Heat balance during plasma immersion ion implantation

The substrate temperature was measured during plasma immersion ion implanta tion (PIII) of nitrogen as a function of the pulse bias voltage and the rep etition frequency. The variation of the equilibrium frequency for temperatu res between 150 and 500 degreesC and pulse voltages between -5 and -30 kV w as investigated. Using these data, the relative dose per pulse for differen t voltages was obtained and its voltage dependence compared with different models for the plasma sheath expansion during PIII. A higher plasma density than measured for a static plasma without pulses, due to the interaction o f secondary electrons with the plasma, must be assumed. Good agreement with dose measurements of N implanted in Si was also observed. For high pulse f requencies above 1 kHz a deviation was observed, clearly showing that deple tion of the ions from the plasma during the pulses leads to reduced average plasma density at high repetition rates.