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Precision laser metallization
Microelectronic Engineering 56 (2001) 273–279 www.elsevier.com / locate / mee
Precision laser metallization a ,1 a b, An-Chun Tien , Zachary S. Sacks , Frederick J. Mayer * a
Center for Ultrafast Optical Sciences, University of Michigan, Ann Arbor, MI 48109, USA b Mayer Applied Research, Inc., 1417 Dicken Dr., Ann Arbor, MI 48103, USA Accepted 24 October 2000
Abstract We demonstrate precision laser deposition of thin metal-film features on glass substrates. One micron deposits are produced with short, low-energy, laser pulses at a kilohertz rate. Numerous applications are expected for production of electrically conducting interconnects and vias on microelectronic substrates and for spot repairs on flat-panel displays and photolithographic masks. 2001 Elsevier Science B.V. All rights reserved. Keywords: Laser deposition; Metal-film features
1. Introduction There have been numerous patents [1–5] and technical papers [6–12] that have been concerned with pulsed-laser-induced transfer of supported metal films (Fig. 1) for applications in microelectronics, photolithographics, and other areas. This process, referred to by many different acronyms such as laser-induced forward transfer (LIFT) or microstructuring by explosive laser deposition (MELD, as we refer to it), has seen considerable research but few practical applications. Although these investigations have demonstrated the physical principles involved in the process, they were deficient in one or more important practical characteristics, mainly the short-comings of the lasers used in the deposition experiments. Some of the laser short-comings were: (1) the lasers were single-pulse systems with long times between pulses; (2) the laser pulse lengths were too long, usually a few nanoseconds or longer, therefore laser heating continued after the film was heated throughout its ˚ aluminum film is less than 50 ps); (3) the laser pulse depth (the thermal diffusion time for a 1000 A amplitudes could not be made sufficiently reproducible shot-to-shot; and (4) the available laser systems were unreliable over the long periods required in industrial applications. All of these factors *Corresponding author. Tel.: 1 1-734-662-3841; fax: 1 1-734-662-3920. E-mail address: [email protected] (F.J. Mayer). 1 Present address: IntraLase Corporation, 30 Hughes, Suite 208, Irvine, CA 92618, USA. 0167-9317 / 01 / $ – see front matter PII: S0167-9317( 00 )00496-2
2001 Elsevier Science B.V. All rights reserved.
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Fig. 1. The basic pulsed-laser thin-metal film deposition configuration.
contributed to producing metal deposits of poor quality. Because of these drawbacks and lacking a practical operating regime (discussed below) the laser metal transfer process has not seen the potential for substantial industrial applications until now. The important advance that allows practical and precision laser metallization has been the development of a new type of continuously pulsed, short-pulse laser [13] system: the chirped-pulse amplified (CPA) laser. CPA lasers do not have the drawbacks of the previous systems employed in MELD-type experiments. These drawbacks of older laser systems should be clear after we present our results and the precision laser metallization [15] regime. We begin with a description of the basic physics of the supported thin-metal film laser interaction (Section 2). Next, we discuss the precision operating regime (Section 3) and show the experimental results (Section 4). We conclude with a look ahead to practical precision laser metallization in applications (Section 5).
2. Basic physics of the laser metal-film interaction ˚ thick and supported on a thick glass substrate. A laser Thin-metal films are typically 1000 A heating pulse is focused through the glass at an intensity below the intensity that would produce plasma breakdown on the glass surface ( # 10 13 W/ cm 2 ). A small fraction (a few percent) of the laser ˚ of the metal film energy in the pulse is deposited by ‘skin-depth’ absorption in the thin layer ( | 50 A) at the interface between the glass and the metal film. The deposited heat is carried away from the deposition region by thermal conduction primarily into the metal, which has a much higher thermal conductivity than does the glass. (The thermal diffusivity of the glass is 100 times that of aluminum, which we will consider from here on as representative.) The pressure gradients are unbalanced in the forward direction. The metal film is accelerated off the target substrate and decompresses as it moves forward. All of these processes proceed at the same time: they are not sequential. If the laser pulse is too long and / or of too high energy, then laser heating continues even after the metal film has partially decompressed. The metal vapor is turned into a plasma and tends to lose its forward directionality (the
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case for previous experiments) and, therefore, ‘splatters’ onto the working substrate. If the laser pulse is too short, insufficient heating of the metal results in insufficient or no propulsion. In between these two extremes lies the regime of optimal practical applications. There are a few non-linear effects of importance in the dynamics which we mention briefly. First, the absorptivity of the metal film increases as the temperature increases to and above melting. This effect tends to optimize the peak intensity zone for material acceleration. Second, the thermal conductivity of the metal film also increases with temperature, further increasing acceleration in the highest intensity zone. These and other aspects of the laser thin-metal film interaction will be described elsewhere [16].
3. The precision operating regime With short laser pulses ( # 1 ps), it is possible to confine the heating of the metal film to a period before decompression begins and to control the amount of heating. This confinement allows the metal to be heated just above the melting point but well below the vaporization point. This results in a heated metal region experiencing a pressure gradient to accelerate the now-melted region in the forward direction without excess heat to disassemble it in flight. Furthermore, the short heating pulse does not allow any lateral heat flow. This lateral heat flow may cause transverse metal removal or loss of energy from the heated metal region into the glass substrate. In this regime, the metal is rapidly melted and accelerated. In addition, deposition of the metal onto the working substrate is a ‘rapid quench’ process. There are a number of important points about this regime. First of all, the amount of heat contained ˚ aluminum film (Fig. 2). Therefore, only in the metal is only | 3 3 10 210 J / mm 2 in a typical 1000 A very small laser pulse energies are required for deposition. This low energy indicates why previous experiments have ‘over-driven’ the metal films in deposition experiments. The high power is required to quickly heat the metal film but late arriving energy is detrimental to the deposition because it easily vaporizes or otherwise distorts the metal film as it is launched. Moreover, in applications, this very small amount of heat in the metal is rapidly dissipated when deposited onto the working substrate, which may be quite important for delicate substrates.
4. Experimental results The laser beam was focused through the target substrate (a fused silica slide 1 mm thick) onto a ˚ aluminum film (see Fig. 1). The numerical aperture of the focusing lens was 0.5 and the 1000 A 22 e -intensity beam radius at the waist was 3 mm. The working substrate was another glass slide located opposite to the metal film. The laser was a 1 kHz diode-pumped 1.06 mm Nd:glass CPA laser ˚ at system [17] operated with 20 mJ, 1 ps pulses. The skin-depth in the aluminum film is about 50 A this wavelength. The laser pulse energy was adjusted by inserting neutral density filters into the beam. Both the target and the working substrates were placed in contact and attached to a translation stage in order to examine the aluminum deposition shot by shot. An important practical point to notice is that no vacuum system was employed in these deposition experiments. After laser exposure, the samples
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Fig. 2. The energy per unit mass required to heat aluminum to temperature T (8C). Note the latent heat of melting at 9338C. ˚ aluminum film is 2.7 3 10 24 ng / mm 2 . The areal mass of a 1000 A
were examined with a scanning electron microscope. Figs. 3–5 show the images taken with the electron microscope. The laser pulse energy for the depositions shown in Figs. 3–5 was 0.14 mJ giving a fluence of | 1 J / cm 2 at the spatial peak of the focused beam. The reflectivity is about 95%. Assuming absorption of
Fig. 3. Scanning electron photomicrograph of the working substrate. The separation between adjacent deposited spots is about 20 mm and was controlled with a computerized translation stage. The laser energy was 0.14 mJ per pulse.
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Fig. 4. Magnified electron photomicrograph of one deposited spot from Fig. 3. The spot diameter is about 0.8 mm.
5%, the absorbed energy fluence at the peak is about 0.05 J / cm 2 . This is to be compared to the energy ˚ thick aluminum film. The energy in excess of flux of about 0.03 J / cm 2 required for melting a 1000 A melting is the energy that provided the acceleration of the metal film. Notice the near-perfect circular aluminum spot deposits in Fig. 3 spaced about 20 mm apart. About 1 ms passed with no material deposited outside of the intended spots. A close-up view of one of the spots is shown in Fig. 4. Notice that the spot deposit has a diameter of only about 0.8 mm. Finally, the electron microscope image of a spot removed from the target substrate is shown in Fig. 5. Here, again, the removed zone is a near-perfect circular spot. There is, in addition, an irregular ring with a diameter of about 2 mm. This ring is most probably the outer-most region to which melting had occurred. The region between the removed zone and the outer ring apparently had insufficient energy deposited to provide for both melting and material acceleration. Well-defined spot depositions were obtained when the target-to-working substrate distances were
Fig. 5. Scanning electron photomicrograph image of the target substrate. The outer ring indicates the outer-most heat-effected zone. The size of the removed central zone is about the same size as the deposited spot in Fig. 4.
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varied from direct contact to about 10 mm separation. At larger distances, the depositions became somewhat distorted, probably due to the intervening air mass. Vacuum tests at larger distances were not attempted. 5. Future applications It seems that there will now be almost limitless applications of this regime of MELD-type precision laser metallization [15]. It is envisioned that the ability to rapidly ‘write’ metal lines will find applications for interconnects in flat surface microelectronics. Vertical metal deposition or ‘build-up’ for via connections will be rapid; for example, a one square micron via, 10 mm deep, can be filled in 0.1 s. MELD metallization on a small scale has an immediate application in the repair of large, flat-panel displays and photolithographic masks. Furthermore, even though in this paper we have discussed aluminum thin films, it should be clear that any metal can be precision laser deposited. Only a slight increase or decrease of the laser energy per pulse will be necessary to adjust for the differences in melting point and reflectivity for other metals. We note also that even though we have ˚ films for demonstrating this precision laser deposition regime, by suitably adjusting the used 1000 A laser pulse length and energy, either thicker or thinner films can be similarly deposited. Because the laser pulse energy per square micron required to access the precision operating regime is so small, metallization can now be performed on either small ( | 1 mm 2 ) or relatively large ( | 100 mm 2 ) spots at kilohertz rates and perhaps even at somewhat higher rates. These deposition rates can be obtained from commercially available CPA lasers [14]. In addition, such metallizations can be either masked or self-masked as our experiments above have shown. Of course, in a straightforward manner, the focal spot on the target substrate can also be adjusted for different deposition geometries, for example a line focus may be preferable in some applications. Even more extensive metallization rates and areal coverage are now becoming practical due to recent [18] and continuing advances in ultrafast laser technology. Finally, we believe that the number of applications of our MELD-type precision laser metallization will be as large as the number of engineers or scientists that have to make precision thin-film metal deposits. Acknowledgements One of us (FJM) would like to thank Dr. Gerard Mourou for encouraging the MELD demonstrations. The authors would also like to thank Douglas Craig, Richard Lai, Madeline Naudeau, and Boh Ruffin for making the supported thin-metal films, Hsiao-Hua Liu for operating the laser, and for the support and collaboration of Dr. John F. Mansfield and Dr. Corinna J. Wauchope of the University of Michigan North Campus Electron Microbeam Analysis Laboratory and for the use of the laboratory’s FEI XL30FEG SEM. References [1] F.J. Mayer, Pulsed laser microfabrication, U.S. Patent [4,752,455, June 21, 1988. [2] E.V. Cook, Radiation induced pattern deposition, U.S. Patent [4,895,735, January 23, 1990.
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[3] B.F. Kim, Method and apparatus for the thin-film deposition of materials with a high-power laser, U.S. Patent [4,970,196, November 13, 1990. [4] T.H. Baum, P.B. Comita, R.L. Jackson, Process for interconnecting thin-film electrical circuits, U.S. Patent [4,880,959, November 14, 1989. [5] R.T. Williams, D.B. Wrisley, Jr., J.C. Wu, Laser transfer process, U.S. Patent [4,997,006, January 22, 1991. [6] J. Bohandy, B.F. Kim, F.J. Adrian, J. Appl. Phys. 60 (1986) 1538–1542. [7] R.J. Baseman, J.C. Andresak, in: M.J. Aziz, L.E. Rehn, B. Stritzker (Eds.), Fundamentals of Beam–Solid Interactions and Transient Thermal Processing, Materials Research Society, Pittsburgh, 1988, pp. 627–636. [8] P. Mogyprososi, T. Szorenyi, K. Bali, Z. Toth, J. Hevesi, Appl. Surf. Sci. 36 (1989) 157–162. [9] E. Forgarassy, C. Fuchs, F. Kerherve, G. Hauchecone, J. Perriere, J. Mater. Res. 4 (1989) 1082. [10] H. Esrom, J.-Y. Zhang, U. Kogelschatz, A.J. Pedraza, Appl. Surf. Sci. 86 (1995) 202–206. [11] D.E. Alexander, G.S. Was, F.J. Mayer, J. Mater. Sci. 23 (1988) 2181–2186. [12] F.J. Mayer, G.E. Busch, J. Appl. Phys. 57 (1985) 827–829. [13] D. Strickland, G. Mourou, Opt. Commun. 56 (1985) 219–223. [14] For example, CPA-2001, Clark-MXR, Inc., 7300 West Huron River Drive, Dexter, MI 48130, USA. [15] F.J. Mayer, Precision laser metallization, patent protection for this technology has been allowed. [16] F.J. Mayer, Dynamics of laser-driven, explosively-heated, thin-metal films (to be published). [17] C. Horvath, A. Braun, H. Liu, T. Juhasz, G. Mourou, Opt. Lett. 22 (1997) 1790–1793. [18] J. Aus der Au et al., Opt. Lett. 25 (2000) 859–861.
Precision laser metallization a ,1 a b, An-Chun Tien , Zachary S. Sacks , Frederick J. Mayer * a
Center for Ultrafast Optical Sciences, University of Michigan, Ann Arbor, MI 48109, USA b Mayer Applied Research, Inc., 1417 Dicken Dr., Ann Arbor, MI 48103, USA Accepted 24 October 2000
Abstract We demonstrate precision laser deposition of thin metal-film features on glass substrates. One micron deposits are produced with short, low-energy, laser pulses at a kilohertz rate. Numerous applications are expected for production of electrically conducting interconnects and vias on microelectronic substrates and for spot repairs on flat-panel displays and photolithographic masks. 2001 Elsevier Science B.V. All rights reserved. Keywords: Laser deposition; Metal-film features
1. Introduction There have been numerous patents [1–5] and technical papers [6–12] that have been concerned with pulsed-laser-induced transfer of supported metal films (Fig. 1) for applications in microelectronics, photolithographics, and other areas. This process, referred to by many different acronyms such as laser-induced forward transfer (LIFT) or microstructuring by explosive laser deposition (MELD, as we refer to it), has seen considerable research but few practical applications. Although these investigations have demonstrated the physical principles involved in the process, they were deficient in one or more important practical characteristics, mainly the short-comings of the lasers used in the deposition experiments. Some of the laser short-comings were: (1) the lasers were single-pulse systems with long times between pulses; (2) the laser pulse lengths were too long, usually a few nanoseconds or longer, therefore laser heating continued after the film was heated throughout its ˚ aluminum film is less than 50 ps); (3) the laser pulse depth (the thermal diffusion time for a 1000 A amplitudes could not be made sufficiently reproducible shot-to-shot; and (4) the available laser systems were unreliable over the long periods required in industrial applications. All of these factors *Corresponding author. Tel.: 1 1-734-662-3841; fax: 1 1-734-662-3920. E-mail address: [email protected] (F.J. Mayer). 1 Present address: IntraLase Corporation, 30 Hughes, Suite 208, Irvine, CA 92618, USA. 0167-9317 / 01 / $ – see front matter PII: S0167-9317( 00 )00496-2
2001 Elsevier Science B.V. All rights reserved.
274
A.-C. Tien et al. / Microelectronic Engineering 56 (2001) 273 – 279
Fig. 1. The basic pulsed-laser thin-metal film deposition configuration.
contributed to producing metal deposits of poor quality. Because of these drawbacks and lacking a practical operating regime (discussed below) the laser metal transfer process has not seen the potential for substantial industrial applications until now. The important advance that allows practical and precision laser metallization has been the development of a new type of continuously pulsed, short-pulse laser [13] system: the chirped-pulse amplified (CPA) laser. CPA lasers do not have the drawbacks of the previous systems employed in MELD-type experiments. These drawbacks of older laser systems should be clear after we present our results and the precision laser metallization [15] regime. We begin with a description of the basic physics of the supported thin-metal film laser interaction (Section 2). Next, we discuss the precision operating regime (Section 3) and show the experimental results (Section 4). We conclude with a look ahead to practical precision laser metallization in applications (Section 5).
2. Basic physics of the laser metal-film interaction ˚ thick and supported on a thick glass substrate. A laser Thin-metal films are typically 1000 A heating pulse is focused through the glass at an intensity below the intensity that would produce plasma breakdown on the glass surface ( # 10 13 W/ cm 2 ). A small fraction (a few percent) of the laser ˚ of the metal film energy in the pulse is deposited by ‘skin-depth’ absorption in the thin layer ( | 50 A) at the interface between the glass and the metal film. The deposited heat is carried away from the deposition region by thermal conduction primarily into the metal, which has a much higher thermal conductivity than does the glass. (The thermal diffusivity of the glass is 100 times that of aluminum, which we will consider from here on as representative.) The pressure gradients are unbalanced in the forward direction. The metal film is accelerated off the target substrate and decompresses as it moves forward. All of these processes proceed at the same time: they are not sequential. If the laser pulse is too long and / or of too high energy, then laser heating continues even after the metal film has partially decompressed. The metal vapor is turned into a plasma and tends to lose its forward directionality (the
A.-C. Tien et al. / Microelectronic Engineering 56 (2001) 273 – 279
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case for previous experiments) and, therefore, ‘splatters’ onto the working substrate. If the laser pulse is too short, insufficient heating of the metal results in insufficient or no propulsion. In between these two extremes lies the regime of optimal practical applications. There are a few non-linear effects of importance in the dynamics which we mention briefly. First, the absorptivity of the metal film increases as the temperature increases to and above melting. This effect tends to optimize the peak intensity zone for material acceleration. Second, the thermal conductivity of the metal film also increases with temperature, further increasing acceleration in the highest intensity zone. These and other aspects of the laser thin-metal film interaction will be described elsewhere [16].
3. The precision operating regime With short laser pulses ( # 1 ps), it is possible to confine the heating of the metal film to a period before decompression begins and to control the amount of heating. This confinement allows the metal to be heated just above the melting point but well below the vaporization point. This results in a heated metal region experiencing a pressure gradient to accelerate the now-melted region in the forward direction without excess heat to disassemble it in flight. Furthermore, the short heating pulse does not allow any lateral heat flow. This lateral heat flow may cause transverse metal removal or loss of energy from the heated metal region into the glass substrate. In this regime, the metal is rapidly melted and accelerated. In addition, deposition of the metal onto the working substrate is a ‘rapid quench’ process. There are a number of important points about this regime. First of all, the amount of heat contained ˚ aluminum film (Fig. 2). Therefore, only in the metal is only | 3 3 10 210 J / mm 2 in a typical 1000 A very small laser pulse energies are required for deposition. This low energy indicates why previous experiments have ‘over-driven’ the metal films in deposition experiments. The high power is required to quickly heat the metal film but late arriving energy is detrimental to the deposition because it easily vaporizes or otherwise distorts the metal film as it is launched. Moreover, in applications, this very small amount of heat in the metal is rapidly dissipated when deposited onto the working substrate, which may be quite important for delicate substrates.
4. Experimental results The laser beam was focused through the target substrate (a fused silica slide 1 mm thick) onto a ˚ aluminum film (see Fig. 1). The numerical aperture of the focusing lens was 0.5 and the 1000 A 22 e -intensity beam radius at the waist was 3 mm. The working substrate was another glass slide located opposite to the metal film. The laser was a 1 kHz diode-pumped 1.06 mm Nd:glass CPA laser ˚ at system [17] operated with 20 mJ, 1 ps pulses. The skin-depth in the aluminum film is about 50 A this wavelength. The laser pulse energy was adjusted by inserting neutral density filters into the beam. Both the target and the working substrates were placed in contact and attached to a translation stage in order to examine the aluminum deposition shot by shot. An important practical point to notice is that no vacuum system was employed in these deposition experiments. After laser exposure, the samples
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Fig. 2. The energy per unit mass required to heat aluminum to temperature T (8C). Note the latent heat of melting at 9338C. ˚ aluminum film is 2.7 3 10 24 ng / mm 2 . The areal mass of a 1000 A
were examined with a scanning electron microscope. Figs. 3–5 show the images taken with the electron microscope. The laser pulse energy for the depositions shown in Figs. 3–5 was 0.14 mJ giving a fluence of | 1 J / cm 2 at the spatial peak of the focused beam. The reflectivity is about 95%. Assuming absorption of
Fig. 3. Scanning electron photomicrograph of the working substrate. The separation between adjacent deposited spots is about 20 mm and was controlled with a computerized translation stage. The laser energy was 0.14 mJ per pulse.
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Fig. 4. Magnified electron photomicrograph of one deposited spot from Fig. 3. The spot diameter is about 0.8 mm.
5%, the absorbed energy fluence at the peak is about 0.05 J / cm 2 . This is to be compared to the energy ˚ thick aluminum film. The energy in excess of flux of about 0.03 J / cm 2 required for melting a 1000 A melting is the energy that provided the acceleration of the metal film. Notice the near-perfect circular aluminum spot deposits in Fig. 3 spaced about 20 mm apart. About 1 ms passed with no material deposited outside of the intended spots. A close-up view of one of the spots is shown in Fig. 4. Notice that the spot deposit has a diameter of only about 0.8 mm. Finally, the electron microscope image of a spot removed from the target substrate is shown in Fig. 5. Here, again, the removed zone is a near-perfect circular spot. There is, in addition, an irregular ring with a diameter of about 2 mm. This ring is most probably the outer-most region to which melting had occurred. The region between the removed zone and the outer ring apparently had insufficient energy deposited to provide for both melting and material acceleration. Well-defined spot depositions were obtained when the target-to-working substrate distances were
Fig. 5. Scanning electron photomicrograph image of the target substrate. The outer ring indicates the outer-most heat-effected zone. The size of the removed central zone is about the same size as the deposited spot in Fig. 4.
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A.-C. Tien et al. / Microelectronic Engineering 56 (2001) 273 – 279
varied from direct contact to about 10 mm separation. At larger distances, the depositions became somewhat distorted, probably due to the intervening air mass. Vacuum tests at larger distances were not attempted. 5. Future applications It seems that there will now be almost limitless applications of this regime of MELD-type precision laser metallization [15]. It is envisioned that the ability to rapidly ‘write’ metal lines will find applications for interconnects in flat surface microelectronics. Vertical metal deposition or ‘build-up’ for via connections will be rapid; for example, a one square micron via, 10 mm deep, can be filled in 0.1 s. MELD metallization on a small scale has an immediate application in the repair of large, flat-panel displays and photolithographic masks. Furthermore, even though in this paper we have discussed aluminum thin films, it should be clear that any metal can be precision laser deposited. Only a slight increase or decrease of the laser energy per pulse will be necessary to adjust for the differences in melting point and reflectivity for other metals. We note also that even though we have ˚ films for demonstrating this precision laser deposition regime, by suitably adjusting the used 1000 A laser pulse length and energy, either thicker or thinner films can be similarly deposited. Because the laser pulse energy per square micron required to access the precision operating regime is so small, metallization can now be performed on either small ( | 1 mm 2 ) or relatively large ( | 100 mm 2 ) spots at kilohertz rates and perhaps even at somewhat higher rates. These deposition rates can be obtained from commercially available CPA lasers [14]. In addition, such metallizations can be either masked or self-masked as our experiments above have shown. Of course, in a straightforward manner, the focal spot on the target substrate can also be adjusted for different deposition geometries, for example a line focus may be preferable in some applications. Even more extensive metallization rates and areal coverage are now becoming practical due to recent [18] and continuing advances in ultrafast laser technology. Finally, we believe that the number of applications of our MELD-type precision laser metallization will be as large as the number of engineers or scientists that have to make precision thin-film metal deposits. Acknowledgements One of us (FJM) would like to thank Dr. Gerard Mourou for encouraging the MELD demonstrations. The authors would also like to thank Douglas Craig, Richard Lai, Madeline Naudeau, and Boh Ruffin for making the supported thin-metal films, Hsiao-Hua Liu for operating the laser, and for the support and collaboration of Dr. John F. Mansfield and Dr. Corinna J. Wauchope of the University of Michigan North Campus Electron Microbeam Analysis Laboratory and for the use of the laboratory’s FEI XL30FEG SEM. References [1] F.J. Mayer, Pulsed laser microfabrication, U.S. Patent [4,752,455, June 21, 1988. [2] E.V. Cook, Radiation induced pattern deposition, U.S. Patent [4,895,735, January 23, 1990.
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[3] B.F. Kim, Method and apparatus for the thin-film deposition of materials with a high-power laser, U.S. Patent [4,970,196, November 13, 1990. [4] T.H. Baum, P.B. Comita, R.L. Jackson, Process for interconnecting thin-film electrical circuits, U.S. Patent [4,880,959, November 14, 1989. [5] R.T. Williams, D.B. Wrisley, Jr., J.C. Wu, Laser transfer process, U.S. Patent [4,997,006, January 22, 1991. [6] J. Bohandy, B.F. Kim, F.J. Adrian, J. Appl. Phys. 60 (1986) 1538–1542. [7] R.J. Baseman, J.C. Andresak, in: M.J. Aziz, L.E. Rehn, B. Stritzker (Eds.), Fundamentals of Beam–Solid Interactions and Transient Thermal Processing, Materials Research Society, Pittsburgh, 1988, pp. 627–636. [8] P. Mogyprososi, T. Szorenyi, K. Bali, Z. Toth, J. Hevesi, Appl. Surf. Sci. 36 (1989) 157–162. [9] E. Forgarassy, C. Fuchs, F. Kerherve, G. Hauchecone, J. Perriere, J. Mater. Res. 4 (1989) 1082. [10] H. Esrom, J.-Y. Zhang, U. Kogelschatz, A.J. Pedraza, Appl. Surf. Sci. 86 (1995) 202–206. [11] D.E. Alexander, G.S. Was, F.J. Mayer, J. Mater. Sci. 23 (1988) 2181–2186. [12] F.J. Mayer, G.E. Busch, J. Appl. Phys. 57 (1985) 827–829. [13] D. Strickland, G. Mourou, Opt. Commun. 56 (1985) 219–223. [14] For example, CPA-2001, Clark-MXR, Inc., 7300 West Huron River Drive, Dexter, MI 48130, USA. [15] F.J. Mayer, Precision laser metallization, patent protection for this technology has been allowed. [16] F.J. Mayer, Dynamics of laser-driven, explosively-heated, thin-metal films (to be published). [17] C. Horvath, A. Braun, H. Liu, T. Juhasz, G. Mourou, Opt. Lett. 22 (1997) 1790–1793. [18] J. Aus der Au et al., Opt. Lett. 25 (2000) 859–861.