Deposition Rate Monitoring using Laser Induced Fluorescence
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DEPOSITION RATE MONITORING USING LASER INDUCED FLUORESCENCE TIMOTHY C. REILEY, ERNESTO E. MARINERO, HARRIS NOTARYS IBM-Almaden Research Center, 650 Harry Road, San Jose, CA 95120 ABSTRACT Ultra thin films (< 10 nm) prepared using sputtering or other deposition techniques are becoming more technologically important, with promise of increased importance in the future, particularly in certain magnetic structures. For example, giant-magnetoresistive structures may incorporate individual layers having a thickness < I rim. Such a small thickness is commonly associated with relatively short deposition times (-10 s) and may place limits on the reproducibility and accuracy of the conventional techniques for in situ thickness monitoring or integrated rate monitoring. Experiments have been performed to use laser induced fluorescence (LIF) as a rate monitoring technique for ultra thin films. An RF diode sputtering system was combined with a YAG-pumped, frequency-doubled dye laser to monitor the deposition rate of copper over a range of conditions. When coupled with an absolute calibration reference, the LIF signal gave a reproducible, well-behaved output over a range of pressure and temperature. The technique is potentially advantageous for depositions where rapid (-I1 s) measurements are needed. LIF is also projected to be a valuable tool for detecting very low deposition rates, and it offers the potential of sensitive, real time, spatially-resolved detection in time regimes extending to the nanosecond regime. INTRODUCTION Recently, considerable attention has been directed at magnetic structures exhibiting the so-called Giant Magnetoresistive (MR) effect. These structures contain ultra-thin, metallic magnetic layers which, upon the application of an externally-applied magnetic field, cause substantial overall resistance changes [1-3]. Some of these structures incorporate layers having a thickness -.1 nm. An immediate application of such structures is to provide increased sensitivity for detecting magnetic transitions in magnetic storage data. One problem that is briefly considered here, is the means by which the material deposition process is monitored to ensure reproducibility and accuracy of such thin layers. DEPOSITION RATE MONITORING TECHNIQUES Means of monitoring the rate of material deposition have been developed over the last several decades, with the primary manufacturing reliance being on time/deposition power relationships and on quartz microbalance techniques. The former relies on the stability of a well-characterized deposition tool and its consistency with respect to periodic calibrations. The second relies on the deposition of material on a vibrating quartz disk, whose resonant frequency is dependent on the mass deposited thereon. Both are capable of extremely precise deposition thickness measurements. A new regime of thin film deposition requirements has been recently entered, based on magnetic structures containing individual layers of thicknesses on the order of a few atoms. It appears that new means of depos
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