臺灣博碩士論文加值系統

論文提要
本論文的主題是研製具有溝槽式結構的鍺奈米晶粒快閃記憶體單胞元。首先利用TMAH溶液對(100)晶向的矽晶圓進行蝕刻，形成凹陷的溝槽結構，然後藉由乾式氧化成長氧化層在矽基板上，之後以電漿助長化學氣相沉積系統沉積非晶矽/非晶矽鍺/非晶矽多層膜，再以高溫爐管進行氧化處理，形成鍺奈米晶體包埋在氧化層內；鍺奈米晶體的形成是利用矽鍺合金中的矽與鍺在高溫氧化速率不同，鍺原子會自氧化物釋放出來並埋藏在氧化物與矽鍺合金介面的特性，利用此技巧可製造奈米尺寸的鍺奈米晶體。本研究引用此技巧將鍺奈米晶體成長在溝槽側壁，利用製程自然地將儲存媒介分立，以期能得到多位元的快閃記憶體單胞元。
為探討單胞元的電荷儲存特性，研究時亦首先製作金屬-氧化層-半導體電容結構，藉由電容-電壓量測得知元件的記憶窗口大小約為0.25伏特。接著藉由電流-電壓量測雙位元記憶體單胞元的IDS-VGS特性曲線圖，發現臨界電壓有偏移的效果，記憶窗口大小最大約為12.5伏特。希冀以此具有溝槽結構的鍺奈米晶體快閃記憶體單胞元可應用在未來的記體體工業中。

Abstract
In this thesis, the Ge nanocrystal flash memory cells with trench structure have been fabricated and demonstrated. Firstly, the trench structure was formed by etching of (100) silicon wafer with TMAH solution. Then, oxide was grown on the Si substrate with a dry oxidation process. After that, the amorphous silicon (a-Si)/amorphous silicon germanium (a-SiGe)/a-Si multilayer were prepared with a plasma- enhanced chemical vapor deposition system. Finally, the a-Si/a-SiGe/a-Si multilayers were thermally oxidized by using a high-temperature furnace to form the Ge nanocrystals. The nano-meter scale Ge crystal dots were formed by Ge segregation and agglomeration during the SiGe oxidation process. It was expected that the multi-bit operation of flash memory cells could be obtained by the charge storage medium of Ge nanocrystals formed on the sidewalls of trench accordingly.
In order to investigate the charge storage phenomenon of the formed Ge nanocrystals, the metal-oxide-semiconductor (MOS) capacitors with Ge nanocrystal embedded in oxide matrix were also fabricated. It has been found that a memory window of 0.25 V could be obtained, from the C-V measurements of the MOS capacitors. From the measured IDS-VGS curves of two-bits memory cells, a wide memory window of about 12.5 V was obtained. The Ge-nanocrystals flash-memory cells with trench structure could be a promising candidate in future flash memory application.

Contents
Table Captions………………………………………………… ..Ⅲ
Figure Captions………………………………………..……… ..Ⅳ

Chapter 1 Introduction…...…………………………………...1

Chapter 2 Motivation and Device Operation rinciples…...4
2.1 Motivation…………………………………......4
2.1.1 Quantum confinement effect [3]………....4
2.1.2 Comparison between Ge and Si quantum
dots…..................................6
2.1.3 Formation of Ge quantum-dots…………....6
2.1.4 Effects of Ge concentration……………...8
2.2 Operation principles of nonvolatile
memory…..................................12
2.2.1 Basic program mechanisms………………...12
2.2.2 Basic erasing mechanisms………………...13
Chapter 3 Device Fabrication and Measurement
Techniques….................................18
3.1 Device Fabrication…………………………....18
3.2 MeasurementTechniques…….................31
3.2.1 Transmission electron microscopy (TEM).31
3.2.2 Scanning electron microscopy (SEM)…….31
3.2.3 Micro-Raman spectroscopy………………….31
3.2.4 Capacitance-Voltage meter…………………32

Chapter 4 Experimental Results and Discussion……………33
4.1 The formation of groove structure………….33
4.2 The Characterization of Ge nanocrystals….37
4.2.1 Scanning electron microscopy (SEM)…….37
4.2.2 Raman scattering spectra………………….43
4.2.3 Transmission electron microscopy (TEM).45
4.3 C-V measurements of MOS capacitors…………46
4.4 I-V measurements of two-bits cell………….54
4.5 Operation of two-bits………………………….63
Chapter 5 Conclusion…………………………………………….71

References………………………………………………………….73

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