ToF-SIMS characterization of contamination in ultra low-κ dielectric films

摘要

The use of porous ultra low-κ dielectric materials to replace SiO_2 has not only led to significant advances in integrated circuit speed and performance, but also presents challenges for the characterization of these materials. Time of flight secondary ion mass spectrometry (ToF-SIMS) using a low-energy electron gun is able to produce representative results where dynamic SIMS instruments with high energy electron guns fail. It is of particular importance to be able to quantify the presence of contamination such as Cu, Ti, W, Ta coming from the surrounding interconnects and diffusion barriers. Reference samples for typical trace metal contamination in low-κ materials are produced and characterized with the aim of determining relative sensitivity factors (RSFs) for Cu, Ti, W and Ta in low-κ material. Two types of reference samples are investigated. The first type is contaminated using dried droplets containing a known amount of contamination. Large area analysis (macro raster) is used to image the entire droplet residue of typically several millimeters in diameter. The second type is produced by ion implantation with a known dose. The dried droplet technique has the advantage of being quick to implement but the lateral distribution is often inhomogeneous and element dependant. The implanted samples give more realistic RSF values but there is some damage caused to the material during implantation and the samples are less representative of surface contamination. In both cases low-κ samples of different porosity are investigated as well as a silicon wafer to act as a control.