矽化鎳搭配高介電常數薄膜特性之研究

Abstract

本論文研究矽化鎳搭配高介電常數薄膜的特性，利用不同材料分析方法，分析矽化鎳和高介電常數介電質薄膜的材料性質，量測矽化鎳/高介電常數薄膜/矽之金氧半電容結構之電性，綜合材料分析與電性量測結果，了解高介電常數介電質薄膜的特性。 材料分析的結果顯示HfAlO(Hf:Al=9:1)和HfAlO(Hf:Al=7:3)薄膜分別在700℃與900℃的退火後會發生HfO2結晶相形成，意味著增加Al元素的添加可抑制HfAlO薄膜結晶。 高介電常數薄膜電容的電性量測，顯示HfO2薄膜經過600℃退火後介面層成長導致電容等效厚度增加，HfAlO(Hf:Al=9:1)薄膜在800℃亦有介面層成長情形，HfAlO(Hf:Al=7:3)和Al2O3薄膜皆無介面層成長，顯示在高溫熱處理下，薄膜相當穩定。HfAlO(Hf:Al=7:3) 薄膜在900℃退火後，等效電容下降，推測HfO2結晶形成，造成介電常數值升高。 HfO2薄膜經過500℃退火後由於結晶化導致漏電流增加，經過600℃退火後因為介面層厚度增加所以漏電流下降。HfAlO(Hf:Al=9:1)其漏電流情況與HfO2薄膜一樣。HfAlO(Hf:Al=7:3)和Al2O3薄膜漏電流維持定值。 HfO2和HfAlO(Hf:Al=9:1)薄膜在結晶溫度以上的沉積熱退火條件，有崩潰電場下降現象發生，可能是薄膜結晶時晶粒邊界有著大量缺陷或斷鍵而使得薄膜易於崩潰，Al元素的添加可抑制HfAlO薄膜結晶，也提升崩潰電壓。 考慮所有的要素後，HfAlO薄膜因為具有較佳的熱穩定性和可接受的電性，因此HfAlO薄膜為高介電常數材料中較佳的閘極絕緣層的選擇。

The characteristics of NiSi FUSI gate/high dielectric constant dielectric gate stack were investigated. Four kinds of high dielectric constant (high-K) materials including HfO2, HfAlO(Hf:Al=9:1), HfAlO(Hf:Al=7:3), and Al2O3 were studied. The physical characteristics of these films were analyzed by X-ray Photoelectron Spectroscopy (XPS), X-ray diffraction (XRD), and Transmission Electron Microscopy (TEM). The electrical characteristics of high-K films such as hysteresis, effective dielectric constant, leakage current, breakdown field, as well as carrier transport mechanism were studied by measuring MOS capacitors. The role of Hf/Al ratios in the high-K films determines the k-value, interfacial layer growth, crystallization temperature and leakage conductions. Material analysis show that crystallization temperature of HfO2, HfAlO(Hf:Al=9:1), HfAlO(Hf:Al=7:3) and Al2O3 are 500, 700, 900 and over 1000 ºC, respectively. The crystalline phase of HfO2 is only formed in the HfAlO films. The incorporation of Al into HfO2 thin films would suppress the crystallization of HfAlO films during high temperature annealing. After 600℃ annealing, the capacitance equivalent thickness (CET) of HfO2 increases due to the growth of SiO2-like interfacial layer. The growth of interfacial layer appears at 800ºC annealing for HfAlO(Hf:Al=9:1). The HfAlO(Hf:Al=7:3) and Al2O3 film have better thermal stability under high temperature post-deposition anneal (PDA). The CET of HfAlO(Hf:Al=7:3) decrease after 900ºC PDA due to the increase of dielectric constant caused by the formation of higher k-value HfO2 phase. After 500ºC anneal, the leakage current of HfO2 film increase owing to the crystallization. The growth of interfacial layer suppresses leakage current at 600ºC PDA. Similarly, the leakage current of HfAlO(Hf:Al=9:1) samples increase due to the crystallization and then decrease due to the interfacial layer growth. On the contrary, after high temperature PDA, HfAlO(Hf:Al=7:3) and Al2O3 samples almost have an constant leakage current and no interfacial layer growth. The breakdown field of HfO2 and HfAlO(Hf:Al=9:1) decreases above the temperature of crystallization, it may be resulted from the crystallization of high-K films. The crystallization of high-K film will create a lot of defects and broken bonds located in grain boundary. The more Al content in HfAlO film improves the quality and increases breakdown field. In summary, HfAlO is an attractive candidate for next generation gate dielectric material because of its better thermal stability and acceptable electrical properties compared with HfO2.