipes, arbitrary light sources were applicable. However, a violet LED was used because it had a competitive inexpensive price. The central wavelength of the LED was 385 nm. The wavelength was chosen considering the sensitivity of the resist and the visibility of the light for fitting and adjusting the exposure system. A plastic optical fiber with an outer diameter of 750 lm and a core diameter of 735 lm was used. The large diameter was chosen to convey much exposure light energy. In both systems, patterns were delineated scanning the specimen pipes to the steady exposure rods. Developed simple exposure system is shown in Fig. 3. After adjusting the initial positions using the manual x, y, and z stages, the specimen pipes were automatically scanned controlling the rotation stage and the x-direction linear stage by a personal computer. Since the light emitting source sizes were quite large and the light rays spread in wide angles in both exposure rods, pinholes were attached on the light emitting parts. The pinholes, however, should have the appropriately small shapes in addition to the necessary hole diameters. For this reason, the pinholes were fabricated by ourselves [7,8]. At first, resist molds were fabricated on copper-clad plastic substrates using UV optical reduction projection lithography. An example of resist pinhole mold made with negative SU-8 (Microchem Corp.) is shown in Fig. 4. Next, nickel was electroplated in the mold directly on the substrates. After solving the mold in the remover liquid, nickel pinholes were obtained as shown in Fig. 5. Pinholes with an outer diameter of 1.8 mm and hole diameters of 170 and 100 lm were attached on the light emitting parts.
Fig. 4. A resist mould of a pinhole.
Fig. 5. A nickel pinhole with a thickness of 20 lm.
3. Patterning experiments and consideration 3.1. Linear space pattern delineation Patterning characteristics for both type exposure rods were investigated. Aluminum pipes with an outer diameter of 6 mm and an inner diameter of 5 mm were used as specimens. The specimen pipes were coated with a positive resist PMER P-AR 900 (Tokyo Ohka Kogyo). The resist film thickness was more or less 10 lm. The aluminum pipes were chosen because they were easily cut using a knife and
T. Horiuchi et al. / Microelectronic Engineering 85 (2008) 1043–1046
the roughness of the inner surfaces was comparatively small. The typical mean roughness Ra was 0.63. At first, widths of the linear space patterns in the axial direction (x-direction) were measured for various scan speeds. When the exposure rods were used without pinholes, the space pattern widths were very large since the light emitting parts were large and the light rays widely spread. However, when the pinholes were attached and the exposure rod heads were placed near the inside surfaces of the pipes as close as possible, comparatively fine patterns were delineated as shown in Figs. 6 and 7. The pattern widths steeply changed under the very low scan speed conditions. However, the pattern widths smoothly changed under the moderate or the high scan speed conditions. These tendencies depend on the gradual intensity distribution of the exposure light spots. When excessive exposure doses were given by the low speed scan, vaguely exposed skirt parts of the light spots were widely exposed. On the other hand, the pattern widths became narrower when using the optical fiber exposure rod. This is because the light spread angle for the optical fiber exposure rod is smaller than that for the LED-chip exposure rod.
1200
3.2. Consideration on the pattern width When a pinhole at the exposure rod tip was lightly touched at the inner surface of a pipe specimen, the gap between the resist surface and the pinhole was geometrically calculated to be approximately 170 lm, referring to Fig. 8. Since the pinhole plates were as thin as 20 lm and somewhat flexible, the actual gaps might be smaller. Depending on these gaps, however, the exposure light spot spread. It was considered that the minimum pattern widths of 450 nm and 190 nm for the both exposure rods obtained using the pinholes with a hole diameter of 100 lm were reasonable since the light spread angle of the LED-chip was approximately 140° and the numerical aperture of the optical fiber was 0.52. Intensity distribution of the exposure light spot is like gaussian as shown in Fig. 9. However, the scan exposure energy is proportional to the sectional area shown in the figure. Accordingly, although the peak intensity at the radial position r is I(r), the light intensity skirt length L in the scan direction becomes small when the position r becomes large. For this reason, patterns obtained by the scan exposure should be somewhat finer than the spot patterns exposed without scanning. 3.3. Delineation of various patterns
1000
Pattern width (μm)
1045
Pinhole with a diameter of 170
m
Pinhole with a diameter of 100
m
Since the fundamental patterning characteristics were clarified, various patterns were delineated using the optical
800 600
Pinhole 1.8 mm
400
168 µm 200 0 0
21.1˚ 5
10
15
20
25
30
35
40
5 mm
Scan speed (μm) Fig. 6. Relationship between pattern width and scan speed when the LED-chip exposure rod was used.
Aluminum pipe Fig. 8. Estimation of the exposure gap.
Pattern width (μm)
1200
I (r)
Pinhole with adiameter of 170 μm
1000
Intensity distribution of the light beam (gaussian)
Pinhole with adiameter of 100 μm
800
Scan-exposure energy
600 400 200 0
L
Scan direction 0
5
10
15
20
25
30
35
40
r
Scan speed (μm) Fig. 7. Relationship between pattern width and scan speed when the optical fiber exposure rod was used.
Fig. 9. Consideration on the scan exposure dose.
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T. Horiuchi et al. / Microelectronic Engineering 85 (2008) 1043–1046
Helical patterns
1mm
Fig. 10. Printed helical patterns.
ideas to expose the inside surfaces were proposed. One was the exposure rod with an LED-chip, and the other was that using an optical fiber. Aluminum pipe specimens with an inner diameter of 5 mm were coated with the positive resist PMER P-AR900, and exposed using each exposure rod. Linear space patterns with a width of down to 190 lm were delineated. Helical patterns and character patterns were also delineated successfully. Thus, the ‘‘inside lithography’’ is feasible. It will be applicable to the micro-fabrication of various fine grooves on the inside surfaces of small-diameter pipes and cylinders. Acknowledgments
1mm Fig. 11. Printed character patterns.
fiber exposure rod by simultaneously scanning the x and h stages. Helical patterns with a width of 240 lm are shown in Fig. 10, and character patterns with a width of 200 lm are shown in Fig. 11. Both patterns were delineated successfully as shown in the figures. The photographs were taken by cutting the specimen pipes in halves using a cutting knife. From these results, feasibility of the ‘‘inside lithography’’ was verified. In the experiments, the minimum pattern size was approximately 200 lm. However, the pattern size will be reduced gradually by improving the exposure rods, pinholes and others. 4. Conclusion ‘‘Inside lithography’’ for patterning onto inner surfaces of small-diameter pipes was tried for the first time. Two
This work is partially supported by Grant-in-Aid Q06M-05 from the Research Institute for Science and Technology, Tokyo Denki University, and Tokyo Denki University Science Promotion Fund. This work is also partially supported by Grant-in-Aid 17560036 for Scientific Research (C) from the Japan Society for the Promotion of Science, and The Futaba Electronics Memorial Foundation. References [1] A.D. Feinerman, R.E. Lajos, V. White, D.D. Denton, J. Microelectromech. Syst. 5 (1996) 250–255. [2] H. Mekaru, S. Kusumi, N. Sato, M. Yamashita, O. Shimada, T. Hattori, Jpn. J. Appl. Phys. 43 (2004) 4036–4040. [3] Y. Joshima, T. Kokubo, T. Horiuchi, Jpn. J. Appl. Phys. 43 (2004) 4031–4035. [4] K. Hashimoto, Y. Kaneko, T. Horiuchi, Microelectron. Eng. 83/4–9 (2006) 1312–1315. [5] Y. Kaneko, K. Hashimoto, T. Horiuchi, Microelectron. Eng. 83/4–9 (2006) 1249–1252. [6] T. Horiuchi, M. Katayama, Y. Watanabe, K. Fujita, T. Yasuda, Abstract, 33rd Int. Conf. on Micro- and Nano-engineering, MNE 2007, P-MST-4, 2007. [7] K. Hirota, M. Ozaki, T. Horiuchi, Jpn. J. Appl. Phys. 42 (2003) 4031– 4036. [8] T. Horiuchi, Y. Furuuchi, R. Nakamura, K. Hirota, Microelectron. Eng. 83/4–9 (2006) 1316–1320.
Microelectronic Engineering 85 (2008) 1043–1046 www.elsevier.com/locate/mee
Optical lithography onto inside surfaces of small-diameter pipes Toshiyuki Horiuchi *, Masahiro Katayama, Yuusuke Watanabe, Katsuyuki Fujita 1, Takashi Yasuda 2 Tokyo Denki University, 2-2 Kanda-Nishiki-cho, Chiyoda-ku, Tokyo 101-8457, Japan Received 21 September 2007; received in revised form 17 December 2007; accepted 23 January 2008 Available online 7 February 2008
Abstract Lithography onto inside surfaces of small-diameter pipes was investigated. Two types of exposure rod for inserting into the pipes were developed. One has a chip of light emitting diode (LED) at the rod end, and the other transmits the exposure light through an optical fiber. In the latter case, LED was used as a source, too. Aluminum pipes with an inner diameter of 5 mm were coated with a positive resist PMER P-AR900. The resist thickness was controlled to be approximately 10 lm, and the pipes were exposed to the light beam from the inserted exposure rods. The exposure light beams were narrowed using handmade pinholes with hole-sizes of 170 lm and 100 lm. Patterns were delineated rotating and moving the pipes. As a result, space patterns with a width of less than 200 lm were printed. Not only simple linear patterns but also helicoids and character patterns were successfully printed. The novel ‘‘inside lithography’’ is feasible and will be useful for carving various fine grooves onto the inside surfaces of small-diameter pipes and cylinders. Ó 2008 Elsevier B.V. All rights reserved. Keywords: Inside lithography; Small-diameter pipe; Exposure rod; Light emitting diode; Optical fiber
1. Introduction Lithographic patterning technology onto the outer surfaces of shafts and pipes has been developed and it enabled to fabricate various useful micro-mechanical components such as micro-screws, splines, springs, coils and others [1– 5]. On the other hand, patterning technology onto inner surfaces of small-diameter pipes has not been considered yet. Inner surface patterning may also be one of the most difficult processes for other micro-fabrication methods. For example, precise cutting and laser abrasion patterning are not convenient because the cutting tools and laser heads are hard to access to the narrow recesses. However, fine fluid bearing grooves, minute screw nuts, spline nuts and other micro components will be precisely carved if the resist-coated inner surfaces were arbitrarily patterned by applying lithography. For this reason, feasibility of the *
1 2
Corresponding author. Tel.: +81 3 5280 3407; fax: +81 3 5280 3571. E-mail address: [email protected] (T. Horiuchi). Present address: Canon Semiconductor Equipment Inc. Present address: Sayama Precision Co., Ltd.
0167-9317/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2008.01.084
‘‘inside lithography’’ is investigated [6]. Immediate targets are the inner diameter of less than 5 mm and the pattern width of less than 200 lm, considering the practical use.
2. Exposure principle for ‘‘inside lithography’’ It seemed difficult how to coat a resist in the pipes and to expose the resist for arbitrarily sensitizing it. However, the ‘‘draw-up method’’ which had been already developed to coat a resist on outside surfaces of shafts [3] was also effective for coating the resist on the inside surfaces. For this reason, deliberation was mainly concentrated on the exposure schemes. As an ordinary but a certain procedure, we decided to insert an exposure rod into the specimen pipes. Figs. 1 and 2 show the two ideas. In Fig. 1, an exposure rod that had a blue light emitting diode (LED) chip was used. Electric power was supplied through a copper ribbon tape pasted on the acrylic rod with a rectangular cross section. The central wavelength of the LED light was 428 nm depending on the availability of the LED-chip. The lighting size was approximately 0.45 mm by 0.6 mm.
1044
T. Horiuchi et al. / Microelectronic Engineering 85 (2008) 1043–1046
Exposure rod (Acrylic bar)
Pinhole
Exposure light
Rotation
Exposure rod
Specimen pipe coated with a resist
Automatic rotation stage
Linear motion Resist
LED
Aluminum specimen pipe
Fig. 1. Exposure rod with a light emitting diode chip.
Exposure rod (Aluminum pipe) Optical fiber
Pinhole
Rotation
Manual Y, Z-stage Linear motion Lens LED
Resist
Manual X-stage
Automatic X-stage
Fig. 3. Developed exposure system.
Aluminum specimen pipe
Fig. 2. Exposure rod using an optical fiber.
In Fig. 2, an optical fiber was used for supplying the exposure light. Since the light source was placed at the outside of the specimen pipes, arbitrary light sources were applicable. However, a violet LED was used because it had a competitive inexpensive price. The central wavelength of the LED was 385 nm. The wavelength was chosen considering the sensitivity of the resist and the visibility of the light for fitting and adjusting the exposure system. A plastic optical fiber with an outer diameter of 750 lm and a core diameter of 735 lm was used. The large diameter was chosen to convey much exposure light energy. In both systems, patterns were delineated scanning the specimen pipes to the steady exposure rods. Developed simple exposure system is shown in Fig. 3. After adjusting the initial positions using the manual x, y, and z stages, the specimen pipes were automatically scanned controlling the rotation stage and the x-direction linear stage by a personal computer. Since the light emitting source sizes were quite large and the light rays spread in wide angles in both exposure rods, pinholes were attached on the light emitting parts. The pinholes, however, should have the appropriately small shapes in addition to the necessary hole diameters. For this reason, the pinholes were fabricated by ourselves [7,8]. At first, resist molds were fabricated on copper-clad plastic substrates using UV optical reduction projection lithography. An example of resist pinhole mold made with negative SU-8 (Microchem Corp.) is shown in Fig. 4. Next, nickel was electroplated in the mold directly on the substrates. After solving the mold in the remover liquid, nickel pinholes were obtained as shown in Fig. 5. Pinholes with an outer diameter of 1.8 mm and hole diameters of 170 and 100 lm were attached on the light emitting parts.
Fig. 4. A resist mould of a pinhole.
Fig. 5. A nickel pinhole with a thickness of 20 lm.
3. Patterning experiments and consideration 3.1. Linear space pattern delineation Patterning characteristics for both type exposure rods were investigated. Aluminum pipes with an outer diameter of 6 mm and an inner diameter of 5 mm were used as specimens. The specimen pipes were coated with a positive resist PMER P-AR 900 (Tokyo Ohka Kogyo). The resist film thickness was more or less 10 lm. The aluminum pipes were chosen because they were easily cut using a knife and
T. Horiuchi et al. / Microelectronic Engineering 85 (2008) 1043–1046
the roughness of the inner surfaces was comparatively small. The typical mean roughness Ra was 0.63. At first, widths of the linear space patterns in the axial direction (x-direction) were measured for various scan speeds. When the exposure rods were used without pinholes, the space pattern widths were very large since the light emitting parts were large and the light rays widely spread. However, when the pinholes were attached and the exposure rod heads were placed near the inside surfaces of the pipes as close as possible, comparatively fine patterns were delineated as shown in Figs. 6 and 7. The pattern widths steeply changed under the very low scan speed conditions. However, the pattern widths smoothly changed under the moderate or the high scan speed conditions. These tendencies depend on the gradual intensity distribution of the exposure light spots. When excessive exposure doses were given by the low speed scan, vaguely exposed skirt parts of the light spots were widely exposed. On the other hand, the pattern widths became narrower when using the optical fiber exposure rod. This is because the light spread angle for the optical fiber exposure rod is smaller than that for the LED-chip exposure rod.
1200
3.2. Consideration on the pattern width When a pinhole at the exposure rod tip was lightly touched at the inner surface of a pipe specimen, the gap between the resist surface and the pinhole was geometrically calculated to be approximately 170 lm, referring to Fig. 8. Since the pinhole plates were as thin as 20 lm and somewhat flexible, the actual gaps might be smaller. Depending on these gaps, however, the exposure light spot spread. It was considered that the minimum pattern widths of 450 nm and 190 nm for the both exposure rods obtained using the pinholes with a hole diameter of 100 lm were reasonable since the light spread angle of the LED-chip was approximately 140° and the numerical aperture of the optical fiber was 0.52. Intensity distribution of the exposure light spot is like gaussian as shown in Fig. 9. However, the scan exposure energy is proportional to the sectional area shown in the figure. Accordingly, although the peak intensity at the radial position r is I(r), the light intensity skirt length L in the scan direction becomes small when the position r becomes large. For this reason, patterns obtained by the scan exposure should be somewhat finer than the spot patterns exposed without scanning. 3.3. Delineation of various patterns
1000
Pattern width (μm)
1045
Pinhole with a diameter of 170
m
Pinhole with a diameter of 100
m
Since the fundamental patterning characteristics were clarified, various patterns were delineated using the optical
800 600
Pinhole 1.8 mm
400
168 µm 200 0 0
21.1˚ 5
10
15
20
25
30
35
40
5 mm
Scan speed (μm) Fig. 6. Relationship between pattern width and scan speed when the LED-chip exposure rod was used.
Aluminum pipe Fig. 8. Estimation of the exposure gap.
Pattern width (μm)
1200
I (r)
Pinhole with adiameter of 170 μm
1000
Intensity distribution of the light beam (gaussian)
Pinhole with adiameter of 100 μm
800
Scan-exposure energy
600 400 200 0
L
Scan direction 0
5
10
15
20
25
30
35
40
r
Scan speed (μm) Fig. 7. Relationship between pattern width and scan speed when the optical fiber exposure rod was used.
Fig. 9. Consideration on the scan exposure dose.
1046
T. Horiuchi et al. / Microelectronic Engineering 85 (2008) 1043–1046
Helical patterns
1mm
Fig. 10. Printed helical patterns.
ideas to expose the inside surfaces were proposed. One was the exposure rod with an LED-chip, and the other was that using an optical fiber. Aluminum pipe specimens with an inner diameter of 5 mm were coated with the positive resist PMER P-AR900, and exposed using each exposure rod. Linear space patterns with a width of down to 190 lm were delineated. Helical patterns and character patterns were also delineated successfully. Thus, the ‘‘inside lithography’’ is feasible. It will be applicable to the micro-fabrication of various fine grooves on the inside surfaces of small-diameter pipes and cylinders. Acknowledgments
1mm Fig. 11. Printed character patterns.
fiber exposure rod by simultaneously scanning the x and h stages. Helical patterns with a width of 240 lm are shown in Fig. 10, and character patterns with a width of 200 lm are shown in Fig. 11. Both patterns were delineated successfully as shown in the figures. The photographs were taken by cutting the specimen pipes in halves using a cutting knife. From these results, feasibility of the ‘‘inside lithography’’ was verified. In the experiments, the minimum pattern size was approximately 200 lm. However, the pattern size will be reduced gradually by improving the exposure rods, pinholes and others. 4. Conclusion ‘‘Inside lithography’’ for patterning onto inner surfaces of small-diameter pipes was tried for the first time. Two
This work is partially supported by Grant-in-Aid Q06M-05 from the Research Institute for Science and Technology, Tokyo Denki University, and Tokyo Denki University Science Promotion Fund. This work is also partially supported by Grant-in-Aid 17560036 for Scientific Research (C) from the Japan Society for the Promotion of Science, and The Futaba Electronics Memorial Foundation. References [1] A.D. Feinerman, R.E. Lajos, V. White, D.D. Denton, J. Microelectromech. Syst. 5 (1996) 250–255. [2] H. Mekaru, S. Kusumi, N. Sato, M. Yamashita, O. Shimada, T. Hattori, Jpn. J. Appl. Phys. 43 (2004) 4036–4040. [3] Y. Joshima, T. Kokubo, T. Horiuchi, Jpn. J. Appl. Phys. 43 (2004) 4031–4035. [4] K. Hashimoto, Y. Kaneko, T. Horiuchi, Microelectron. Eng. 83/4–9 (2006) 1312–1315. [5] Y. Kaneko, K. Hashimoto, T. Horiuchi, Microelectron. Eng. 83/4–9 (2006) 1249–1252. [6] T. Horiuchi, M. Katayama, Y. Watanabe, K. Fujita, T. Yasuda, Abstract, 33rd Int. Conf. on Micro- and Nano-engineering, MNE 2007, P-MST-4, 2007. [7] K. Hirota, M. Ozaki, T. Horiuchi, Jpn. J. Appl. Phys. 42 (2003) 4031– 4036. [8] T. Horiuchi, Y. Furuuchi, R. Nakamura, K. Hirota, Microelectron. Eng. 83/4–9 (2006) 1316–1320.