High Energy Implantation of Boron in 4H-SiC
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P.O.Box Electrum 233, S-164 40 Kista Stockholm, Sweden Institute of Technology, Department of Solid State Electronics, P.O.Box Electrum 229, S-164 40 Kista Stockholm, Sweden 3ABB Corporate Research c/o IMC, P.O.Box Electrum 233, S-164 40 Kista Stockholm, Sweden 11MC,
2 Royal
ABSTRACT The high energy implantation of boron into n-type Silicon Carbide epitaxial layers of the polytype 4H was investigated for various sample temperatures during implantation and different doping concentrations. Depth profiling using secondary ion mass spectrometry was applied to determine the boron distribution in the as-implanted epilayers and the re-distribution of boron atoms during a half hour heat treatment at a temperature of 1700 0C. The SIMS boron profiles are compared to numerical Monte Carlo calculations using the program TRIM96 and to electrical profiling by scanning capacitance microscopy. In general we found that boron is moving towards the implantation damage already during the implantation of a profile with four different energies. The defect enhanced diffusion of boron is more pronounced during the high temperature anneal, where a higher concentration of boron diffusing towards the sample surface was observed. Into the bulk of the epilayer the boron diffusion is on a lower level and shows an exponential decay with a length of up to 5 Pm. An out-diffusion of boron during the post implantation anneal was not observed at implantation temperatures up to 500 'C. Electrical profiling using scanning capacitance microscopy revealed that complicated layer structures with several pn-junctions can occur due to the re-distribution of boron during post implantation anneal. INTRODUCTION The intrinsic material properties of SiC motivate the fabrication of a next generation of high power, high frequency devices, operating at high temperatures or in aggressive media. To fabricate these next generation of devices a reproducible control of the incorporation and activation of dopants is crucial. Besides the dopant incorporation during crystal growth, implantation is widely used for doping of SiC, whereas diffusion is less applicable because of the low diffusion coefficients of the commonly used acceptor and donor dopants. Only small elements like hydrogen, lithium, beryllium, and boron have a significantly larger diffusion coefficient in SiC. For device structures, where dopants have to be incorporated locally in a precise way, implantation is the technique to be used. To activate the implanted dopants and to reduce the created damage the implantation process is commonly combined with a high temperature treatment [1,2]. During this post implantation anneal process temperatures in the range of around 1700 'C for a duration of 30 min are applied. In addition, it has been shown that implantation at elevated temperatures (T < 1200'C) leads to a higher activation of the introduced dopants and a further reduction of the created damage [2]. 469 Mat. Res. Soc. Symp. Proc. Vol. 512 ©1998 Materials Research Society
We have investigated high energy
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