Takanori Yoshida

Neutralization of wafer charging in nitrogen gas

In an attempt to prevent wafers from getting charged in the N/sub 2/ gas sealed semiconductor manufacturing process, the authors have developed a neutralization method employing ultraviolet (UV) irradiation. This method depends on the fact that the N/sub 2/ molecule is ionized when it absorbs ultraviolet light. This method is superior to the neutralization method employing corona discharge in terms of neutralization capability in the inert gas ambient. The neutralization rate is very high; the residual potential caused by the unbalanced ion distribution is always 0 V after the neutralization. Neutralization is rapid. The neutralization capability is enhanced by decreasing the ambient pressure. The neutralization capability is further enhanced by replacing the N/sub 2/ gas ambient with the Ar gas ambient. >

Antistatic protection in wafer drying process by spin-drying

As part of an effort to produce a static-free wafer spin-dryer the authors developed an ionizer for use with spin-dryers and evaluated its charge removing and particle rejecting effects. Particle generation due to sputtering of the discharge electrodes themselves was prevented. The protection of the discharge electrodes with quartz glass completely prevents particle generation by ion and electron sputters, and the concentration of ozone generated is reduced to less than 1/10 of the usual level. This ionizer is excellent in its charge-removing performance taking only about 1 s to reduce the wafer potential from +or-5 kV to +or-0.1 kV. The residual potential due to the imbalance of ion polarity is extremely low, only 10 V at the maximum. The ionizers charge removing effect to prevent particle deposition was also evaluated, and almost complete success is reported in preventing the statically induced deposition of particles to wafers while they are being dried by a spin-dryer. >