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A second hysteresis effect of reactive magnetron sputtering in compound mode

: Pflug, A.; Siemers, M.; Szyszka, B.; Severin, D.

Society of Vacuum Coaters -SVC-, Albuquerque/NM:
Society of Vacuum Coaters. 49th Annual Technical Conference 2006. Proceedings : April 22 - 27, 2006, Washington, D.C. USA
Albuquerque: SVC, 2006
Society of Vacuum Coaters (Annual Technical Conference) <49, 2006, Washington/DC>
Fraunhofer IST ()

An improved theoretical understanding of the reactive magnetron sputtering process is mandatory for future advancement of high-precision film homogeneity control and advanced process stabilization within this technology. Reactive sputtering experiments reveal a non-monotonic behavior of the target voltage with respect to reactive gas flow as well as sometimes a non-linear process response upon modulation of external process parameters. Such behavior can not be obtained in a simulation model with a simplified target poisoning model which only considers oxidation of the first atomic layer.
This work introduces a reactive sputtering model, where the mechanism of target poisoning is assumed to involve two layers, whereof the first layer can react with non-ionized reactive gas via chemisorption, while ionized reactive gas is implanted into the second layer. Both layers can be either metallic or oxidized. Via combination, this yields a total of four different target states, which can be characterized by four different sputtering yields and secondary electron emission coefficients.
We present a parameter set by which a series of experimentally obtained voltage and deposition rate characteristics of the reactive HfO2 process can be almost completely described within this new model.
Recently, we have presented a work on modeling the film thickness profile on a moving substrate which is deposited via a reactive in-line sputtering process in compound mode. The substrate movement led to pressure fluctuations resulting in a varying deposition rate. While for certain process conditions, it was possible to describe the measured film thickness profile with a simulation model based solely on chemisorption at the target surface, we also encountered situations, where the reactive in-line deposition process showed a "second hysteresis" behavior in compund mode, which could not be explained, yet.
It terms of the new two-layer model of the target, it appears that this non-linear process response could be attributet to a temporarily increased deposition rate for intermediate oxidation states.