GR-Th-P19 - Qualification of AlN substrates after different surface treatments
1. GrowthGloria Kurth1, Gleb Lukin1, Roland Weingärtner1, Sven Besendörfer1
1 Fraunhofer Institute for Integrated Systems and Device Technology IISB, 91058 Erlangen, Germany
Abstract text
Aluminium nitride (AlN) is an emerging ultra-wide bandgap with a direct bandgap of 6.0 eV and a critical field of 15.4 MV/cm, and thus suitable for power and RF applications. However, one of the remaining challenges is the time consuming and costly process technology ranging from crystal growth to Epi-Ready wafers as well as the realization of Epi-Ready surfaces themselves [1]. To verify surface as Epi-Ready, epitaxy can be performed. However, a non-destructive method to evaluate the spatial distribution of process-induced crystalline defects would be highly beneficial to save time and costs. This enables more efficient surface preparation and substrate classification for epitaxy and device processing.
This study investigates the correlation between subsurface damage and wafer bow induced by residual stress in AlN substrates. The primary focus is on characterizing surface roughness, waviness, and subsurface damage. Quantitative surface topography and roughness measurements are performed using tactile and optical profilometry after different surface treatments. To map surface damage, dislocations, and defect clusters on a full wafer scale, X-ray topography (XRT) is employed in both reflection and transmission modes. This method provides qualitative imaging of local inhomogeneities in the surface and subsurface regions, which is essential for qualifying the epi-ready surface after polishing. By precisely locating the remaining polishing scratches, a quantitative comparison with optical profilometry was performed to identify the regional topology. Additionally, XRT in transmission mode was experimentally utilized to capture cross-sectional recordings for a comparative analysis of front- and backside damage. The implementation of non-destructive evaluation techniques will enhance process efficiency, reduce costs, and improve the selection of high-quality AlN substrates for more reliable and scalable power electronics and optoelectronic devices.
[1] M. Xu, D. Wang, K. Fu, D.H. Mudiyanselage, H. Fu, Y. Zhao, 2022. A review of ultrawide bandgap materials: properties, synthesis and devices. Oxford Open Materials Science 2, itac004. https://doi.org/10.1093/oxfmat/itac004.