Microtrench Generation in SiO2 Trench Etching for Damascene Interconnection Process

The mechanism of microtrench generation in SiO2 trench etching in fluorocarbon gas chemistry is presented using the magnetron etch system under a 40–80 mTorr pressure condition. In the previous study, we pointed out that the microtrench is caused by the etch rate increase at the trench bottom edge where the fluorocarbon film is thin, because the thicker fluorocarbon film was formed more easily at the center of the trench bottom where the solid angle is larger than at the edge of the trench bottom. In this study, the experimental condition is extended to lower pressures. The microtrench ratio becomes higher in accordance with a larger pattern size at pressures higher than 40 mTorr. However, the pattern dependence of the microtrench ratio is reversed at 20 mTorr. This is explained by the effect of a constant residence time, the dilute gas effect, and the inverse-reactive ion etching (RIE) lag which is observed at 20 mTorr. In conclusion, the microtrench formed by the shadowing effect for fluorocarbon radicals is offset by increasing the bombarded ions at the trench bottom with the decrease of pressure to a condition such as 20 mTorr pressure.