碳化矽基金屬/薄氧化層/半導體元件結構在紫外光照射下的電特性研究

Abstract

本篇論文探討不同厚度絕緣層材料 (＜5奈米的二氧化矽與＜20奈米的氧化鋁) 搭配不同圖樣閘極設計 (方形與同心環狀) 製作的金屬/薄氧化層/半導體碳化矽元件在紫外光照射下的電特性研究。對於使用二氧化矽、方形圖樣的金氧半結構，當光源的能量小於碳化矽的能隙，由價帶被激發的電子會被介面陷阱捕捉，導致光電流下降、電容－電壓曲線右移；而光源的能量大於碳化矽的能隙時，少數載子的密度上升將引發光電流增加、電容－電壓曲線左移。對於使用氧化鋁、方形圖樣的金氧半電容，隨著堆疊的絕緣層越厚，在閘極電壓掃描至反轉區後，少數載子造成的低頻電容現象越明顯，量測的漏電流密度為2.76×10－10 A/cm2，平能帶附近的陷阱密度可以降低至3.01×1011 eV－1 cm－2，另外元件的崩潰電場強度能夠達到11.8 MV/cm，穩定度表現也會因為介面特性改善而明顯提升。對於使用二氧化矽、同心環狀圖樣的橫向閘控穿隧二極體，藉由控制外環穿隧二極體的偏壓可以調變內圓穿隧二極體的電流，使得元件的光對暗電流比值上升至12841，在不同的紫外光照度下，響應率也將顯著增加至0.0052 A/W，適合用作高靈敏度的紫外光感測器。對於使用氧化鋁、同心環狀圖樣的耦合設計，經由紫外光照射產生的少數載子有機會從外環穿隧二極體側向流入內圓穿隧二極體，只要氧化層的厚度維持在最佳值，耦合效應就會有效增強內圓穿隧二極體的反轉行為；此外內圓電流－內圓電壓與內圓電流－外環電壓的關係相當類似一般電晶體的輸出與轉移特性，在高低電流比例為104的範圍，切換斜率也成功低於60 mV/decade，可望應用在新型碳化矽電晶體的元件設計。

This dissertation mainly investigates the electrical characteristics of SiC metal–thin oxide–semiconductor (MOS) devices employing different insulator dielectrics (＜5 nm SiO2 and ＜20 nm Al2O3) and various gate patterns (square and annular). For the square pattern Al/SiO2/n–SiC structure, electrons optically excited from the valence band can be captured by interface traps so long as the light source energy is less than the SiC bandgap, which will give rise to the decrease in photocurrent and the right shift of C－V behavior. On the contrary, when the light source energy is more than the SiC bandgap, appreciable minority carriers may be produced by illumination, thereby resulting in the increase of photocurrent and the left shift in C－V response. Concerning the stacked Al/Al2O3/SiO2/n–SiC structure, the inversion feature at low frequency arising from the presence of minority carriers becomes more noticeable, and the leakage current gets lowered as the gate bias continues sweeping to more negative voltages. In addition, the breakdown strength and the reliability performance will be considerably enhanced thanks to the improvement of interface quality. As to the laterally gated Al/SiO2/n–SiC structure, the current of the inner tunnel diode (TD) can interrelate with the bias of the outer TD, thus significantly amplifying the optical current ratio and ameliorating the responsivity with the increasing UV irradiance as well. Accordingly, the laterally gated MOS structure is appropriate for functioning as a UV sensor with high irradiance sensitivity. Referring to the coupled Al/Al2O3/SiO2/n–SiC structure, photogenerated carriers from the outer TD is likely to augment the inversion capacitance of the inner TD in case the optimum oxide thickness ought to be achieved in order to take advantage of the coupling effect. The relationships between the current of the inner TD with respect to the voltage of the inner TD and the bias of the outer TD strikingly resemble the output and the transfer characteristics of a conventional transistor, and the calculated switching slope will effectively be less than 60 mV/decade. Hence, the coupled TD scheme can be applied to the construction of a novel SiC transistor.