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

Abstract

Corona ionizers are widely used in MOS device manufacturing processes to mitigate electrostatic hazards such as the destruction of ultra-thin gate insulators that decreases production rates. However, unbalanced corona ionizers may deposit charges increasing electrostatic hazards. In the present 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 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.

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