Monitoring of low-dose ion implantation in silicon

Monitoring of low-dose arsenic or boron ion implantation (doses: 5*10/sup 10/ to 1*10/sup 13/ cm/sup -2/) in silicon, which is required for threshold voltage control of MOS transistors, is studied. The thermal-wave (TW) signal intensity decreases monotonically with decreasing dose. The lowest detection limit for As/sup +/ and B/sup +/ implantations is 5*10/sup 10/ and 1*10/sup 11/ cm/sup -2/, respectively. Correlation of the TW signal intensity versus damage density, TW intensity versus dose, and laser Raman intensity versus dose is obtained. The TW intensity is also correlated with the sheet conductance, and the threshold voltage of the transistor. Therefore, this technique is useful as a nondestructive, highly sensitive dose monitor for low-dose implantation to achieve tight threshold voltage control in MOS transistors.<
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