Recrystallization Characteristics of Amorphous Si
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RECRYSTALLIZATION CHARACTERISTICS OF AMORPHOUS Si RODNEY A. HERRING AND ERIC M. FIORE Martin Marietta Laboratories, 1450 South Rolling Road, Baltimore, MD21227-3839. ABSTRACT The microstructure of high-energy (0.5-6.0 MEV)As-ion implanted Si and rapid thermal annnealed (RTA'd) Si has been studied by transmission electron microscopy (TEM). The implantations formed buried amorphous layers that recrystallized during RTA at different temperatures and became either single crystal or polycrystalline depending on their •plan~ation energy and fluence. At energies > 2.5 MeV and fluences < 10 cm-, recrystallization occurred below 4000C ajg reg~owth was single crystal. At an energy of 6 MeY and fluence of 5 x 10 cm- recrystallization occurred above 6000C and regrowth was polycrystalline. When ýhe implantation energy and fluence were reduced to 0.5 MeV and 2 x 10k' cm- , respectively, recrystallization occurred above 6000 C and regrowth was polycrystalline. The above results are explained by both the formation mechanisms of amorphous Si resulting from ion implantation and the structural order of a-Si. INTRODUCTION At present there is very little information on the implanted and annealed structures resulting from high-energy implants. High-energy implants into semiconductor materials are important for fabrication of new types of electronic devices requiring deep doped regions. We have implanted Si with a range of high-energy (0.5-6.0 MeV) As ions for use as an extrinsic-Si infrared detector and found the implanted and annealed structures to depend on implant energy and fluence. The implantations create amorphous Si (a-Si), which can exist as different locally-ordered structures. The low-order and high-order amorphous phases differ in the fluctuations of the bond angle of the tetrahedrally coordinated Si, with the high order having the smallest deviation. These variations have recently been measured by the Raman scattering technique [1] for energies between 30 and,420 keV in ionimplanted Si to fluences varying from 10 to 4 x 10 cm- . High- and low-order amorphous phases were obtained by varying the energy, dose, and mass of implanted ions, with the high order a-Si forming at the higher energies. Kirillov et al. [1] attributed the formation of high order a-Si to ion beam annealing (IBA) effects. IBA has been seen to decrease the aSi layer thickness as the dose rate is increased [2,3]. In addition, Kirillov et al. [1] annealed the amorphized Si by RTA and found that the regrowth of the high order a-Si was much faster and started at a lower temperature (-450 0 C) than the low order a-Si (-600C). We have seen similar regrowth variations although we have increased the implantation energy by about an order of magnitude and used TEM techniques to characterize the microstructure. Our results show that from the highenergy As-ion implanted and annealed microstructure both orders of a-Si are likely to be present. Based on these results, we explain why a-Si recrystallizes polycrystalline in some cases and single crystal in others.
Mat. Res
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