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研究生:江佩錞
研究生(外文):Pei-Chuen Jiang
論文名稱:氮化鎢薄膜之製備及閘極特性之研究
論文名稱(外文):Preparation of W-N thin film and its characteristics as gate electrode
指導教授:陳貞夙陳貞夙引用關係
指導教授(外文):Jen-Sue Chen
學位類別:碩士
校院名稱:國立成功大學
系所名稱:材料科學及工程學系碩博士班
學門:工程學門
學類:材料工程學類
論文種類:學術論文
畢業學年度:90
語文別:中文
論文頁數:114
中文關鍵詞:氮化鎢閘極氮化鎢薄膜
外文關鍵詞:WN gateWN thin filmMOS capacitance
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本研究主要分為兩階段,第一階段以氮化鎢薄膜的性質為探討重點,利用物理氣相沉積系統濺鍍氮化鎢薄膜,濺鍍參數分別為射頻功率,基板偏壓和氮氣流量。研究不同濺鍍條件下氮化鎢薄膜的電性,結構,鍵結型態,以及成分的差異。經由這些研究找出最適合做為金屬-氧化物-半導體(MOS)結構之閘極電極的氮化鎢薄膜,以進行第二階段的研究。第二階段採用氮化鎢/氧化鉭/矽之MOS電容器結構,利用不同的退火溫度及退火氣氛退火MOS結構,觀察MOS電容器的熱穩定性及其電性表現。
在固定基板偏壓為-100V,氮氣流量為25sccm下,隨著射頻功率的增加,氮化鎢薄膜的沉積速率上升,電阻率下降,薄膜的結構均為W2N相,薄膜的鎢含量則會隨著射頻功率的增加而增加。
在固定射頻功率為150W,氮氣流量為25sccm下,隨著基板偏壓的增加,氮化鎢薄膜的沉積速率會降低,電阻率下降,薄膜的結構均為W2N相,而薄膜的鍵結型態及成分則不隨著基板偏壓的改變而有變化。
在固定射頻功率為150W,基板偏壓為-100V,隨著氮氣流量的增加,薄膜的沉積速率會下降,電阻率上升,而薄膜結構變化則為W→W+W2N→W2N→W2N+pseudo-WN,薄膜在形成pseudo-WN相後,電阻率會明顯上升。由θ-2θX光繞射(XRD)結果發現隨著氮流量增加,相同結構之薄膜其晶格有膨脹現象。在W2N結構的薄膜中,其成份分析為W:N=1:0.8,顯示有過多的氮原子會填入W2N晶格中,因而造成晶格膨脹現象。由X光光電子能譜(XPS)鍵結分析可以發現薄膜中含有W-N與W-O鍵結,而隨著氮氣流量增加,W-N鍵結能往高能量偏移,而在W2N+pseudo-WN薄膜結構中,XPS鍵結分析顯示薄膜為WN鍵結,而成份分析顯示W:N=1:1.57,可得知此時薄膜仍含有過多的氮原子。
在固定射頻功率為50W,基板偏壓為-100V,隨著氮氣流量的增加,薄膜的沉積速率會下降,電阻率上升,由於沉積速率小於射頻功率為150W且基板偏壓為-100V的試片,因此在濺鍍過程中容易含有較多的雜質,因此其電阻率遠大於射頻功率為150W且基板偏壓為-100V的薄膜。而在此功率(50W)下,隨著氮氣流量的升高,薄膜仍維持為W2N相,當氮氣流量達到50sccm時,低掠角XRD結果顯示薄膜含有不明顯的pseudo-WN相。由XPS鍵結分析發現薄膜的W-N鍵結能隨著氮含量升高而增加,但仍未形成WN鍵結。
在氮化鎢/氧化鉭/矽(W2N/Ta2O5/Si)的MOS電容器中,Ta2O5會經由不同的氧氣退火溫度以控制其結晶或非結晶結構,而非晶結構Ta2O5所製成的MOS電容器會有較高的崩潰電壓,結晶結構Ta2O5所製成之MOS電容器會有較少的氧化層固定電荷(Fixed oxide charge)。而在將MOS電容器經氮氣退火後,在退火溫度達500℃閘極出現氧化鎢(WO3)相,退火溫度達600℃則氮化鎢閘極全被氧化為WO3相,因而喪失其功能。在氫氣退火MOS結構後,可以降低Ta2O5氧化層與矽基材間的界面捕獲電荷(Interface trapped charge)。由AES縱深分析結果可以發現氮化鎢閘極之氮原子在經過高溫退火後,會揮散至空氣中,而閘極之氧原子也會明顯增加。
In this dissertation, the material characteristics of reactive r.f. sputtering WNX thin films and the possibility of employing WNX thin films as the metal gate of the MOS structure are investigated. The WNX thin films are sputtered with various sputtering powers, substrate biases and nitrogen flow ratios. The crystal structure, chemical bonding state, composition and electrical resistivity of the films are investigated by X-ray diffraction, X-ray photoelectron spectroscopy, Auger electron spectroscopy, Rutherford backscattering spectrometry and four-point probe. After finding out the characteristics of the sputtered WNX films, we select W2N film and apply it as the metal gate of the metal-oxide-semiconductor(MOS)capacitors. After annealing the MOS capacitors at 400-600℃ in H2 or N2 for 30 min, the thermal stability are investigated by X-ray diffraction, Auger electron spectroscopy, and the electrical properties are evaluated from current-voltage(I-V)and capacitance-voltage(C-V)measurements.
At the different sputtering powers, the resistivity and nitrogen concentration of W-N films decrease with increasing sputtering power. At the different substrate biases, the resistivity of W-N films decrease with increasing bias. The crystal structure, chemical bonding state, and nitrogen concentration are not changed with bias.
Using 150W of sputtering power and –100V of substrate bias, resistivity of W-N films increase with increasing nitrogen flow ratio. Crystalline W2N phases is observed with 10-25% of nitrogen flow ratio and W2N+pseudo-WN phases is observed at high(≧40%)nitrogen flow ratio. With increasing nitrogen partial flow, nitrogen concentration in the W-N films increases continuously, and the binding energy of W 4f core levels changes gradually from the metallic W state to the WN state. By reducing the sputtering power to 50 W, we have found that film resistivity also increases with increasing nitrogen partial flow but crystalline W2N phase can be obtained with 10-40% of nitrogen partial flow rate.
As for the W2N(200nm)/Ta2O5(25nm)/Si capacitors, the MOS capacitors with amorphous Ta2O5 have low breakdown field, and the MOS capacitors with crystalline Ta2O5 show low fixed oxide charge. The thermal stability of the MOS structure is investigated by N2 annealing up to 600℃, and H2 annealing up to 500℃. The interface trapped charge can be decreased by H2 annealing at 400 or 500℃. However, by N2 annealing, the W2N gate metal becomes partially oxidized after annealing at 500℃ and completely transforms to WO3 phase after annealing at 600℃. In addition, AES reveals the interdiffusion of W2N and Ta2O5 after annealing. The electrical performance of the MOS capacitor is consequently degraded due to the oxidization and interdiffusion.
第一章 前言
1-1何謂MOS結構…………………………………………1
1-2研究目的………………………………………………6
第二章 理論基礎
2-1氮化鎢薄膜相關文獻回顧……………………………7
2-2MOS結構中氧化層缺陷之型態及其影響……………10
2-2.1Fixed Oxide Charge……………………………11
2-2.2Oxide Trapped Charge…………………………14
2-2.3Interface Trapped Charge……………………15
2-2.4Mobile Ionic Charge …………………………17
第三章 實驗方法與步驟
3-1實驗材料………………………………………………18
3-2實驗設備………………………………………………19
3-3實驗流程………………………………………………20
3-3.1WNX 薄膜製程 ……………………………………21
3-3.2MOS(Metal-Oxide-Semiconductor)製程……23
3-4鍍層性質分析
3-4.1 電阻率及膜厚量測…………………………………27
3-4.2 θ-2θX光繞射結構分析…………………………29
3-4.3 低掠角入射X光繞射結構分析……………………30
3-4.4 X光光電子能譜化學鍵結分析 ……………………31
3-4.5 歐傑電子能譜表面成分與縱深分析………………32
3-4.6 拉塞福背向散射成分分析…………………………34
第四章 實驗結果與討論
4-1 WNX薄膜性質…………………………………………36
4-1.1 沉積速率與電阻率量測結果………………………38
4-1.2 θ-2θXRD與GIAXRD結構分析結果………………43
4-1.3 XPS化學鍵結分析結果 ……………………………51
4-1.4 AES與RBS成分分析結果 …………………………59
4-1.5 RBS薄膜密度分析結果 ……………………………68
4-2 W2N / Ta2O5 / Si MOS結構之性質………………69
4-2.1 θ-2θXRD與GIAXRD分析結果……………………71
4-2.2 AES縱深分析結果 …………………………………75
4-2.3 I-V量測結果 ………………………………………82
4-2.4 C-V量測結果 ………………………………………87
第五章 結論…………………………………………94
參考文獻…………………………………………………95
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