Spin-on methylsilsesquioxane (MSQ) exhibits low dielectric constant and is an important and promising material to reduce the capacitive coupling between metal layers in semiconductor integrated circuits. However, MSQ has lower film density and therefore more porous than the traditional silicon dioxide film and could pose reliability issues. This paper characterises the MSQ using a metal oxide semiconductor capacitor (MOSC) structure with evaporated aluminium (Al) and copper (Cu) using the filament evaporation method deposited on top of a spin-on MSQ layer. Bias-temperature stressing was performed to understand the reliability of this MOSC structure with thin film MSQ as dielectric. Electrical characterisation with the aid of C-V and I-V measurements were used to understand the effect of evaporated Al and Cu on MSQ thin film. This study shows that Cu+ injection through the MSQ from the evaporated Cu gate could induce electrons trapping generated from the silicon substrate. However, there is little effect observed from the evaporated Al gate on MSQ thin film. Therefore, a suitable barrier layer is necessary to stop Cu+ injection through MSQ thin film before it can be integrated in very large scale integration circuit as an inter-layer dielectric material. (C) 2003 Elsevier Science B.V. All rights reserved.