Microstructure of ZnO thin films produced by magnetron sputter oblique deposition

ZnO films deposited at different oblique angles of 40, 60 and 80°, under different Ar pressures 0.27, 0.67, 1.33 and 2.67 Pa, DC currents of 0.15 and 0.25 A, and distances of 10-15 cm from the target were studied. It was found that the film grains grow at an angle to the substrate when deposition angle is above 40°. It was shown that the grains consisted of a number of small crystals growing one on top of the other and shifted towards the target with the crystal orientation not along the grain growth but perpendicular to the substrate. Crystal size decreased with the deposition angle and internal stress disappeared when α = 80°. It was found that 1.33 Pa pressure provided the best balance between the deposition parameters. Growth rate reached maximum, samples had the biggest crystal size and high crystal density. However, crystal spatial alignment changed gradually with pressure and distance.