Advanced reactive Sputter gas controller
Plasma Emission Monitor

speedflo™ is a multi-channel closed loop control system for high speed adjustment of a reactive gas for magnetron sputter processes. It is an advanced direct digital control system which is adaptive to flow requirements and has many advantages over analog PID based solutions. It has a PC networked set-up and monitoring program, but the control algorithm is 'nested' in a stand-alone control box located near to the process chamber.

Sensor Head Options Supplied by Gencoa: PEM (narrow band-pass filter) PEM (CCD type spectrometer) Target voltage cables (to power supply output voltage pin) Lambda sensor head Atomic Absorption (light source for non-plasma vapour sources - feedback control to evaporators to control alloy composition) Sensors form other suppliers EIES(vapour ionzer source - uses Gencoa PEM to collect data)

What Speedflo can do Speedflo uses an input from any sensor within the process to provide a high speed actuation to the gas flow. The sensor traditionally used is the plasma intensity of the metal or reactive gas species (e.g. oxygen). This method is called plasma emission monitoring or PEM. Speedflo's advanced control architecture can also use other sensor types to provide the feedback from the process. Allmodes of signal input can be used to control outputs from 1 to 8. Input signals can also be combined to provide a better 'picture' of the process and a more robust control solution in demanding situations (e.g. target voltage, metal line, oxygen line & argon).

In addition to its function as fast feedback system, it is equally able to eliminate long term drift in processes by maintianing precise levels of metal to gas species as well as the target surface condition (via the target voltage). This is key when a complex material system moves to a production environment and both control and system monitoring / fault prediction is required. The software can establish both fast and slow response control loops in order to balance uniformity requirements in large area processing with high rate operation in the 'transition' zone.

Why choose Speedflo?

Speedflo is designed for the demands of real processes. It has now been proven on over 100 different industrial plasma based deposition machines, all with varying demands. The software and also the control algorithms have evolved based upon this experience. Many different software functions have been added so that the controller can deal with anything that is presented to it. The history of the key staff members in Gencoa is from the process environment and this is how we think and develop products - for the demands of the process. From this point of view, Gencoa can help customers tune their processes remotely or on-site, and offer a complete reactive gas set-up and process control package - magnetrons, gas bars, controller & process know-how.

Why reactive gas control?

It is a well known and troublesome phenomenon that the reactive sputtering processes are highly unstable. Over the last 20 years there is a large body of work illustrating the difficulties. A magnetron target can very quickly switch from a metallic state into a fully poisoned condition. This change, unless its prevented will make the process unworkable and results in large variations in the sputtering rate; see the hysteresis curve illustrated.
A solution is to use the target in fully poisoned mode (i.e. reaction product all over the target). However the compounds on the target sputter at a much lower rate than a pure metal, hence it is usually not desirable.
A different solution is to use a feedback control system that can very quickly adjust the reactive gas flow in response to the plasma conditions, in order to hold the process in high rate metallic or transition mode. speedflo™ is an advanced form of this type of control system.

speedflo™´s aim is to use its high speed control algorithm and hardware structure to hold the process anywhere on the reactive sputtering hysteresis curve. The feedback from the plasma is provide by plasma emission monitoring (PEM). This is the most universal technique, although some materials can be controlled via the target voltage change as the feedback parameter. The PEM method works by measuring the intensity of light at a particular wavelength in the visible or IR spectrum.

The speedflo™ works by monitoring and controlling the level of the plasma intensity or other sensor by adjusting at high speed the input of reactive gas. The wavelength of the light intensity is selected by interchangeable narrow band pass optical filter window. The filter's wavelength corresponds to the peak intensity for the specific target material being sputtered. speedflo+™ has a CCD type array that can display the full plasma spectrum hence replacing the filter. This yields more quantitative information and is useful for process development and production processes.

For relatively small targets < 0.5m a single channel monitoring is usually sufficient for effective control. For larger area targets, especially were coating uniformity is critical, it is recommended to use multiple inputs and outputs for the same target. The speedflo™ unit can then control the different gas outputs at different levels across the target surface. This is very useful to tune the uniformity and establish the right balance between control response time and gas distribution. Typically on targets of >1m in length 3 control points should be used with separate gas output tubes. For targets of > 2.5m in length 3 or 5 separate points should be considered for effective control and uniformity balance.

Process Scale

High Speed Apart from the high speed solid state nature of the electronics, the unit has the ability to vary the structure of control which enables it to exhibit what is known as sliding mode control. This basically means it can identify how long the valve needs to be maintained at its maximum level, before it has to approach the steady state value necessary to maintain the final setpoint tracking. This high speed is illustrated in the test graphs, which show that even when the power supply is switched off and back on to mimic a severe process interruption, the control system is able to regain the setpoint in less than a second.

speedflo™ is a very powerful tool for rate enhancement & control in reactive sputtering. Its architecture is both cost effective and highly reliable. The advanced variable structure control algorithm offers significant performance improvements in terms of speed and robustness when compared to conventional PID control techniques. speedflo™ can be supplied with custom designed fibre-optics and gas distribution tubes.