Evaluation of Cu Contamination at Backside Surface of Thinned Wafer in 3-D Integration by Transient-Capacitance Measurement

The influence of Cu contamination at backside surface of a thinned wafer in three-dimensional LSI was electrically evaluated by capacitance-time (C-t) measurement. A MOS capacitor was fabricated using a thinned wafer of 50-μm thickness. The (C-t) curves of the MOS capacitor were severely degraded even after initial annealing at 300 °C for 5 min. It means that Cu atoms at the back surface reach the Si-SiO₂ interface of the front surface, and the generation lifetime is significantly reduced. The quantitative relationship between the generation lifetime and surface concentration of Cu atom was evaluated. The (C-t) measurement is a highly promising method to electrically characterize the influence of Cu contamination on device reliability in fabricated LSI wafers.