Observation of the floating sheath distribution on Al2O3 and silicon targets adjacent to a DC biased metal substrate

This study investigated the effect of plasma charging of the dielectric materials on the floating sheath distribution. The sheath measurements were conducted with two targets with heterogeneous material junctions, the Al2O3-metal target and the Si wafer-metal target, with a bias of -100 V on the metal target. The potential difference of the floating sheath formed on the Al2O3 was enlarged compared with that of the Si because of the smaller plasma charge accumulation because of low dielectric constant on the Al2O3. The accumulation charges are lost through the leakage current and the nonuniformity of sheath distribution for Si wafer-metal target was enhanced. Hence, the sheath electric field strength was stronger, the tilt angle was steep, and the nonuniform region became wider. This work demonstrated the plasma charging effect on the distribution of sheaths on the edge ring and the sheath electric field formed at the interface of nonconducting and conducting materials varied with the dielectric property of nonconducting material.