Investigation of the ion dose non-uniformity caused by sheath-lens focusing effect on silicon wafers

The ion dose non-uniformity induced on the wafer surface by modal and discrete focusing effects is investigated for different plasma densities and implantation parameters. Measured impact radius agrees well with values obtained by simulation. The optical pattern observed on the wafer surface is correlated with the ion dose by FT-IR measurements. The applicability of a previously proposed vertical ring is demonstrated, the ring being able to considerably improve the ion flux uniformity by shifting the discrete focusing effect out of the wafer surface and reducing the modal focusing. Experiments are performed in an inductively coupled plasma produced in hydrogen.