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Basics of the COPRA

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COPRA´s Basics
COPRA is a filamentless, Radio Frequency (RF) driven, low-pressure plasma source technology. The RF power is inductively coupled to the plasma through a matching network and a single-turn excitation electrode. An essential feature of the design is the tunable matching network which is incorporated into the source itself.The matching network comprises resonant circuits which employ variable capacitors to match impedance and hence maximize the power transfer efficiency to the plasma. Remotely matched sources are normal applied for all industrial applications. The beam produced by the COPRA is quasi-neutral i.e. it contains roughly the same number of ions and electrons permitting deposition, etching and surface modification of both conducting and insulating substrate materials without significant charge build-up.

One essential feature of the COPRA Plasma Technology is that due to the particular excitation mechanism of the plasma, for any kind of molecular gases the degree of dissociation is always close to 100%. The high amount of atomic species is only controlled by the COPRA design itself and is not depending on the rf-power. Beside the high degree of dissociation in all COPRA sources the plasma density can always reach values of more than 1E12/cm³, which is guaranteed by a high power coupling efficiency of up to 90%.

Atomic Nitrogen Plasma
energy vs power current vs power
The independent control of Ion Energy and Ion Current Density as a function of rf-power makes the COPRA so important for the next innovation step in precision optics thin film deposition. It is well know that the Energy of the ions itself is responsible for the required densification during deposition whereas the current density just needs to be sufficient high enough. Ions with kinetic energies of more than 15 eV can already overcome all surface binding energies and densification will take place, but if the ion energies are too high above 150eV re-sputtering and defect generation occurs. The COPRA plasma assist allows one to operate with ion energies which only will cause densification without creating defects and simply by increasing the ion current density by increasing the rf power leads you to a thermally stable drift free solid film.