Investigation of Moisture Uptake in Low-$\kappa$ Dielectric Materials

Abstract

The influence of moisture on the electrical properties of PECVD SiCOH and a PECVD porous ultralow- κ (pULK) material has been investigated in comparison with a thermal oxide and a PECVD oxide. Capacitance-time (C -t) measurements are performed on metal-insulator-metal structures during exposure to different humidity conditions (0% to 80% RH) to determine the effect on the relative permittivity. The results show a big difference in the amounts of moisture absorbance of the investigated materials. While the PECVD oxide and the thermal oxide show no effect on exposure to a humid atmosphere, the increase in the permittivity of SiCOH due to moisture uptake is 7%, and surprisingly, the change in the permittivity of the porous dielectric material is 1.75%. Within these experiments, the diffusion process of moisture into the dielectric materials could be observed in situ, and a diffusion model is created to extract diffusion constants and a value for the saturation concentration. Furthermore, the flatband voltage shift of SiCOH and the pULK material in metal-insulator-semiconductor structures at different ambient humidity levels has been studied. The findings suggest that moisture uptake causes a positive charge inside the dielectric materials, which is responsible for the observed flatband voltage shift.