AVS 50th International Symposium
    Vacuum Technology Wednesday Sessions
       Session VT-WeM

Paper VT-WeM7
Advanced Closed Loop Control Method and Sensor for a Reactive Sputtering Drum Coater

Wednesday, November 5, 2003, 10:20 am, Room 323

Session: Dynamic Vacuum Systems
Presenter: M.A. George, Deposition Sciences, Inc.
Authors: M.A. George, Deposition Sciences, Inc.
E.A. Craves, Deposition Sciences, Inc.
R. Shehab, Ametek, Inc.
K. Knox, Ametek, Inc.
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The reactive sputtering process is characterized by a hysteresis of reactive gas concentration and reactive gas flow.@footnote 1,2@ The precise control of the reactive sputtering process requires operating at a points on the hysteresis that ensures the desired high sputter flux and deposited thin film stoichiometry. The hysteresis is highly non-linear in these preferred operating regimes. The practical challenge of meeting this in the batch coating system requires a control system that can compensate for changes in reaction rate for various sputtered metals, system pumping speed changing with thermal variations and dynamic compensation of detrimental periodic cathode arcs. Closed loop control algorithms that rapidly bring the reactive sputtering system to the desired hysteresis steady state operating point are desired for multi-layer applications such as thin film interference filters that require many target starts (and stops). Conventional methods of starting the reactive sputtering process such as temporally ramping target power, voltage or current and target shutters are undesirable for precision thin film interference filters We will present control system hardware and closed loop control algorithms that permit the achievement of steady state operating points in less than 500 milliseconds on several different reactive sputtering drum coaters. The key feature of the hardware and control algorithms employed on these drum coaters is the determinism required for successful operation. We will discuss the reactive gas sensor and the algorithms employed for ensuring a temporally accurate signal of reactive gas concentration and the closed loop control method using this signal as an integral part of the loop. @FootnoteText@ @footnote 1@S. Schiller, U. Hesig, G. Beister, K. Steinfelder, J. Strumpfel, Chr. Kondorfer, and W. Sieber, Thin Solid Films, 118(1984), pp 255-270. @footnote 2@J. Affinito and R.R. Parsons, J. Vac. Sci. Technol. A, Vol. 2, No. 3, pp 1275-1284.