Defects in 4H-SiC Induced by High Energy Helium Implantation
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Defects in 4H-SiC Induced by High Energy Helium Implantation Marie F. Beaufort, Erwan Oliviero, Marie L. David, Alain Declémy, Christian Blanchard, Esidor Ntsoenzok1 and Jean F. Barbot Laboratoire de Métallurgie Physique UMR6630, BP30179, 86960Chasseneuil-Futuroscope, France 1 CNRS-CERI, 4A rue de la Férollerie, Orléans
ABSTRACT 1.6 MeV He+ ions were implanted at room temperature into (0001) 4H-SiC at a dose of 1x1017 cm-2 and then annealed at 1500°C for 30 min. Small bubbles are readily observed in the as-implanted sample but also an amorphous layer. After a 1500°C annealing, recrystallization of the amorphous state occurs and large bubbles or cavities are observed. However their shape strongly depends of their location inside the buried layer. The recrystallization consists of polytypisme, 4H-SiC growth along the c-direction from the substrate, columnar 4H-SiC and epitaxial growth of 3C-SiC.
INTRODUCTION In silicon, the implantation of helium or hydrogen ions leads to the formation of gasvacancy complexes that evolve in gas bubbles for a sufficient amount of incident ions. After subsequent annealing gas desorption occurs and large cavities or voids are observed [1]. These stable cavities show many technological applications such as impurity gettering or local lifetime control in power devices [2]. Since the wide band gap semiconductor SiC is of great interest as a material for power control and high speed communication devices, it should be also interesting to from stable cavities in these materials. A fundamental understanding of irradiation damage in SiC as well as their recovery is needed to advance in technological applications. However, ion implantation into SiC generates strong damage up to the amorphization [3] and recrystallization will occur during sufficient annealing. In this study we have examined cavity formation in n-type 4H-SiC by room temperature MeV helium implantation. MeV energy implantation provides the opportunity of localizing the damaged band and to minimize the surface effects.
EXPERIMENTAL DETAILS Cree research single-crystalline 4H-SiC (0001) wafers were implanted at room temperature with 1.6 MeV He+ ions using a van de Graaff accelerator. The ion dose used was 1x1017 cm-2 leading to a maximal ion peak concentration larger than the 1.6 at% required for bubble formation in silicon [1]. Annealing was thus done for 30 min at 1500°C under high vacuum. Cross-sectional TEM samples were prepared by an ion milling thinning procedure. The microstructure of the implanted zone was examined using a Jeol 200CX microscope operating at 200 KV.
RESULTS As observed in silicon small bubbles, 2-3 nm in diameter, are readily formed in the asimplanted SiC sample. As observed after the implantation of much heavier ions in SiC [4,5] E9.19.1
the helium implantation-induced microstructure can be divided in three parts. The central zone is amorphous whereas the top and bottom regions are single-crystalline zones of small defects (not shown here). Figure 1 shows a cross sectional TEM micrograph of annealed sa
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