Papers by Author: Masataka Satoh

Abstract: In this paper, we demonstrate triple ion implanted 4H-SiC bipolar junction transistor (BJT) with etched extrinsic base regions. At the result of etching extrinsic base regions by mask of contact metals, maximum common emitter current gain was improved from 0.7 to 1.6.

Abstract: The impact of CF4 plasma treatment on the surface roughening of SiC has been investigated for N ion implanted SiC(0001) which is implanted with the energy range from 15 to 120 keV at a dose of 9.2 x 1014/cm2. The N ion implanted sample, which is processed by CF4 plasma, shows small surface roughness of 1.6 nm after annealing at 1700 oC for 10 min, while the sample without CF4 plasma treatment shows the large surface roughness (6.6nm) and micro step structure. XPS measurements reveals that CF4 plasma treatment is effective to dissolved the residual oxide on the surface of SiC which is not removed by BHF acid of SiO2 layer on SiC. It is strongly suggested that the formation of micro step structure with the increase of the surface roughness is promoted by the residual oxide such as SiCOx, on SiC.

Abstract: Electrical properties of p+n 4H-SiC(0001) diode formed by Al ion implantation to n-type epitaxial layer have been investigated as a function of Al doping concentration ranging from 1 x 1020 to 6 x 1020 /cm3 and the operation temperature. The n-type 4H-SiC(0001) epitaxial layer with a net donor concentration of 1 x 1016 /cm3 are multiply implanted by Al ions in the energy range from 30 to 170 keV at elevated temperature of 500 oC with a implantation layer thickness of 350 nm, followed by the annealing at 1900 oC for 1min using EBAS. On-state resistance of diode with Al concentration of 1 x 1020 /cm3 is estimated to be about 4.5 mcm2, while that for diode with Al concentration of 6 x 1020 /cm3 is 1.8 mcm2 at 25 oC. In the sample with Al concentration of 6 x 1020 /cm3 shows the positive temperature coefficient of on-state resistance of diode, while that for sample with Al concentration less than 3 x 1020 /cm3 is negative. The diode formed by Al implantation at the concentration of 6 x 1020 /cm3 is able to operate at the constant current density of 80 A/cm2 at the bias of 2.9 V independent to operation temperature.

Abstract: We investigate the structural and electrical properties of polycrystalline 3C-SiC obtained from P ion implanted 4H-SiC with the box-shaped doping profile (NP: 6 x 1020/cm3, thickness: 400 nm, ion dose: 1.6 x 1016/cm2, room temperature). RBS measurement reveals that the highly defective region is formed by P ion implantation, which remains even after annealing at 1700 oC. X-TEM observation shows the P ion induced amorphous layer is recrystallized to twinned-3C-SiC. After annealing at 1300 oC, a sheet resistance of 950 /sq. and sheet carrier concentration of 1 x 1015/cm2 was obtained. By increasing the annealing temperature from 1500 to 1700 oC, the sheet resistance was drastically decreased to about 200 /sq., while there was a small change in the sheet carrier concentration. For the sample annealed at 1700 oC, the electrical activity of the P impurity was estimated to be about 10 % which is comparable to the case of hot implanted sample.

Abstract: It is demonstrated that Si ion implantation is useful to fabricate GaN/AlGaN/GaN HEMTs with extremely low gate leakage current and low source resistance without any recess etching process. The source/drain regions were formed using Si ion implantation into undoped GaN/AlGaN/GaN on sapphire substrate. Using ion implantation into source/drain regions with energies of 30 and 80 keV, the performances were significantly improved. On-resistance reduced from 9.9 to 3.5 Ω·mm. Saturation drain current and maximum transconductance increased from 300 to 560 mA/mm and from 75 to 160 mS/mm, respectively.

Abstract: The I-V characteristics of p+n 4H-SiC diode formed by Al ion implantation have been investigated as a function of annealing temperature. Al ions are implanted at the elevated sample temperature of 500 oC in order to fabricate p-type doped layer on the n-type epitaxial layer, grown on n+ 4H-SiC substrate. The implanted sample is annealed using electron bombardment annealing system in the annealing temperature ranging from 1700 to 1900 oC. The Al implanted sample, annealed below 1800 oC shows the deteriorated I-V characteristics in which the forward current includes the resistive current components and the reverse current is in the order of 10-4 A/cm2. The p+n diode formed by annealing at 1900 oC reveals the forward current without extra-current components and the reverse current as low as 10-6 A/cm2. It is suggested that the annealing above 1900 oC is effective in reducing the implantation-induced defect at the interface between Al implanted p+ layer and the underlying n-type epitaxial layer.

Abstract: We fabricate pn-junction diode on p-type 4H-SiC(0001), in which n-type region is formed by N ion implantation at room temperature (total dose: 2.4 x 1015 /cm2, thickness: 300 nm) and subsequently annealed for 5 min using electron bombardment annealing system (EBAS). The root-mean-square (RMS) surface roughness and sheet resistance (Rs) for N ion implanted region, annealed at 1900 oC is estimated to be 0.7 nm and 940 4/sq., respectively. The alloyed Ni ohmic contact to N ion implanted layer, annealed at 1900 oC, shows the contact resistance (Rc) of 8.3 x 10-5 4cm2. The forward drop voltage at 100 A/cm2 and on-resistance of mesa-type pn junction diode is estimated to be 3.1 V and 1.3x10-2 4cm2. The reverse bias leakage current of that is 2.2 x 10-5 A/cm2 at 100 V. It is demonstrated that EBAS is able to apply for the fabrication of pn-junction diode.

Abstract: The specific contact resistance of Al, Ti and Ni ohmic contacts to N+ implanted 3C-SiC(100) has been investigated by means of TLM method. The p-type epitaxial layer grown on n+ substrate is multiply implanted with N ions with energy ranging from 15 to 120 keV at a total dose of 1.4×1015 cm-2 at room temperature and is subsequently annealed by RF annealer at a temperature of 1400 oC for 10 min in Ar gas flow, resulting in the sheet resistance of 130 0/sq. The deposited Al layer on the annealed sample shows the extremely low specific contact resistance of about 1×10-7 0cm2. The ohmic contacts of Ti and Ni also show the specific contact resistance of 5×10-6 and 2×10-5 0cm2, respectively. The obtained specific contact resistance is proportional to the Schottky barrier height of metal cotact to n-type 3C-SiC. The annealing of Ni ohmic contact above 600 oC results in the considerable reduction of specific contact resistance due to the silicidation of Ni.

Abstract: The encapsulating annealing of N+ implanted 4H-SiC(0001) is performed using diamondlike- carbon (DLC) films for the suppression of surface roughening. 4H-SiC(0001) sample with an off-orientation of 8o is multiply implanted by N+ with energy ranging from 15 to 120 keV at a total dose of 2.4×1015 cm-2 at room temperature. DLC films with thickness ranging from 0.3 to 1.8 μm are deposited on the surface of implanted sample using plasma-based ion implantation equipment with C2H4 gas. The DLC capped sample is annealed at 1500 oC for 5 min using IR image annealer. After annealing, DLC film is removed by the oxidization. The sample capped by DLC film with a thickness of 0.3 μm shows the root mean square (RMS) surface roughness of 0.6 nm while the annealed sample without DLC film shows RMS surface roughness of 5.2 nm. As the thickness of DLC film is increased from 0.3 to 1.8 μm, the RMS surface roughness is decreased from 0.6 to 0.2 nm.

Abstract: The electrical properties of N ion implanted 3C-SiC(100) have been investigated by means of Hall effect measurement. The p-type epitaxial layer grown on n+ substrate is multiply implanted with N ions with energy ranging from 15 to 120 keV at a total dose of 2.4×1015 cm-2 at room temperature, which corresponds to the doping layer with a N concentration of 1×1020 cm-3 and a thickness of 250 nm. The implanted sample is annealed by RF inductive heating annealer at temperature ranging from 1000 to 1500 oC for 10 min in Ar gas flow. The sample annealed at 1000 oC shows the sheet resistance of 1 k./sq. The sheet resistance of the implanted sample is decreased with the increase of annealing temperature. The sample annealed at 1500 oC shows the sheet resistance of 81 ./sq. and the sheet carrier concentration of 1.6×1015 cm-2. The electrical activity of implanted N impurity is estimated to be 68 %, which is much larger than that of N ion implanted 4H-SiC (about 0.9 %). The higher electrical activity of implanted N impurity is attributed to the shallower donor level than that in 4H-SiC.