The scattering matrix approach between the clean and dirty limits is developed for the study of tunnelling spectra in a ferromagnetic film in proximity to a superconductor. The minigap and the damped oscillation from ’0’ to ’π’ state in tunnelling conductance are attributed to the phase coherence of the electrons and the corresponding Andreev-reflected holes in the ferromagnetic film. The calculated results provide a reasonable explanation for the behaviour observed in recent experiments.