Silicon carbide (SiC), a material long known with potential for high-temperature, high-power, high-frequency, and radiation hardened applications, has emerged as the most mature of the wide-bandgap (2.0 eV ≲ Eg ≲ 7.0 eV) semiconductors since the release of commercial 6HSiC bulk substrates in 1991 and 4HSiC substrates in 1994. Following a brief introduction to SiC material properties, the status of SiC in terms of bulk crystal growth, unit device fabrication processes, device performance, circuits and sensors is discussed. Emphasis is placed upon demonstrated high-temperature applications, such as power transistors and rectifiers, turbine engine combustion monitoring, temperature sensors, analog and digital circuitry, flame detectors, and accelerometers. While individual device performances have been impressive (e.g. 4HSiC MESFETs with fmax of 42 GHz and over 2.8 W mm−1 power density; 4HSiC static induction transistors with 225 W power output at 600 MHz, 47% power added efficiency (PAE), and 200 V forward blocking voltage), material defects in SiC, in particular micropipe defects, remain the primary impediment to wide-spread application in commercial markets. Micropipe defect densities have been reduced from near the 1000 cm−2 order of magnitude in 1992 to 3.5 cm−2 at the research level in 1995.

Status of silicon carbide (SiC) as a wide-bandgap semiconductor for high-temperature applications: A review

Experimental studies on aluminum (Al) and boron (B) implantation in 4H/6H SiC are reported; the implantation is conducted at room temperature or elevated temperatures (500 to 700 C). Both Al and B act as ``shallow`` acceptors in SiC. The ionization energy of these acceptors, the hole mobility and the compensation in the implanted layers are obtained from Hall effect investigations. The degree of electrical activity of implanted Al/B atoms is determined as a function of the annealing temperature. Energetically deep centers introduced by the Al{sup +}/B{sup +} implantation are investigated. The redistribution of implanted Al/B atoms subsequent to anneals and extended lattice defects are monitored. The generation of the B-related D-center is studied by coimplantation of Si/B and C/B, respectively. (orig.) 60 refs.

Doping of SiC by Implantation of Boron and Aluminum

Silicon carbide with its outstanding physical properties is a material of choice for special optoelectronic and electronic devices working under extreme conditions. Synthesis as well as processing are complicated compared to other materials. The present paper summarizes some aspects of crystal growth and processing and discusses arising problems.

Silicon carbide: Synthesis and processing

Silicon carbide semiconductor devices and methods of fabricating silicon carbide semiconductor devices have a silicon carbide DMOSFET and an integral silicon carbide Schottky diode configured to at least partially bypass a built in diode of the DMOSFET. The Schottky diode may be a junction barrier Schottky diode and may have a turn-on voltage lower than a turn-on voltage of a built-in body diode of the DMOSFET. The Schottky diode may have an active area less than an active area of the DMOSFET.

Silicon carbide MOSFETs with integrated antiparallel junction barrier Schottky free wheeling diodes and methods of fabricating the same

Silicon carbide (SiC) devices have the potential to yield new components with functional capabilities that far exceed components based on silicon devices. Selective doping of SiC by ion implantation is an important fabrication technology that must be completely understood if SiC devices are to achieve their potential. One major problem with ion implantation into SiC is the surface roughening that results from annealing SiC at the high temperatures which are needed to activate implanted acceptor ions, boron or aluminum. This paper examines the causes and possible solutions to surface roughening of implanted and annealed 4H-SiC. Samples consisting of n-type epilayers (5 × 1015 cm−3, 4 µm thick) on 4H-SiC substrates were implanted with B or Al to a total dose of 4 × 1014 cm−2 or 2 × 1015 cm−2, respectively. Roughness measurements were made using atomic force microscopy. From the variation of root mean square (rms) roughness with annealing temperature, apparent activation energies for roughening following implantation with Al and B were 1.1 and 2.2 eV, respectively, when annealed in argon. Time-dependent activation and surface morphology analyses show a sublinear dependence of implant activation on time; activation percentages after a 5 min anneal following boron implantation are about a factor of two less than after a 40 min anneal. The rms surface roughness remained relatively constant with time for anneals in argon at 1750°C. Roughness values at this temperature were approximately 8.0 nm. Annealing experiments performed in different ambients demonstrated the benefits of using silane to maintain good surface morphology. Roughnesses were 1.0 nm (rms) when boron or aluminum implants were annealed in silane at 1700°C, but were about 8 and 11 nm for B and Al, respectively, when annealed in argon at the same temperature.

Surface roughening in ion implanted 4H-silicon carbide

Low (keV) and high (MeV) energy Al and B implants were performed into n‐type 6H‐ and 3C‐SiC at both room temperature and 850 °C. The material was annealed at 1100, 1200, or 1400 °C for 10 min and characterized by secondary ion mass spectrometry, Rutherford backscattering (RBS), photoluminescence, Hall and capacitance‐voltage measurement techniques. For both Al and B implants, the implant species was gettered at 0.7 Rp (where Rp is the projected range) in samples implanted at 850 °C and annealed at 1400 °C. In the samples that were amorphized by the room temperature implantation, a distinct damage peak remained in the RBS spectrum even after 1400 °C annealing. For the samples implanted at 850 °C, which were not amorphized, the damage peak disappeared after 1400 °C annealing. P‐type conduction is observed only in samples implanted by Al at 850 °C and annealed at 1400 °C in Ar, with 1% dopant electrical activation.

Al and B ion‐implantations in 6H‐ and 3C‐SiC

A1 and B implantations were performed into n-type 6H-bulk SiC and epitaxial layers at both room temperature and 850°C. Annealings were performed in the temperature range of 1100–1650°C in a SiC crucible. For single-energy implants, the implant gettered to the 0.7Rp location for annealing temperatures ≥1400°C. For the 850°C implanted samples the RBS yield in the annealed material is comparable to the yield in the as-grown material, indicating a good lattice recovery. A maximum activation of 18% for Al-implanted samples was observed. PN junction diodes were made using Al-implanted material.

PN junction formation in 6HSiC by acceptor implantation into n-type substrate

Multiple-energy Al implantations were performed with and without C or Si coimplantations into 6H-SiC epitaxial layers and bulk substrates at 850°C. The C and Si co-implantations were used as an attempt to improve Al acceptor activation in SiC. The implanted material was annealed at 1500, 1600, and 1650°C for 45 min. The Al implants are thermally stable at all annealing temperatures and Rutherford backscattering via channeling spectra indicated good lattice quality in the annealed Al-implanted material. A net hole concentration of 8 × 1018 cm−3 was measured at room temperature in the layers implanted with Al and annealed at 1600°C. The C or Si co-implantations did not yield improvement in Al acceptor activation. The co-implants resulted in a relatively poor crystal quality due to more lattice damage compared to Al implantation alone. The out-diffusion of Al at the surface is more for 5Si co-implantation compared to Al implant alone, where 5Si means a Si/Al dose ratio of 5.

Peter Griffiths

Papers

Al and B ion‐implantations in 6H‐ and 3C‐SiC

PN junction formation in 6HSiC by acceptor implantation into n-type substrate

Al, Al/C and Al/Si implantations in 6H-SiC

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