Unintended Gas Discharges in Plasma Sources for Semiconductor Fabrication*

The occurrence of unintended gas breakdown in the narrow gaps of plasma processing chambers is a critical challenge in developing advanced plasma sources for semiconductor fabrication. We present a combined experimental and theoretical study of unintended discharges in the narrow gaps of plasma processing chambers, focusing on the gas injection hole of an Inductively Coupled Plasma (ICP) source. Our experiments indicate a significant drop in the gas breakdown voltage compared to the known Paschen curve when a background plasma faces the gap. This drop becomes more severe after subsequent discharges due to wall erosion. On the theoretical side, results from our 2D particle-in-cell simulation indicate that the charged particle influx from the background plasma into the gap is responsible for the onset of early breakdown. The higher charged particle density within the gap modifies the electric field profile, allowing unintended breakdowns to occur at a significantly reduced threshold voltage. Our results not only explain why the industry has observed these discharges more frequently than expected but also suggest how to mitigate this problem by addressing the fundamental cause: the particle influx.