Ion-current difference measurement by light intensity modulation ( lCD ) is introduced as a convenient method to determine the number flux of neutral free radicals produced by photo-deionization of a negative ion beam for the purpose of surface-reaction-selective device processing. The lCD setup developed in this study exhibited the high precision and the high sensitivity under the experimental condition that the beam kinetic energy of the neutral free radicals was higher than 10 keV.
Two measurement methods to determine the rate of neutral free radical production by the photo-deionization of negative ion beams ( PDINIB ) are introduced. These methods, namely, photoelectron-current measurement by low-frequency electro-modulation probe ( PMMP ) and measurement of decrease in the negative-ion beam current ( DNIC ) were employed to evaluate the production rate in a trial surface-processing apparatus developed in the author's laboratory utilizing a steady-flux refined beam of neutral free radicals produced by the PDINIB procedure. A 63Cu negative ion beam of kinetic energy E, varied up to 15 keY was irradiated with a 514.5 nm visible light beam from a 25 W CW Ar ion laser. The detection limit of the production rate by the PMMP setup was as high as 6x109 Is under the condition that E, = 15 keV, the negative ion beam current I = 4 j.tA, and the laser power P = 6 W. The DNIC method is simpler but less reliable than the PMMP method owing to larger uncertainty resulting from the fluctuation of the negative-ion beam current.
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