Abstract
Thin AlOx films were grown on 4H-SiC by plasma-assisted atomic layer deposition (ALD) and plasma assisted electron-beam evaporation at 300°C. After deposition, the films were annealed in nitrogen at temperatures between 500°C and 1050°C. The films were analyzed by X-ray reflectivity (XRR) and atomic force microscopy (AFM) in order to determine film thickness, surface roughness and density of the AlOx layer. No differences were found in the behavior of AlOx films upon annealing for the two different employed deposition techniques. Annealing results in film densification, which is most prominent above the crystallization temperature (800°C). In addition to the increasing density, a mass loss of ~5% was determined and attributed to the presence of aluminum oxyhydroxide in as deposited films. All changes in film properties after high temperature annealing appear to be independent of the deposition technique.
Highlights
Due to its excellent dielectric properties, aluminum oxide (AlOx) thin films have been regarded as high-k materials to replace SiO2, for example, as gate dielectric in MOSFETs [1]
The surface morphology of as-deposited AlOx films appears to be very smooth with a decoration of the initial atomic steps on the SiC substrate and a root mean square roughness of ~0.2 nm (Figure 1(a))
After annealing at higher temperatures, features appear due to a crystallization of the films and the roughness increases to about 0.5 nm (Figure 1(b))
Summary
Due to its excellent dielectric properties, aluminum oxide (AlOx) thin films have been regarded as high-k materials to replace SiO2, for example, as gate dielectric in MOSFETs [1]. It is expected that the formation of crystalline Al2O3 via high temperature annealing could further reduce fixed interface charges [5] [6], stabilizing the electrical properties of the material [7]. Hafnium oxide with a substantially higher dielectric constant of ∼25 forms silicate at the interface with Si and crystallizes during post deposition annealing. Combination of aluminum oxide with other high-k dielectrics, which have relatively high dielectric constant, but are not as robust as AlOx to high temperature post deposition annealing can strongly improve thermal and electric stability of gate dielectric stacks [9]
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