Complete parameterization of the dielectric function of microcrystalline silicon fabricated by plasma-enhanced chemical vapor deposition

Abstract

The dielectric functions of microcrystalline silicon (μc-Si:H) layers deposited by plasma-enhanced chemical vapor deposition have been determined by applying real-time spectroscopic ellipsometry (SE) in an attempt to construct an optical database for μc-Si:H. The μc-Si:H dielectric functions have been parameterized completely by a dielectric function model that employs two Tauc-Lorentz peaks combined with one Harmonic oscillator peak. This parameterization scheme has been applied successfully to describe the structural variation from hydrogenated amorphous silicon (a-Si:H) to highly crystallized μc-Si:H. Moreover, to express the microstructure of μc-Si:H, the μc-Si:H structural factor κ has been defined based on the amplitude of the E2 optical transition with a critical point energy of 4.3 eV. From the value of κ, a variety of Si microstructures, including complete a-Si:H phase (κ = 0), μc-Si:H with a-Si:H-rich grain boundaries (κ ∼ 0.5), and μc-Si:H with void-rich grain boundaries (κ = 1), can be distinguished. The μc-Si:H structures estimated from the above SE analyses show excellent correlation with those deduced from the Raman spectroscopy. From the SE analysis procedure developed in this study, the layer thickness as well as the microstructure of μc-Si:H can be characterized rather easily.