Quantum well (QW) states of thin Cu films deposited on Co (100) are studied using high resolution photoemission. In order to obtain a smooth Co-Cu interface, Cu films were prepared by evaporating the interfacial layer at 100 K. This allows us to obtain better defined QW features at the valence band. Furthermore, following this preparation method we are able to observe for the first time QW states at the neck of the Cu Fermi surface, which are not observable when the interfacial layer is deposited at 300 K. Using these high-quality films we also study; final-state-related oscillations in the intensity of the photoemission spectra as well as the lifetime broadening of the QW states.