| The scaling issues resulting from diminishing device feature sizes have prompted the investigation of alternative materials and deposition techniques for copper diffusion barrier applications. As device sizes shrink to sub 100-nm technology nodes, the allowable copper diffusion barrier thickness falls to less than 10 nm. In this respect, novel materials are needed to stop copper diffusion into surrounding materials. TaSiN has been regarded as one of the most promising materials for copper diffusion barrier applications, owing to its excellent thermal stability, amorphous structure, and low resistivity.; In this respect, a plasma assisted chemical vapor deposition (PACVD) process using TaF5, SiI4, N2, H2, and in-situ radio frequency (RF) plasma was optimized for depositing ultrathin TaSiN films, employing a design of experiments (DOE) approach. Film properties were characterized using Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA), Auger electron spectroscopy (AES), x-ray diffraction (XRD), atomic force microscopy (AFM), four-point resistivity probe, and cross-section scanning electron microscopy (CS-SEM). The TaSiN films, deposited via optimized process conditions, exhibited low resistivity, low contamination levels, smooth surface morphology, good step coverage, excellent thermal stability, and amorphous structure.; The copper diffusion barrier performance of optimized PACVD TaSiN films was assessed in Cu/TaSiN/Si structures using traditional high temperature annealing methods and in Cu/TaSiN/SiO2/Si structures using a triangular voltage sweep (TVS) method. The results from the former technique show that the diffusion barrier performance of TaSiN films with higher silicon concentration, corresponding to a more prevalent amorphous structure, leads to worse Cu diffusion barrier performance. The results from the TaSiN barrier testing also show that thinner TaSiN films (≤5 nm) performed better as Cu diffusion barriers than thicker TaSiN films (≥10 nm). Investigation of the failure mechanism of the TaSiN films revealed that blistering of TaSiN films as a result of high temperature stress led to copper diffusion into Si.; In order to understand the relevance of these results and the possible effects of the high stress temperatures employed in these tests, TVS measurements were also carried out on these samples. The TVS measurements determined that thicker TaSiN films performed better as copper diffusion barriers than thinner TaSiN films, and that both stress temperature and voltage had significant effects on testing results. Since the maximum stress temperature in TVS measurements was only 300°C and Cu/TaSiN stacks did not blister at this stress temperature, thicker films performed better than thinner films as Cu diffusion barriers. |
