Invited Paper EM+AS+MS+SS-WeA1
Effects of Nitrogen and Antimony Impurities at SiO₂/SiC Interfaces

Wednesday, October 21, 2015, 2:20 pm, Room 211C

4H-SiC is an attractive material for devices operating at high power and high temperatures because of the large bandgap energy, 3.23 eV, the high critical breakdown field, 2.0 MVcm^-1, and high electron mobility,

850 cm²V^-1s^-1. Commercialization of 4H-SiC MOSFET technology was long delayed due to the high density of defects near the SiO₂/SiC interface. Post oxidation annealing in NO ambient, the process that enabled the commercialization of SiC Power ICs in 2011, significantly reduces the density of near-interface traps and results in typical effective MOSFET channel electron mobility (µ_FE) values of ~20 cm²V^-1s^-1 [1]. The relatively high density of near-interface traps having energy levels within 0.5 eV of the SiC conduction band was investigated using constant capacitance transient spectroscopy (CCDLTS). These measurements showed that NO annealing reduced the density of the two near-interface oxide trap distributions, attributed to Si interstitials and substitutional C pairs in SiO₂, by as much as a factor of 10 [1,2].

It has also been shown that introducing impurities such as Na, P, or Sb near the SiO₂/SiC interface further increases µ_FE , to peak values of 104 cm²V^-1s^-1 and to 50 cm²V^-1s^-1 at high electric field for Sb [3]. The much higher value of µ_FE in Sb-implanted MOSFETs was attributed to counter-doping by Sb in SiC near the interface. To investigate the effects of Sb at SiO₂/SiC interfaces, Sb ions were implanted near the surface of the 4H-SiC epitaxial layer and the wafer was annealed at 1550 ̊C in Ar to activate the Sb donors. Dry thermal oxidation was done at 1150 ̊C and the sample was then NO-annealed at 1175 ̊C for 30 or 120 min. CCDLTS results of Sb-implanted MOS capacitors were compared with those having no Sb implant but with similar dry oxidation and NO-annealing processes. The density of near-interface oxide traps was similar in samples with and without Sb, indicating that Sb has little effect on those defects. However, CCDLTS spectra taken at bias and filling pulse conditions that reveal defects in the SiC depletion region, show both the deeper of the two N donor levels at E_C - (0.10±0.01) eV and a second energy level only in Sb-implanted samples at E_C - (0.12±0.01) eV. To our knowledge this is the first measurement of Sb donors in SiC and it confirms counter doping of SiC by Sb near the SiO₂/SiC interface.

[1] P.M. Mooney and A.F. Basile, in Micro and Nano-Electronics: Emerging Device Challenges and Solutions, Ed. T. Brozek (CRC Press, Taylor and Francis, 2014) p. 51.

[2] A.F. Basile, et al., J. Appl. Phys. 109, 064514 (2011).

[3] A. Modic, et al., IEEE Electron Device Lett. 35, 894 (2014).