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研究生:宋文祥
研究生(外文):Wen-Hsiang Sung
論文名稱:氟化效應對低溫多晶矽薄膜電晶體之特性探討
論文名稱(外文):Fluorine Effects on the Characterization of LTPS Thin-Film Transistors
指導教授:賴朝松高泉豪
指導教授(外文):Chao-Sung LaiChyuan-Haur Kao
學位類別:碩士
校院名稱:長庚大學
系所名稱:電子工程研究所
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:2007
畢業學年度:95
語文別:英文
論文頁數:69
中文關鍵詞:氟化效應低溫多晶矽薄膜電晶體負偏壓不穩定性
外文關鍵詞:Fluorine EffectsLow-Temperature Polycrystalline SiliconThin-Film TransistorsNegative Bias Temperature Instability
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在低溫多晶矽薄膜電晶體的研究上,閘極氧化層的成長技術大都使用TEOS 氧化層或是電漿增強型化學氣相沉積之氧化層…等等,因此為了使低溫多晶矽薄膜電晶體的電性更好,所以在未來必須使用高介電係數材料來減少等效氧化層厚度,以得到較佳的特性。因此二氧化鉿在最近被提議應用在低溫多晶矽薄膜電晶體的絕緣介電材料上。但是有很多的研究發現,當二氧化鉿經過了退火處理或是其他製程步驟所造成的熱積存影響後,二氧化鉿將不再被氫氟酸的溶液所蝕刻。因此較厚的二氧化鉿薄膜在低溫多晶矽薄膜電晶體積體化的應用上將出現一個很大的危機。在本論文中,我們使用額外的氧離子電漿去轟擊二氧化鉿薄膜並利用氫氟酸或是SF6氣體再次進行蝕刻,經過這種兩階段式的蝕刻步驟將使得二氧化鉿薄膜的蝕刻速率有明顯的提升。
我也使用CF4 電漿處理應用於複晶矽氧化層電容和低溫多晶矽薄膜電晶體上,其電性上也有改善,有對於複晶矽氧化層電容中的崩潰電場、缺陷捕捉速率、電荷至崩潰累積電荷。在低溫多晶矽薄膜電晶體的改善部分包含了截止區的漏電流、導通區的驅動電流、導通區的崩潰電壓以及多晶矽邊界的缺陷密度。這些改善的現象是由於氟去填補多晶矽邊界的缺陷密度以及在多晶矽和絕緣層的表面上形成比較強的矽-氟鍵結去取代原本較弱的矽-氫鍵結。
最後,我們也使用氟離子佈值於低溫多晶矽薄膜電晶體,並研究其負偏壓溫度不穩定性的可靠度分析比較,我們可以發現經過了氟離子佈值的低溫多晶矽薄膜電晶體的次臨界轉變的變化量、臨界電壓的漂移變化量、場效遷移率變化量以及多晶矽表面的缺陷密度變化量都有明顯的改善,而這些改善也被歸因於在多晶矽的表面缺陷密度和多晶矽邊界的缺陷密度被氟有效的填補並形成較強的矽-氟鍵結去取代原本較弱的矽-氫鍵結。
In LTPS TFTs research, the gate oxides were usually deposited as TEOS or PECVD oxide and so on. As the same, EOT shrinking trend in CMOS technology, hafnium oxide (HfO2) was applied as gate insulators of LTPS TFT to have better performance. However, many researchers have found that the etching rates of HfO2 with post-deposition-anneal (PDA) or thermal budget process decrease rapid in dilute HF solutions, so the etching of thick HfO2 is an issue for process integration of LTPS TFTs. Therefore, the additional O2 ion-bombardment process is proposed to enhance the etching rate for HfO2 films of as-deposited and PDA 600℃with dilute HF and SF6 dry etching by two-step etching method.
In this thesis, we also demonstrated that it has been improved which including electric field of breakdown, trapping rate and Weibull distribution of charge-to-breakdown for polyoxide capacitors, consequently the off-state current, on-state breakdown voltage and grain-boundary trap-density are also improved on LTPS TFTs by CF4 plasma pre-treatment. These improvements have been attributed to reduce grain-boundary trap-density effectively and produce strong Si-F bond than Si-H bond at interface region.
Finally, the Negative Bias Temperature Instability (NBTI)reliability experiment has been finished discussion for conventional and fluorine implantation of p-channel LTPS TFTs. The variation of subthreshold swing, threshold voltage shift, field-effect mobility and interface trap states for fluorine implantation of LTPS TFTs are relative decreased than conventional LTPS TFTs under NBTI stress. These improvements have been attributed strong Si-F bond to replace weak Si-H bond at interface and grain-boundary region.
Acknowledgment i
Chinese Abstract ii
English Abstract iv
Contents vi
Content of Figures viii
List of Tables xiii
Chapter 1 Introduction……………………………………………………………1
1.1 Background……………………………………………………………1
1.2 Motivation……………………………………………………………3
1.3 Thesis Organization………………………………………………4
Chapter 2 The Etching Characterization of Hafnium Oxide Films…7
2.1 Introduction…………………………………………………………7
2.2 Experiments……………………………………………………………8
2.3 Results and Discussion…………………………………………9
2.3.1 Etching of as-deposited HfO2 films……………………9
2.3.2 Etching of HfO2 films with PDA treatment……………10
2.4 Summary………………………………………………………………10
Chapter 3 Characteristics of Low Temperature In-Situ PEOxide of Polyoxide Capacitor and Polycrystalline Silicon Thin-Film Transistors with CF4 Plasma Treatment……………………………………19
3.1 Introduction………………………………………………………19
3.2 Experiments…………………………………………………………20
3.2.1 Fluorined Polyoxide Process………………………………20
3.2.2 LTPS TFTs Device Process……………………………………21
3.3 Results and Discussion…………………………………………22
3.3.1 Fluorinated Polyoxides ……………………………………22
3.3.2 Fluorinated LTPS TFTs………………………………………24
3.4 Summary………………………………………………………………26
Chapter 4 Characteristics of Negative Bias Temperature Instability for p-channel LTPS TFTs with Fluorine Ion Implantation…………44
4.1 Introduction………………………………………………………44
4.2 Experiments…………………………………………………………45
4.3 Results and Discussion…………………………………………46
4.4 Summary………………………………………………………………48
Chapter 5 Conclusions and Future Works…………………………………62
5.1 Conclusions…………………………………………………………62
5.2 Future works………………………………………………………63
Reference………………………………………………………………………………64
Publications List……………………………………………………………………69
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