Wetteroth, T.; Wilson, S. R.; and Powell, Adrian R., "Carrier concentration and lattice absorption in bulk and epitaxial silicon carbide determined using infrared ellipsometry" (1999 Carrier concentration and lattice absorption in bulk and epitaxial silicon carbide determined using infrared ellipsometry We have measured the dielectric function of bulk nitrogen-doped 4H and 6H SiC substrates from 700 to 4000 cm Ϫ1 using Fourier-transform infrared spectroscopic ellipsometry. Photon absorption by transverse optical phonons produces a strong reststrahlen band between 797 and 1000 cm Ϫ1 with the effects of phonon anisotropy being observed in the region of the longitudinal phonon energy ͑960 to 100 cm Ϫ1 ͒. The shape of this band is influenced by plasma oscillations of free electrons, which we describe with a classical Drude equation. For the 6H-SiC samples, we modify the Drude equation to account for the strong effective mass anisotropy. Detailed numerical regression analysis yields the free-electron concentrations, which range from 7ϫ10 17 to 10 19 cm Ϫ3 , in good agreement with electrical and secondary ion mass spectrometry measurements.Finally, we observe the Berreman effect near the longitudinal optical phonon energy in nϪ/nϩ homoepitaxial 4H SiC and hydrogen implanted samples, and we are able to determine the thickness of these surface layers.

Articles you may be interested inVisible to vacuum ultraviolet dielectric functions of epitaxial graphene on 3C and 4H SiC polytypes determined by spectroscopic ellipsometry Details of below band-gap uniaxial dielectric function of SiC polytypes studied by spectroscopic ellipsometry and polarized light transmission spectroscopy Spectroscopic rotating-analyzer ellipsometry employing a compensator and optical transmission were used to measure the dielectric functions of bulk 4H and 6H SiC from 0.72 to 6.6 eV for light propagating nearly parallel to the hexagonal axis. The measurements below the band gap show the presence of a thin surface layer, which was modeled as SiO 2 . The data are similar to results for cubic ͑3C͒ and 6H SiC from the literature, but differences are notable, particularly above 4 eV. At 5.56 eV, we observe a critical point in 4H SiC, which is assigned to direct interband transitions along the UϭM ϪL axis in the hexagonal Brillouin zone after comparison with band structure calculations. No evidence for direct transitions below 6.5 eV was found in 6H SiC. We apply our results to the analysis of a 4H SiC film on insulator ͑SiCOI͒ produced by high-dose hydrogen implantation and direct wafer bonding on Si. For comparison, we also studied a 1 m thick epitaxial layer of 3C SiC on Si, where the interference oscillations are influenced by surface and interface roughness.

H + implantation of SiC is the basis for a thin-film transfer process, which when combined with oxidation and hydrophilic wafer bonding, can be exploited to produce silicon carbide-on-insulator material useful as a wide-band-gap semiconductor. This thin-film transfer process has been successfully applied to Si to produce a commercial silicon-on-insulator material. The efficacy of hydrogen to produce thin-film separation was studied by investigation of H+-induced exfoliation in implanted SiC. Results showed that the onset and degree of exfoliation of SiC depends initially upon the concentration of implanted H+. However, the dose dependence of exfoliation exhibits a rather marked retrograde behavior. The degree of exfoliation eventually starts to decrease with increasing ion dose until exfoliation is completely suppressed. This behavior is attributed to a competition between the positive effects of hydrogen on exfoliation and the negative effects of ion-induced damage. Experiments were done to isolate the effects of the hydrogen–silicon chemistry from that of implant damage. Damage is reduced independently of H+ dosage by elevating the temperature of the SiC during implant in order to promote dynamic annealing. This will be shown to have a dramatic effect upon exfoliation. The “hot” implant lowers the H+ fluence required to affect thin-film separation, making the process more efficient, and producing SiC material with fewer defects.

Lateral gettering is implemented in thin-film silicon-on-insulator (TFSOI) substrates by introducing crystalline defects in the vicinity of metal-oxide-semiconductor device channel regions prior to gate oxidation. As a result of the gettering a significant improvement in gate oxide integrity is achieved, with increased oxide breakdown voltages and charge-to-breakdowns, as well as a reduction in localized oxide charge trapping. The same gettering effect on separation-by-implantation-of-oxygen and bonded silicon-on-insulator substrates suggests that the lack of effective gettering is mainly responsible for the oxide degradation regardless of the TFSOI type. This work also demonstrates the feasibility of achieving bulk-comparable gate oxides on TFSOI substrates.

Thin film silicon-on-insulator (SOI) devices have an advantage of excellent isolation due to the buried oxide layer leading to reduced capacitance coupling and no latchup in complementary metal-oxide-silicon circuits compared with bulk silicon devices. Reduced junction area should lead to lower leakage for a given device. However, because of the buried oxide, stress is built up in the Si island during isolation processes, especially near the island edges, inducing new kinds of leakage currents, which are not observed in bulk silicon devices. This letter proposes five leakage current models of the partially depleted SOI devices, identifies their origins, and suggests methods to prevent each type.