The drain current asymmetry of 130 nm MOSFETs due to extension implant shadowing originated by mechanical angle error in high current implanter

The drain current asymmetry of 130 nm n-MOSFETs due to extension and source/drain ion implantation shadowing at the edge of gate electrode has been investigated. The ion implantation angle error is occurred even the tilt and twist angles are mechanically set as 0 degree. This ion implantation angle error is remarkable at periphery area of 200 mm wafer. This angle error originated in wheel design and scanning method of a high current ion implanter. Those are structural limitation of a high current batch type ion implanter. The drain current asymmetry can be dramatically reduced by using 4-step (Tilt/Twist=0/0, 0/90, 0/180, 0/270 deg.) ion implantation for extension implant similar to pocket implant. Therefore, even the low energy, high current ion implantation such as extension and source/drain implant, 4-step ion implantation is indispensable to reduce the drain current asymmetry.