Strain Analysis of High Energy Implanted 4H-SiC Epiwafer By Synchrotron X-Ray Plane Wave Topography

Abstract

Silicon Carbide (SiC) is a promising wide bandgap semiconductor for power devices. Due to excellent properties of SiC, such as wide band gap, high break down voltage and thermal stability, SiC devices are able to be operated under harsh environment, such as high temperature, high voltage and high frequency environment [1]. 4H-SiC high voltage devices are highly sought for applications, such as hybrid vehicles, shipboard and power grid systems, and high-speed trains. Usually, such medium or high voltage devices are fabricated on 4H-SiC wafers with thick epilayers that will increase the resistance of the device specially at high temperatures. Deep implanted SiC superjunction devices have the potential to replace planar devices for medium voltage applications [2] However, forming deep implanted pillars into thick epilayers is quite challenging. An optimized solution of selective area doping is utilizing multi-steps high energy ion implantation system. Such a system has been developed at the Tandem Van de Graaff accelerator facility at Brookhaven National Laboratory with the capability of multi-steps high energy implantation at energies up to 150 MeV [3]. By employing such a system, medium voltage charge balance devices and 2 kV superjunction structure PIN diode have been demonstrated [4-5]. Implantation employing high energy ions can create lattice strain in the epilayer by displacing the host atoms. Therefore, characterization of strain in as-implanted epilayer is critical to understand the nature of damage introduced by the high energy implantation.Here, we employ synchrotron X-ray plane wave topography (SXPWT), where X-rays with energy of 8 keV is initially monochromatized by double crystal Si (111) monochromator followed by tuning with an asymmetric Si (331) beam conditioner. The effective width of the resultant X-ray beam is lowered to 0.5” due to the asymmetric factor of the beam conditioner [6]. Therefore, the angular resolution of SXPWT is vastly enhanced, enabling miniscule distortions in the lattice to be detected.The diffraction intensity profile from a 4H-SiC epiwafer implanted with Al ions to (concentration) using this effectively plane wave X-ray beam is shown in Fig. 1. Two high intensity peaks and weak intensity fringes in between, with an angular separation of only 2ʹʹ can be observed. This illustrates non-uniform strain in the implanted epilayer. Intensity profile of peaks and fringes is extracted from the topograph then fitted with commercial Rocking-curve Analysis by Dynamical Simulation (RADS) software developed by Bede to obtain the strain profile. The fitted curve and strain profile are shown in Fig.2. The strain profile will be analyzed and compared with doping profile obtained by Secondary Ion Mass Spectrometry (SIMS).[1] J. Guo, Y. Yang, B. Raghothamachar, T. Kim, M. Dudley, J. Kim, J. Cryst. Growth[2] L. C. Yu and K. Sheng, Solid State Electron., vol. 50, no. 6, pp. 1062-1072, 2006.[3] P. Thieberger, C. Carlson, D. Steski, R. Ghandi, A. Bolotnikov, D. Lilienfeld, P. Losee, Nucl. Instrum. Methods Phys. Res. B: Beam Interact. Mater. At.[4] R. Ghandi, C. Hitchcock, S. Kennerly, ECS Transactions 104, 67 (2021)[5] R. Ghandi, A. Bolotnikov, S. Kennerly, C. Hitchcock, P.-m. Tang, T.P. Chow, 2020 32nd International Symposium on Power Semiconductor Devices and ICs (ISPSD), IEEE, 2020, pp. 126-129.[6] H. Peng, Z. Chen, Y. Liu, B. Raghothamachar, X. Huang, L. Assoufid and M. Dudley, J. Appl. Crystallogr. (accepted) Figure 1