Comparative study on the effects of suspension way of sample holder on the large-aperture uniformity of refractive index of HfO2 films

Abstract

For large-aperture dielectric film optics, the uniformity of film refractive index across the aperture is crucial to the uniformity of reflectance and transmittance. Herein, a comparative research has been performed on the refractive index uniformity of HfO2 films across the Φ560 mm-aperture sample holder for inclined suspension and horizontal suspension. It’s revealed that the refractive index of HfO2 film at edge position of sample holder increased about 1.52% compared to that of HfO2 film at center position for inclined suspension, while the refractive index varied only about 0.25% for horizontal suspension. The further analysis performed on film crystallization, morphology and microstructure show that the large variation of refractive index between the films at center and edge positions of inclined suspension sample holder was attributed to the different growth properties. The film at the edge crystallized more slightly and was denser, thus being of higher refractive index. And the different growth properties of the two films at center and edge positions can be explained in the light of the co-effects of atomic shadowing, reemission and diffusion of ad-atoms during film growth.