Techniques for Depth Profiling of Dopants in 4H-SiC

Three different methods for measuring the depth distribution of dopants in 4H-SiC have been investigated: (1) Spreading Resistance Profiling (SRP), (2) Scanning Capacitance Microscopy(SCM) and (3) Scanning Electron Microscopy (SEM). The investigated samples included p- and n-type epitaxial layers grown by vapor phase deposition with doping concentrations of 10E16 - 10E20 cm-3. Also p+n implanted profiles using a combination of Al and B multi-energy implantation were studied. All techniques were able to provide doping profiles qualitatively corresponding to Secondary Ion Mass Spectrometry (SIMS) data. The SRP results suggest a lower limit of the p-doping concentration below which the ohmic contact between the probe tip and sample become more Schottky-like. The magnitude of the SCM signal corresponds well to the chemical doping profile except in the depleted region surrounding the metallurgical junction of the p+n structure.