Plasma assisted particle contamination control: plasma charging dependence on particle morphology

With the introduction of EUV lithography, the control of contamination in advanced semiconductor processes has become increasingly critical. Our work is a joint effort (TU/e and VDL-ETG) and is aimed at the development of plasma-assisted contamination control strategies mainly focusing on airborne particles in a low pressure gas. We present experiments comparing the charge-to-mass ratio of single spherical micron-sized particles with that of non-spherical agglomerates thereof in the spatial plasma afterglow. It is shown that the charge-to-mass ratio of two-particle clusters deviates only 6% from that of singlets. This means that for the proposed mitigation strategy, of which the efficiency is based on the charge-to-mass ratio, it is acceptable to study the charging of spherical particles and to extrapolate the results towards non-spherical particles within a reasonable range.