Y. Negoro

Electronic behaviors of high-dose phosphorus-ion implanted 4H–SiC (0001)

High-dose phosphorus-ion (P+) implantation into 4H–SiC (0001) followed by high-temperature annealing has been investigated. Annealing with a graphite cap largely suppressed the surface roughening of implanted SiC. The surface stoichiometry of implanted SiC was examined by x-ray photoelectron spectroscopy. Electronic behaviors of P+-implanted SiC are discussed based on Hall effect measurements. There is no significant difference in the sheet resistance between SiC annealed with a graphite cap and without a graphite cap. The sheet resistance (resistivity) takes a minimum value of 45 Ω/□ (0.9 mΩcm) at an implant dose of 6.0×1016 cm−2. The sheet resistance shows a weak temperature dependence.

Stability of deep centers in 4H-SiC epitaxial layers during thermal annealing

N-type epitaxial 4H-SiC layers grown by hot-wall chemical vapor deposition were investigated with regard to deep centers by capacitance-voltage measurements and deep level transient spectroscopy (DLTS). The DLTS spectra revealed that the concentrations of deep centers were reduced by one order of magnitude by annealing at 1700°C, compared to those in an as-grown material. The Z1∕2 center with an energy level of 0.59±0.03eV and the EH6∕7 center with an energy level of 1.66±0.11eV below the conduction band edge are annealed out at a temperature of 1700°C or higher.

Electrical activation of high-concentration aluminum implanted in 4H-SiC

High-dose aluminum-ion (Al+) implantation into 4H-SiC (0001) and (112¯0) has been investigated. The dependences of the electrical properties on the implanted Al+ dose and on the annealing time were examined by Hall-effect measurements. A low sheet resistance of 2.3kΩ∕◻ (0.2μm deep) was obtained in a (0001) sample by implantation of Al+ with a dose of 3.0×1016cm−2 at 500°C and a subsequent high-temperature anneal at 1800°C for a short time of 1min. In the case of (112¯0) samples, even room-temperature implantation resulted in a low sheet resistance of 2.3kΩ∕◻ (0.2μm-deep) after anneal at 1800°C. The Hall data are compared with the calculated values determined by using the doping-concentration dependent ionization energy of Al acceptors. The experimentally obtained free-hole concentrations agree well with the theoretically expected values. Hole mobilities are not as high as the empirical mobilities obtained in Al-doped epitaxial layers. The differences in the electrical properties between the experimental d...

Carrier compensation near tail region in aluminum- or boron-implanted 4H-SiC(0001)

Electrical behavior of implanted Al and B near implant-tail region in 4H–SiC (0001) after high-temperature annealing has been investigated. Depth profiles of Al and B acceptors determined by capacitance-voltage characteristics are compared with those of Al and B atoms measured by secondary-ion-mass spectrometry. For Al+ (aluminum-ion) implantation, slight in-diffusion of Al implants occurred in the initial stage of annealing at 1700°C. The profile of the Al-acceptor concentration in a “box-profile” region as well as an “implant-tail” region is in good agreement with that of the Al-atom concentration, indicating that nearly all of the implanted Al atoms, including the in-diffused Al atoms, work as Al acceptors. Several electrically deep centers were formed by Al+ implantation. For B+ (boron-ion) implantation, significant out- and in-diffusion of B implants occurred in the initial stage of annealing at 1700°C. A high density of B-related D centers exists near the tail region. In the tail region, the sum of ...

Remarkable lattice recovery and low sheet resistance of phosphorus-implanted 4H–SiC (112̄0)

High-dose ion implantation of phosphorus into 4H–SiC has been investigated. Phosphorus ion implantation with a 1×1016 cm−2 dose at 800 °C into 4H–SiC (0001) has resulted in a sheet resistance of 80 Ω/□ after annealing at 1700 °C. A similar sheet resistance of 110 Ω/□ was achieved even by room-temperature implantation when 4H–SiC (1120) was employed, owing to excellent recrystallization of this face revealed by Rutherford backscattering channeling spectroscopy. The sheet resistance could be further reduced down to 27 Ω/□ by 800 °C implantation into 4H–SiC (1120) followed by annealing at 1700 °C. 4H–SiC (1120) showed a very flat surface after annealing.

Avalanche phenomena in 4H-SiC p-n diodes fabricated by aluminum or boron implantation

Characteristics of p-n junction fabricated by aluminum-ion (Al/sup +/) or boron-ion (B/sup +/) implantation and high-dose Al/sup +/-implantation into 4H-SiC (0001) have been investigated. By the combination of high-dose (4/spl times/10/sup 15/ cm/sup -2/) Al/sup +/ implantation at 500/spl deg/C and subsequent annealing at 1700/spl deg/C, a minimum sheet resistance of 3.6 k/spl Omega///spl square/ (p-type) has been obtained. Three types of diodes with planar structure were fabricated by employing Al+ or B+ implantation. B/sup +/-implanted diodes have shown higher breakdown voltages than Al/sup +/-implanted diodes. A SiC p-n diode fabricated by deep B+ implantation has exhibited a high breakdown voltage of 2900 V with a low on-resistance of 8.0 m/spl Omega/cm/sup 2/ at room temperature. The diodes fabricated in this study showed positive temperature coefficients of breakdown voltage, meaning avalanche breakdown. The avalanche breakdown is discussed with observation of luminescence.

Robust 4H-SiC pn diodes fabricated using (1120) face

Pn diodes with a planar structure were fabricated by acceptor-ion implantation into 4H–silicon carbide (SiC) (110). The (110) diode exhibited an on-resistance of 13.5 mΩcm2 and could block 1850 V. The width of intrinsic layers formed near the junction interface was analyzed using a model originally developed by the authors. The forward characteristics of the (110) diodes were negligibly deteriorated during a long-term stress measurement at a constant current density of 100 A/cm2 for 3 h, although most diodes fabricated using (0001) were degraded abruptly and irreversibly. This characteristic is very attractive for robust bipolar SiC devices using the (110) face.

Epitaxial Growth and Device Processing of SiC on Non-Basal Planes

Recent progress in silicon carbide (SiC) crystal growth and device processing technologies has enabled the fabrication of prototype high-power and high-frequency devices which outperform the conventional Si or GaAs counterparts. Since the development of step-controlled epitaxy [1], 4H- and 6HSiC(0001) wafers with several-degree off-angles have exclusively been employed for SiC homoepitaxy and device development except a few reports [2]–[5]. However, SiC metal-oxide-semiconductor field effect transistors (MOSFETs) have suffered from unacceptably low channel mobility, especially in 4H-SiC. Although significant improvements in channel mobility have been reported [6, 7], the maximum inversion-channel mobility of 4H-SiC(0001) MOSFETs is still below 30–50 cm2/Vs. From our demonstration of high channel mobility in MOSFETs using the (11–20) face [8], bulk and epitaxial growth, characterization, and device processing on this face have attracted attention from both scientific and industrial viewpoints. The authors have also proposed 4H-SiC(03–38), which is tilted by 54.7° from (0001) toward [01, 2, 3, 4, 5, 6, 7, 8, 9, 10], as a novel face with potentially superior quality of MOS interface [9].