臺灣博碩士論文加值系統

濕式化學蝕刻法被廣泛的應用在異質結構的平台蝕刻及閘極侵蝕上，乃因其在蝕刻過程中不會對元件過度損害而造成元件特性的衰退，而乾式蝕刻法就有這項顧慮。本實驗主要在討論濕式蝕刻法對三五族砷化鎵的蝕刻表現。
我們使用兩種蝕刻系統。磷酸、雙氧水及MX03的混合溶液之蝕刻率可達200 Å/sec，適合用來蝕刻厚度較厚的砷化鎵層。而檸檬酸、檸檬酸鉀、雙氧水及水的混合溶液由於其具有穩定且低的蝕刻率，其蝕刻率可被良好掌握且可避免過多的側向蝕刻。
對磷酸系統，前導實驗提供了影響蝕刻均勻度的重要因子，再分別對晶片的水平及垂直方向做蝕刻均勻度的最佳化實驗後，針對整片晶片找出最佳化條件。此最佳化條件為︰在1.5oC環境下，用1000毫升磷酸、11000毫升雙氧水、12毫升MX03混合液蝕刻，並佐以30psi的氮氣，可達到5.6％的蝕刻均勻度。
對檸檬酸系統，371克檸檬酸、120克檸檬酸鉀、351毫升雙氧水、及4983毫升水的混合液，在400小時的觀察時間內，表現出穩定的蝕刻率。而緩衝液（檸檬酸與檸檬酸鉀的水溶液）與雙氧水在體積比5.6：2時，其對砷化鎵及磷化銦鎵之蝕刻率分別為66.4 Å/sec及0.052 Å/sec，表現出的蝕刻選擇比高達1277，是良好的平台侵蝕及閘極蝕刻蝕刻液。

Wet etching has been widely used in mesa etch and gate recess process in GaAs device process. We prefer to use wet etching when low damage is required since dry etching always accompanies with damage.
In this thesis, two etchant systems were used for GaAs wet etching in heterojunction structure. H3PO4/H2O2/MX03 mixture was used to etch GaAs layer with thicker layer thickness due to its etch rate of about 200Å/sec. Citric acid (CA)/KCA/H2O2/H2O mixture was optimized to derive stable and low etching rate so that etch rate can be well controlled and lateral etching can be prevented. Besides, InGaP etchant was optimized to improve etch uniformity.
In H3PO4-based system, the etch process was optimized in horizontal and vertical directions respectively. The following experiment conducted for the whole wafer showed that the wet etching uniformity for GaAs wafers in the cassette can be improved to be 5.6%, with the setting of the optimum etching condition of 11000ml H2O2 mixed with 1000ml H3PO4 and 12 ml MX03 with 30psi N2 bubble around by 1.5oC.
In CA-based system, CA/KCA/H2O2/H2O=371g/120g/351ml/4983ml performed stable etch rate in an observation duration of 400 hours. Etchant composed of Buffer (CA and KCA in water): H2O2 = 5.6:2 in volume demonstrated GaAs/InGaP etch selectivity of 1277 with the average etch rate of 66.4 Å/sec and 0.052 Å/sec for GaAs and InGaP respectively. This is a suitable etchant for mesa etch and gate recess of GaAs/InGaP heterojunction device.

Chapter 1 Introduction………………………………………………1
Chapter 2 Technical Background…………………………………….3
2.1 Wet Etching Techniques ……………………………………3
2.1.1 Introduction…………………………………………3
2.1.2 Crystallography of GaAs………………………… 4
2.1.3 Principles of Wet Etching……………………… 5
2.1.4 Etching Solutions for GaAs………………………7
2.2 Taguchi Method………………………………………………10
2.2.1 Design of Experiment…………………………… 10
2.2.2 Orthogonal Arrays…………………………………10
2.2.3 Optimization of Process Parameters Utilizing S/N Ratio Analysis.........................................11
Chapter 3 Experimental……………………………………………..17
3.1 Etching Experiments……………………………….......17
3.1.1 Wafer Preparation…………………………………17
3.1.2 Etchant Preparation………………………………17
3.1.3 Etching Procedure…………………………………19
3.1.4 Etching Depth Measurement………………………19
3.1.5 Equipment (APT-3245)…………………………… 20
3.2 Experimental Design of H3PO4-based solution system.21
3.2.1 Initial Experiment…………………………………21
3.2.2 Optimization in Horizontal Direction…………22
3.2.3 Optimization in Vertical Direction……………22
3.2.4 Optimization for the Whole Wafer………………23
3.3 Experimental Design of CA-based solution system……24
3.3.1 Optimization of InGaP Etching Process……...24
3.3.2 Character of Tripotassium Citrate Monohydrate (KCA)……...................................................25
3.3.3 Optimization of Etchant Composition to Achieve Etching Rate Stability……………………………................25
3.3.4 Etching Selectivity of GaAs/InGaP…………… 27
Chapter 4 Results and Discussions…………………………………38
4.1 H3PO4-based solution system……………………………. 38
4.1.1 Initial Experiment…………………………………38
4.1.2 Optimization in Horizontal Direction…………39
4.1.3 Optimization in Vertical Direction……………40
4.1.4 Optimization for the Whole Wafer………………41
4.2 CA-based solution system………………………………… 42
4.2.1 Optimization of InGaP Etching Process……… 42
4.2.2 Character of Tripotassium Citrate Monohydrate (KCA)…………...............................................42
4.2.3 Optimization of Etchant Composition to achieve Etching Rate Stability……………………......................43
4.2.4 Etching Selectivity of GaAs/InGaP…………… 46
Chapter 5 Conclusion………………………………………………...79
Reference………………………………………………………………...80

1. Stanley Wolf Ph.D. and Richard N. Tauber Ph.D. “Silicon processing for the VLSI ERA”, 1990.
2. M. J. Howes, D. V. Morgan, “Gallium Arsenide”, John Wiley & Sons Ltd 1985.
3. T. Ya. Gorbach, G. Svechnikov, “Spontaneous anisotropic chemical etching as a nanostructure surface modification method for the AIIIBV semiconductors”, Material Science and Engineering B35 (1995) 224-229.
4. S. K. Ghandi, “VLSI Fabrication Principles, Si and GaAs”, Wiley, New York, 1983.
5. C. I. H. Ashby, “Etching of GaAs: as overview, in Properties of Gallium Arsenide”, third edition, INSPEC, London (1996).
6. Lepore, J. J., ”An improved technique for selective etching of GaAs and Ga1-xAlxAs”, J. Appl. Phys, 51, 12, 6441, 1998.
7. R. Williams, “ Modern GaAs Processing Method”, Artech House, Inc., Massachusetts, 1990.
8. David C. Hays, “selective etching of compound semiconductors”, university of Florida, 1999.
9. DeSalvo, Gregory C., W. F. Tseng, and J. Comas. J. Electrochem. Soc., 139,3,831,1992.
10. Don W. Shaw, “Enhanced GaAs Etch Rates Near the Edges of a Protective Mask”, Journal of the electrochemical society, pp.958 Sep. 1966.
11. Y. Tarui, Y. Komiya, and T. Yamaguchi, “Self-aligned GaAs Schottky barrier gate FET using preferential etching”, J. Jap. Soc. Appl. Phys., Suppl., 42, 78-87, 1973.
12. Y. Mori and N. Watanabe, “A new etching solution system, H3PO4-H2O2-H2O, for GaAs and its kinetics”, J. Electronchem. Soc., 125, 1510-14,1978.
13. S. Iida and K. Ito, “Selective etching of GaAs crystals in H2SO4-H2O2-H2O system”, J. Electronchem. Soc., 118, 768-71, 1971.
14. E. Kohn, “A correlation between etch characteristics of GaAs etch solutions containing H2O2 and surface film structure”, J. Electronchem. Soc., 127, 505-8, 1980.
15. B. Tuck, “The chemical polishing of semiconductors”, J. Mater. Sci., 10, 321-39, 1975.
16. K. Kenefick, “Selective etching characteristics of peroxide/ammonium-hydroxide solutions for GaAs/Al0.16Ga0.89As”, J. Electronchem. Soc., 129, 2380-2, 1982.
17. Hanfoug Rabah, Salesse Alain, Alibert Claude, “Study of GaAs chemical etching in a mixture of hydeogen peroxide/succinic acid and ammonia. Thiourea effect on the surface roughness and on the presence of surface states after etching”, Applied Surface Science 171 (2001) 34-43.
18. H. C. Liu, S. H. Tsai, J. W. Hsu, H. C. Shih, “The phase identification of the H2SO4-etched GaAs by X-ray diffraction”, Materials Chemistry and Physics 61 (1999) 117-123.
19. D. W. Shaw, “Localized GaAs etching with acidic peroxide solutions”, J. Electrochem. Soc., 128, 874-80, 1981.
20. J. Nishizawa, Y. Oyama, H. Tadano, K. Inokuchi, and Y. Okuno, “Observations of defects in LPE GaAs revealed by new chemical etchant”, J. Cryst. Growth, 47, 434-6, 1979.
21. M. Otsubo, T. Oda, H. Kumabe, and H. Miiki, “Preferential etching of GaAs through photoresist masks”, J. Electrochem. Soc., 123, 676-80, 1976.
22. E. Y. Chang, Yeong-Lin Lai, Y. S. Lee, and S. H. Chen, “A GaAs/AlAs Wet Selective Etch Process for the Gate Recess of GaAs Power Metal-Semiconductor Field-Effect Transistors”, Journal of The Electrochemical Society, 148 (1) G4-G9 (2001).
23. Sadao Adachi and Kunishige Oe, “Chamical Etching Characteristics of (001) GaAs”, J. Electrochem. Soc. Vol.130, No.12, 1983.
24. Min-Gu Kang, Seung-Hoon Sa, Hyung-Ho Park, Kyung-Soo Suh, Kyung-Hui Oh, “The Characterization of etched GaAs surface with HCl or H3PO4 solutions”, Thin Solid Films, 308-309 1997 634-642.
25. J. J. Gannon and C. J. Nuese, “A Chemical Etchant for the Selective Removal of GaAs Through SiO2 Masks”, J. Electrochem. Soc.: Solid-State Science and Technology, Sep. 1974.
26. C. Juang. K. J. Kuhn, and R. B. Darling, “selective etching of GaAs and Al0.30Ga0.70As with citric acid/hydrogen peroxide solutions”, J. Vac. Sci. Technol. B 8 (5), Sep/Oct 1990.
27. G S. Roy. “A Primer to the TAGUCHI Method”, Society of Manufacturing Engineering, 1990.
28. Jong-Lam Lee, Eun-A Moon, Jung-Woo Oh, Seong Wook Ryu and Hyung Mo Yoo, “Selective wet etching of GaAs on Al0.24Ga0.76As for GaAs/Al0.24Ga0.76As/In0.22Ga0.78As PHEMT”, Electronics Letters 9th Nov. 2000, Vol.36 No.23.
29. B. C. Schmukler, P. E. Brunemeier, W. R. Hitchens, B. D. Cantos, W. A. Strifler, D. H. Rosenblatt, R. D. Remba, “Highly Selective Citric Buffer Etch-Stop Process for the Manufacture of Very Uniform GaAs/AlGaAs FETs”, GaAs IC Symposium, IEEE, 1993 pp325-328.
30. J. W. Lee, S. J. Pearton, C. R. Abernathy, W. S. Hobson, F. Ren and C. S. Wu, “Investigation of wet etching solutions for In0.5Ga0.5P”, Solid-State Electronics Vol.38, No.11, pp. 1871-1874, 1995.
31. David Danzilio and Aleen Hanson, “In0.5Ga0.5P Etch-Stop Process for PHEMT Manufacturing”, 1999 GaAs Mantech.