The Effects of Collimator Life Time on the Ti and Tin Film Growth Rates and Conformalities in Sputter Deposition Process
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Hung Liao, Hannes Stippel*, Krishna Reddy*, Sam Geha*, Kevin Brown*, Philipp Lindorfer*, Samar Saha*, Zhou Lin, and Timothy Cale Center for Solid State Electronics Research, Arizona State University, Tempe, AZ 85287 *National Semiconductor Corp., Santa Clara, CA 95052
ABSTRACT Experimental and simulation studies were conducted in an attempt to understand the effects of collimator life time on the Ti and TiN film growth rates and conformalities in sputter deposition processes. The Ti and TiN films were deposited with and without collimation. The hexagonal cells of the collimator used in this study have a 1:1 aspect ratio. A Monte Carlo based simulator was used to calculate the angular distributions of species exiting from a collimator cell and the percentage decrease in the rate of film growth as a function of the collimator life time. Then, a low pressure deposition process simulator, EVOLVE, was used to predict the conformalities of deposited films in contacts or vias, assuming that the films were uniformly deposited on the side-walls of collimator cells. We conclude that the loss in growth rate is largely due to the shrinkage in the cross sectional area of the collimator cell inlets. We arrive at this conclusion after comparing an estimated film thickness on the collimator side-walls with experimental measurements. With extended collimator usage, the predicted and experimental film profiles in contacts or vias show increasing bottom coverage and decreasing side-wall coverages. INTRODUCTION Collimated sputter deposition is widely used to improve step coverage of sputter deposited films [1,2]. Liu et al. [3] combined experiments and simulations to study collimated sputter deposition of Ti and Al thin films. Toprac et al. [4] compared the predictions of EVOLVE [5], and experimental film thicknesses as a function of position inside contact structures for uncollimated and collimated TiN PVD. Their results show that collimated sputter systems provide enhanced bottom coverage by restricting the off-axis molecules from reaching the wafer surface. However, the filtered material deposits on the collimator side-walls, shrinks the collimator cells, and increases the effective aspect ratio of the collimator. In this work, we combine experiments and simulations to study the effects of film growth (collimator life time/extended usage) on collimator cell side walls on deposited Ti and TiN film growth rates and conformalities on the wafer surfaces. We assume that the pressure is low enough that the transport inside the collimator cells and from the collimator exit to the wafer surface is free molecular flow; i.e., there are no gas phase molecule-molecule collisions, and assume that the films uniformly grow on the collimator cell side-walls. The flux distributions at the exit of collimator cells are predicted using Monte Carlo simulations of transport through collimator cells. We first estimate the sticking factor and the parameter of the generalized cosine 263 Mat. Res. Soc. Symp. Proc. Vol. 389 0 1995 Materials Research Society
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