臺灣博碩士論文加值系統

SiGe(矽鍺)材料在國內外的研究已行之有年，但結合Si與Ge二者良好材料特性於一身的SiGe至今仍然無法在應用端上有著廣泛的使用，其原因為欲將SiGe 材料製備於目前在應用上至為成熟的Si基板上時，由於Ge與Si間晶格不匹配達4.2%會導致SiGe磊晶層中隨著Ge成分的增加會有愈多缺陷產生，嚴重影響利用此磊晶基板所研製元件效能。
為解決上述問題，一般磊晶法需經由繁複Ge組成漸變緩衝層（每μm增加Ge組成0.1至0.2）來獲致高組成SiGe表層。本研究採用簡易的LPE(Liquid phase epitaxy, 液相磊晶)法搭配使用SiO2材質選擇性開窗罩膜形式來進行橫向磊晶 (Epitaxial lateral overgrowth, ELO) 的技術直接求取低缺陷密度(Etch pit density, EPD)高Ge組成SiGe層。具體而言，首先在Si(111)基板表面鍍上一層約200nm SiO2後，使用設計好的光罩圖案進行微影蝕刻，由於SiGe僅會在開窗部分進行成長，因此能有效侷限晶格不匹配所致缺陷上傳至磊晶層表面，而橫向磊晶部分則可期待無缺陷產生，如此一來將可降低整體SiGe磊晶層EPD。本研究分別使用方格、圓形陣列以及平行線條三種形式窗罩進行磊晶實驗，優化其各項生長參數，並探討其磊晶成長機制，完成後樣品利用微分干涉顯微鏡(Nomarsky differential interference contrast microscopy, NDIC) 以及掃描式電子顯微鏡(Scanning electron microscopy, SEM)觀察表面結構，並使用能量散佈X射線光譜分析儀(Energy dispersive spectroscopy, EDS)確認SiGe層元素組成。

Silicon-germanium (SiGe) has been studied by a lot of researchers for many years because of the specific properties of Si and Ge. However, SiGe is still not widely used in practical applications due to the defects in SiGe epitaxial layers resulting from large lattice mismatch (4.2%) between Ge and Si. In order to solve the above problems, complicated buffer layers with gradually modulated Ge composition (10 – 20% per micrometer) are required by using conventional epitaxial methods and it would inevitably take time and cost to prepare high-Ge-composition SiGe layers on Si substrate.
In this study, low etch pit density (EPD)/ high Ge composition SiGe layers were grown successfully on SiO2-patterned Si substrates using the epitaxial lateral overgrowth (ELO) technique realized by a liquid phase epitaxial (LPE) system. Specifically, SiGe is limited to grow only through the window portions of SiO2 pattern (thickness: 200 nm) and then the distribution of lattice mismatch related defects is effectively confined, leading to the defect-free lateral epitaxial layers. Therefore, the overall EPD of SiGe epitaxial layer can be further lowered. The epitaxial experiments were carried out on three kinds of opening pattern including square array, circular array, and parallel lines. The growth parameters were optimized and the epitaxial growth mechanism was discussed. After sample preparation, the Nomarski differential interference contrast (NDIC) microscope and scanning electron microscopy (SEM) were used to observe the surface structures of SiGe, and also the elemental composition of SiGe layers was confirmed by energy dispersive spectroscopy (EDS).

摘要 I
Abstract III
致謝 V
Content VIII
List of Figures X
List of Tables XV
CHAPTER 1 PREFACE 1
1-1 Research Motivation 1
CHAPTER 2 EXPERIMENT OVERVIEW 6
2-1 Liquid Phase Epitaxy 6
2-2 Epitaxial Lateral Overgrowth (ELO) 8
2-3 Liquid Phase Epitaxial System and Equipment 12
2-4 Experimental Process 15
2-4-1 Cleaning Process 17
2-4-2 Preparation Before Heating and Epitaxial Process 18
2-4-3 Sample Characterizations 20
CHAPTER 3 RESULTS AND DISCUSSION 21
3-1 ELO on Square-Window-ARRAY Mask 21
3-1-1 Effect of Window Size Variation 21
3-1-2 Effect of Cooling-rate & Growth Time Variation 23
3-1-3 Effect of Weight-Percentage-Ratio [Sn:Ge] Variation 26
3-2 Si(111) Circular Window Array and Parallel Line Window Mask 30
3-2-1 Circular Window Array Mask 32
3-2-2 Parallel Line Window Mask 60
CHAPTER 4 CONCLUSIONS AND FUTURE PROSPECTS 65
4-1 Conclusions 65
4-2 Future Prospects 70
Reference 72

List of Figures
Figure 1- 1. Absorption coefficient of semiconductor [3]. ................................... 2
Figure 2- 1. Three common cooling methods used for LPE................................. 7
Figure 2- 2. The schematic of conventional LPE and ELO growth of SiGe-on-Si.
..................................................................................................................... 10
Figure 2- 3. Schematic diagram of different styles of mask molds used for ELO.
..................................................................................................................... 10
Figure 2- 4. Schematic of LPE System used in this study. ................................. 13
Figure 2- 5. LPE System used in this study. ....................................................... 14
Figure 2- 6. A flowchart illustration for the research steps used, including: the
source material cleaning, epitaxial growth, and film characterizations...... 16
Figure 2- 7. A schematic illustration of the LPE source materials’ placement... 19
Figure 2- 8. LPE Experimental temperature-time diagram. ............................... 20
Figure 3- 1. ELO results on square-window-array masks with different window
sizes. ............................................................................................................ 23
Figure 3- 2. Epitaxial surface of ELO samples obtained using different coolingrates. Red scale bar: 10 µm. ........................................................................ 25
Figure 3- 3. SEM/EDS analysis results of samples prepared with 0.53-g Ge solute.
..................................................................................................................... 28
Figure 3- 4. SEM/EDS analysis results of samples prepared with 0.2-g Ge solute.
..................................................................................................................... 29
Figure 3- 5. Raman spectra of ELO samples measured at different positions.... 30
Figure 3- 6. MO images of SiGe ELO Sample (S10) & cleavage planes {111} of
Si(111) wafers and the diagram illustrating the relationship between different
directions. .................................................................................................... 31
Figure 3- 7. OM image of S22 (Diameter 5 µm, Interval 5 µm). Red scale bar: 100
µm................................................................................................................ 33
Figure 3- 8. OM image of S22 (Diameter 5 µm, Interval 10 µm). Red scale bar:
10 µm........................................................................................................... 33
Figure 3- 9. OM image of S25 (Diameter 5 µm, Interval 5 µm) Red scale bar: 100
µm................................................................................................................ 35
Figure 3- 10. OM images of S34-37 (Diameter 20µm, Interval 10µm). Red scale
bar: 100 µm. ................................................................................................ 37
Figure 3- 11. OM images of S35 and S38 (Diameter 20 µm, Interval 10 µm) Red
scale bar: 100 µm. ....................................................................................... 39
Figure 3- 12. OM images of S35, S40, and S42 (Diameter 20 µm, Interval 10 µm).
Red scale bar: 100 µm................................................................................. 41
Figure 3- 13. Epitaxial layer surrounding white area (S25, Left picture: Interval
20 µm, Right picture interval 100 µm). ...................................................... 42
Figure 3- 14. SEM surface image of S28 (Diameter 20 µm, Interval 10 µm) with
the regions marked for EDX analysis. ........................................................ 43
Figure 3- 15. SEM surface image of S28 (Diameter 20 µm, Interval 100 µm) with
the regions marked for EDX analysis. ........................................................ 44
Figure 3- 16. OM image of S37 (D: 20 µm). Inside the red frame epitaxial layer
grown without masking could be observed due to the peel-off of oxide layer.
Red scale bar: 10 µm................................................................................... 45
Figure 3- 17. Top-view SEM image of S15 (Line length 250 µm, Interval 100 µm).
..................................................................................................................... 46
Figure 3- 18. Cross-sectional SEM image of S15 (Line length 250 µm, Interval
100 µm). ...................................................................................................... 46
Figure 3- 19. Top-view SEM image of S28 (Diameter 20 µm, Interval 100 µm).
..................................................................................................................... 47
Figure 3- 20. Cross-sectional SEM image of S28 (Diameter 20 µm, Interval 100
µm). ............................................................................................................. 47
Figure 3- 21. Cross-sectional SEM image of S15 (Line length 250 µm, Interval
100 µm). ...................................................................................................... 48
Figure 3- 22. An illustration diagram of SiGe growth mechanism..................... 49
Figure 3- 23. A diagram illustrating an alternative method for the supply of Si
atoms by meltbacking substrate for growing SiGe on Si............................ 50
Figure 3- 24. OM images of S56(5 μm), S57(20 μm) and S58(10 μm). Red scale
bar: 100 µm. ................................................................................................ 53
Figure 3- 25. OM image of S57 (20 μm). Red scale bar: 100 µm...................... 54
Figure 3- 26. OM image of S28 (20 μm). Red scale bar: 100 µm...................... 54
Figure 3- 27. OM images of ELO layers. Left: S57 interval 20 μm, Right: S58
interval 5 μm. Red scale bar: 100 µm. ........................................................ 55
Figure 3- 28. AFM image of S56 (D – I: 5 µm-5 µm)........................................ 58
Figure 3- 29. AFM image of S60 (grown without pattern)................................. 58
Figure 3- 30. Roughness analyzed by AFM for ELO samples prepared on the mask
of circular openings with various diameters and intervals.......................... 59
Figure 3- 31. OM image of S29. Red scale bar:100 µm..................................... 62
Figure 3- 32. OM image of S50. Red scale bar:100 µm..................................... 62
Figure 3- 33. OM image of S50. Red scale bar:100 µm..................................... 63
Figure 4- 1. SiGe Research history in our Lab. .................................................. 66
Figure 4- 2. A diagram illustrating a more favorable epitaxial structure can be
expected to achieve good ELO layers......................................................... 71


List of Tables
Table 1- 1 Comparison of the properties of Si and Ge.......................................... 3
Table 2- 1 Comparison of various epitaxial methods. .......................................... 8
Table 2- 2 Detailed classification of window patterns used for ELO. ................ 11
Table 3- 1 Growth parameters for ELO on square-window-array patterned
substrate....................................................................................................... 22
Table 3- 2 Growth parameters for ELO on 250-μm-sided window with different
cooling rates. ............................................................................................... 25
Table 3- 3 Growth parameters for ELO with a growth solution of weight
percentage ratio for Sn to Ge = 85%: 15%. ................................................ 27
Table 3- 4 Growth parameters for S22 (Diameter 5 μm Circle). ........................ 32
Table 3- 5 Growth parameters for S25 (Diameter 5 µm).................................... 35
Table 3- 6 Growth parameters for S34-37 (Circle Diameter 20µm)................... 36
Table 3- 7 Growth parameters for S35 and S37 (Diameter 20 µm Circle)......... 39
Table 3- 8 S35、40、42、45 (Diameter 20 µm Circle) Growth parameters..... 40
Table 3- 9 EDX analysis results for S28 (Diameter 20 µm, Interval 100 µm)... 43
Table 3- 10 S28 (Diameter 20µm, Interval 100µm) EDX Analysis table .......... 44
Table 3- 11 EDX Analysis results of S15 (Line length 250 µm, Interval 100 µm).
..................................................................................................................... 49
Table 3- 12 Growth parameters for S56, S57, and S58 (Growth time 400 min.).
..................................................................................................................... 52
Table 3- 13 Comparison of epitaxial area on S28 & S57. (Unit: µm2
)............... 54
Table 3- 14 AFM roughness survey of each area of the S56-58......................... 57
Table 3- 15 Growth parameters for S29 and S50................................................ 63

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