ENERGY-DISTRIBUTION AND YIELD MEASUREMENT OF SECONDARY ELECTRONS TO EVALUATE THE EQUILIBRIUM CHARGING VOLTAGE OF AN ISOLATED ELECTRODE DURING NEGATIVE-ION IMPLANTATION

The negative-ion implantation method has the advantage that the chargi ng voltage of an isolated electrode, or electrically insulated conduct ive material, stays as low as at most +10 V during implantation withou t any charge neutralization. The significant parameters, the energy di stribution and the yield of secondary electrons in negative-ion implan tation, have been measured in the energy range below 40 keV. The resul ts show that the energy distribution, which is independent of ion ener gy in shape, has a low energy peak together with a long tail extending toward the high-energy region, and that the yield increases with ion energy. Furthermore, the equilibrium charging-voltage equation of an i solated electrode during negative-ion implantation is presented. The c harging voltages estimated according to the equation are found to be i n good agreement with those measured directly with a high-input-impeda nce voltmeter. It is also demonstrated that the charging voltage is pr oportional to the yield and to ion velocity in the linear region of th e kinetic electron emission.