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 SF ₅. 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.