We study the surface substrate inhomogeneity effect on the wetting of a spin-1/2 Ising ferromagnetic film in an external magnetic field $H$, using Monte Carlo simulations. It is found the inhomogeneity leads to the formation of islands of positive spins in each layer. However, depending on the values of $H$, for a fixed surface magnetic field $H_s$, each layer exhibits three different phases; totally wet, nonwet and partially wet (PW). In the latter case, we show the existence of three distinct configurations namely: A configuration (PWTD) in which the layer is partially wet with a total disconnection between islands; (PWPD) a configuration in which the layer is partially wet with a partial disconnection between islands; (PWTC) a configuration in which the layer is partially wet and the islands are totally connected. Furthermore, we show that an increase of $H_s$ values breaks the bonds connecting some islands of the phase (PWTC) which leads to an expansion of the (PWPD) region. On the other hand, the frequency distribution and the mean size of island are investigated in the (PWTD) region for fixed values of temperature $T$, $H_s$ and $H$. Moreover, we show the existence of 3D-islands resulting from the formation of islands in each layer.