Reliability Tests of a Real Time Charge Monitor (RTCM)

Wafer charging effects that result from the ion implantation process are typically mitigated by employing a plasma flood gun to provide electrons to neutralize the positive ion beam as it strikes the wafer surface. As gate oxide thickness of semiconductor devices continues to shrink, control of the wafer charge-up during ion implantation becomes critical. Varian Semiconductor Equipment Associates (VSEA) has designed and built a real time charge monitor (RTCM) for in situ measurement of the beam-induced charging potential. Mounted close to the wafer and in the beam path, the RTCM continuously measures the deviation from quasi-neutrality as the wafer passes through the beam. In this paper we present reliability tests of this device for high current implanters over varied implantation conditions and failure modes. When correlated with the yield of antenna device test wafers, it was found that the RTCM signal is a sensitive and reliable tool to predict charging damage to the semiconductor devices.