Charging on resist-patterned wafers during high-current ion implants

Charging characteristics of As
⁺
and BF
₂
⁺
high-current ion implants were measured using bare and resist-covered CHARM®-2 wafers patterned with a six-field mask containing holes ranging from 2 μm to 0.5 μm (as well as clear and resist-covered fields). The results show surprising differences in the charging characteristics of high-current ion implanters compared to contemporary plasma-based process tools. In plasma tools, the electron-shading"" effects increase positive (and decrease negative) potentials and current densities as hole size decreases. On the contrary, high-current ion implants exhibited positive and negative potentials independent of hole size. The positive and negative current densities were also independent of hole size (but significantly higher than in the clear field). These results indicate that charging damage in high-current ion implanters should not increase when implant mask features are scaled down (other factors being equal). We also explain the apparent absence of damage in contemporary high-current ion implanters in spite of the very high positive current densities and high positive potentials.