This page intentionally left blank Transport in Laser Microfabrication Emphasizing the fundamentals of transport phenomena, this book provides researchers and practitioners with the technical background they need to understand laserinduced microfabrication and materials processing at small scales It clarifies the laser materials coupling mechanisms, and discusses the nanoscale confined laser interactions that constitute powerful tools for top-down nanomanufacturing In addition to analyzing key and emerging applications for modern technology, with particular emphasis on electronics, advanced topics such as the use of lasers for nanoprocessing and nanomachining, the interaction with polymer materials, nanoparticles and clusters, and the processing of thin films are also covered Costas P Grigoropoulos is a Professor in the Department of Mechanical Engineering at the University of California, Berkeley His research interests are in laser materials processing, manufacturing of flexible electronics and energy devices, laser interactions with biological materials, microscale and nanoscale fluidics, and energy transport Transport in Laser Microfabrication: Fundamentals and Applications COSTAS P GRIGOROPOULOS University of California, Berkeley CAMBRIDGE UNIVERSITY PRESS Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, São Paulo, Delhi, Dubai, Tokyo Cambridge University Press The Edinburgh Building, Cambridge CB2 8RU, UK Published in the United States of America by Cambridge University Press, New York www.cambridge.org Information on this title: www.cambridge.org/9780521821728 © C Grigoropoulos 2009 This publication is in copyright Subject to statutory exception and to the provision of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press First published in print format 2009 ISBN-13 978-0-511-59515-8 eBook (EBL) ISBN-13 978-0-521-82172-8 Hardback Cambridge University Press has no responsibility for the persistence or accuracy of urls for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate To Mary, Vassiliki, and Alexandra Contents Preface Fundamentals of laser energy absorption 1.1 1.2 1 21 32 Lasers and optics 33 2.1 2.2 2.3 2.4 2.5 2.6 33 36 39 48 50 51 57 Lasers for materials processing Some specific laser systems Basic principles of laser operation Definition of laser intensity and fluence variables Optical components Beam delivery References Thermal processes in laser–materials interactions 60 3.1 3.2 3.3 3.4 60 61 72 75 84 Macroscopic transport Conductive heat transfer Melting Ablative material removal References Desorption at low laser energy densities 4.1 4.2 4.3 Classical electromagnetic-theory concepts Optical properties of materials References page xi Vapor kinetics Time-of-flight instruments Kinetic distributions of ejected particles References 87 87 90 96 107 Dynamics of laser ablation 109 5.1 5.2 109 111 Introduction Laser-induced plasma formation viii Contents 5.3 5.4 5.5 146 6.1 6.2 6.3 146 147 6.5 6.6 6.7 6.8 7.2 7.3 7.4 7.5 7.6 7.7 Introduction Femtosecond-laser interaction with metals Femtosecond-laser interaction with semiconductor materials Phase transformations induced by femtosecond laser irradiation Generation of highly energetic particles Ultrafast phase explosion Nonlinear absorption and breakdown in dielectric materials Application in the micromachining of glass References Laser processing of thin semiconductor films 7.1 116 122 133 141 Ultrafast-laser interactions with materials 6.4 Modeling of ablation-plume propagation Diagnostics of laser-ablated plumes Picosecond-laser plasmas References Modeling of energy absorption and heat transfer in pulsed-laser irradiation of thin semitransparent films Continuous-wave (CW) laser annealing Inhomogeneous semiconductor-film melting Nanosecond-laser-induced temperature fields in melting and resolidification of silicon thin films Nucleation in the supercooled liquid Lateral crystal growth induced by spatially modified irradiation Mass transfer and shallow doping References 158 160 168 172 176 195 196 202 202 203 205 209 217 222 231 235 Laser-induced surface modification 240 8.1 8.2 8.3 240 245 256 263 Hydrodynamic stability of transient melts Capillary-driven flow Glass-surface modification References Laser processing of organic materials 265 9.1 9.2 9.3 265 265 273 278 Introduction Fundamental processes Applications References