Wafer charge monitoring by disk current

Wafer charging during high current ion implantation has been an important issue and will be more significant as gate oxide thickness is reduced for the device shrink. A charge neutralizing system, like the plasma flood gun of the NV-GSDIII-LE, must be used to compensate the charging. An in-situ monitoring of charging is important in order to measure whether the neutralization is being done adequately during implantation. The effect of charge neutralization by the plasma flood gun is originally measured by the charge sensor on the rotating wafer-disk. Appropriateness of the charge neutralization process is judged with the charge sensor signal. However, there is a problem in the charge sensor. It is known that the degradation of the insulation between the charge sensor and wafer-disk may cause a shift of sensor output. “Disk current (Id)” is another solution to monitor the wafer charging during implantation. Id is the total current flowing into the wafer-disk, which indicates the charge balance of ions and electrons coming into the wafer. In this paper, the correlation between output of an in-situ charge monitor (Vp) and disk current is confirmed. It guarantees the reliability of wafer-charge monitoring by the disk current with the plasma flood system. As a reference, charging voltages of CHARM-2 wafers are also measured