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To explain the tensile behavior of the crystalline dielectric and metal films, today mostly the grain boundary model is applied [1]. According to the model, the interactions across the grain boundaries in the polycrystalline dielectric films play a vital role in the development of film stress. Lattice relaxation forced by the energetic interaction between grain boundaries presents an elastic deformation, which expresses itself microscopically as observable mechanical stress. When two grains are attracted by van-der-vaals force to each other across the gap formed in the deposition process a local tensile stress field arises. If the gap is small enough so that repulsion between the grains takes place then compressive stress field may arise. Ion bombardment during thin film deposition enforces densification processes in the films by reducing the gaps, which consequently results in less tensile and even compressive stress. Absorption of residual gases by the film in the vacuum chamber or in air can play a vital role in the stress development, causing a reduction of the surface free energy and hence the tensile stress with possible transformation to compressive stress.