Evaluation of selective tungsten plugs on TiN, W and AlSi by analytical and electrical measurements

This paper focuses on the examination of selective tungsten plugs grown by silane reduction of WF6 on different base layers (TiN, W, AlSi). The influence of selected ex situ wet and situ plasma pretreatments on the interface formation was estimated and the composition of the plugs was analysed by high resolution TEM (HRTEM) investigations at cross-section samples. Via resistance measurements in a two level aluminium metallization were used to evaluate the electrical contact quality. Depending on the base layer material α-W and β-W were detected at different locations of the plug. No interfacial layer was detected between the CVD-W and TiN, PVD-W and AlSi base layer, respectively, by HRTEM at cross-section samples. Small amounts of AlF3 were detected at the AlSi surface after different pretreatments. Via resistances for W plugs on TiN and PVD-W were found to be sufficiently low (e.g. below 2 Ω0.8 μm via on TiN). For W plugs on AlSi, a hydrogen annealing had to be performed to obtain good contact quality.