Hardness, Modulus, and Refractive Index of Plasma-Assisted Atomic-Layer-Deposited Hafnium Oxide Thin Films Doped with Aluminum Oxide

Abstract

Coatings with tunable refractive index and high mechanical resilience are useful in optical systems. In this work, thin films of HfO2 doped with Al2O3 were deposited on silicon at 300 °C by using plasma-enhanced atomic layer deposition (PE-ALD). The mainly amorphous 60–80 nm thick films consisted Al in the range of 2 to 26 at. %. The refractive indexes varied from 1.69 to 2.08 at the wavelength of 632 nm, and they consistently depended on the composition. The differences were higher in the UV spectral region. At the same time, the hardness of the films was from 12–15 GPa; the modulus was in the range of 160–180 GPa; and the mechanical properties did not have a good correlation with the deposited compositions. The deposition conditions, element contents, and refractive indexes at respective wavelengths were correlated. The results indicated that it is possible to tune optical properties and retain mechanical properties of atomic layer-deposited thin films of HfO2 with Al2O3 as doping oxide. Such films could be used as mechanically resilient and optically tunable coatings in, for instance, micro- or nano-electromechanical systems or transparent displays.

Hafnium Aluminate–Polymer Bilayer Dielectrics for Organic Light-Emitting Transistors (OLETs)

“…Figure a shows the GIXRD spectra for (top) HfAlO x mixture, (middle) HfO 2 , and (bottom) Al 2 O 3 , where all the layers have been grown by atomic layer deposition, and each panel is labeled accordingly. HfO 2 film is polycrystalline, as recognized by XRD studies, and the peak positions clearly indicate the monolithic and tetragonal phases (ICDD PDF-2 card #01-075-6426 and DD PDF-2 card #01-075-6426) . In the Al 2 O 3 film, there are no distinctive diffraction peaks except the one identified for the silicon wafer, supporting the amorphous nature of the film.…”

“…HfO 2 film is polycrystalline, as recognized by XRD studies, and the peak positions clearly indicate the monolithic and tetragonal phases (ICDD PDF-2 card #01-075-6426 and DD PDF-2 card #01-075-6426). 47 In the Al 2 O 3 film, there are no distinctive diffraction peaks except the one identified for the silicon wafer, supporting the amorphous nature of the film. Such a nearly amorphous structure is maintained in the HfAlO x samples.…”