Tommaso Sgrilli, Joseph Brindley, Benoit Daniel, Victor Bellido-Gonzalez, Dermot Monaghan, Gencoa Limited, Liverpool, United Kingdom
Developments in reactive magnetron sputtering processes have unlocked great possibilities in controlling film stoichiometry and physical properties. For some material/reactive gas combinations, it is crucial that the reactive gas flow is regulated via a closed-loop feedback system, able to capture the system status and adjust the reactive gas input at any given time. In this context, the deposition of consistent and reproducible film properties relies as well on the selection of one or more quick responding sensors that can provide relevant information on the nature of the material being deposited. Examples of these sensors include direct plasma measurements, such as plasma emission intensities, electron temperature and plasma frequencies, or indirect system measurements, such as reactive gas partial pressure and sputtering target voltage.
Having the flexibility to choose a sensor that will enable the best cost to performance formula is a primary concern.
In this work we present a new feedback control platform to sense and control any form of reactive sputtering process. The system can use upto 16 different sensor inputs and outputs in a ‘plug and play’ arrangement. Despite the high number of simultaneous control loops, the speed of signal acquisition to gas value ‘feedback’ is within 1 msec.
The flexibility to easily ‘switch’ sensor type to enact the process feedback control, allows the optimum solution to be arrived at as quickly as possible and at the lowest cost. The sensor types available vary from:
• ‘In-situ’ or ‘remote’ plasma emission via either a standard or high sensitivity HS spectrometer
• 'In-situ’ or ‘remote’ plasma emission via an optical narrow bandpass filter and photomultiplier
• Sputter target voltage from the magnetron source power supply
• Partial pressure signal of oxygen from a Lambda type of process sensor
Typically, an optimum control strategy might require multiple sensor signals to be combined as the input to the feedback control algorithm controlling a reactive sputtering zone. This signal ratioing can be performed within a msec based upon the new control architecture. Whilst the system sensing and control hardware is more sophisticated, a built-in auto tuner ensures simple operator interface.
The process control benefits of this new control platform for reactive sputtering will be presented.