高功函數銥金屬奈米晶體於非揮發性記憶體之應用

Abstract

近來非揮發性奈米晶體記憶體被用來廣泛的研究來克服傳統的浮動閘極記憶體的極限。利用奈米晶體被用來克服傳統浮動閘極元件在微縮時遇到電荷流失的問題、容許更薄的穿隧氧化層、更低的工作電壓，及更好的容忍度和電荷保存能力。比較半導體奈米晶體和金屬奈米晶體兩者，金屬奈米晶體作為浮動閘極有許多優點：對於電容特性改變量、較多種可供利用並設計的功函數、在費米能階周圍有高的狀態密度以及不易受載子侷限效應所引起能階擾動等等。本研究，利用銥(Ir)取代浮動閘極的地位的原因有兩個，ㄧ個是它擁有較高的功函數，另一個則是對於非揮發性記憶體的製程應用中具有良好熱穩定性。Ir 金屬形成奈米晶體的方法為透過超薄的金屬膜和快速退火(RTA)的製程來完成其製備。本研究針對銥奈米晶體的形成條件以及研究製作在SiO2 與HfO2 層中置入Ir 奈米晶體後的電容結構的特性，做了一系列實驗和討論。並在論文最後試著將此技術應用在記憶體元件上。

Recently, nonvolatile memory with nanocrystals (NCs) has been widely studied to overcome limitations of conventional floating gate memory. The use of NCs as distributed floating gates minimized the problems of charge loss encountered in conventional floating-gate devices, allowing thinner tunnel oxide and, thereby, a smaller working voltage, better endurance and retention, and faster program/erase (P/E) speed. Compared to the semiconductor NCs, metallic NCs as floating gates possesses several advantages, such as larger change of electric capacity, stronger coupling with the conduction channel, a wide range of available work functions, higher density of states around the Fermi level, and a smaller energy perturbation due to carrier confinement. In this thesis, iridium was chosen as floating gates for its properties of high work function and thermal stability for NVM application. The metallic thermal agglomeration was investigated using thin iridium films under different rapid thermal annealing (RTA).Mechanism of nanocrystals formation has been investigated. A MOS capacitor with iridium NCs (Ir-NCs) embedded in SiO2 and HfO2 layers has been demonstrated for investigation of electrical properties. Furthermore, incorporation of Ir-NCs into process of MOSFETs has been demonstrated for the feasibility of this study in NVM application.