Direct measurement of topography-dependent charging of patterned oxide/semiconductor structures

Electron shading, or topography-dependent charging, occurs during plasma exposure of wafers with high-aspect-ratio features due to an imbalance between the electron and ion currents that reach the feature bottoms. High-aspect-ratio pit structures were exposed to an electron cyclotron resonance plasma. The surface potential of the structures after plasma exposure was measured with scanning surface-potential microscopy (SSPM). The results show that SSPM can be used to measure the differential charging in a high-aspect-ratio pit. In situ depletion of the plasma-induced charge with ultraviolet radiation was time resolved using SSPM. A circuit model is used to explain the experimental results.