Papers by Author: Masami Shibagaki

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: 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: We developed EBAS-100, which is available to 100 mm diameter SiC wafer, for post ion implantation annealing in order to realize silicon carbide (SiC) device with large volume production. EBAS-100 is able to perform the rapid thermal process due to the vacuum thermal insulation and small heat capacity of susceptor. Electrical power consumption density was 18.8 Wh/cm2 for EBAS-100, which is one-third smaller than that of our previous system (EBAS-50). Samples used in this study were p-type epitaxial 4H-SiC (0001) grown on 8o off SiC substrate. P+ ions (total dose; 2.0 x 1016 /cm2, thickness; 350 nm) were implanted into SiC samples at 500 oC. The root-mean-square (RMS) of surface roughness is estimated to be 0.21 nm for the sample annealed at 1700 oC for 5 min, which is much smooth than that of the sample annealed by the conventional RF inductive annealing (RMS value: 5.97 nm). Averaged sheet resistance (RS) value of 63.3 ohm/sq. is obtained with the excellent non-uniformity of RS (+/- 1.4 %) for the diameter of 76.0 mm.

Abstract: We develop the rapid thermal anneal system of the implanted SiC, Electron Bombardment Anneal System (EBAS), which is able to heat up to 1900 oC with a rate of 320 oC/min in vacuum. Using this novel system, the annealing of N+ implanted SiC samples (total dose: 2.4 x 1015 cm-2, thickness: 220 nm) at 1900 oC for 0.5 min results in a low sheet resistance of 1.39 x 103 ohm/sq. with extremely low roughness of the surface (RMS value: 0.32 nm). It is also demonstrated that EBAS can anneal the sample with low electric power consumption.