The Effect of Hydrogen Retention in AlN (Aluminum Nitride) on the Initiation of ICP Plasma Discharge

Plasma initiation at very low pressure ranges (even below 1e-2 Pa) has been observed using a 13.56 MHz RF inductively coupled plasma (ICP) source with an AlN dielectric cylinder. The results indicate that plasma initiation is closely related to hydrogen retention in the AlN material. When attempting to initiate Ar plasma using an AlN cylinder that had been heated or preconditioned by exposure to Ar plasma at relatively high pressure and high RF power for several minutes, plasma initiation did not occur at very low pressures. Conversely, after exposing the AlN to hydrogen (H₂) plasma, RF powers in the range of 10 W to 20 W were sufficient to initiate Ar plasma at very low pressures. For H₂ plasma initiation, the required pressure was significantly lower than that for Ar plasma initiation. Interestingly, higher RF powers failed to initiate plasma. Additionally, increasing the RF power post-initiation did not enhance power transfer to the plasma discharge, resulting in plasma disappearance at very low pressures. These observations suggest that hydrogen retention in AlN enhances plasma initiation by modifying the surface properties of the dielectric material and the RF breakdown. To further investigate these mechanisms, various experiments were conducted using a residual gas analyzer (RGA), combining different experimental conditions to identify the most critical variables affecting plasma initiation.