Plasma Beam Source (PBS)

The Plasma Beam Source (PBS), is a new, patent pending plasma source invented by APT in 2002. This source produces a dense, uniform, cm's wide line of plasma extending 10’s of centimeters out of a source nozzle.

    Features of PBS operation are:
  • A high electron and ion current plasma flows out of the nozzle. At a discharge power level of 800W DC with N2O gas flowing through the source and a chamber pressure of 5mTorr, the beam electron saturation current is 375mA/cm2 with the probe biased at +5VDC. The beam ion saturation current is 17mA/cm2 with the probe biased below -40VDC. The probe floating voltage was ~-30VDC. Calculating plasma density from these currents indicates a very dense plasma, >1012/cm3.
  • The beam is uniform over wide substrate widths. This is because the internal magnetron is a uniform electron source and the electron Hall current remains evenly confined in the exiting plasma.
  • The plasma appears as a uniform blade approximately 1-2 cm wide over the length of the source. The figure below shows the defined nature of the beam.
  • Without filaments, low work function materials, or hollow cathodes, the PBS can ‘burn’ oxygen or other reactive gases directly – no argon is required. This lowers system pumping speed requirements and increases reactive process efficiencies.
  • The plasma beam emanating from the source extends >20cm beyond the source nozzle (refer to figures).


Top view of PBS at 1kW in pure O2

 

View of PBS at 1kW in pure O2

Applications

PECVD Processes
The plasma can be directed at a substrate or parallel to the substrate. The precursor can be fed directly into the source or introduced downstream.

Plasma Treatment
Similar to PECVD, directing the PBS beam onto a substrate brings a dense, active plasma to clean or treat a surface. Because the beam extends out many cm’s, three dimensional substrates can be treated or coated.

Assisted Reactive Evaporation
As an alternative to hollow cathode or other non-uniform plasma sources, the PBS can assist an evaporation process. Toward this application, a PBS can direct a pure reactive plasma across the entire evaporant stream.

Ion Densification of Thin Films
The PBS can be configured as an ion source to densify thin film coatings. To control the ion energy striking the substrate, the plasma potential can be raised above ground or substrate bias can be applied. Substrate bias is relatively easy with web substrates because mid-frequency AC power can penetrate the web surface

Assisting reactive sputtering is another application area. Similar to reactive evaporation, the linear, uniform plasma produced by the PBS can be used in conjunction with magnetron sputtering.

The following paper on the PBS was presented at the AIMCAL 2003 Fall Technical Conference "Production of Atomic Oxygen Using Linear Plasma Beam Source for Reactive Deposition and Plasma Treatment."