Comparison of charge control technologies for advanced high current ion implantation systems

Reduction of gate oxide thickness with device design rule dictates increasingly precise compensation of ion beam positive space charge with electrons and reduction of beam potential. In the present work we investigate charging damage to thin gate oxides due to high current ion implants performed on implanters equipped with different types of hardware for beam space charge neutralization. We are comparing GSD-200/E² high current implanters equipped with either Secondary Electron Flood (SEF) or Plasma Electron Flood (PEF) and the ULE2 ultra-low energy high current implanter, which employs the latest charge control technology (Plasma Cell) introduced by Eaton. Gate-antenna type capacitors and SPIDER structures were used to evaluate beam neutralization. We performed charge-to-breakdown (Q_BD) measurements on MOS capacitors to evaluate gate oxide wearout, and V_t and charge pumping measurements on SPIDER structures to measure concentration of charge traps generated within the oxide and at the Si/SiO₂ interface. Good correlation of the data collected from Q_BD charge pumping, device parametrics (V_t) measurements, and readings of in situ beam potential monitors is demonstrated. Experimental results demonstrate that Plasma Cell technology employed in the ULE2 family of ultra-low energy implanters under optimum conditions provides the best charging performance and allows achievement of minimal gate oxide wearout and lowest concentration of charge traps at the gate stack SiSiO₂ interface in the SPIDER structures