臺灣博碩士論文加值系統

在本論文中，我們討論新結構電晶體與傳統電晶體的電性效能、可靠度與其製程的研究。為了增加電晶體的電性效能，我們首先提出兩種以選擇性複晶矽鍺應用在汲極/源極或閘極的新結構電晶體。與傳統電晶體比較，此新結構電晶體可增加導通電流與降低漏電流。此外，在經過直流stress後，新結構的可靠度比傳統結構電晶體來的佳。在超高真空化學氣相沈積系統選擇性成長複晶矽鍺薄膜溫度為550°C，可適用於傳統在玻璃上的製程溫度。除了低溫成長外，新結構電晶體尚有製程簡單、自我對準與不需要額外光罩等優點。
此外我們也探討有關雷射退火與離子佈植後雷射活化電晶體的特性與可靠度的研究。結果顯示，在雷射退火後，與傳統爐管退火比較，電晶體導通電流、臨界電壓與載子遷移率皆有變好的趨勢。然而，在離子佈植雷射活化後，電晶體的漏電流與可靠度與傳統爐管活化比較卻變得較差了。此外雷射退火後的電晶體在整片晶片上的均勻度與表面平坦度方面較以爐管退火方式為差。因此，在製程、電性效能與可靠度三點考量上，雷射方法的優缺點有其取捨。
接下來我們以超高真空化學氣相沈積系統沈積複晶矽並製作複晶矽薄膜電晶體，並與低壓化學氣相沈積系統先沈積非晶矽薄膜再以爐管方式退火製作複晶矽薄膜電晶體作比較，結果顯示兩者電晶體經過鈍化(passivation)處裡後所量測的缺陷密度、臨界電壓與開/關電流比例類似，但超高真空系統所製作的薄膜電晶體不需要經過長時間的爐管退火且有較好的均勻度。然而，與低壓系統所製作的電晶體比較，高真空系統直接沈積的複晶矽仍有缺點─載子遷移率較前者為低，這是因為超高真空系統直接沈積複晶矽所致，而直接沈積的複晶矽表面將有較大的粗糙度。
為了提昇薄膜電晶體的導通狀況，我們利用NH3、N2 與N2O等三種不同的氣體源為薄膜電晶體作鈍化處裡，但本實驗發現經過頓化處理後的薄膜電機體雖然導通特性變好，但卻有可靠度的問題。我們經過直流電壓stress後發現，經過頓化的電晶體其劣化程度較未頓化的電晶體來得大，這是因為經頓化後電晶體內部的缺陷雖然被頓化氣體原子填補而使導通特性變好，但經過直流stress後，這些已填補的氣體原子斷裂而造成特性變得較差。

In this dissertation, the performance, reliability and manufacturability of polycrystalline-Si thin-film transistors (poly-Si TFTs) and novel TFTs with SiGe on source/drain or gate regions have been fully studied. To improve the device performance, two novel TFTs with selective growth of poly-SiGe on either source/drain or gate regions were proposed. The resulting transistors have the advantage of increased turn-on current and reduced leakage current while compared to their conventional counterparts. In addition, the reliability of the proposed structure after DC stress is superior to that of the conventional TFTs. Furthermore, the poly-SiGe was deposited by ultrahigh vacuum chemical vapor deposition (UHVCVD) system under the temperature of 550°C, which is suitable for low-temperature manufacture of TFTs on glass substrate. In addition to lower deposition temperature, the manufacturability of the proposed TFTs includes the simple process, self-alignment in nature and the advantage that no additional masks are required.
It has also been studied on the device performance and reliability issue for the TFTs fabricated by laser crystallization or post-implant laser activation. It has been found that after laser crystallization or activation, the device performance such as turn-on current, threshold voltage, and mobility became superior. However, the leakage current and long-term reliability after post-implant laser activation was inferior as compared to furnace activation. In addition, the poorer uniformity and surface roughness after laser crystallization limit the improvement of device performance for TFTs. Therefore, for manufacturability of laser applied TFTs, we may have some trade-off among uniformity, device performance and reliability.
Next, we compared the characteristics and performances of UHVCVD deposited poly-Si films and low-pressure chemical vapor deposition (LPCVD) deposited a-Si followed by SPC method. It has been shown that UHVCVD deposited poly-Si TFTs after plasma treatment have almost the same trap-state density as well as threshold voltage and ON/OFF current ratio as the LPCVD SPC poly-Si TFTs. Furthermore, for manufacture consideration, UHVCVD deposited poly-Si film does not need long recrystallization time, and the uniformity is better than that of LPCVD SPC poly-Si film. However, there is a trade-off between the LPCVD and UHVCVD methods. The mobility of UHVCVD deposited poly-Si TFT after plasma treatment is still smaller compared with LPCVD SPC poly-Si TFT, which is due to the rougher surface in the poly-Si film prepared by UHVCVD.
Finally, plasma passivation using NH3, N2 and N2O for 2 hours has been applied to improve the device performance. However, it is found that after plasma passivation, the devices become unstable and result in poorer stress endurance compared to that of unpassivated device. This is because that the dangling bond once had been passivated by plasma treatment in poly-Si had been broken after stress, so that degradation for passivated device is pronounced as compared to unpassivated one.

Chapter 1 Introduction
Chapter 2 Polycrystalline Silicon Thin-Film Transistor With SiGe Raised Source/Drain
Chapter 3 Lightly Doped Drain Polycrystalline Silicon Thin-Film Transistor With Selective Growth of SiGe Spacer
Chapter 4 Comparison of TFT Characteristics Fabricated by Solid Phase Crystallization and Laser Crystallization Methods
Chapter 5 Characteristics and Reliability of Laser-Activated Low Temperature Polycrystalline Silicon Thin-Film Transistor
Chapter 6 Manufacturability and Reliability of Poly-Si TFTs Prepared by UHVCVD and LPCVD
Chapter 7 Conclusions and Recommendations for Furture Study

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