Feasibility study for monitoring of tendency of particle generation in plasma etching by load impedance measurement

Particles in plasma etching process decrease the production yield and the overall equipment effectiveness (OEE) at LSI mass production line. In this study, we have tried monitored the tendency of particle generation in plasma etching by load impedance measurement. The reactive ion etching (RIE) equipment is used as the experimental apparatus and the particles, which originate from etching reaction product deposited on a gas shower type electrode, are investigated under the condition that a Si wafer is etched by SF₆ plasma. The particle is observed during each etching process by using the laser light scattering (LLS) method. The detection system introduces a sheet-like laser beam into the process chamber approximately 4 mm below the electrode. Scattered light by particle is detected by charge-coupled device (CCD) camera. In addition to the particle detection, the impedance monitoring system measures load impedance from a 50 ohm transmission line during the etching process. The measurement results of load impedance clarify that the imaginary part of the impedance decreases with the increase in the number of particles observed by the LLS method. We have demonstrated that load impedance monitoring method can monitor the tendency of particle generation caused by the flaking off of the deposited film. This non-invasive impedance measurement can be easily applied to the process equipment at mass-production line and contribute to improvement of the production yield and the OEE.