Effect of a dielectric layer on plasma uniformity in high frequency electronegative capacitive discharges

Abstract

The authors use a fast 2D axisymmetric fluid-analytical code to study the effect of adding a dielectric layer over the wafer electrode of a high frequency capacitively coupled plasma (CCP) reactor. At higher frequencies and larger areas, the wavelengths of the radially propagating surface waves in the plasma can become significantly shorter than the reactor dimensions, leading to center-high plasma nonuniformities. These wavelengths increase with increasing sheath widths, suggesting that a method to suppress wave effects in a high frequency CCP is to increase the effective sheath width by adding a dielectric layer over the wafer electrode. The authors conducted simulations with and without a dielectric layer and found that the dielectric layer improved plasma uniformity. The authors also studied the effect of adding a thin conducting or resistive silicon wafer above the dielectric layer and found that a conducting silicon wafer shorts out the fields and shields the discharge from the dielectric layer, while the resistive silicon wafer allows the fields to pass through to the dielectric layer.