Electrical and Reliability Characteristics of Low-K SiCOH Dielectrics with Metal Integration

In modern microelectronic devices, copper (Cu) and low dielectric constant (low-k) dielectric materials have been used in the back-end-of-line (BEOL) interconnects. However, the migration and diffusion of Cu into the low-k films become challenging during the integration of Cu/low-k interconnects, causing degradation of electrical performance and reliability. A metal barrier is introduced between Cu and low-k dielectrics to prevent Cu diffusion. With further scaling of technology node, the resistance of Cu metal lines significantly increases because of Cu surface and grain boundary scattering and additional metal barrier. To decrease the line resistance, the thickness of the metal barrier should be reduced. To reduce the surface and grain boundary scattering effect, different metals with low resistance can be employed. Potential candidates to replace Cu can be determined by lower product value of bulk resistivity and electron mean free path than that of Cu. Based on this criteria, cobalt (Co) and molybdenum (Mo) were selected. In this study, the integration of Co or Mo with the low-k materials was conducted and electrical and reliability characteristics were investigated.<br/>Low-k SiCOH thin films were fabricated on p-type Si (100) wafer by plasma-enhanced chemical vapor deposition (PECVD) of tetrakis(trimethylsilyloxy)silane precursor at ambient temperature. To investigate electrical and reliability characteristics of low-k SiCOH dielectrics with metal integration, metal-insulator-silicon (MIS) structures were fabricated. Four different metals Al, Cu, Co, and Mo were deposited on the low-k SiCOH films using a sputtering deposition or electron beam evaporation methods. Thickness of each metal was approximately 120-130 nm. The fabricated MIS capacitors were then annealed in N₂ atmospheres at 400 °C for 1 h. The electrical characteristics of the MIS structures were measured from capacitance-voltage (C-V) and current-voltage (I-V) curves using a semiconductor parameter analyzer. The C-V curves of Al-gate, Cu-gate, Co-gate, and Mo-gate MIS capacitors were compared before and after thermal stress. The typical C-V curves were obtained with accumulation, transition, and depletion regions from the negative to positive bias application. Depending on the type of metal-gate, the accumulation capacitance was different, suggesting that the deposition of metal gate may affect the capacitance of the underlying low-k film. The thermal annealing reduced the accumulation capacitance of the MIS capacitors. An increase in the k-value suggests that the low-k thin film was damaged by plasma during metal sputtering deposition. After annealing, the k-values were reduced, indicating that plasma-induced damage to the film could be recovered by annealing process. The shift in the C-V curve was the evidence of the diffusion of metal ions into the low-k film by annealing process. An increased leakage current after annealing demonstrates that the diffusion of metal ions occurred in the low-k film. The elemental composition including Si, O, and C was investigated by X-ray photoelectron spectroscopy (XPS). Metal diffusion into the low-k film at the interface between the low-k film and each metal after annealing affected C-V and I-V characteristics. Effects of different metals on the electrical properties and reliability of the low-k SiOCH films under thermal stress were compared in this study.