A Method to Improve Activation of Implanted Dopants in SiC
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A Method to Improve Activation of Implanted Dopants in SiC O. W. Holland and D. K. Thomas Oak Ridge National Laboratory, Oak Ridge, TN 37831-6048
ABSTRACT Implantation of dopant ions in SiC has evolved according to the assumption that the best electrical results (i.e., carrier concentrations and mobility) are achieved by using the highest possible processing temperature. This includes implantation at > 600°C followed by furnace annealing at temperatures as high as 1750°C. Despite such aggressive and extreme processing, implantation suffers because of poor dopant activation, typically ranging between < 2%–50% with p-type dopants represented in the lower portion of this range and n-types in the upper. Additionally, high-temperature processing can led to several problems including changes in the stoichiometry and topography of the surface, as well as degradation of the electrical properties of devices. A novel approach for increasing activation of implanted dopants in SiC and lowering the activation temperature will be discussed. This approach utilizes the manipulation of the ion-induced damage to enhance activation of implanted dopants. It will be shown that nearly amorphous layers containing a small amount of residual crystallinity can be recrystallized at temperatures below 900°C with little residual damage. It will be shown that recrystallization traps a high fraction of the implanted dopant residing within the amorphous phase (prior to annealing) onto substitutional sites within the SiC lattice. INTRODUCTION Silicon carbide is a wide band-gap semiconductor that offers advantages over silicon for use in fabricating devices for high-power, high-temperature applications [1]. The ability to fabricate discrete devices and integrated circuits depends, in part, upon techniques for selective-area doping. Since the diffusivity of dopants in SiC is extremely low, selective-area doping by diffusion from a gaseous source is not viable. Therefore, dopant-ion implantation has come to the forefront as the technique of necessity, if not choice. However, successful implementation of implantation in SiC has been slow and uncertain, thus hindering efforts to develop SiC technology as an alternative to Si. By comparison, implantation of Si led the revolution in manufacturing that yielded electronic circuits at unprecedented levels of integration. The problem in SiC is that implanted dopants are difficult to activate [2]. This has lead to a “conventional” wisdom that teaches the use of extreme measures to activate implanted dopants including the use of annealing temperatures ≥ 1600°C, and heating the samples during implantation at ≥600°C [3]. Adherence to this wisdom does, however, create many problems. First, it is expensive and requires the development of implantation masks that can withstand irradiation at high temperature. Secondly, sublimation during high-temperature annealing disrupts the stoichiometry of the surface layer, which can lead to substantial surface roughening [4].
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A number of reports are at odds with this
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