氮化鋁覆蓋層應用於氧化鋯鉿鐵電元件之電性分析

Abstract

隨著科技近年日新月異的發展越加迅速，科技也在不斷的創新，帶動人工智慧(AI)、物聯網(IoT)應用技術、5G/6G通訊、汽車自動駕駛、高效能運算(HPC)等關鍵技術的成長，數據存取及整理相對重要，鐵電記憶體就扮演格外重要的角色，以其低功耗、讀寫快、耐久度優異的表現，成為其半導體發展重點。本研究使用氨電漿沉積氮化鋁作為覆蓋層，希望能減少介面缺陷產生，穩定上電極與氧化鋯鉿薄膜的介面品質，並且調變氮化鋁覆蓋層的氮含量10%、20%、40%、50%，探討其對氧化鋯鉿鐵電/反鐵電元件特性之影響。根據實驗結果皆以退火溫度600 °C為最佳條件，氮化鋁覆蓋層鐵電結構在操作電壓2.5 V下，在氮含量50%有最優異的兩倍殘餘極化量20.52 µC/cm²，在漏電流量測可以得知所有氮化鋁覆蓋層鐵電結構的漏電流值介在1.49×10-10 A ~ 1.15×10-9 A之間皆低於無覆蓋層鐵電結構2.25×10-9 A，氮化鋁覆蓋層反鐵電結構在操作電壓3.5 V下，氮化鋁覆蓋層反鐵電結構(N:20%、50%)表現出明顯反鐵電雙遲滯曲線特徵，且所有氮化鋁覆蓋層結構的漏電流值皆低於無覆蓋層反鐵電結構，觀察到在氮含量50%氮化鋁覆蓋層應用在鐵電或反鐵電結構上顯著提升極化特徵，並且抑制漏電流，推測高氮含量可以強化氮化鋁覆蓋層鍵結，提升熱穩定性，相較於其他氮含量結構，更有利於鐵電/反鐵電相的形成，同時達到抑制漏電流的效果。在耐久度分析中，從實驗結果得知與氮化鋁覆蓋層鐵電結構經過108次循環操作次數測試後的衰減率介在80.8% ~ 86%之間，皆低於無覆蓋層鐵電結構的89.9%。接著討論無覆蓋層反鐵電結構經過108次循環操作次數測試後的衰減率為13.5%，其中氮化鋁覆蓋層反鐵電結構(N:20%、40%、50%)的兩倍殘餘極化量略為提高，以上實驗結果顯示氮化鋁覆蓋層應用於鐵電/反鐵電結構中可以提升元件耐久度，改善的主要歸因於氮化鋁覆蓋層也可作為介面調控層，均勻分散電場應力於鐵電層上，且也能有效減少介面缺陷產生，降低元件漏電流、使元件在長期操作下仍能維持穩定的電性表現。再進一步探討比較在電壓3 V與退火溫度700 °C條件下，結果顯示鐵電結構於10⁷次循環即發生崩潰，而反鐵電結構則可穩定運作至10⁸次，然而反鐵電結構相比鐵電結構具備更持久可靠度，可能歸因其內部氧空位較少，能有效延緩薄膜擊穿，並且氮化鋁覆蓋層反鐵電結構的衰減率低於無覆蓋層反鐵電結構的66.5%，顯示出氮化鋁覆蓋層可以減少介面缺陷並穩定介面品質。With the rapid and continuous advancement of technology in recent years, innovations in fields such as Artificial Intelligence (AI), the Internet of Things (IoT), 5G/6G communication, autonomous driving, and high-performance computing (HPC) are accelerating. As a result, data access and organization have become increasingly important. Ferroelectric memory plays a crucial role in this context due to its low power consumption, fast read/write speed, and excellent endurance, making it a key focus in semiconductor development.In this study, aluminum nitride (AlN) capping layers were deposited using ammonia (NH₃) plasma with the aim of reducing interface defects and stabilizing the interfacial quality between the top electrode and the HfZrO (hafnium-zirconium oxide) film. The nitrogen content in the AlN capping layers was varied (10%, 20%, 40%, and 50%) to investigate its effect on the properties of HfZrO-based ferroelectric and antiferroelectric devices.According to the experimental results, an annealing temperature of 600 °C was found to be optimal. Under an operating voltage of 2.5 V, the ferroelectric structure with an AlN capping layer containing 50% nitrogen exhibited the highest 2Pr value of 20.52 µC/cm². Leakage current measurements showed that all AlN-capped ferroelectric structures had leakage currents ranging from 1.49×10⁻¹⁰ A to 1.15×10⁻⁹ A, which were lower than that of the uncapped structure (2.25×10⁻⁹ A). For antiferroelectric structures operated at 3.5 V, those with AlN capping layers containing 20% and 50% nitrogen displayed clear antiferroelectric double hysteresis loop characteristics. Moreover, the leakage current in all AlN-capped antiferroelectric structures was lower than that in the uncapped counterparts.It was observed that AlN capping layers with 50% nitrogen content significantly enhanced polarization characteristics and suppressed leakage current in both ferroelectric and antiferroelectric structures. This is likely due to stronger bonding and improved thermal stability at higher nitrogen contents, which facilitate the formation of ferroelectric/antiferroelectric phases while reducing leakage.In endurance analysis, after 10⁸ switching cycles, the degradation rate of AlN-capped ferroelectric structures ranged from 80.8% to 86%, all lower than the 89.9% observed in uncapped structures. For antiferroelectric structures, the uncapped device showed a degradation rate of 13.5% after 10⁸ cycles, while those with 20%, 40%, and 50% nitrogen in the AlN capping layer showed slightly improved 2Pr values. These results indicate that the AlN capping layer enhances the endurance of both ferroelectric and antiferroelectric devices. The improvements are mainly attributed to the AlN layer acting as an interfacial tuning layer, which helps evenly distribute electric field stress across the ferroelectric layer, reduce interface defects, suppress leakage current, and maintain stable electrical performance under long-term operation.Further investigations under a higher annealing temperature of 700 °C and an operating voltage of 3 V revealed that the ferroelectric structure failed after 10⁷ cycles, whereas the antiferroelectric structure remained operational up to 10⁸ cycles. This suggests that antiferroelectric structures possess better long-term reliability, potentially due to fewer oxygen vacancies that help delay film breakdown. Moreover, the degradation rate of AlN-capped antiferroelectric structures was lower than that of uncapped ones (66.5%), indicating that the AlN capping layer effectively reduces interface defects andstabilizes interface quality.