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The crystallographic orientation of aluminum and titanium planar sputtering targets is shown to influence via bottomcoverage and collimation efficiency. A model is developed for predicting the transmission of sputtered atoms through acollimator, based on the measured crystallographic orientation distribution function (ODF). Experimental sputtering resultsare found to agree with the simulation results. Monte Carlo simulation of step coverage is performed using the angularlyresolved sputtering yields derived from the ODF. Improvements in via bottom coverage, greater than 100% (relative), areobserved for different crystallographic orientations. The combined effects of crystallographic orientation, target erosionprofile, and gas pressure are discussed.Keywords: sputtering target, crystallographic orientation, angular emission, collimation, step coverage, via fill, filmuniformity 1. INTRODUCTION1.1 Motivation behind this investigation The high packing density and complexity of modem integrated circuit manufacturing has increased the requirements onmetal deposition processes. Narrow contact holes (vias) are difficult to fill with sputter deposited metal, for barrier layer or"reflow wetting" layer creation. Techniques such as collimated sputtering, or long throw sputtering, have been utilized toimprove the step coverage of high aspect ratio vias. Conversely, a recent application requires poor step coverage duringsputtering so as to close off the via opening, leaving a void inside.1 In this case a high pressure process is used to extrude thePVD metal into the via, after deposition. Such deviations from conventional PVD require sputtering targets with atypicalmicrosiructure for performance optimization. Film thickness uniformity requirements across 200mm wafers place additionalrequirements on target microstructure. A marriage of PVD system design with target microsiructure is required to get the bestmix of step coverage and film uniformity.The ability to predict the performance of a sputtering target, based on its microstructure, is valuable for target and systemdesign. This investigation focuses on the effect of target crystallographic texture on the angularly resolved sputtering yield.This in turn can influence parameters such as via step coverage, efficiency of collimated sputtering processes, and filmuniformity. A model is developed which predicts these performance parameters, based on the target's measuredcrystallographic texture. |
