雙重電漿處理對二氧化鉿金屬-絕緣層-半導體結構電特性之改善研究

Abstract

過去的三十多年來，在MOS-based的結構裡閘極介電質選擇使用二氧化矽。而隨著金氧半場效電晶體的微縮，傳統使用二氧化矽當作閘極介電層將面臨到物理和電性的限制。當閘極的長度小於70奈米，則閘極氧化層厚度必須要小於1.5奈米，此時的氧化層只有兩到三個原子的厚度，這會導致很大的閘極漏電流。使用氧化鉿是目前以及未來最為推廣的材料，但是high-k閘極介電層在C-V曲線中被發現有遲滯現象，此現象會導致MOS元件中平帶電壓飄移以及臨界電壓的不穩定。本研究製造了Al/Ti/HfO2/Si 金屬絕緣層矽(MIS)結構之電容，作為分析的樣品。首先，在二氧化鉿薄膜上，使用不同氣體(氮氣、氧化氮和氨氣)做不同時間下的電漿處理，並且從這些不同條件中挑選最佳的電漿處理條件。然後，在矽基板上，使用四氯化碳做不同時間的電漿處理，並且從這些不同條件中選擇最佳的電漿處理條件。接著，在金屬絕緣層矽結構之電容中，結合電漿氟化作用和電漿氮化作用，這種方法稱做雙重電漿處理。最後，利用測量電容－電壓曲線、漏電流－電壓和磁滯曲線去探討介電質薄膜在不同電漿處理的條件下的基本特性。這結果可以發現經過電漿處理後的介電質薄膜，可以得到較高的電容密度、較低的漏電流以及較小的磁滯現象。這是因為電漿源中的氟原子可以抑制介電層和矽之間的氧化層成長並且修復介電質中的缺陷，氮原子可以修補介電層的缺陷。因此經由電漿處理過後的金屬絕緣層矽結構之電容漏電流較低，而且電荷較容易累積使得電容值提高。

For more than 30 years, SiO2 films have been the preferred material for gate dielectric in MOS-based structure. The aggressive scaling of MOS devices is almost reaching the fundamental and electric limits of convention SiO2 as the gate insulator. When the gate length is below 70nm will need an oxide thickness of less than 1.5 nm, which corresponds to two or three layers of silicon dioxide atoms. The oxide of using Hafnium-based is a most promising material for future MOSFET gate oxide applications. Unfortunately, for high-k gate dielectrics, there is a hysteresis phenomenon in its capacitance-voltage (C-V) characteristics. This hysteresis induces a flatband voltage shift, and threshold voltage instability when it is applied to MOSFETs. In this study, we fabricated Al-Ti-HfO2-Si MIS capacitor as our analysis device. First, the HfO2 film were treated in different source gas (N2, N2O, and NH3) for different time, and we selected the best conditions among these conditions. Second, Si surface were treated in CF4 plasma for different time, and we selected the best conditions among these conditions. Third, the MIS capacitors combined plasma fluorination with plasma nitridation, which the method called dual plasma treatment. Final, the electrical characteristics of the film under different plasma conditions were discussed by C-V, J-V, and hysteresis curves. After plasma treatment, the results show higher capacitance, lower leakage current density, and lower hysteresis voltage. It might be that fluorine could suppress the formation of interfacial layer between the HfO2/Si interface, the nitrogen also can repair defects at bulk dielectric to decrease the leakage current. Moreover, the films after nitridation will more easier accumulate charges, the capacity values will be more higher.