Hf0.5Zr0.5O2正交晶體下電極最佳化與動力學分析

Abstract

隨著近年人工智慧的迅速發展，產學界對於可用於記憶體內運算的低功耗記憶體興趣也越發強烈。鐵電隨機存取記憶體因為它利用殘留極化量保存數據而不需要外加電壓或時時重新寫入的特性，被認為是次世代記憶體技術的有力競爭者。 氧化鉿鋯在製程微縮時仍能維持良好鐵電特性，且與現有CMOS製程相容性極佳，因此現今的鐵電隨機存取記憶體研究大多集中在研究此材料。因為提高氧化鉿鋯層殘留極化量可以增加鐵電隨機存取記憶體讀取高電位與低電位的差異，而殘留極化量來自氧化鉿鋯的正交晶體，如何在氧化鉿鋯層中分析正交晶體是否存在成為一個至關重要的題目。 在本研究中我們分析金屬-鐵電-金屬電容的下電極結晶度與表面粗糙度對氧化鉿鋯殘留極化量的影響，發現非晶態且表面平滑的下電極最有利於提高殘留極化量。我們也分析了退火溫度對氧化鉿鋯正交晶體的影響，並利用微區繞射及電性量測確定在400oC退火後存在氧化鉿鋯正交晶體，在500oC退火後因為氧化鉿鋯層整體結晶度上升，正交晶體比例也上升，在800oC退火後雖然整體結晶度非常高，但正交晶體卻不見蹤影。我們利用密度泛函理論模擬氧化鉿鋯自由能，並畫出在不同退火溫度下，及退火結束降溫時的自由能圖，以解釋實驗所見，高溫退火不利正交晶體產生的現象。

Following the booming development of artificial intelligent, the interest in low power consumption memory devices for in-memory computation also increase drastically. The ferroelectric random-access memories, which store data by holding remanent polarization without the need of constant voltage or refreshing, is considered a promising candidate for next generation memory technology. Due to its favorable scalability and CMOS compatibility, the hafnium zirconium oxide (HZO) is the material of choice for FeRAM development nowadays. To maximus the disparity of FeRAM high and low read out voltage, it is very important to develop HZO film with high remanent polarization. Since the remanent polarization comes from the HZO ferroelectric orthorhombic phase (o-phase) crystals, distinguishing HZO o-phase from other phases becomes crucial for FeRAM development. In this work, the crystallinity and surface roughness of bottom electrode for metal-ferroelectric-metal capacitors are analyzed for their effects on HZO remanent polarization, showing amorphous and flat bottom electrode favors o-phase formation. The effects of annealing temperature are also experimentally and theoretically studied. The existence of o-phase after HZO film annealed at different temperatures are tested with nanobeam electron diffraction and their remanent polarization measurement. o-phase exists after annealing at 400oC, increases in constitution due to higher HZO crystallinity after annealing at 500oC, and disappears after annealing at 800oC. The results are explained with free energy diagrams simulated using density functional theory.