XPS characterization of interfacial reaction between SiCOH low-k dielectric and TaN barrier layer

For Cu interconnect processing for 90nm node and beyond, barrier layers play a very important role in low dielectric constant (low-k) material and copper. It can stop copper migrate into low-k and offer better adhesion to low-k as well. However, Interfacial properties between barrier and low-k dielectric should be carefully researched in order to obtain an excellent interconnect system. In this work, in a Transmission Electron Microscope (TEM) picture of low-k material (SiCOH) and TaN stack we can observe that TaN has a smooth interface with low-k and do not diffuse into low-k material. Moreover, with atomic force microscopy (AFM), we find the surface roughness of PVD TaN is satisfactory. Reactions between low-k material (SiCOH) and TaN barrier have been investigated with XPS. SiCOH low-k dielectric films are deposited by plasma-enhanced chemical vapor deposition (PECVD) and then TaN are deposited on it by physical vapor deposition (PVD). After annealing the stack under different temperatures (250°C, 350°C, 450°C), XPS is used to analyze the change happened on the interface. We fing that Ta-O and Ta-C peaks in the XPS spectrum of unannealed sample are obvious, and they have no significant difference when the annealing temperature getting higher. The result indicates that the main reactions between TaN barrier and low-k happen in the process of deposition and TaN is stable in a range of temperature (from 250°C to 450°C).