Study of hafnium oxide thin films deposited by RF magnetron sputtering under glancing angle deposition at varying target to substrate distance

Glancing angle deposition of HfO2 thin films by RF magnetron sputtering technique has been explored with respect to two vital deposition parameters visualizing angle of deposition (at 82° and 86° glancing angles) and target to substrate distance, DTS in the range 70-125 mm. AFM and spectroscopic ellipsometry measurements show that at optimum DTS of 110 mm and glancing angle 82°, the films exhibit nanostructures with an estimated lowest refractive index ∼1.63 at 550 nm. For both the deposition angles, with decrease in DTS the round shaped grains of the film surface as obtained from AFM images are found to coalesce and produce films with elliptical shaped grains at shorter target to substrate distance. With increase in DTS the deposition rate first decreases up to DTS = 110 mm and subsequently increases. The phenomenon has been ascribed to the competition between reduced deposition flux density and increased sticking coefficient due to decrease in adatom kinetic energy with the increase in DTS. GIXRD measurement reveals that all the films exhibit monoclinic crystal structure. At lower DTS, the crystallinity has improved with increase in deposition angle whereas at higher DTS (>90 mm) the crystallinity becomes poorer with increase in deposition angle. The fact has been explained in light of variation of shadowing effect and deposition rate.