6 June 2013
Welcome to the June edition of the Gencoa newsletter.
April and May saw the Gencoa team participating at conferences and exhibitions in USA and China. The Gencoa team are soon to be busy exhibiting again, and will be present at the following exhibitions and trade shows:
June 12: IOP Plasmas, Surfaces and Thin Films London, UK
July 10-12: ISSP 2013 Kyoto, Japan
August 21-23: Guangzhou International Vacuum Industrial Show Guangzhou, China
August 25-30: AEPSE 2013 Jeju, Korea (in association with KCMC)
In the first of a new series of Gencoa technical papers, this month's focus is on how control of reactive sputtering processes can lead to a more consistent deposition rate and controlled uniformity. A summary of the paper can be read below, with the full PDF document available to download from the Technical Papers section of our website, or by clicking the following link: Gencoa technical paper, June 2013.
Feedback control of reactive gas enables improved deposition rates, coating properties and process reliability, which is not possible to achieve with constant flow.
With most reactive sputtering processes proving to be highly unstable, there are two available solutions; using the target in fully poisoned mode, or to use a feedback control system.
The latter option provides a better solution and can ensure that the reactive gas flow is quickly adjusted in response to the plasma conditions, in order to maintain high coating rates.
Coating rates at different sensor setpoints for SiOx. 'A' denotes reactive rates; 'B' denotes contant flow rate.
Of great importance for many coatings is the uniformity of deposition over the substrate area.
This is a challenge for systems with large target areas, and multiple gas injection zones are required across the target length to shape the deposition profile.
With multiple zones comes increased control complexity and more control options. The complexity arises from the interaction between the zones; a control action on one zone will have an effect on the control dynamics of neighbouring zones.
Two main modes of control can be used when controlling multiple zones; individual feedback control of each zone, or a master/slave principal.
The flexibility of the Speedflo controller allows for up to eight simultaneous feedback control loops and any combination of master/slave operation to suit every possible system configuration.
Schematic illustrating master/slave control principal
Finding the right gains for a reactive gas control system can be difficult as they are a factor of many variables.
An understanding of the cause and effect relationships between the controller gains and the controlled system dynamics is critical for the controller to be tuned efficiently.
Whilst a model of the system that can be used for designing controller gains is currently out of reach, it is possible to create a generic model of a reactive sputtering process by analysing actuator and sensor data.
Using this proprietory model, Gencoa has developed a simulation of the Speedflo controlled sputtering system to provide the user with "virtual" experience of control system tuning.
The Speedflo Simulator package provides a complete real-time simulation of the actual Speedflo interface and includes almost all features found in the real system.
Comparison of simulation data (red) and real data (green). Real actuator data (blue) was fed into the simulation and compared with the corresponding sensor data.
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