Decoration of particles by thin tantalum films

Surface particle defects smaller than the minimum detection limit (MDL) of particle detection metrology, may, after a thin-film deposition step, get decorated and become larger than the MDL. Chip manufacturers may therefore incorrectly identify the thin-film deposition step as the defect creation step and allocate resources incorrectly. The effect of thin film deposition on pre-existing poly-styrene latex (PSL) spheres on the wafer surface was studied. Results show that both the physical size and scattering cross section of the spheres increased after thin film deposition. For a film thickness of 128 nm, the increase in size of the PSL spheres was found to be about 60-80 nm depending on original particle size. Experimental results are in good agreement with feature scale simulations. Shadowing at the interface of large PSL spheres and the wafer surface was predicted by simulations and confirmed by experimental observations.