Effect of the pattern structures on the charging damage during metal etching

Two dominant mechanisms govern charging damage: one is plasma nonuniformity and the other is topological effects of the wafer surface. Electron shading damage is well known as a typical topographical effect in plasma charging. In the case of electron shading, excess ion current flows through the gate oxide and the gate oxide reaches breakdown. Recently, phenomena such as local side etching of aluminum at particular space widths or bi-directional charging during plasma processing have been reported. Moreover, two kinds of charging damage have been distinguished: around the end point or during overetching, depending on the process conditions or hardware design. By using giant antenna probes, we revealed the possibility of bidirectional damage current flowing into the gate oxide. It was shown that, during metal overetching, negative charges could flow from the metal sidewall to the gate oxide. The negative current and charge-up voltage measured using the probe increased with increasing space width and electron temperature. Hence, open space and high electron temperature can induce major damage in real devices. These results can be explained by extending the electron shading effect (Hasegawa et al., 1998). In this paper, we measured the charging damage during metal etching, using the threshold voltage shift and subthreshold voltage swing shift of MOS transistors. We show the conditions for negative damage current generation at a MOS transistor connected to a sparse antenna.