An on-wafer probe array for measuring two-dimensional ion flux distributions in plasma reactors

In plasma etching processes, the spatial distribution of ion flux across the wafer surface determines the uniformity and profile evolution when etching is ion limited. We have designed and built a two-dimensional array of planar Langmuir probes on a 200 mm diameter silicon wafer to measure the radial (r) and azimuthal (theta) variation of ion flux impinging on the wafer surface in plasma etching reactors. Herein we demonstrate the use of this probe array to obtain two-dimensional ion flux distributions in Ar, Cl-2, and Cl-2/HBr/He discharges in an inductively coupled plasma reactor. The results obtained using the probe array are in good agreement with Langmuir probe measurements but also reveal azimuthal asymmetries, due to irregularities in chamber geometry such as the pumping port and radio frequency coil configuration, that cannot be detected using radially movable Langmuir probes. The probe array can also be used to investigate the spatiotemporal fluctuations of the ion flux in the 1-100 Hz range. (C) 2002 American Institute of Physics.