POWERMANAGEMENT
response, until the plasma stabilizes. This is a much more effective and flexible approach that adapts to any given process for better control.
How the power supply re-ignites the plasma is also becoming more advanced to prevent new or persistent arcs from forming. Applying too much energy after shut down (overshoot) can create a subsequent arc. Some new power supplies incorporate a soft-start feature that gradually ramps power after an arc response. This limits the total number of arcs and therefore the number of possible defects.
Maintaining Set Point While Controlling Responses to Arc Events The power set point is a user-selected value to provide the necessary film thickness. In heavy arcing conditions, a power supply may shut down so frequently that the amount of actual delivered power falls below set point.
Some power supplies can now automatically regulate delivered power to maintain the set point and the sputter rate, compensating for the cumulative off time through sophisticated algorithms. This ensures the same deposition rate at the beginning and end of target life, resulting in more linear deposition over the power supply operating range—critical to maintaining line speed and throughput for consist and homogeneous films.
Engineered to store extremely low energy and gradually ramp power after an arc event, the latest power supply technology ensures that the power supplies themselves do not induce any arcs. For those unavoidable arcs that the target or process materials generate, power supplies are quickly extinguishing them through sophisticated techniques for arc detection and advanced multi- level arc response.
Innovative power supplies that incorporate these new arc-management technologies are helping solar cell process engineers to overcome many of the quality and process control issues that they must constantly battle.
Authors Ken Nauman received his BSPS and MSME from Colorado State University. He is a senior applications technologist at Advanced Energy Industries, Inc., Fort Collins, CO. Skip Larson received his BSME from the Colorado School of Mines and his MBA from Southern Methodist University. He is a director of product marketing for the DC power group at Advanced Energy Industries, Inc., Fort Collins, CO.
Fig 5. Some power supplies can extinguish arcs while compensating for any loss in sputter rate, maintaining a stable set point throughout the process. This illustration shows severe arcing during a process and the effect that set point compensation (SPC) can have on maintaining the average power (Pave) equal to set point
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Fig 6 Actual waveform of set point compensation in action—a set point of 40 kW with a simulated arc rate of 500 arcs per second. The power supply (red) maintains a power delivery average value of 39,875 kW
www.solar-pv-management.com Issue VI 2010
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