Magnesium fluoride thin films have been deposited on silica glass and single crystal silicon substrates by argon ion beam-assisted deposition (IBAD). The structure, composition, mass density of films deposited at ambient temperature were investigated as functions of the flux and kinetic energy of argon ions striking the film surface. The residual stresses in the films calculated from the change of the radius of curvature of silicon substrates, were studied as functions of the normalized momentum (P-N) transferred from incident argon ions to deposited atoms. The respective contributions of thermal, intrinsic and extrinsic stresses in residual stresses were also determined. Thin films produced with a P-N value of approximately 55 g(1/2) mol(-1/2) eV(1/2) exhibited appropriate characteristics for optical applications.