INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING Vol. 13, No. 5, pp. 641-648 MAY 2012 / 641 DOI: 10.1007/s12541-012-0083-6 NOMENCLATURE l T = thermal diffusion length D = heat diffusivity τ l = diffusion time 1. Introduction The micro-machining of silicon components for use in the MEMS fabrication and microelectronics industry is well-established and the demand for semiconductors started to recover after the 2008 downturn. Laser micro-drilled interconnect via holes is an application that has been applied in high volume manufacturing since 1995. In 2006, the laser held 70% of the microvia market because of its broad processing capabilities with a wide range of materials. 1 The common chip interconnect packaging consists of a multilevel structure of fine wiring, 2 where different layers are electrically connected through metalized microvias of sub 100 μm diameters, which are also used to connect both sides of silicon wafer. 3 The photovoltaic (PV) industry has experienced enormous growth over last few years, and it forecasts to grow to $100 billion between 2008 and 2013 (Lux Research, NY). As the most important material, c-Silicon has 77% of market share of world production of solar cells. 4 Additionally, many novel high efficiency solar cell concepts (Emitter Wrap Through & Metal Wrap Through) are only feasible with laser technology, since it satisfies the requirement of drilling a few thousand holes (50-100 μm in diameter) per second in c-Si. The state of the art for Si micro-drilling and micro-machining is the Q-switched Diode Pumped Solid State (DPSS) UV laser. 5,6 A wavelength less than 532 nm has advantages of higher absorption coefficients, shorter optical penetration depths, less plasma absorption 7 and smaller focal spot diameters. One could say that the laser industry has already approached the best Si machining output with DPSS UV laser systems using rods or discs as the gain medium. In order to achieve higher levels of power rating, beam quality, and wall plug efficiency, manufacturers are forced to deal with increasingly complex designs. Stable resonators, pump energy delivery and thermal management offer considerable challenges during scale-up. Recent advances in source technology have produced fiber laser architectures that offer a highly competitive technology platform with improved operational performance compared to existing laser systems. Fibre Laser Microvia Drilling and Ablation of Si with Tuneable Pulse Shapes Kun Li 1,# and William O’Neill 1 1 Institute for Manufacturing, Department of Engineering, University of Cambridge, Cambridge, CB3 0FS, UK # Corresponding Author / E-mail: kl330@cam.ac.uk, TEL: +44-1223-764622, FAX: +44-1223-464217 KEYWORDS: Drilling, Fibre laser, Pulse profile, Silicon The dramatic increase in hole quality on single crystalline silicon with an 1 µm fibre laser has been reported recently, it redefines the processing options for Si at that wavelength. This study investigated the effects of the MOPA based pulse tuning on the changes of the machined depth and the mass removal mechanism for the generation of microvia holes. Hole depths were measured and surface morphology studied using SEM and optical interferometric profilometry. The pulse peak power was found to strongly influence the material removal mechanism with fixed pulse duration. High peak powers (>1 kW) gave vaporisation dominated ablation, left a limited resolidified molten layer and clean hole formation. The pulse duration was found to strongly influence the machined depth. Longer pulse durations generated deeper holes with constant peak power (>1 kW). In comparison with the DPSS UV laser, the IR fibre laser of longer pulse durations machined deeper holes and generated less resolidifed melt beyond the hole rim at high fluencies. The comparison suggests that some applications (microvia drilling) of the DPSS UV laser can be replaced with the more flexible, low cost IR fibre laser. Manuscript received: November 19, 2010 / Accepted: December 22, 2011 © KSPE and Springer 2012