日本大学生産工学部研究報告A(理工系)第52巻第2号
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─ 4 ─not appear in the pattern. Failure of detection of the NiSi layer indicates that the layer is very thin, which agrees with the pre-vious reports9). On the other hand, the free carbon will not ap-pear if it is amorphous. Also the pattern (b) consists of the peaks of SiC and Ni2Si, being similar to the pattern (a). The initial thicknesses of the Ni and Ti layers of this sample are 100 and 16 nm, respectively, which corresponds approximate-ly to the composition of Ni-10 mol%Ti. Therefore, the peaks of NiSi, TiC and Ni3Ti are expected to appear in addition to those present in the pattern. It is likely that the Ti layer is con-sumed by the interlayer reaction before the Ni adjacent to SiC changes to Ni3Ti. SiC starts to react with this unchanged Ni. In this way, the XRD pattern of the sample becomes almost the same with the pattern (a). In the pattern (c) of Fig. 3, a peak of TiC appears at the dif-fraction angle of 41.88°, indicating that a considerable amount of TiC is successfully formed at the interface and thus the for-mation of the free carbon is suppressed. Even in this pattern, however, the peaks of Ni-Ti intermetallic compounds are not found. It is hardly expected that the lm of which total thick-ness is 180 nm is completely consumed by the reaction with SiC. A further analysis is needed to clarify the interfacial phe-nomena during annealing and the resultant structure. The interfacial reaction fails to form Ni-Si compounds and TiC when the Ti layer is very thick. In the pattern (d) of Fig. 3, Ti5Si3 and Ti3SiC2 are detected instead of TiC. Furthermore, the lm after annealing is easily peeled off the substrate even under a careful handling. Therefore, the electrical and me-chanical properties of this sample could not be measured. The results shown in Fig. 3 suggest that there is an opti-mum thickness of the Ti layer to facilitate the TiC formation. Among the samples shown in Fig. 3, the sample with a 100-nm-thick Ni layer and a 80-nm-thick Ti layer seems to be the closest to the optimum condition. The composition of the lm corresponds approximately to Ni-33 mol%Ti. The Ni-Ti binary phase diagram suggests that Ni3Ti and NiTi are stable at the composition18), i. e., the results agree with the thermo-dynamic consideration described in the former section. Fig. 4 shows the electrical current–voltage proles of the SiC/Ni, SiC/Ni/Ti (16 nm), SiC/Ni/Ti (80 nm), and SiC/C/Ti samples after annealing at 1273 K for 0 s. The plots of each sample lie on a rst-order least-square line in good agreement, indicating that all samples show Ohmic conduction. Among the samples, the highest electrical conductance is obtained with the SiC/Ni/Ti (80 nm) and SiC/Ni samples. On the other hand, the lowest electrical conductance is obtained with the SiC/C/Ti samples. Although it is proven that TiC is an ohmic contact former for n-type SiC, NiSi contacts exhibit higher electrical conductance. Nevertheless, TiC is an indispensable phase for improving both the electrical and mechanical prop-erties of the electrode by eliminating the free carbon phase. The electrical conductance of SiC/Ni/Ti (16 nm) appears low-er than that of the SiC/Ni samples. Fig. 5 shows the mechanical indices of the samples against their electrical conductance. The highest mechanical index is obtained with the SiC/C/Ti samples. This result evinces the successful formation of TiC at the interface, i. e., it is likely that the high hardness of TiC made the trench shallow. In ad-dition, the adhesion between the contact electrode and the substrate is strong and ductile enough to endure the scratch test. The SiC/Ni/Ti (80 nm) sample also endures the scratch test. Although its mechanical index appears lower than those of the SiC/C/Ti samples, it achieves high electrical conduc-tance and mechanical strength simultaneously. On the other hand, the mechanical indices of the SiC/Ni and SiC/Ni/Ti (16 Fig. 3 XRD patterns of the SiC/Ni/Ti samples after annealing at 1237 K for 0 s in vacuum. The initial thicknesses of the Ti layers are (a) 0, (b) 16, (c) 80, and (d) 640 nm.Fig. 4 Comparison of I-V characteristics among four electrodes produced in the present study.-2-1.5-1-0.500.511.52-300-200-1000100200300 Initial structure: SiC / Ni SiC / Ni / Ti (16 nm) SiC / Ni / Ti (80 nm) SiC / C (50 nm) / Ti (50 nm)Voltage, V [V]Current, I [mA]

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