X-ray and AFM analysis of Al2O3 deposited by ALCVD on n-type 4H-SiC

Al2O3 grown by Atomic Layer Chemical Vapour Deposition (ALCVD) on n-type 4H-SiC with a nominal thickness of 100nm has been characterized by Grazing Incidence X-Ray Diffraction (GIXD) and Specular X-Ray Reflectivity (SXR) measurements. After post-deposition, the samples were annealed at different temperatures and durations in argon atmosphere. The GIXD results reveal crystallization at temperatures above 900 degrees C, most likely in the form of theta-Al2O3 or gamma-Al2O3. However, the formation of a new, non-stoichiometric Al2O3 phase cannot be excluded. The crystalline domain size, evaluated from the peak FWHMs after subtraction of the instrumental broadening, is found to be almost equal (18 +/- 1 nm), independent of T in the range 900 degrees C <= T <= 1100 degrees C and time in the range 1h <= t <= 3h. From SXR, mass density profiles are derived. Whereas the as grown film exhibits the lowest mass density, at 800 degrees C a low-density interface layer forms. At the same time, it appears that the initial crystallization starts at the surface. At 900 degrees C, the density increases sharply (this process involves film crystallization) and the film thickness correspondingly reduces. Whereas the density increase and thickness reduction still continue for T > 900 degrees C (tendency to the density alpha-Al2O3), the density of the interfacial layer has a minimum at 900 degrees C and gradually increases for higher temperatures. From Atomic Force Microscopy (AFM) investigations it could be revealed that the starting of the crystallization at 900 degrees C is accompanied with a substantial surface roughening. For annealing at higher temperatures, the surface roughness is in the range of the one of the as-grown sample (about 6 angstrom).