| Si C MOS(metal-oxide-semiconductor) power devices have been an important part of Si C devices for high voltage and high power applications. When Si C reaches its critical breakdown electric field 3MV/cm, according to Gauss’ law(CCoxideoxide Si Sik =Ek E), the electric field in Si O2(k=3.9) reaches up to 7.4-7.7MV/cm. The high electric field will greatly reduce the reliability of the oxide layer. With the increasing demands on the voltage and power of devices, how to improve the reliability of the device in the high electric field is the hot spots now. The Si O2 can be substituted with high k materials, such as Hf O2, Al2O3, La2O3, Hf Al O, and whether the device characteristics can be improved is the key point in this paper.The high k material La2O3 is mainly studied in this paper, and the effect of the different thickness of Si O2 on the electrical characteristics of La2O3/Si O2 stacked dielectric is compared, as well as the different characteristics of the two kinds of high k materials: La2O3 and Al2O3. The Si O2 were grown on n type 4H-Si C(~8×1015cm-3)by the thermal oxidation process, then the about 20 nm La2O3 were grown on Si O2 by atomic layer deposition method, and finally the MOS capacitors were prepared. It can be tested by spectroscopic ellipsometry(SE) that the thicknesses of Si O2 with the 5min, 10 min and 30 min oxidation time are 3.36 nm, 4.35 nm and 8.06 nm, respectively. The element compositions of the dielectric and the band structure of high k/Si C are analyzed by XPS test. It is obtained that the energy gap of La2O3 and Al2O3 are 5.87 e V and 6.96 e V, and the conduction band offsets of La2O3/Si C and Al2O3/Si C are 0.88 e V and 1.72 e V, respectively.The capacitance-voltage(C-V) characteristics of MOS capacitors are tested. The current-voltage(I-V) and current density-electric field(J-E) of the capacitors are obtained to analyze the gate leakage current and its leakage mechanism. The experimental results show that, although the conduction band offset of Al2O3/Si C is bigger than that of La2O3/Si C, the leakage current of Al2O3/Si C is serious owing to the high interface states density. The La2O3/Si O2/Si C sample with the thinnest Si O2(3.36nm) transition layer has the largest gate leakage current density, because the lanthanum silicate is formed in the Si O2 transition layer, which introduces more oxide charge and interface charge and the energy gap of Si O2 is deduced. The La2O3/Si O2/Si C sample with the thickest Si O2(8.06nm) transition layer has the lowest gate leakage current density. This is due to the high barrier of Si O2/Si C and the lower oxide trap charge and the interface trap charge density. Thus, the chances of electron tunneling are obviously reduced, and the ability of Si O2 to be subjected to the high electric field is improved. Therefore, the Si O2 transition layer is the key to decide the electrical characteristics of La2O3/Si O2 stacked dielectric. |
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