Microwave Plasma Sources

In GHz frequency range, only electrons can follow the oscillations of electric field. However, it is seen that the electromagnetic wave cannot fully penetrate the plasma because of skin depth. Application of external magnetic field allow better coupling of electron with wave field creating a resonance between two. Such plasmas are called electron cyclotron resonance plasma. Such plasma sources operate at low pressures 10^-1 – 10^-3mTorr since at higher pressures, collision can destroy electron coupling with wave field. These sources produce very high electron density (10¹¹ – 10¹² cm^-3) and temperature (5-10 eV). High-density plasmas uniformly covering large surface areas are required for semiconductor processing.

A novel plasma source operated with 2.45 GHz microwave solid state generators have been developed by SAIREM, it is named as Aura-Wave. Large surface plasmas have been achieved by using a distribution of elementary sources as shown in figure below. The position and the power of each source have been optimized and the calculations have been validated by experimental measurements. High plasma densities >10¹¹ cm⁻³ over large areas > 400 mm in diameter with only 13 plasma sources have been achieved with all tested gases (N₂, O₂, Ar). An increase of compactness i.e., increasing the sources number over the same area, allows to have the same plasma surface while increasing the plasma density up to 5 × 10¹¹ cm⁻³ .

Figure 1 (a) Picture of the plasma reactor with 25 Aura-Wave sources, (b) picture of the Aura-Wave source and an oxygen plasma generated by 25 sources with 10 KW total microwave power. (DOI: https://doi.org/10.1088/2516-1067/ac0499)