Proceedings Volume 3933

Laser Applications in Microelectronic and Optoelectronic Manufacturing V

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Proceedings Volume 3933

Laser Applications in Microelectronic and Optoelectronic Manufacturing V

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Volume Details

Date Published: 7 June 2000
Contents: 13 Sessions, 56 Papers, 0 Presentations
Conference: Symposium on High-Power Lasers and Applications 2000
Volume Number: 3933

Table of Contents

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Table of Contents

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  • Fundamental Processes I
  • Fundamental Processes II
  • Lasers and Techniques I
  • Lasers and Techniques II
  • Poster Session
  • Lasers and Techniques II
  • Pulsed Laser Deposition I
  • Pulsed Laser Deposition II
  • Pulsed Laser Deposition III
  • Lasers and Techniques III
  • Laser Microengineering I
  • Poster Session
  • Laser Microengineering II
  • Laser Microengineering III
  • Laser Microengineering IV
  • Poster Session
  • Laser Microengineering IV
  • Laser Microengineering I
Fundamental Processes I
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Investigations of laser desorption from modified surfaces of ionic single crystals
Christos Bandis, Mary L. Dawes, Y. Kawaguchi, et al.
Wide band gap insulators irradiated with UV and/or IR pulsed lasers have been shown to yield neutrals, photoinduced electrons, and energetic positive ions suggesting occupied electronic defect states in the band gap. We explore the consequences of applying a variety of stimuli, which can generate defects on single crystal surfaces of inorganic ionic crystals. The stimuli include electron beam irradiation, a second laser beam, mechanical treatment, and thermal treatment. Our experiments on a wide variety of ionic crystals find that a common theme evolves where these stimuli generate sites that strongly interact with the probing laser beam. Such interactions lead to dramatic decrease in the laser intensities needed for ejection of ions, neutrals, as well as eventual plume formation, and result in increased vulnerability of the materials to the laser radiation.
Dynamical Stark effect in small quantum dots
Joseph Thomas Andrews, Pratima Sen
Using time dependent perturbation technique, Stark shift and self-energy correction in semiconductor quantum dot are studied. The analytical results are obtained by incorporating the important excitonic and biexcitonic effects. The numerical estimations are made for potentially important II-VI semiconductor quantum dot CdS of size smaller than the bulk exciton Bohr radius. The demonstration of analytical and numerical result predicts a red shift of (Delta) E/3 with (Delta) E being the biexciton binding energy. The Stark shift and self energy correction are found to have higher amplitudes at high excitation intensities due to the presence of biexcitons.
Fundamental Processes II
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Explosive femtosecond ablation from ionic crystals
Juergen Reif, Matthias Henyk, Dirk Wolfframm
Femtosecond laser ablation of positive ions from transparent ionic crystals is studied by time-of-flight mass spectrometry. We find an explosive emission of positive ions. The ion yield dependence eon the laser fluence is highly nonlinear. The material is emitted in characteristic bursts, depending chaotically on the number of laser pulses hitting the sample. The mean kinetic energy of the positive ions is on the order of 100 eV while their temperature is only around 1 eV, very similar to supersonic expansion of a molecular jet. The last observation is independent of the ion species, indicating that all ions were born at the same instant and kicked out of the material simultaneously with identical kinetic energy. Negative ions, on the contrary, appear considerably later and are much slower. Al ablation is preceded by effective electron emission. We suggest that the laser generates a high-density plasma. The resulting electrons may possibly escape, due to the short pulse duration, without being disturbed by the build-up of a space charge zone. Subsequently, positive ions are expelled by Coulomb explosion of the unstable surface .Negative ions may be produced much later form the hot sample or by secondary processes.
Interaction of shock electromagnetic waves with transparent materials: classical approach
Anastasia S. Gruzdeva, Vitali E. Gruzdev
There is discussed a theoretical model of initiating of laser-induced damage and ablation of transparent materials by femtosecond pluses based on properties of shock electromagnetic wave (SHEW). Advantages of this model are increased efficiency of SHEW-induced ionization and possibility of effective straight action of SHEW front on ions at crystal-lattice points. It is presented simplified description of SHEW-induced processes within approach of classical mechanics and electrodynamics: atoms are described as dipoles with certain ionization energy interacting with SHEW in potential well formed by crystal lattice. There are considered possibilities of laser-induced ionization by higher harmonics appearing during SHEW formation and point- defect formation and delocalization of ions at crystal points by SHEW. Obtained results and predictions are compared with experimental data and shown to be capable of explaining many observed regulations of femtosecond laser interactions with transparent media.
Analysis of laser ablation process in semiconductor due to ultrashort-pulsed laser with molecular dynamics simulation
Koji Watanabe, Yuri Ishizaka, Etsuji Ohmura, et al.
Rapid fusion and evaporation phenomena of silicon with ultrafast laser irradiation were simulated using the 3D molecular dynamics. Surface structure dependence of laser shock phenomena, fusion and evaporation process was examined for the Si(100) and Si(111) surface structures. It was shown that the crystal orientation influences the propagation velocity of shock wave and that heat conduction but laser absorption in the materials, that is, absorption coefficient affects the fusion depth when the pulse width is subpicosecond.
Lasers and Techniques I
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Laser technologies for manufacturing of advanced materials and devices
As demand is growing for devices capable of performing new and increased numbers of operations within an ever shrinking physical volume the laser has become an increasingly important tool helping to overcome the limitations of conventional microfabrication techniques. In addition to classical applications of lasers such as via hole drilling, trimming or pulsed laser deposition of thin films, there have been new developments of laser-based technologies for the fabrication of advanced micro- and nano-devices. Of particular interest for optoelectronic and photonic applications is the potential of the laser for the fabrication of integrated and monolithically integrated photonic devices and circuits.
Nonlinear optical characterization of silicon wafers: in-situ detection of stacking faults and external stress
Juergen Reif, Thomas Schneider, Reiner P. Schmid, et al.
Femtosecond second harmonic generation from the surface of as-grown 6-inch silicon wafers is used as a tool for in-situ characterization. Czochralski-grown crystal are not homogeneous over their cross section. A central zone of vacancy-rich and as outer zone of interstitial-rich crystal are separated by a ring of stacking faults. Gate oxide layers grown on such substrate show different quality in their dielectric properties, making it desirable to locate these zones before producing different devices. Exploiting the symmetry sensitivity of surface SHG, we use a particular two-pulse arrangement, similar to a conventional pump-probe setup, to obtain a non-destructive, in-situ information about the location of the three different crystal zones. Further, we demonstrate the potential of surface SHG to monitor external stress, exerted on the sample for instance by improper mounting, providing a tool for on-line optimization of process parameters. Finally, the applicability of the technique for on-line analysis and control during the growth of different types of gate dielectrics is discussed.
Influences of hydrogen in precursor Si films on excimer laser crystallization
Michiko Takahashi, Masakazu Saitoh, Kenkichi Suzuki, et al.
The excimer laser crystallization (ELC) is a key technology of the low temperature polycrystalline silicon (LTP) thin film transistor (TFT) processes. The precursor Si for ELC is amorphous Si (a-Si) film, and hydrogen in the film has to be eliminated down to a certain concentration to prevent explosive evolution of hydrogen gas when excimer laser is irradiated. Hydrogen has been concerned only with respect to the effect for practical applications. This paper points out another aspect of hydrogen effect. There is correction between the bonding environments of precursor and polycrystalline Si (p-Si) structures produced through ELC process. The effect becomes explicit under 0.8 at percent of hydrogen conceits, and are clearly manifested in differences in lattice spacings of p-Si films. Variations of microscopic structure of the precursors are provided by three kinds of deposition methods, and dehydrogenation conditions. This paper also shows that transient boiling behaviors by the excimer laser discriminate prominently the differences among precursors. Although relationships between the behavior and microscopic structures are not clear, it gives an efficient measure for the bonding environment. It is also shown that the constants of p-Si is typically 1018/cm3 after multishot ELC process, and effusion of the hydrogen at one shot is rather small. This may lead to the inferences that hydrogen influence profoundly ELC process, and also contributes to preserve characteristic structure of the precursors.
Laser chemical process for clean applications of semiconductor manufacturing
David Yogev, Michael Y. Engel, Shaike Zeid, et al.
Cleaning applications in the semiconductor manufacturing industry are tougher to meet as the device dimensions decrease. The uniqueness of Oramir-Laser-Chemical process relies on the mutual combination and effectiveness of laser particle removal mechanisms and laser induced photon- thermal-chemical reaction in the mixture of O2/O3/NF3 gases. The process involves ozone blast wave, photodecomposition of O3 into O radicals, photo-thermal decomposition of NF3 into fluorine radicals, thermal effects and thin liquid-chemical ablation enhanced particle removal. Recent results on Bare Si wafers, photomasks, EUV masks and scalpel masks show substantial removal efficiency, up to 100 percent for certain applications.
Lasers and Techniques II
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Present status and future aspects of high-power diode laser materials processing under the view of a German national research project
High power diode lasers from a few Watts up to several Kilowatts have entered industrial manufacturing environment for materials processing applications. The technology has proven to show unique features, e.g. high efficiency, small size, low energy consumption and high reliability. In the first part of this paper a short description of state-of- the-art high power diode laser technology and applications is provided and the benefits and restrictions of this laser technology will be evaluated. For large scale penetration into the manufacture market, the restrictions, especially the rather poor beam quality of high power diode lasers compared to conventional lasers have to be overcome. Also, the specialities of the high power diode lasers, i.e. their modular structure and their extremely small size have to be translated into laser manufacturing technology. The further improvement of high power diode lasers as well as the development of new diode laser specific manufacturing technologies are the essential topics of a National German Minister Priority Project entitled 'Modular Diode Laser Beam Tools': 22 Partners from industry and institutions, 4 semiconductor experts, 5 laser manufacturers and 14 applicants are working together in frame of this project to work out and transfer a joint strategy and system technology to the benefits of the future of high power diode laser technology. The goals, the structure and the work of this project will be described in the second part of this paper.
Direct writing of electronic materials using a new laser-assisted transfer/annealing technique
Alberto Pique, J. M. Fitz-Gerald, Douglas B. Chrisey, et al.
MAPLE direct write is anew laser-based direct write technique which combines the basic approach employed in laser induced forward transfer with the unique advantages of matrix assisted pulsed laser evaporation. The technique utilizes a laser transparent donor substrate with one side coated with a matrix consisting of the electronic material to be transferred mixed with an organic binder or vehicle. As with LIFT, the laser is focused through the transparent substrate onto the matrix coating. When a laser pulse strikes the coating, the matrix is transferred to an acceptor substrate placed parallel to the donor surface. Ex situ thermal or laser treatments can be used to decompose the matrix and anneal the transferred material, thus forming structures with the desired electronic properties. MAPLE DW is a maskless deposition process designed to operate in air and at room temperature that allows for the generation of complex patterns with micron scale linewidths. The various structures produced by MAPLE DW were characterized using 3D surface profilometry, scanning electron microscopy and optical microscopy. The electrical resistivity of the silver metal lines made by MAPLE DW was measured using an impedance analyzer. Patterns with Zn2SiO4:Mn powders were fabricated over the surface of a dragon fly wing without damaging it. An overview of the key elements of the MAPLE DW process including our current understanding of the material transfer mechanisms and its potential as a rapid prototyping technique will be discussed.
Poster Session
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Laser-induced temperature-rise measurement by infrared imaging
Jianhui Gu, Siu Chung Tam, Yee Loy Lam, et al.
The characteristics of laser-induced temperature-rise are important information in laser material processing. In our experiment, several kinds of metals such as mild carbon steel, stainless steel, aluminum alloy and copper, and non-metals namely epoxy and polymethyl methacrylate were irradiated by using a high-power CW CO2 laser beam, while the temperature distribution and variation on their surfaces were measured by using a fast scanning infrared camera to image the laser irradiated area. The CO2 laser beam power was varied from several tens of Watts to several hundreds of Watts for the irradiating of different materials. 2-D and 3-D temperature distributions and the temperature variations against the time of laser irradiation on certain points within the laser-irradiated area were recorded and measured. It is found that the temperature distribution on the surfaces of the irradiated materials was tightly related to the laser beam mode, and the temperature fluctuations corresponded to the laser beam power fluctuations. The results of this research could be applied to laser material processing.
Lasers and Techniques II
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Stress measurements in silicon microstructures
Sherwin Amimoto, Dick J. Chang, Andra D. Birkitt
Raman spectroscopy is used as a non-contact probe of stress with high spatial resolution in micro-machined silicon structures. The motivation for this work is that reliability or cycle life can be substantially increased by understanding the origin of stress including residual stress. Excessive stresses induced by workmanship shortcomings or design constraints may be addressed by Raman measurements. In microelectronics, stress is known to play a significant role in interconnects which limits reliability, life, and ultimately cost of many circuits. We wish to demonstrate the utility of Raman spectroscopy as a tool for the development and design of silicon microstructures. The equations for a general 2D stress field are discussed. Calibration studies using macro-mechanical fixtures for single crystal silicon specimens under 2D stress field are presented. Our measurements show good agreement with the theoretical values and thus validate the approach taken. Stress maps of conventionally fabricated test structures, laser machined, and polysilicon structures are presented.
Pulsed Laser Deposition I
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Pulsed-laser deposition of electronic oxides: superconductor and semiconductor applications
David P. Norton, Chan Park, Y. E. Lee, et al.
Over the past decade, pulsed-laser deposition (PLD) has proven to be one of the most versatile and effective methods for obtaining high-quality electronic oxide thin-film materials. Much of this success can be attributed to its initial use in depositing high temperature superconducting materials. However, pulsed-laser deposition is now a leading research tool in the development of various electronic oxide thin-film technologies. In this paper, recent progress in the deposition of oxide materials on dissimilar materials for both superconductor and semiconductor applications is discussed. Recent developments in the synthesis of superconducting wires via epitaxial growth of superconducting oxides on biaxially textured metal tapes is described. In addition, efforts to integrate high-k dielectric oxides on semiconductor surfaces using pulsed- laser deposition are highlighted.
Optical and electronic properties of amorphous WO3 thin film irradiated by laser in air
H. Qiu, Yongfeng Lu
To study the potential in optical recording, the laser induced chromism of amorphous WO3 thin films has been investigated. The original film can be colored from grey to purple by one pulse of the KrF excimer laser at 248 nm and bleached to dark grey by one pulse of Nd:YAG laser at 1.06 micrometers in air. Spectroscopy measurements were applied to study the films at the three alternate states: original, colored and bleached. The changes of refractive index and extinction coefficient from colored states to bleached states, could be measured by ellipsometry spectroscopy that showed increasing and decreasing tendency, respectively in luminous range at colored state. X-ray photoelectron spectroscopy was used to study the chemical states. With some W5+ ions existed in the original films by pulsed laser deposition, more lower stats ions, such as the W3+ ions were produced along with decreasing W6+ states in films colored by KrF excimer. Laser bleaching was accompanied with decreasing of W5+, W3+ states and increasing of W6+ states in films. The purple color was thought due to the polaron transition between W3+ states and W4+ states or, W5+ states and W4+ states. Scanning tunneling spectroscopy showed that the colored films had more characteristics of n type semiconductor after coloring. We attribute the coloring and bleaching process to photochemical activation and photothermal oxidation, respectively. Raman spectroscopy showed slight crystallization after coloration in films. From temperature field calculation, the crystallization is suggested most likely caused by ion intercalation instead of thermal crystallization. The color states in films are very stable after long-time exposure in air, as well as in oxygen.
Effect of film thickness on the properties of indium tin oxide thin film grown by pulsed-laser deposition for organic light-emitting diodes
Transparent conducting indium tin oxide (ITO) thin films were grown by pulsed laser deposition (PLD) on glass substrates. The structural, electrical and optical properties of these films were investigated as a function of film thickness. Films were deposited using a KrF excimer laser at a fluence of 2 J/cm2, at substrate temperature of 300 degrees C and 10 mTorr of oxygen pressure. For ITO films deposited at 300 degrees C in 10 mTorr of oxygen pressure, the resistivity of 2-4 X 10-4 (Omega) - cm was observed and the average transmission in the visible range was about 85-90 percent. The Hall mobility and carrier density for ITO films were observed to be in the range of 24-27 cm2/V-s and 5-9 X 1020 cm-3, respectively. We have used the ITO thin films, deposited by PLD on silica substrates, as the anode contact in organic light emitting devices and studied the effect of ITO film thickness on the device performance. The optimum thickness of the ITO anode for the maximum device efficiency was observed to be about 500-1000 angstrom. The device shoed an external quantum efficiency of about 0.8 percent at 100 A/m2.
Pulsed Laser Deposition II
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Developments of laser processing technologies in the Japanese MITI project
Takehito Yoshida, Toshio Sato, Yoshiaki Yoshida, et al.
The 'Advanced Photon Processing and Measurement Technologies' project was started in August 1997 as part of the Industrial Science and Technology Frontier Program of the Agency of Industrial Science and Technology, the Ministry of International Trade and Industry in Japan. Thirteen private companies, one university, and four national research institutes are developing new technologies using high-quality photon beams, in the three technology fields: 'Photon-applied processing technology', 'Photon- applied measurement technology', and 'Photon generation technology'. Recent topics in the 'Photon generation technology' field are 3.3 kW output power form LD-pumped all-solid-state Nd:YAG lasers of both rod-type and slab- type, and 20 W VU output power via CLBO crystals. There are various topics also in the other two technologies. In 'Photon-applied processing technology' field, high speed defects-free welding properties have been confirmed for 10 mm thick stainless steel, by using a 8.5 kW iodine laser and nitrogen assist gas. Furthermore, we have developed integrated process systems of pulsed laser ablation in helium background gas, size classification using a differential mobility analyzer, and deposition onto a substrate, for the purpose of synthesizing for semiconductor and refractory metal nanoparticles size-controlled accurately. Consequently, we have deposited the size- controlled accurately. Consequently, we have deposited the size-controlled nanoparticles onto substrates with sharp size distributions in geometrical standard deviation: 1.2.
TiN growth by hybrid radical beam-PLD for Si barrier metal
Kotaro Obata, Koji Sugioka, Koichi Toyoda, et al.
Combination of PLD and nitrogen radical beam has grown high quality TiN films on Si substrate without silicidation at the interface between TiN thin film and Si substrate even at growth temperature more than 700 degrees C. Additionally, X- ray photoelectron spectroscopy revealed that this method achieved synthesis of almost stoichiometric TiN films. Diffusion barrier characteristics of the grown film were examined by deposition of Al thin films of about 400 nm thick on the TiN grown films, followed by post-thermal treatment at 500 degrees C for 30 minutes. Scanning electron microscopy (SEM) observation and Rutherford backscattering spectroscopy analysis revealed that sharp interfaces between Al and TiN were maintained after the thermal treatment, indicating excellent property of the TiN films as Si barrier metal.
Laser ablation of solid films at a cryogenic temperature
In order to create new possibilities of laser ablation technique, the laser ablation of nitrogen solid films deposited on a copper plate at 10 K was performed upon irradiation with a picosecond UV laser in vacuum. UV and visible emissions, which were ascribed to the transition form excited molecular and atomic nitrogen, were detected on the film during the laser irradiation at the fluence of 5 J/cm2/pulse. These excited species would be produced in a multi-photon absorption process of the nitrogen by the ps- laser irradiation. At the fluence of ca. 10 J/cm2/pulse, ablation of the film was observed. Plume of the ablation reacted with the surface of graphite. XPS analysis indicated that nitrides formed don the graphite surface by the exposure to the plume. A novel technique for surface modification of materials is made possible by the ps-laser ablation of nitrogen solid film.
Pulsed-laser deposition of AlN thin films
Yongfeng Lu, ZhongMin Ren, H. Q. Ni, et al.
Aluminium nitride thin films were deposited at room temperature on silicon substrates by nitrogen-ion-assisted pulsed laser ablation of a hexagonal AlN target. A KrF excimer laser with pulse duration of 23 ns and wavelength of 248 nm was used as a laser source for the ablation. With this technology, it is possible to independently control the energy of the AlN radicals in the ablated plasma and the nitrogen ions in the ion beam to improve the quality of the deposited thin films. Moreover, the nitrogen ion implantation can also compensate the loss of nitrogen species in the ablation process. X-ray diffraction (XRD), Raman spectrum and x-ray photoelectron spectroscopy (XPS) were used to characterize the deposited thin films. The deposited thin films exhibit good crystal properties with sharp XRD peaks. The influences of the nitrogen ion beam energy on the electronic and structural properties of the deposited thin films were studied. The nitrogen ions can effectively promote the formation of stable Al-N bonds and improve the crystal properties of the deposited thin films. A nitrogen ion energy of 400 eV is proposed.
Pulsed Laser Deposition III
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Production of photoluminescent Si-based nanostructures by laser ablation: effects of ablation and postdeposition conditions
Andrei V. Kabashin, M. Charbonneau-Lefort, Michel Meunier, et al.
A method of Pulsed Laser Ablation (PLA) from a Si target in an inert He ambient has been applied in combination with different post-deposition oxidation procedures for the fabrication of Si/SiOx nanocrystalline structures on Si substrates. After the growth of a thin natural oxide layer on the film surface, the structures exhibited a strong visible photoluminescence (PL), which remained stable even under a prolonged continuous irradiation of the sample by an excitation laser light. The peak energy of the PL spectra could be finely varied between 1.58 and 2.15 eV by a change in the residual gas pressure during the deposition process. An effect of thermal annealing on the PL properties of the Si/SiOx films has been examined and compared with the results for Si-based films produced by thermal evaporation from a Si target in vacuum. For both deposition techniques, the thermal annealing led to a dramatic change of PL properties giving rise to a fixed PL peak around 2.2 eV. Photoluminescent properties of particles formed by PLA with natural oxidation were different than those of thermally oxidized amorphous Si films. A recombination through oxygen- related compounds in the upper film layer is considered as the most probable mechanism of PL.
Pulsed-laser deposition growth of SBN and correlation study of structure and optical properties
Felix E. Fernandez, Yelitza Gonzalez, Huimin Liu, et al.
Strontium barium niobate thin films were grown by PLD and characterized as to their structure, composition, and both linear and nonlinear optical properties. Attempted composition of very nearly x equals 0.61 was achieved, as shown within experimental error of RBS and PIXE techniques. Films were deposited on MgO and fused silica substrates at a range of growth rates, while keeping other factors constant. Films with excellent texture, and oriented with the c-axis normal to the substrate surface where obtained on the MgO substrates. Films grown on fused silica showed a range of structures, from essentially amorphous to well oriented, again with c-axis normal to the substrate surface. The absorption edge of the films was determined to be substantially blue-shifted in comparison with bulk material. This effect appears to correlate with film microstructure, with more disordered films grown on glass showing the largest shifts. Degenerate four-wave-mixing techniques were used to study the nonlinear optical response of the amorphous films. A considerable enhancement, by 2 orders of magnitude, of the third order nonlinear susceptibility (Chi) (3) in transverse alignment was found to occur with respect to bulk values.
Electric signal diagnostics of plasma dynamics at an early stage of laser ablation
Plasma dynamics at early stage of laser ablation is investigated by a tiny metal probe. There are tow negative peaks with different distributions in an electric signal. The first peak has a duration about 50 ns and delays 30 ns with respect to laser irradiation. The waveform and peak maximum position do not change with probe distance. It is attributed to plasma-induced electric field at the early stage. The second peak appears about 250 ns laser with a profile duration higher than 1 microsecond(s) . The peak maximum position moves forward as probe distance reduces due to earlier charge particle arrival of the probe. Experimental results and theoretical model in show that electric signal of plasma-induced electric field is resulted from an electric dipole with negative charge in front. It is constructed by electrons and positive ions emitted at early stage of laser ablation. Dependence of electric signal profile on probe distance, laser fluence and pulse number is studied. The electric signal detection can be used to monitor laser removal of metallic oxide layer in real time. Influence of substrate bias on the signal waveform is also analyzed. It may be applied to modify plasma dynamics and laser ablation.
Lasers and Techniques III
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KrF-excimer-laser-induced ohmic metallization of ZnO substrate
Toshimitsu Akane, Koji Sugioka, Katsumi Midorikawa
A non-alloy ohmic contact is fabricate on hydrothermally grown n-type ZnO substrate by KrF excimer laser pre- irradiation and metal deposition. The laser irradiation breaks Zn-O bonding, and turns ZnO surface layer to Zn-rich one which has lower sheet resistance than that of bulk, and has n-type conduction. The Zn-rich pre-metallized layer enables current conducting into ZnO substrate with ohmic characteristics. Au/In/ZnOx and In/ZnOx contact fabricated by single pulse laser irradiation has specific contact resistivity of approximately 7 X 10-1 (Omega) cm2. Deterioration of contact resistance is confirmed after 5 minutes annealing at 300 degrees C in N2, which is originated by re-bonding of Zn-O in laser irradiated area.
Achievements in near-field investigations in Russia (IFMO SPb)
Vadim P. Veiko, Nikolay B. Voznesensky, Tatyana V. Ivanova
Nowadays near-field optics is one of the most attractive area for research, both for theoretical and experimental. Properly in the problem of near-field optics the most important things now are - the creation of more suitable and simpler approach to the description of near-field than MMP method and the creation of new generation of scanning near- field optical instruments (SNOI) such as microscopes, spectroscopes, light generators for lithography, etc. The key of this SNOI generation is a variety of SNOM tips with the higher resolution and transparency and else one what may be even more important, the creation of method for SNOM tips certification. Both of these problems are being investigated in Russia. Short review of other directions for near-field investigation in Russia is also given, including important applications for quantum dots studying and investigation of optical strength of SNOM tips.
Scribing blue LED wafer using laser-induced plasma-assisted ablation with a Q-switched Nd:YAG laser
JongMoo Lee, Jun-Ho Jang, Tae-Kyung Yoo
Transparent materials, such as sapphire, are found to be scribed and cut freely by sparks form metal surface on which q-switched Nd:YAG laser beam is focused through the transparent materials. This method is successfully applied to split each device for a blue LED wafer including about ten thousands of blue LEDs grown on a sapphire wafer.
Laser Microengineering I
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Microfabrication by femtosecond laser irradiation
Hiroaki Misawa, Hong-Bo Sun, Saulius Juodkazis, et al.
Femtosecond (fs) laser microfabrication has been gathering more research interests due to its ability to create micro- and sub-micrometer 3D structures. An extremely high light intensity enables multiphoton absorption in transparent materials, upon which the spatial resolution of fabricated elements is confined to the sizes even smaller than optical diffraction limit. Our report will formulate the principles of the laser microfabrication of such applications. A direct application of single-shot pulse-induced optical damage is a 3D optical memory with a storage density of ca. 100 Gbits/cm2 in silica. Photonic and optoelectronic applications such as optical gratings, 3D inlayed-'atom'- like and 2D cylinder-consisted photonic crystals have been fabricated in silica. Also, photopolymerization of photoresist by a scanning of focal point of laser irradiation solidifies submicrometer rods, which forms photonic lattices when packed into well-defined 3D pattern. Photonic bandgap effects of above-mentioned structures were corroborated by IR Fourier spectroscopy and numerical simulations, by which the success of laser microfabrication was evidenced. Self-focusing of fs-pulses is another possibility of the microstructuring of transparent materials, which is demonstrated in the case of silica. This could find its application in sub-diffraction-limited recording.
Laser micromachining: new developments and applications
Nadeem Hasan Rizvi, David K. Milne, Phil T. Rumsby, et al.
Excimer laser micromachining has developed into a mature production method and many industrial applications such as the drilling of ink-jet printer nozzles, production environments. The important concepts of excimer laser micromachining systems are described and the novel methods which have been developed in this area are presented. In particular, techniques for the production of complex, multi- level 3D microstructures are described and examples of such features are used to illustrate the relevant applications. Furthermore, some initial micromachining result from a sub- nanosecond, solid-state fiber laser are presented to highlight the rapidly-growing area of laser micro processing using ultra-short pulse lasers.
Excimer lamp stereolithography
Saburoh Satoh, Takao Tanaka, Satoshi Ihara, et al.
For the laser stereo-lithography, a XeCl excimer lamp with cylindrical tube has been adopted to achieve a lower cost type UV light source. Because of excellent high output efficiency, it is possible to be down sizing of a power supplier and a lamp head and to be air-cooling. And moreover to extract the maximum output power and efficiency, we applied an optical fiber system for its lithography optics. With this excimer lamp the maximum UV emission per pulse 25 (mu) J at 100 Hz and the maximum average power 10 mW at 1000 Hz were obtained.
Poster Session
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New infrared stereolithography: control of the parameters of the localized curing thermosensitive materials
Marco A. F. Scarparo, Andre L. J. Munhoz, Gilson Marinho, et al.
In normal practice, stereolithography has been used for photosensitive resins where ultraviolet light (HeCd laser λ=O.352μm) initiates the curing process for prototypes construction. In this work we developed a new aspect of stereolithography, using CO2 laser (λ=1O.6μm) in thermosensitive materials where no shrinkage and post-cure treatment was observed. The bulk curing process in resins, epoxy unlike, has been proved useful in a new tethnique for fabrication of prototypes. Control of the laser parameters appears as an important tool for localized cure in the material. Our resin basic sample is composed by the thermosensitive epoxy resin proved to be (in weight) 10 parts, 1,4 parts diethilene triamine (the curing agent) and 0.7 parts silica powder. Silica play an important hole in the curing process Tests with fumed silica and non treated fumed silica showed considerable difference in the obtained final product We also developed a physical and chemical models of the setting process determine the time delay for onset of curing as a function of temperature and the profiles of the isotherms in the sample. In order to model the flow of the heat in laser-induced cunng we used theoretical approach to solve the time dependent heat equation in cylindrical coordinator. The data show the curing rate as function of temperature. Activation energy results were derived from differential scanning calorimetry (d.s.c.).
Laser Microengineering II
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Custom specific fabrication of integrated optical devices by excimer laser ablation of polymers
Thomas Klotzbuecher, Martin Popp, Torsten Braune, et al.
Excimer laser ablation was used for direct writing of multimode waveguide structures with passive fiber alignment grooves in polymers. First, integrated optical multimode components were simulated by the method of beam propagation to optimize the optical performance of the design. Then the CNC codes for laser machining were created directly from the corresponding CAD data. ArF Excimer laser radiation of wavelength (lambda) equals 193 nm was used for ablation of adjacent grooves with a cross sectional area of 50 X 50 micrometers 2 and lengths in the order of several mm. The laser-written grooves were filled with a liquid pre-polymer which after UV-curing served as the waveguiding structures. The smoothest surfaces during laser ablation were achieved by applying several ablation scans with reduced material removal rates but higher feedrates. Debris formation, also influencing the surface roughness, was suppressed or minimized by making use of capable polymers. With the method of laser ablation linear waveguides of length 1 equals 10 mm with insertion losses Li in the rang of 1.3 to 1.9 dB have been realized for (lambda) equals 1310 nm, depending on the polymer used. By means of 1 X 2-splitters, 4 X 4 as well as 4 X 16 starcouplers it was shown that laser ablation is a well suited tool for rapid prototyping of integrated optical multimode elements.
Laser-based microscale bending for microelectronics fabrication
This paper presents experimental and theoretical work on laser-based microscale bending. High precision bending of stainless steel and ceramic specimens is achieved with the use of a pulsed or a CW laser. Experiments are conducted to study the bending behavior of stainless steel and ceramics due to laser irradiation. The amount of bending is correlated with various laser and processing parameters. A theoretical model of the laser bending process is presented base don thermo-elasticity/plasticity. The laser bending process is explained as the result of the laser-induced non- uniform distribution of the residual strain. Numerical simulations are carried out to calculate the laser-induced temperature field, the residual stress field, and the amount of bending for both pulsed and CW laser irradiation. Applications of the laser bending technique in microelectronics fabrication are discussed.
Fabrication of microgrooves with excimer laser ablation techniques for plastic optical fiber array alignment purposes
Kris Naessens, An Van Hove, Thierry Coosemans, et al.
Laser ablation is extremely well suited for rapid prototyping and proves to be a versatile technique delivering high accuracy dimensioning and repeatability of features in a wide diversity of materials. In this paper, we present laser ablation as a fabrication method for micro machining in of arrays consisting of precisely dimensioned U-grooves in dedicated polycarbonate and polymethylmetacrylate plates. The dependency of the performance on various parameters is discussed. The fabricated plates are used to hold optical fibers by means of a UV-curable adhesive. Stacking and gluing of the plates allows the assembly of a 2D connector of plastic optical fibers for short distance optical interconnects.
Spectroscopic investigation of SiO2 surfaces of optical materials for high-power lasers
Stavros G. Demos, Lynn Matthew Sheehan, Mark R. Kozlowski
High quality surfaces of fused silica optical materials were studied using microscopic fluorescence imaging as well as Raman and emission micro-spectroscopy. For as-polished surfaces optically active defect formations were detected on the surface of the material which vary in geometry, relative intensity and concentration depending on the polishing process. A partial correlation of these defects with subsequent laser damage sites was indicated. Following laser-induced damage the Raman and photoluminescence spectra indicated extensive materials modification within the damage sites. Emission spectra show at least three characteristic luminescence bands centered at 1.9 eV, 2.2 eV and approximately 4.7 eV. Raman scattering indicates that laser irradiation leads to compaction.
Laser Microengineering III
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Excimer laser micromachining for fabrication of diamond diffractive optical elements
Vitali I. Konov, V. V. Kononenko, Sergej M. Pimenov, et al.
Results of the development of multilevel diamond diffractive optical elements for high power CO2 lasers are reported. For this purpose, the technique of selected-area laser ablation was applied to create a given phase microrelief on mechanically polished CVD polycrystalline diamond plates. High precision micromachining of the diamond plates was performed using a KrF excimer-laser-based system. The spherical and cylindrical Fresnel lenses with an aperture up to 6 by 6 mm6 were produced and tested with a cw CO2 laser. The diffraction efficiency of the developed DOE measured in the case of the cylindrical lens was found to be only 1-2 percent lower than the theoretical value. Also a diffractive shaper transforming a Gaussian beam of a CO2 laser into a uniformly filled-in rectangle was designed and fabricated.
Microprocessing of glass materials by laser-induced plasma-assisted ablation using nanosecond pulsed lasers
In this paper, we demonstrate formation of micro-grating in fused silica by laser-induced plasma assisted-ablation using different wavelength lasers projected through a metallic mask. With becoming longer wavelengths from 266,532 to 1060nm, the ablation rate of fused silica at 1.5J/cm2 decreases from 21,2 to nm/pulse. While the ablation threshold of laser fluence increases from 0.7, 1.5 to 3.75 J/cm2. The 2.0mm deep through holes in Pyrex glass are drilled by single-beam 532nm-laser ablation. While the same deep through holes in fused quartz are only drilled by double-pulse-train of 532nm-laser ablation with a time-delay of 3.3ns. Finally, the ablation process was analyzed by an in-situ observation of laser-produced plasma, revealing different natures for surface patterning and channel- drilling.
Novel technique for high-quality microstructuring with excimer lasers
Stephan Roth, Manfred Geiger
Laser micromachining has become increasingly established in many microsystem applications during the past years. These new fields occasion higher demands on the quality of micromachiend devices combined with high resolution and working velocity. Due to the disadvantages of conventional excimer laser processing, a novel technique is required to meet these demands. The main problems of conventional excimer laser machining are the redeposition of ablated material on the irradiated work piece and the formation of a strong melting phase especially for metals. These difficulties greatly reduce the applicability of excimer laser material processing for manufacturing microsystems technology components. By applying a thin water film to the substrate surface, the redeposition of ablated material can be completely avoided, which results in a better quality of the microstructures. Usage of a water film, however, has proved to lead to a marked reduction of the ablation rate for the examined materials - ceramics and stainless steel. Therefore, one of the objectives of future research will be to raise the ablation rate in order to render excimer laser processing more interesting economically. Adding alcoholic additives, among others, has improved the wetting of the liquid films on the surface. The effect of the modified chemical composition of the liquid on ablation rate and structure quality for various materials is presented here.
Micromachining by laser ablation of liquid: superheated liquid and phase explosion
Jun Wang, Hiroyuki Niino, Akira Yabe
Transparent materials such as quartz, calcium fluoride and fluoropolymer, are difficult to fabricate by conventional laser processing. We fabricated them successfully with a micro-size by laser ablation of liquid layer attached on the backside of the target. The threshold fluence for etching depends on absorption coefficient of liquid, and thermal properties of target materials. In the further study, we observed the dependency of the etch rate on etch size. The results suggest that the thermal energy diffuses more efficiently when the irradiation area is too small. However, when increase the etch depth to high aspect ratio, in the strong laser fluence, the etch rate becomes faster than that with large irradiation area and low aspect ratio. We discussed that the mechanism is due to the combination of two processes in the interface of a target material and a liquid: one is a heating process by the superheated liquid and the other is an attacking process by high temperature and pressure. We suggested that the temperature of the superheated liquid can exceed the thermodynamic critical temperature Tc upon irradiation at a high laser fluence, and the liquid corresponded to 'transient supercritical fluid'. The generation of super-heated liquid is based on a enormous heat release form organic molecule by a cyclic multiphoton absorption mechanism.
Laser Microengineering IV
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Analysis of excimer laser patterning process of Cu thin film
Tomokazu Sano, Isamu Miyamoto, Hideaki Hayashi, et al.
The front and rear patterning process of metal thin film irradiated by the KrF excimer laser is analyzed in this study. In the font patterning of Cu thin film with a thickness of 0.1-0.6 micrometers on polymer substrate, high speed shadowgraphs were taken by irradiating a SHG YAG laser beam co-axially with the excimer laser beam. At the optimal fluences, the molten film separated along the outer edge of the laser-irradiated region was driven toward the center of the irradiated region by the surface tension force, and the was detached from the substrate as small droplets. No explosive removal was observed in our laser patterning experiment contrary to the case reported in the literature. Under this condition, little change in the reflectivity, approximately 25 percent, was observed during laser irradiation. At the excess fluences, the recoil force of evaporation provided the outward radial flow to extend the patterning zone into the unirradiated zone so that the edge of the unirradiated region was peeled off by the momentum of the metal driven by the recoil force. As a result, the reflectivity decreased drastically in the latter half of laser pulse. In the rear patterning, the feature of the deposited metal on opposite substrate removed from the thin film was observed by an optical microscope. Intensities of incident and transmitted beam were measured simultaneously using PIN-photodiodes. Film removal started after approximately 1/100 of that of the incident beam. In the rear patterning process it was found that the recoil force of the evaporation and plasma expansion generated between the film and the substrate pressed the film subsequently, the molten part at the edge of the unirradiated part was peeled and flied away by the momentum for the recoil force.
Laser beam joining of optical fibers in silicon V-grooves
Stefan Kaufmann, Andreas Otto, Gerhard Luz
The increasing use of optical data transmission systems and the development of new optical components require adjustment-insensitive and reliable joining and assembling techniques. The state of the art includes the utilization of silicon submounts with anisotropically etched V-grooves. Several glass fibers are fixed in these V-grooves with adhesive. Adhesive bonds tend towards degradation under the influence of temperature and moisture. For this reason, the alternative joining processes laser beam welding and laser beam soldering are relevant. The goal is a reliable joining of optical fibers in V-grooves without damage to the fibers or the silicon submount. Because of the anomaly of silicon during phase transformation, a positive joining can be realized by laser beam welding. A melt pool is created through the energy of a Nd:YAG-laser pulse. During solidification, the volume of silicon increases and a bump is formed in the center. Experiments have shown that this phenomenon can be used for joining optical fibers in silicon-V-grooves. With suitable parameters the silicon flows half around the fiber during solidification. For each fiber, several welding points are necessary. Another promising joining method is laser bema soldering. In this case, a second silicon sheet with a solder deposit is placed on the fibers which lie in the V-grooves of the metallized silicon submount. The laser heats the upper silicon until the solder metals by heat conduction.
CO2 laser drilling of printed wiring boards and development of in-process monitoring system
Takayuki Nakayama, Tomokazu Sano, Isamu Miyamoto, et al.
In this paper, CO2 laser drilling process for printed wiring board and the application to the in-process monitoring of the via hole quality are described. The process of CO2 laser drilling was investigated on the basis of high speed photograph, the light emission and thermal conduction. It was found that the temperature of the decomposed epoxy resin suddenly increased when the smear thickness become less than 2μm. Based on this analysis, a simple in-process monitoring technique was developed to estimate the smear feature by detecting the light emission using a photo sensor. The removing process of the smear by KrF excimer laser was also investigated on the basis of the spectrum of the light emission and the reflected excimer laser. The electric contact was accomplished by excimer laser removal the smear.
Poster Session
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Pulsed x-ray emission by laser-plasma-triggered electron beam
Yuzo Nagumo, Shigeki Hayashi, Takashi Yagi, et al.
Pulsed hard X-ray was radiated from the electrode at positive high electric potential, when a laser plasma was created on the grounded electrode positioned a few cm apart from the positively charged electrode. We considered the possibility that electrons extracted from the laser plasma were accelerated and coffided with positively charged electrode, radiating the pulsed X-ray. The dependence of dosage and pulse width of the X-ray on laser pulse energy and on electrode spacing was investigated, and some evidence to describe the X-ray radiation mechanism was obtained.
Light scattering by rough dielectric surface
Vitali E. Gruzdev, Anastasia S. Gruzdeva
Numerical modelling is applied to investigation of scattering of plane linearly polarized monochromatic wave by sine variations of dielectric surface relief. The modelling is based on finite-difference time-domain technique. Results of modelling include 1) space distribution of scattered light, 2) dependence of field amplification on ratio of roughness amplitude to laser wavelength, and 3) dependence of field amplification on ratio of roughness period to laser wavelength. Obtained results show that for TE polarization a) transmitted signal is more sensitive to roughness parameters than reflected one, b) there is narrow resonance in dependence of amplitude of scattered field on laser wavelength and roughness period, c) dependence of amplitude of scattered field on roughness amplitude is described by parabolic function for small values of relief amplitude. Depending on relief amplitude and period, scattering by sine roughness can result in formation of inhomogeneous space field distribution consisting of periodic field maxima inside dielectric or formation of homogeneous distribution such that both transmitted and reflected signals are close to plane wave. We consider the following applications of obtained results: 1) possibility to develop a new technique for in-situ surface roughness charactensation, 2) possible mechanisms of feedbacks during laser-induced formation of surface ripples, and 3) anti-reflection effect.
Capacitive discharge excilamps
Edward A. Sosnin, Mikhail V. Erofeev, Alexei N. Panchenko, et al.
Investigation was made ofthe characteristics ofXeCl (λ ~ 308 nm), KrC1 (λ ~ 222 nm) and Xci (λ ~ 253 nm) capacitive discharge excilamps. High efficiency of exciplex molecules and simple design have been obtained under capacitive HF discharge excitation. Cylindrical excilamps with radiation output through side surface ofthe cylinder and through one or two windows placed on the tube ends have been developed. High UV radiation power and electrical power deposition to fluorescence conversion resulted in efficiencies of up to 12%. The study of XeC1, KrCl and XeI excilamps have shown, that it is possible to create sealed-off samples with lifetime more than 1000 hours. The stability of output parameters ofthe capacitive discharge excilamps is studied and the mechanism of chlorine losses in low pressure halogencontaimng excilamps made of quartz was determined. The possibility of creation of capacitive discharge excilamps with short pulse duration was studied. In capacitive discharge cylindrical KrClexcilamp, at λ~222 nm the radiation pulse power up to 2.5 kW was obtained. Powerful radiation pulses 50 ns in duration were obtained at pulse repetition rate of 1 kHz.
Optimization of nanosecond UV laser illumination for semiconductor materials (Si, HgCdTe, InSb)
Andrew R. Novoselov, Anatoly G. Klimenko, Evgeny V. Fedosenko, et al.
We studied stages of formation of laser craters for the purpose of decreasing a defeat zone of a semiconductor material close to laser craters. The researches were carried out using SEM and optical microscopy. This paper is devoted to results of optimization of the laser radiation for applications in microelectronics. The principles of optimization of a wavelength, pulse duration and repetition frequency of laser radiation are determined. The effect of the diameter of a laser spot onto the process of formation of a laser crater is shown. It is opinion of the authors, that the main criteria that necessarily should be taken into account when doing the laser scribing of semiconductor wafers, are as follows: Selection of a laser source wavelength with maximum coefficient of absorption in a target. The energy density in a laser spot on target must be less than threshold for the material; The time gap between pulses is determined by time of the ending of processes in the material ofthe target. The decrease in diameter of a laser beam allows maximum depth to diameter relation to be achieved.
Reprography method of nondestructive testing of micro-cracks inside the wall of a pinhole micromanufactured by laser
Chenbo Zhou, Wenying Yu, Jinzuo Sun, et al.
A new method of reprography and detection employing scan electron microscope (SEM) for the non-destructive testing the micro-cracks with width about 1 μm on the inner surface of the pinhole has been presented in this paper. The results show that the new method is a feasible approach to test the micro-cracks of the inner surface of the pinhole with sub-millimeter aperture.
Model predicting the microhole profiles of laser drilling processes in carbon fiber composites
Frank F. Wu, Richard D. Pilkington
Laser induced ablation of materials has became an extremely important area of research and application. The laser sources for ablation cover the wavelengths from ultraviolet (most are excimer lasers), visible (copper vapor lasers, argon ion lasers) to the infrared (Nd:YAG lasers, CO2 lasers). The laser material processing technique is intensely used in both the electronic and aerospace industries. In this paper, a new theoretical model describing laser microhole drilling processes in carbon fiber composites (CFC) has been developed, which can predict the profiles ofthe microholes for certain incident beam profiles. The calculated results for several specific incident beams will be presented in this paper. We show how the peak fluence, the beam diameter, and the material parameters (absorption coefficient, threshold ablation fluence) affect the hole shapes. Although the model is specific to CFC, it can be applied to any other laser micromachining process for materials such as polyimide, polymethylmethacrylate (PMMA), polyethylene terephthalate (PET) etc. We not only present a new method to model the drilling hole profiles but also explain why hole drilling will stop under certain circumstances in the low fluence regime for polymers and fiber reinforced composites. The model explains tapered wall formation and stabilized drilling, from which, high efficient laser drilling and cutting can be predicted in low fluence regimes. This new model is suitable for most well defined beams and materials such as polymers, fiber CFC, glass fiber composites and some ceramics.
Microscopic observation of laser-induced forward transfer process by two-dimensional laser-induced fluorescence technique
Yoshiki Nakata, Tatsuo Okada, Mitsuo Maeda
The behaviors of atomic particles and droplets in laser-induced forward transfer (LIFT) process were observed by two-dimensional laser-induced fluorescence (2D-LIF) technique and by thermal emission detection. The behavior of the ejected particles in gas phase was observed with different parameters such as ablation laser energy, film thickness, gas pressure. The interaction of the particles with substrate was also observed.
Ion-source-assisted pulsed-laser deposition of carbon nitride thin films
Z. F. He, Yongfeng Lu, ZhiHong Mai, et al.
Ion source assisted pulsed laser deposition has been used to synthesize carbon nitride thin films. This synthesis method has both advantages of pulsed laser deposition (PLD) and ion implantation. The average ion beam current, the beam voltage, the laser pulse energy, and substrate temperature can be controlled systematically. Scanning tunneling microscopy (STM) has been used to study the surface properties. The (dI/dV)/(I/V) values have been calculated to study the local density of states (LDOS) on the film surface. Experiment results have been analyzed by Raman spectra to see the influence of the substrate temperature. Thin films CNx with nitrogen content of 32% have been investigated by X-ray photoelectron spectroscopy (XPS). The results can reveal the formation of different bonds. Fourier transform infrared spectra (FTIR) was also used to study the bonding of films. The hardness of the synthesized thin film was analyzed by a nanoindentor. The result shows that the carbon nitride films have high hardness.
Pulsed-laser deposition of hydrogenated amorphous carbon films from a polymeric target
The phenylcarbyne polymer possesses a diamond-like structure. Because of its special structure, this polymer can be converted into diamond-like carbon phases at atmospheric pressure by thennal decomposition. In this article, we report on the growth of hydrogenated amoiphous carbon films (a-C:H) films by pulsed laser (KrF excimer, λ =248 mn) ablation of a phenylcarbyne polymer target under vacuum. a-C:H films were deposited with various laser fluences and at different substrate temperatures. Chemical and siructural characteristics of these films were analysed using X-ray-excited Auger electron spectroscopy (XAES), photoelectron loss spectroscopy (PELS), and Ranian speciroscopy. It was found that the fourfold-coordinated component increases with laser fluence at 80°C or increases with temperature increasing from 25°C to 60°C at a fluence of 1 x 1O9cm2. When the deposition temperature is increased from 60°C to 200°C at a fluence of 1 x 109 W/cm2, the graphitic component increases. The variation in chemical structures of these films is explained in terms of the changes in the fraction of sp2-bonded clusters and changes in the termination of the gmphitic clusters and sp3-bonded networks by hydrogen in the a-C:H films.
Preparation of polyperinaphthalenic organic semiconductor thin films by excimer laser ablation and application to anode electrodes for ultrathin rechargable lithium ion batteries
Satoru Nishio, Sigenori Kuriki, Yukari Tsujine, et al.
Amorphous organic semiconductor thin films are prepared on temperature-controlled substrates by excimer laser ablation (ELA) of 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA) or PTCDA/Co mixture target with a 308(XeCl) pulsed excimer laser beam. Drastic increase in conductivity was observed along with decrease in the IR peak intensities related to the side groups of PTCDA monomers for films prepared on substrates above 200°C. Electric conductivity of a film prepared on a substrate at 300°C comes up to 10-1Scm-1. Although carbon radicals are detected to some extent, indicating incomplete polymerization. Raman spectroscopic measurement reveals that this film basically consists of polyperinaphthalene (PPN) structure. This material is named polyperinaphthlenic organic semiconductor (PPNOS). ELA of mixture target of PTCDA and Co enables us to obtain PPNOS at room temperature. Electrochemical doping of PPNOS films with lithium ion suggests the passable performance of this film as anode electrodes of ultra thin rechargeable lithium ion batteries.
Novel thin-film deposition method and system with IR-FEL
Masato Yasumoto, Norimasa Umesaki, Takio Tomimasu, et al.
We propose a novel method for thin film deposition with an IR-FEL using the IR-FEL wavelength tunability in infrared region. This is an unique method in which only the vapor deposition molecule is activated by applying laser of vibrational excitation wavelength of the vapor deposition molecule on the substrate surface, when the thin film intends to deposit on the substrate. We developed two equipments in order to realize and evaluate the new method. One is IR-FEL assisted RF sputter deposition chamber system, the other is IR-FEL assisted laser ablation chamber system. Moreover using the former equipment, we carry out the preliminary experiment on the preparation of ITO (In-Sn-O) thin film.
Structure and properties of porous PZT ceramics synthesized by selective laser sintering method
Ekaterina Yu. Tarasova, Galina V. Kryukova, Alexei L. Petrov, et al.
A method of layer by layer selective laser sintering is prosed to synthesize structural piezoelectric elements out of PZT ceramics. The dependence of density of sintered elements on the regimes of sintering was investigated. X-ray diffraction and x-ray phase analysis were performed. It is shown that phase content and lattice structure had changed as a result of laser treatment.
Selectively deposited copper on laser-treated polyimide using electroless plating
Gang Zhao, Harvey M. Phillips, HongYu Zheng, et al.
Many reviews about the interconnection line fabrication by laser processing method were reported recently. UV laser process polyimide has been studied thoroughly during the past decade. In this report, we discussed the utilization of surface potential changing on polyimide film irradiated by excimer KrF laser and metallized the UV laser treated polyimide surface by electroless copper deposition. A new negatively charged polymer stabilized Pd solution was applied as catalyst in this experiment. We also produced pattern-wised fine line on KrF laser induced PI surface using this method.
Laser Microengineering IV
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High-accuracy microdrilling of steel with solid state UV laser at a rate of 10 mm/sec
We investigated wavelength- and intensity-dependence of ablation rate achievable with a diode-pumped Q-switched Nd:YAG laser with frequency doubling and tripling. The laser produced 15 ns-long pulses at a repetition rate of 10 kHz and output power of 28 W in the fundamental beam, and 15 W and 10 W in the second and third harmonics, respectively. We found that in thin stainless and carbon steel foils, fast ablation starts at the laser fluence level of 10 J/cm2. The ablation rate remains close to 1 micrometers per pulse with very little change as the laser fluence increases by more than order of magnitude above this threshold exit of the hole. This attenuation is strongly dependent on the laser wavelength. Particularly, using third harmonic output, we were able to sustain average drilling speed of more than 1 micrometers per pulse in samples up to 1 mm thick. At the same time, removal rate at fundamental wavelength decreased by almost an order of magnitude.
Laser Microengineering I
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Femtosecond pulse laser machining of InP wafers
Jerzy M. Wrobel, Joern Bonse, Joerg Krueger, et al.
Ablation of indium phosphide wafers in air was performed with 130 fs laser pulses at a wavelength of 800 nm at a low repetition rate of 10 Hz. In order to evaluate the role of the incubation effects, the relationship between the number of laser pulses used for the ablation and the threshold fluence was studied. Particular attention was paid to the chemical composition, surface morphology and structural variations of the ablated area.