Diagnostics of neutral species in the low-angle forward-reflected neutral beam etching system

The reactive ions extracted from an ion gun were neutralized by reflecting the ions at the angle of 5° on the reflector installed in front of the ion gun. Their neutralization characteristics were investigated for SF6 as a function of acceleration voltage and RF power of the ion gun. When the ion current density was measured as a function of acceleration voltage and RF power of the ion gun using a Faraday cup for both with and without the reflector, the ion current density measured with the reflector was drastically decreased to 99.7% compared to those measured without the reflector suggesting the neutralization of most of the reflected ions. The reactive ions extracted from the ion gun were SF+, SF2+, SF3+ and SF5+. After the reactive ions were reflected at the reflector, the species were neutralized and changed to F2, SF, SF2, SF3 and SF5. The increase of acceleration voltage of the ion gun increased the lower mass peaks such as SF2, SF and F2 and decreased the higher mass peaks such as SF3 and SF5 suggesting the formation of lower mass neutrals at the reflector by the cracking and neutralization of the higher mass ions such as SF3+ and SF5+. The formation of F2 was significant with the increase of the acceleration voltage.