PC-Mon-P12 - Determination of the bulk refractive index of AlN by spectroscopic ellipsometry
2. Physics and characterizationZsombor Pap1, Bálint Fodor1, László Makai1, Roland Weingärtner2, Sven Besendörfer2
1 Semilab Semiconductor Physics Laboratory Co. Ltd., Budapest, Hungary
2 Fraunhofer Institute for Integrated Systems and Device Technology IISB, Erlangen, Germany
Abstract text
As an ultra-wide bandgap material with a bandgap of 6.2 eV and excellent thermal conductivity, Aluminum nitride (AlN) is a very promising candidate for future high-frequency and power electronics applications.The refractive index of AlN is a key parameter for various technological applications, from optoelectronics to thermal management. Moreover, a thorough understanding of its optical properties in the widest spectral range is essential for modelling AlN-based structures for further metrology applications.
Former studies on AlN refractive index were carried out on thin layers by spectroscopic ellipsometry [1] and spectroscopic transmission measurements [2], which may differ from the bulk optical properties. In contrast, this study is dealing with the determination of the refractive index of bulk AlN grown by physical vapor transport with very high crystalline quality.Spectroscopic ellipsometry is a highly effective method [3] for measuring the bulk refractive index of Aluminum Nitride.
Spectroscopic ellipsometry is an absolute optical measurement method which measure the change in polarization of light upon reflection form a surface. It is highly sensitive around the Brewster’s angle when polarization component in the incident plane (p polarization) vanishes and the phase shift of the two polarization components changes from 0° to 180°. This sensitivity reveals the top surface structure of the sample. For extracting layer thickness and optical properties from the measured spectra a parametric model must be built, and fit must be performed on the parameters to conclude on the actual values describe sample properties. The aim of this study to investigate the bulk AlN optical dispersion from the UV to the IR range, revealing information about the top surface structure as well.For the AlN bulk samples a system of an individual layer on a semi-infinite substrate needs to be assumed to model the data. The substrate is the bulk AlN and exhibits a refractive index of 2.068 and the layer is a near-surface layer of a fitted thickness of 3.3 nm and a refractive index of 1.504. This layer might be related to surface oxide and/or to sub-surface damage due to polishing.
Spatially resolved spectroscopic ellipsometry measurements in comparison to complementary methods as X-Ray Topography will give further insights on the lateral surface structure of the AlN wafers.