| 研究生: |
黃薰瑩 Huang, Shiun-Ying |
|---|---|
| 論文名稱: |
熱處理及下電極材料對五氧化二鉭電容器之特性影響 Influences of thermal processes and bottom electrodes on the characteristics of Ta2O5 capacitors |
| 指導教授: |
陳貞夙
Chen, Jen-Sue |
| 學位類別: |
碩士 Master |
| 系所名稱: |
工學院 - 材料科學及工程學系 Department of Materials Science and Engineering |
| 論文出版年: | 2002 |
| 畢業學年度: | 90 |
| 語文別: | 中文 |
| 論文頁數: | 107 |
| 中文關鍵詞: | 電容器 、五氧化二鉭 |
| 外文關鍵詞: | Ta2O5, capacitor |
| 相關次數: | 點閱:81 下載:6 |
| 分享至: |
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中文摘要
本研究將探討熱處理及下電極材料對五氧化二鉭( Ta2O5 )薄膜電容器之特性影響。實驗中分別以多晶矽( poly-Si )、氮化鉭( TaN )、氮化鈦( TiN )及釕( Ru )四組不同材料,作為Ta2O5電容結構之下電極進行研究,並且各組試片皆分別經500℃或700℃氧氣氛退火30分鐘。本實驗大致可分為兩個部分:第一部分為Ta2O5/ 下電極之材料微結構分析;第二部分則為電性量測之探討。最後將材料微結構與電性表現相互比較,在兩者之間尋求其關聯性。
試片製備方面,使用反應式濺鍍法沉積各層薄膜於多晶矽基板上,並使用掃描式電子顯微鏡、低掠角X光繞射儀、歐傑電子能譜儀、原子力顯微鏡、穿透式電子顯微鏡及所附的X光能量散佈光譜儀分析其材料特性。由實驗結果顯示:Ta2O5經500℃退火後可明顯觀察到Ru下電極發生部分氧化,但其他電極則無明顯氧化現象;而700℃退火後,各組電容結構中的Ta2O5介電層,皆因形成β-Ta2O5結晶態而變得較粗糙,poly-Si下電極表面無法明顯觀察到被氧化產生的界面層,TaN及Ru下電極已完全被氧化,且TaN氧化成Ta2O5使體積膨脹了約十倍,TiN下電極則發生部分氧化,但TiN的柱狀結構仍清晰可見。
電性量測方面,以poly-Si為下電極之電容結構雖具有較低的漏電流,卻無法經由氧氣氛退火大幅提高電容值。TaN下電極易與擴散經過Ta2O5的氧氣反應,退火製程造成介電層厚度增大而降低電容值。TiN下電極與Ta2O5之間不易形成界面介電層,因此電容結構經退火後具較高電容值,且經500℃退火後仍維持良好的接面品質,若能改善退火製程使Ta2O5介電層的氧空缺獲得填補,應可進一步降低漏電流。Ru下電極於氧氣氛退火時會氧化成RuO2,並且RuO2與Ta2O5介電層發生相互擴散的現象,造成電容結構之並聯電阻效應極強,因此漏電非常大,已超出可量測範圍。
四組電容結構中,以TiN為下電極材料的Ta2O5薄膜電容,具有較高的發展性。其優點為:抗氧化性優於TaN及Ru、與Ta2O5間的接面品質佳、鍍製於其上的Ta2O5具有較高的電容值等。若改變後處理製程,避免TiN處在高溫氧氣氛的環境中,應可得一高電容值及低漏電流的電容結構。
Abstract
Characteristics of Ta2O5 thin-film capacitors on various bottom electrodes, were investigated in this thesis. The bottom electrodes include poly-Si, TaN, TiN and Ru, and the capacitors were characterized before and after annealing at 500°C or 700°C in oxygen atmosphere for 30min. The experiment contains two parts: one is the microstructural analysis of Ta2O5/bottom electrode multi-layers, and the other is the electrical measurements on the capacitors. Meanwhile, the correlation between the material characteristics and electrical properties is discussed.
In the experiment, poly-Si/n-type Si and poly-Si/SiO2/n-type Si wafers were used as the substrates, for microstructural analysis and for electrical characterization, respectively. All of the films were deposited by reactive sputtering, and the samples were analyzed using scanning electron microscopy( SEM ), glancing incident angle X-ray diffraction spectra( GIA-XRD ), Auger electron spectroscopy( AES ), atomic force microscopy( AFM ) and cross-sectional transmission electron microscopy ( TEM ) with energy dispersive spectroscopy( EDS ). After annealing at 500°C, Ru bottom electrode was partially oxidized, but other bottom electrodes didn’t reveal any indication of oxidation. After annealing at 700°C, the Ta2O5 dielectric film was crystallized and roughed in all of the capacitors. Both TaN and Ru bottom electrodes were completely oxidized, the thickness of oxidized TaN was ten times larger than as-deposited TaN owing to the volume expansion. But TiN bottom electrode was only partially oxidized, and still showed columnar structure.
The capacitor using poly-Si bottom electrode exhibited lower leakage current, but the improvement of capacitance after annealing was minimal. Oxidation of TaN and Ru bottom electrodes after annealing were inevitable, which is harmful for devices in application. The low capacitance of TaN capacitor structure was due to the increase of dielectric thickness via oxidation. Ru bottom electrode oxidized easily to form a conductive phase, RuO2, in the oxygen atmosphere at elevated temperature. Besides, the interdiffusion of Ta2O5 and RuO2 occurred not only at the interface of dielectric layer and bottom electrode, but also in the entire capacitor structure if higher annealing temperature was applied. Ta2O5 dielectric layer on TiN bottom electrode exhibited high capacitance and good interface quality, even after annealing at 500°C. The leakage current of this capacitor can be further improved. TiN bottom electrode is provided with better barrier ability, and is feasible for application after a proper heat treatment.
TiN bottom electrode seems to be a more suitable for Ta2O5 capacitor than poly-Si, TaN or Ru. The advantages of TiN are as follows: better anti-oxidation ability, good interface quality, and large capacitance. Large capacitance and low leakage current can be obtained by using TiN bottom electrode if the post-annealing process is well-controlled.
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