Static Elimination Performance of a Corona Ionizer in Nitrogen-Based Electronegative Gases

Corona ionizers are widely used in metal-oxide-semiconductor (MOS) device manufacturing processes to mitigate electrostatic hazards, such as the destruction of ultrathin-gate insulators that decreases production rates. However, unbalanced corona ionizers may deposit charges increasing electrostatic hazards. In this study, static neutralization characteristics of an ac corona ionizer in oxygen-free gas atmospheres, such as mixed N
₂
-CF
₃
I and N
₂
-SF
₆
gases, have been explored for the first time and compared with those in ambient air and pure nitrogen. In pure nitrogen, the negative emitter current is much larger than the positive one due to difference in the mobility between negative (electrons) and positive (ions) carriers; hence, the product final voltage V
_PF
deviates to a negative value as low as -2 kV. With the introduction of CF
₃
I up to 0.01%, however, V
_PF
reduces to around 0 V, while it happens at as high as 10% in O
₂
. Therefore, it is found that the amount of CF
₃
I needed to improve the ion balance is three orders of magnitude smaller than that of O
₂
due to higher electron affinity of a CF
₃
I molecule.