On - and Off -AXIS Large-Area Pulsed Laser Deposition
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INTRODUCTION Over the past few years Pulsed Laser Deposition (PLD) has become a popular technique for the deposition of a wide variety of thin films, and PLD systems are currently found in numerous industrial, government, university, and military laboratories. At present, it is estimated that well over 200 different materials have been deposited by PLD and the list keeps growing. However, even with all the interest in laser deposition the technique has not yet emerged as an industrial process. At the moment, industry still prefers standard thin film growth techniques such as magnetron and ion beam sputtering, chemical vapor deposition, and electron beam evaporation for production applications. These processes have been in use for decades and have demonstrated the ability to deposit films of most materials over large areas with excellent uniformity at reasonable cost and deposition rates. Furthermore, an entire infrastructure has been built up to support these processes including standardization of deposition rate monitors, power sources, target and crucible sizes, etc. On the other hand, laser-deposition is still an emerging technology, and relatively little infrastructure exists to adequately support either research or industrial applications. Since there are several materials which are difficult if not impossible to grow in thin-film form by more conventional techniques, it is expected that as pulsed laser-deposition matures this unique process will take its rightful place on the manufacturing line. This paper will focus on some of the scale-up issues relating to PLD, and the results presented will demonstrate that large-area laser deposition utilizing laser-beam rastering over large diameter targets is capable of depositing films with uniform properties on substrate sizes which are compatible with today's mainstream semiconductor process lines. Thus, the most relevant issue for the PLD process at present is the elimination of the particulates typically found in laser-deposited films. These particles are characterized by the so-called Normalized Particle Density (NPD) expressed as the number of particles per square centimeter per angstrom of film, and can vary by several orders of magnitude depending on target material, target density, grain size, on-target laser fluence, and other process parameters [ 1]. Recently "off-axis" PLD has become a popular way to deposit films with reported low NPD's [2,3]. Issues relevant to the scaling-up of off-axis PLD process will be examined, and the properties of films grown by both on- and off-axis PLD will be compared.
MATERIALS AND METHODS A variety of PLD techniques have been used to deposit films over substrates of at least 75 mm (3-inch) in diameter including Off-Set [4,5] and Rotational/Translational PLD [6,7]. The alternative large-area approach, which utilizes laser beam rastering over large diameter targets has been scaled to 125 mm (5-inch) [8] and more recently 150 mm (6-inch) diameter substrates [9]. Laser beam rastering offers advantages over these other "fixed be
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