Determination of microparticle characteristics in an etching plasma

The properties of one single melamine formaldehyde microparticle, levitated in the sheath of a low-pressure radio frequency-driven plasma, are determined with a novel procedure using in situ Mie scattering. By placing the measurement equipment inside the vacuum vessel, optical access is not limited to available viewports, and the complete scatter profile can be measured. The developed fitting routine uses peaks and valleys in the angular scatter profile to accurately determine the particle's refractive index, size, and plasma-induced etch rate. In plasma at a pressure of 13Pa operated at 10 W, obtained refractive indices of 1.657± 0.01 are close to those specified by the supplier, while the initial size (2.168± 0.007μm) is relatively 8% off from the supplier-specified value. With an estimated contamination of ambient air of 4 ± 1% in pristine Ar, etch rates of 1.9±0.2nm/min are measured.