Experimental investigation on the spatial distribution of floating potential at the wafer-level in inductively coupled oxygen plasma

The spatial distribution of floating potential for charging distribution at the wafer-level is measured by using a wafer-type probe array, and the experiment is performed in an inductively coupled oxygen plasma. At low pressures, the floating potential distribution exhibits a convex shape. As the pressure increases, the profile gradually evolves into a concave shape, indicating more negative charge at the center, which is unusual for electropositive plasmas. A similar evolution is observed for positive ion flux under the same discharge conditions. It is noteworthy that the charging distribution at the wafer position in process plasmas at high pressures can be reversed due to negative ions compared to that in electropositive plasmas. In addition, the correlation between the floating potential and electronegativity is also presented. In order to investigate the effect of negative ions on floating potential distribution, a 2D fluid simulation with an electron-heating model is conducted, and the experimental results are in good agreement with those from the 2D fluid simulation.