Optical Thin Film Stress

Optical coatings are used in semiconductor, display, communicate and so on. During coating, there is the transformation of solid-gas-solid, and so there are stresses. Stresses will affect the system and cause the substrate to deform and make the center wave shift. It is important to research stresses in films.Due to the film deposition process, the lattice mismatch, the thermal expansion mismatch and disfigurement, the film/substrate system is inevitably subjected to residual stresses. Stresses, special thermal stresses are the major contributor to the finite service life of microelectronic and photonic components and devices.In order to research the effect of stresses to the service life of microelectronic and photonic components and devices, we do a thorough research.We are the first to use numerical method ANSYS to analyze the effect of stress moment to the service life of the films. It shows that when the moment is negative, in the interface between the films or film and substrate, the films suffer the most tensile stress near the edge and the tensile stress decreases with the distance from the edge and tensile stress will transform compressive stress. In this case the film/substrate is easy to delaminate. If only there is a negative moment, there is the possibility for the films to delaminate and the more the number of negative moment, the more the possibility. When the stress moment is positive, in the interface between the films or film and substrate the films will suffer the most compressive stress near the edge and the compressive stress decreases with the distance from the edge and compressive stress will transform tensile stress. In this case the film/substrate is difficult to delaminate.We also firstly research the relation between service life and the order of the multilayer. It shows that the tensile stress films should be coated first on the substrate.Because of the importance of thermal stresses in the service life of the microelectronic and photonic components and devices, it is important to research the thermal stresses. And the coefficient of thermal expansion (CTE),biaxial modulus of the film is different from that of the same bulk due to the different microstructure . By in situ measurements of the residual stresses as a function of the sample temperature we get the slope of the residual stress-temperature curve . In this paper we analyze the coefficient of thermal expansion (CTE),biaxial modulus of SiO₂ film deposited by electronics beam. And the result is that the CTE of film becomes larger as the deposit temperature is higher, and always less than that ofthe bulk .At the same time the results show that the biaxial modulus E/(1-v) is smaller withhigher deposit temperature, and larger than that of the bulk of the same materials for SiO₂ film deposited by electronics beam.The research of practice component of residual stress is beneficial to lead the coating of the films. In this paper we study the relation between the residual stress and the deposit temperature. It shows that thermal stresses,intrinsic stresses and the external stresses induced by water have different behavior at different substrates.Aging is an important process for the deposited films, because aging can increase the fastness of the films. In this paper we research the effect of aging to residual stresses. And the result shows aging has effect on the intrinsic stresses, and has no effect on the thermal stresses.