Application of non-contact corona-Kelvin metrology for characterization of PV dielectrics on textured surfaces

Non-contact corona-Kelvin metrology has been extensively used in the IC industry for over 20 years and has more recently been utilized in the photovoltaic (PV) industry for dielectric characterization. Application to leaky low temperature PV dielectrics required various enhancements to the technique, such as an accelerated time-resolved charge-measure cycle to mitigate leakage and longer wavelength illumination to eliminate photo-induced leakage observed in silicon-rich silicon nitrides (SiN_x). These enhancements allowed extraction of important passivation properties such as interface state density (D_it) spectra and total dielectric charge (Q_tot) for a wide variety of PV dielectrics. However to this point there has been very little published on the application of corona-Kelvin metrology to the characterization of PV dielectrics on textured surfaces. The ability to measure quickly and accurately on passivated, textured surfaces with minimal impact of leakage is a very important and unique advantage of corona-Kelvin metrology over traditional metal-oxide-semiconductor (MOS) C-V measurements. In this work we present application of the corona-Kelvin technique to the characterization of SiN_x and aluminum oxide (Al₂O₃) dielectrics on textured substrates. Due to the increased surface area of the textured surface a correction factor must be applied to the areal corona charge dose used in the technique. Using planar and textured surfaces passivated with SiN_x and Al₂O₃ deposited under the same conditions, we empirically determine this surface area correction factor for a standard alkaline texture etch which allows accurate determination of passivation properties such as Dit and Qtot on textured surfaces.