The research of relationships between residual stress and columnar angles in oblique deposition of magnesium fluoride thin films

MgF2 films are obliquely deposited on glass substrates using a resistive heating Mo boat at two substrate temperatures room temperature and 220 degrees C. All films clearly have columnar microstructures, as determined by SEM. The columnar angle of the MgF2 films increases with the deposition angle. However, the columnar angle of the MgF2 film that was deposited at a substrate temperature of room temperature does not equal that at 220 degrees C when the MgF2 film was prepared at the same deposition angle. Also, the trend behavior of the stress of the MgF2 films that are deposited at a substrate temperature of room temperature differs from that of those deposited at 220 degrees C because of the formation of thermal stress. The behaviors that are associated with stress in the MgF2 films are measured using a phase-shifting Twyman-Green interferometer and a phase reduction algorithm is applied. Anisotropic stress does not develop in the MgF2 films with tilted columns and the residual stress depends on the deposition and columnar angles of the microstructures of the MgF2 films.