Paper PS1-ThA11
Near-Real-Time Two-Dimensional Wafer Surface Measurements for Process Optimization and Control

Thursday, October 23, 2008, 5:20 pm, Room 304

Optimizing and monitoring plasma etching processes has always relied on one-dimensional data provided by the plasma tool (reflected power, Vdc, optical emission intensity, etc.) or by post-etch measurements such as critical dimensions or film thickness changes. It has long been desired to monitor the plasma condition across the wafer surface in real time. Wafer-level sensors have been developed to measure the temperature of the wafer surface in near real time, and now sensors are being developed to monitor other plasma parameters in a similar way. Here we present measurements of Vrf, a parameter related to the plasma potential, taken from a two-dimensional array of sensors across the surface of a 300 mm wafer processed in a multi-frequency, capacitively coupled industrial plasma for dielectric etching. We show the relationship between Vrf and several process parameters, including RF power, pressure, and CO flow rate. The one-dimensional electrostatic chuck voltage, Vesc, does not respond to these parameters in the same way. Some plasma transients were detected by Vrf that were not detected by Vesc or by optical emission intensity. Vrf appears to correlate with plasma density, and because it is an array of detectors, it proved useful in identifying degraded plasma uniformity at lower CO flows. Such wafer-level Vrf measurements may be valuable for applications such as plasma monitoring, chamber matching, and process optimization to minimize plasma process induced damage.