期刊
JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A
卷 28, 期 3, 页码 495-501出版社
A V S AMER INST PHYSICS
DOI: 10.1116/1.3372833
关键词
aluminium compounds; Auger electron spectra; ellipsometry; III-V semiconductors; light interferometry; reflectivity; refractive index; rough surfaces; semiconductor thin films; surface morphology; surface roughness; transmission electron microscopy; wide band gap semiconductors
The optical and morphological properties of reactively sputtered AlN films on Si substrates have been studied in this work from a self-consistent three-layer optical model developed from spectroscopic-ellipsometry analysis and validated by observations from transmission-electron microscopy, Auger electron spectroscopy, and in situ reflectance interferometry. These properties correlate to the film microstructural properties. Accordingly, the almost thickness-independent refractive index of 2.01 of the bulk AlN layer indicates its polycrystalline microstructure. This layer also appears ungraded, homogeneous, isotropic, and free of excess Al, as if grown through a steady process. The small film absorption points to the Urbach tail states produced by the structural disorder typical of such sputtered films. The films' interface layer consists of a graded Bruggeman intermix of outdiffused Si and AlN materials spreading over 10-12 nm thickness. The surface morphology includes an Al2O3-oxidized outer rough surface gradually becoming AlN bulk with diminishing amounts of Al2O3 and inner pores. The increase in the surface-layer thickness, as the film grows, indicates further surface roughening due to enlarging crystals in a disoriented growth. This spectroscopic-ellipsometry analysis of AlN films has allowed us to study the effect of substrate biasing on the AlN microstructure and to place forward a new processing method for the surface smoothening of rough AlN and diamond films.
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