高介電常數閘極介電質熱氧化氧化鋁在金氧半電晶體的電性及應用

Abstract

由於矽積體電路元件尺寸的縮微，導致不斷的減少閘極氧化層的厚度。然而，隨之而來的高閘極漏電流卻使電晶體的特性變差，並且使元件消耗的功率變大。一個解決的辦法是以高介電常數介電質材料取代傳統熱氧化層，如此可以增加元件的密度而不需要更進一步減少閘極氧化層厚度。雖然高介電常數介電質的使用能有效的減少閘極漏電流，但仍然有一些相關新的問題必須解決。我們發展出一種簡單的沈積介電質的方法，為了避免任何製程在氧化鋁上引起缺陷，先利用物理氣相沈積的方式蒸鍍金屬薄膜，再將其氧化及退火。在我們研究中，我們將氧化鋁沈積在矽基版上，並製作成金氧半電容和電晶體。為了瞭解其被應用為閘極介電質的特性，我們量測了元件參數，閘極漏電流、遷移率和電晶體特性，量測結果顯示，氧化鋁運用在金氧半電容上其漏電流遠低於相同等效厚度的二氧化矽介電質，電子遷移率可比的上文獻發表的熱氧化二氧化矽數據。由電容電壓特性曲線顯示氧化鋁的高介電常數。量測介電質崩潰電壓、定電流應力、定電壓應力和應力產生的漏電流的可靠性測試，根據可靠性分析證實氧化鋁的高品質。為了研究偏壓溫度不穩定性的影響，將10MV/cm的電場和85oC溫度應力加在氧化鋁閘極介電質電晶體上量測臨界電壓的改變，在高電場和高溫應力下，由臨界電壓的改變可以推斷10年壽命下所能承受的最大閘極電壓僅達到1伏特操作下10% 的安全邊緣。此外，我們分別量測氧化鋁和二氧化矽介電質的閘極漏電流、電荷對介電質的崩潰以及應力產生的漏電流在銅污染下的影響。結果顯示，氧化鋁閘極介電質有強大的銅污染阻隔能力。因此，我們使用的這項製程方法，可以將氧化鋁應用在金氧半電晶體所使用的閘極介電質，此外它同時具有簡單，並且與現有超大型積體電路製程技術相容的優點。

The scaling-down of silicon integrated circuits has lead to a constant reduction of the thickness of gate oxide. However, the high gate leakage current degrades the performance of transistors and enlarges the power consumption of the devices. A solution is to replace SiO2 by high dielectric constant insulators, thus allowing an increase of the packing density without a further reduction of gate oxide thickness. Although utilizing high-k dielectrics reduced the gate leakage current effectively, there are still some issues that we have to overcome. We have developed an approach to deposit high-k dielectric. We deposited the ultra thin Al film on Si substrate using PVD followed by oxidation and annealing. The MOS transistor and capacitor devices with Al2O3 dielectrics were fabricated. To investigate the characteristics of Al2O3 used as gate dielectric, we measured the leakage current, mobility and transistor performance. The result indicates that the leakage current of Al2O3 as dielectric of MOS-capacitor is already better than that of SiO2 and the electron mobility is comparable to published mobility data from thermal SiO2. Capacitance-Voltage (C-V) curve shows its higher dielectric constant (k). We also show the high quality of Al2O3 dielectric according to its reliability analysis. Reliability tests were carried out by measuring breakdown voltage, constant current stress, constant voltage stress and stress induced leakage current (SILC) effect. To investigate the Bias-Temperature Instability (BTI) effects on Al2O3 CMOSFETs, the □Vt changes have measured after 10MV/cm and 85oC stress. The 10 years lifetime Vmax-10years is from the extrapolation of □Vt changes at high gate voltage and high temperature that can barely meet the required 1 V operation with 10% safety margin. Furthermore, to characteristics the Cu contamination effect on Al2O3 gate dielectric, we measured the gate dielectric leakage current, charge-to-breakdown and stress-induced leakage current on Al2O3 and SiO2, respectively. The results show the Al2O3 gate dielectric has strong Cu contamination resistance. Therefore, using this approach, we can fabricate Al2O3 high-k dielectric that is suitable in MOSFETs application. More important, this approach is simple and fully compatible with current VLSI technology.