Charging of Glass Substrate by Plasma Exposure

It is probable that charge-up of a glass substrate during plasma processing such as ashing and/or etching deteriorates the production yield of thin-film transistor-liquid-crystal-display (TFT-LCD) devices. In order to keep the production yield at a high level, it is necessary to understand the charging mechanism of glass surface in plasma and then offer countermeasures for the process. We measured the surface potential of the glass substrate during plasma processing. We exposed the glass substrate to plasma in a parallel-plate electrode system by introducing Ar, O2 or SF6 gas into the plasma reactor and exciting with 13.56 MHz RF or DC power supply. As a result, we found that the charging of the glass substrate in plasma depended considerably on the power source and the gas species. We discussed the phenomenon in terms of the behavior of molecular ions in plasma.