POWERMANAGEMENT
output of the power supply plus the energy stored in the cabling.
The latest-generation DC power supplies move beyond conventional micro- and hard-arc distinctions with increasingly sophisticated arc handling. New power supply designs store less energy, take a multi-level approach to arc response, systematically control power recovery, maintain a linear deposition rate, and are rich with custom process management options. Such
advancements help quench arcs at high power levels—without compromising deposition rate and consistency—and thereby prevent unnecessary process interruptions, film damage, and losses in productivity and throughput.
Advanced Power Supply Designs Store Extremely Low Energy
Damaging particles on a film are the result of high energy feeding into an arc event. The shut down of the power supply is intended to reduce energy delivered to the arc. The shut down should be long enough to let the surface cool so that power can be re-applied without reigniting the arc. Therefore, applying less energy to the surface location of the arc event before an arc is extinguished reduces target and substrate damage. Architecturally advanced power supply designs incorporate fast, internal arc switches and minimize stored energy (expressed as mJ per kW).
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A Multi-Level Arc Response Adapts as the Rate and Severity of Arcs Change Over the life of a single target, the arc rate and the severity of arcs will change. For the most stable power delivery throughout the lifetime of the target and the process, a power supply should detect and appropriately respond to actual arcing conditions with fewer persistent arcs and without causing new arcs to occur.
Fig 3. A sophisticated, multi-step response is adaptive to the rate and severity of arcing in any given process. This waveform shows a persistent arc (secondary). Controlled Recovery Minimizes Persistent Arcs
During an arc event, a change in the plasma operating conditions (impedance) causes the output voltage to rapidly approach zero while the output current increases dramatically. New power supplies are engineered to carefully monitor voltage and current and to activate an immediate response once the voltage and/or current pass a specified threshold or set of threshold criteria.
A multi-level arc response is rapidly replacing the conventional micro- and hard-arc distinction. The primary response will always involve the removal of output power to reduce the amount of energy given to the arc. This time should be as short as necessary to provide continuous output power, yet long enough to quench most arcs. If the arc clears, no additional response is required.
Fig 4. A soft start on the power return after an arc shut down helps prevent persistent arcs
However, if the shut-down time in the primary response is insufficient to cool the surface of the arc location and an immediate arc follows (or previous arc persists), a secondary response should set in. If the arc remains persistent, the duration of the response becomes progressively longer, sometimes resulting in a short-circuit
www.solar-pv-management.com Issue VI 2010
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