Alkali fluoride multilayered thin films are promising systems for different optical applications, including light generation and waveguide. Despite this, some of their physical properties are still not well known. The mechanical behaviour of these materials, when evaporated in the form of thin films, plays a fundamental role for the success of the related optoelectronic device. In this work, LiF, NaF and LiF/NaF polycrystalline thin films were deposited onto different substrates at temperatures varying from 50 to 200 degrees C by physical vapour deposition (PVD). Using the X-ray diffraction technique with grazing incidence geometry (GIXRD), the residual stresses and the microstrains present in films deposited in different experimental conditions were measured. The lattice parameters and the mean domain were also estimated. The results show the dependence of the residual stresses in the films upon the cooling rate and the type of substrates and give, for the first time, an order of magnitude of these quantities for such systems.