Plasma density is estimated from the target voltage and current characteristics of the pulse modulator circuit in plasma-based ion implantation. The voltage recovery time constant directly reflects the ion sheath characteristics, and the sheath resistance is related to the ion density inside the transient sheath. The stationary current also provides information on the sheath parameters. The ion density obtained by equating the measured characteristics with an equivalent circuit can be converted to plasma density using a continuity equation. Thus, the plasma density is estimated can be controlled by the degree of vacuum and the applied voltage.
