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Ion implantation is extensively used in semiconductor device manufacturing to introduce dopants and it has been an extremely successful technique for elemental semiconductors such as silicon. In compounds it has proven much more difficult to activate the implanted species and anneal the lattice damage, which is an inevitable part of the implantation process. One of the most advanced wide bandgap semiconductors is silicon carbide (SiC), but even for this material there is a lack of understanding of damage production during ion implantation, and the post-implant annealing process.
Here we investigate the damage resulting from He ion implantation in 4H-SiC. We implanted several fluencies, up to 3×1014 cm-3, and energies of 4.0, 5.0, and 6.0 MeV of 4He+ in highly doped substrate wafers. Based on deep level transient spectroscopy (DLTS) results and simulation of the He-induced damage using TRIM, the fluency was selected to produce a damage level that would considerably compensate the substrate doping around the mean projected range, but still preserve the crystalline order.
The induced doping compensation was monitored by scanning spreading resistance microscopy (SSRM) on cross sections of the implanted samples. SSRM uses an atomic force microscope to measure the probe/sample resistance, which is mostly dominated by the spreading resistance of the investigated sample. The implanted helium ions are electrically neutral, but the deposited energy results in point defects that traps charge carriers and lowers the net doping in the sample. Due to the highly non-linear energy deposition process, the concentration of point defects is peaked close to the end-of-range of the He ions. The mean projected range and shape of the damage profiles agrees well with TRIM simulations of the carbon and silicon vacancy distribution.
Quantitative information about the number of trapping defects can be obtained from the SSRM data, assuming a constant mobility. These defect concentrations are of the same order of magnitude as the doping concentration, around 1019 cm-3 , and we also compare these values with defects concentration values measured by DLTS at lower ion fluencies, and Rutherford backscattering spectrometry data recorded for higher fluencies. |