Investigation of the Layered Structure of Polycrystalline Diamond Thin Films Grown by ECR-Assisted CVD by Spectroscopic Phase Modulated Ellipsometry

摘要

Polycrystalline diamond thin films deposited by the electron cyclotron resonance-assisted chemical vapor deposition (ECR-CVD) were investigated using Spectroscopic ellipsometry (SE) from the near IR to UV range (830 nm-270 nm). Employing the conventional Bruggeman effective medium approximation (EMA) and linear regression analysis (LRA) to the raw ellipsometry data (Ψ(λ_I), Δ(λ_I) provided the details about the film microstructure: (ⅰ) the multilayer structure and the ovearall thickness of the films; (ⅱ) the volume fraction of the constituents (sp3 - and sp2 - bonded carbon) and of voids in the bulk layer; (ⅲ) the inhomogeneity of the structure along the growth axis and its variation with the seeding density; and (ⅳ) the surface roughness layer. A simplified three-layer structural model consisting of an interfacial layer, an intermediate (or bulk) layer and the top surface roughness layer has been proposed to simulate the ellipsometry data. The results obtained through ellipsometry modeling such as surface roughness layer and overall film thickness were compared with rms surface roughness from atomic force microscopy (AFM) and profilometry respectively, in order to validate the model employed. The results such as f_v and f_(sp)~2 c for the bulk layer and its behavior with respect to process parameters are discussed.