In- and Ex-Situ Analysis of Silicon Oxide, Silicon Oxynitride, and Silicon Nitride Interfaces by Second Harmonic Generation and Correlation with Other Linear Optical Techniques

Abstract

Our objective is to gain insight about the physics and chemistry of silicon-dielectric (mainly Si-SiO) interfaces by nondestructive optical techniques: in-situ second harmonic generation (SHG) after interface processing, and ex-situ SHG, spectroscopic ellipsometry (SE), and reflectance difference spectroscopy (RDS) before and after high temperature anneals. The linear optical spectroscopies, SE and RDS, illustrate differences in dielectric responses due to chemical differences at interfaces and vicinal-sample cut directions, and assist in the interpretation of the SHG data. We analyzed the SHG anisotropy with a primitive phenomenological model that associates adjustable parameters for electric field amplitude and phase to each Fourier component expected in the observed anisotropy. Ambiguities of this model limited our ability to interpret the SHG data in terms of the parameters found by least squares analysis. To overcome these limitations we introduce a new model that describes SHG data in terms of the microscopic nonlinear polarization of individual bonds, and generates the observed far-field radiation in terms of dipole radiation resulting from these bonds. The adjustable parameters in this microscopic model correspond to complex polarizabilities along each of the onds. Our results show that the nonlinear polarizabilitiesperpendicular to the bonds do not need to be considered, asexpected from the essentially rotationally symmetric nature of the bonds. This greatly simplifies the model by reducing the set of needed parameters to those describing polarization along the bonds. We show that specific lineshape features in the azimuthal dependencies can be related to specific bond properties, allowing in some cases bond properties such as nonlinear absorption to be detected by inspection. We use least squares analysis to obtain changes in bond polarizabilities that occur before and after the anneal procedure. We conclude with a qualitative description of the results of the linear spectroscopic experiments.