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.
SUMMARY
We are developing an electrostatic neutralizer operating in an atmosphere without oxygen for the organic electronics fabrication industry. As a part of the study, we investigated ion generation and neutralization characteristics of an ac‐corona‐discharge‐type ionizer in different atmospheric gases such as ambient air, pure nitrogen, and mixed N2‐O2 and N2‐SF6 gases, with changing the partial pressure of O2 and SF6, respectively. The I–V characteristic of the emitter shows that the negative current in N2 gas is significantly greater than the positive one; thus, the product final voltage VPF gives a significant deviation to a negative value (about –2 kV). However, by introducing SF6 gas by 0.01%, VPF reduces to about 0 V as that in ambient air. The amount of SF6 needed to improve the ion balance is three orders of magnitude smaller than that of O2, due to higher electronic affinity that a SF6 molecule has.
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