The existence of mobile ions in SiO2 layers of MOS structures is one of the important sources of electrical instabilities in MOS devices. In this study, the characteristics of mobile ions in thermally grown oxide layers of 6H- & 4H-SiC MOS capacitors are investigated by capacitance- voltage(C-V) and...
The existence of mobile ions in SiO2 layers of MOS structures is one of the important sources of electrical instabilities in MOS devices. In this study, the characteristics of mobile ions in thermally grown oxide layers of 6H- & 4H-SiC MOS capacitors are investigated by capacitance- voltage(C-V) and thermally stimulated currents(TSC) measurements etc.. The samples used have Pt(Au)/SiO2/α-SiC MOS structures. Oxide layers were grown by thermal oxidation using dry oxygen or wet oxygen (95 ℃ steam, O2 bubbling) at various conditions, and post- oxidation annealing was performed at 1,150~1,250 ℃ for 30 min in Ar-ambient. Especially, the effects of chlorine sources in thermally grown oxide layers were investigated using trichloroethylene(TCE). The thickness of oxide layer, surface morphology and interface characteristics between the SiC and deposited oxide layers were investigated by ellipsometer, FE-SEM, TEM, AFM, and SIMS etc.. For α-SiC MOS capacitors, gate electrodes were formed by evaporation or sputtering of Pt(Au) dots with 300~1,000 ㎛ diameters, and backside ohmic contacts also formed by sputtering of W or Ni. The high-frequency (1MHz) C-V characteristics were measured in the dark, and appropriate bias- temperature stresses(BTS) were applied to a sample at an elevated temperature in order to measure the TSC. A shift of C-V curve caused by a BTS was observed as a result of redistribution of mobile ions and oxide charges in the oxide layer. Polarization charge due to ionic space-charge polarization is obtained from TSC charge or the flatband voltage shift in C-V characteristics. The mobile charge per unit area QTSC is obtained by the integration of TSC curve. In case of the C-V characteristics of a wet oxidized 6H-SiC MOS sample measured at 1 MHz, it seems that the inversion dose not occur and the depletion layer spreads widely, probably owing to the absence of minority carriers because of the large bandgap of 6H-SiC. The C-V curve hysteresis was almost not observed in this sample. A single TSC peak of 6H- & 4H-SiC MOS capacitors was observed at about 450 K, 500 K in the measured temperature ranges, respectively. And the peak might be generated by positive mobile ions. The peak increased slightly and clearly shifted to higher temperatures with increasing the bias voltage Vb. The mobile charge QTSC obtained from the TSC curves increased as Vb increased, and almost coincided with QCV obtained from the flatband voltage shift in C-V characteristics. It is found that the behavior of mobile ions in SiO2 layers of SiC-MOS capacitors is similar to that of Si-MOS capacitors.
The existence of mobile ions in SiO2 layers of MOS structures is one of the important sources of electrical instabilities in MOS devices. In this study, the characteristics of mobile ions in thermally grown oxide layers of 6H- & 4H-SiC MOS capacitors are investigated by capacitance- voltage(C-V) and thermally stimulated currents(TSC) measurements etc.. The samples used have Pt(Au)/SiO2/α-SiC MOS structures. Oxide layers were grown by thermal oxidation using dry oxygen or wet oxygen (95 ℃ steam, O2 bubbling) at various conditions, and post- oxidation annealing was performed at 1,150~1,250 ℃ for 30 min in Ar-ambient. Especially, the effects of chlorine sources in thermally grown oxide layers were investigated using trichloroethylene(TCE). The thickness of oxide layer, surface morphology and interface characteristics between the SiC and deposited oxide layers were investigated by ellipsometer, FE-SEM, TEM, AFM, and SIMS etc.. For α-SiC MOS capacitors, gate electrodes were formed by evaporation or sputtering of Pt(Au) dots with 300~1,000 ㎛ diameters, and backside ohmic contacts also formed by sputtering of W or Ni. The high-frequency (1MHz) C-V characteristics were measured in the dark, and appropriate bias- temperature stresses(BTS) were applied to a sample at an elevated temperature in order to measure the TSC. A shift of C-V curve caused by a BTS was observed as a result of redistribution of mobile ions and oxide charges in the oxide layer. Polarization charge due to ionic space-charge polarization is obtained from TSC charge or the flatband voltage shift in C-V characteristics. The mobile charge per unit area QTSC is obtained by the integration of TSC curve. In case of the C-V characteristics of a wet oxidized 6H-SiC MOS sample measured at 1 MHz, it seems that the inversion dose not occur and the depletion layer spreads widely, probably owing to the absence of minority carriers because of the large bandgap of 6H-SiC. The C-V curve hysteresis was almost not observed in this sample. A single TSC peak of 6H- & 4H-SiC MOS capacitors was observed at about 450 K, 500 K in the measured temperature ranges, respectively. And the peak might be generated by positive mobile ions. The peak increased slightly and clearly shifted to higher temperatures with increasing the bias voltage Vb. The mobile charge QTSC obtained from the TSC curves increased as Vb increased, and almost coincided with QCV obtained from the flatband voltage shift in C-V characteristics. It is found that the behavior of mobile ions in SiO2 layers of SiC-MOS capacitors is similar to that of Si-MOS capacitors.
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