臺灣博碩士論文加值系統

半導體的氧化物可以是元件結構的一部份，如金氧半(MOS)結構；也可提供元件表面的保護作用。隨著氮化鎵材料在光電子元件、高溫及高功率電子元件等方面應用的快速進步，如今氮化物材料的重要性是不可言喻。一般讓氮化鎵自然成長氧化物是運用熱氧化的技術，但是長時間高熱的溫度會讓氮化鎵磊晶品質劣化，進而影響元件的特性。
本論文利用光電化學氧化技術（photoelectrochemical oxidization）在n型氮化鎵上進行氧化實驗，成長原生的三氧化二鎵（Ga2O3）之氧化物。首先，為提升氧化物成長速率，以不同濃度的磷酸為電解液，嚐試以未加偏壓及偏壓1V和2V等條件來成長氧化物，利用α-step、SEM及EDX等儀器來量測氧化物的厚度、表面形態及成份分析。結果發現，以0.0032M的磷酸為例，在未加偏壓時的氧化速率為224nm/h；在偏壓1V下，氧化速率為2.8μm/h；在偏壓2V下，氧化速率為5μm/h。同時，從EDX分析發現氧含量會隨著外加偏壓增加而增加。所以，結果顯示外加偏壓可以幫助氮化鎵的氧化和提高氧化物的成長速率。
最後，為評估三氧化二鎵氧化物的特性以開發可以應用在金氧半場效電晶體或元件表面保護的氧化物材料，實驗中以MOS為測試結構，透過電流－電壓及電容－電壓特性曲線的量測來分析氧化物的特性。於實驗製程中，也發現成長完成之氧化物必須經由高溫退火，才能增加其抗酸鹼的能力，以利後續元件製程的進行。

Oxide of semiconductor could be a part of device structure, like MOS structure, or a layer to provide the surface passivation. With the great progress of the applications of GaN on optoelectronic devices and high temperature/high power electronics, GaN is more attractive than ever. Dry or wet thermal oxidation process is a mature technology for the oxidation of silicon. However, it has only limited success on GaN. High temperature process will deteriorate the crystal quality of GaN and further degrade the performance of devices.
In this thesis we studied the growth of Ga2O3 oxide film on n-type GaN by photoelectrochemical oxidization (PECO) technique. The first, in order to enhance the oxidation rate, we tried to conduct the wet oxidation of GaN in various concentrations of phosphorus acid (H3PO4) solutions with 0, 1, or 2V bias. The tested samples were examined with α-step profiler、scanning electron microscopy (SEM) and energy dispersive spectrometer (EDX) to evaluate the oxide thickness、the surface morphology and the composition of oxide, respectively. We obtained that the growth rates of oxide with 0.0032M phosphorus acid solution were 224nm/h, 2.8μm/h, and 5μm/h for 0, 1, or 2V bias, respectively. Also, the oxygen atom ratio in the oxide increased with bias from EDX analysis. Hence, an external bias could be used to enhance the oxidation rate of GaN and the growth rate of oxide.
In order to evaluate the properties of oxides, the PECO grown oxides were applied to the fabrication of MOS on GaN. Both I-V and C-V measurements were used to characterize the MOS devices. During process, we found the as-grown oxide must be annealed under high temperature to prevent the attack of chemicals during process.

第一章 緒論．．．．．．．．．．．．．．．．．．．．．．．1
1.1研究背景與目的．．．．．．．．．．．．．．．．．1
1.2氮化鎵之基本特性．．．．．．．．．．．．．．．．3
1.3各種氧化物之介紹．．．．．．．．．．．．．．．．6
第二章 光電化學氧化法與金氧半二極體之原理．．．．．．．．7
2.1乾式與濕式熱氧化技術．．．．．．．．．．．．．7
2.1.1 乾式熱氧化法．．．．．．．．．．．．．．．8
2.1.2 濕式熱氧化法．．．．．．．．．．．．．．．8
2.2 光電化學反應．．．．．．．．．．．．．．．．．9
2.3 蕭特基能障之原理．．．．．．．．．．．．．．．11
2.4 光電化學氧化之原理．．．．．．．．．．．．．．13
2.5 金氧半二極體之基本原理．．．．．．．．．．．．17
2.5.1 理想金氧半二極體．．．．．．．．．．．．17
2.5.2 電容－電壓之特性．．．．．．．．．．．．20
第三章 光電化學氧化之實驗方法．．．．．．．．．．．．．24
3.1 氮化鎵表面電極之選擇．．．．．．．．．．．．24
3.2 試片準備步驟．．．．．．．．．．．．．．．．26
3.3 光電化學氧化法之實驗架構．．．．．．．．．．28
3.4 金氧半二極體之實驗步驟．．．．．．．．．．．．30
第四章 結果與討論．．．．．．．．．．．．．．．．．．．32
4.1 氧化速率．．．．．．．．．．．．．．．．．．．32
4.2 掃描式電子顯微鏡（SEM）表面狀態分析．．．．．36
4.3 能量散佈分析儀（EDX）成份分析．．．．．．．．40
4.4 光激發（Photoluminescence）量測．．．．．．．．43
4.5金氧半二極體之電壓－電流量測．．．．．．．．．44
4.6 金氧半二極體之電容－電壓量測．．．．．．．．．47
第五章 結論．．．．．．．．．．．．．．．．．．．．．．50
參考文獻．．．．．．．．．．．．．．．．．．．．．．．．51

【1】 S. P. Jung, D. Ullery, C. H. Lin, and H. P. Lee, “High performance GaN-based light-emitting diode using high-transparency Ni/Au/Al-doped ZnO composite contacts,” Appl. Phys. Lett., vol. 87, pp.181107, 2005
【2】 W. Lanford, V. Kumar, R. Schwindt, A. Kuliev, I. Adesida, A. M.
Dabiran, A. M. Wowchak, P. P. Chow and J. W. Lee, “AlGaN/InGaN HEMTs for RF current collapse suppression,” IEEE Electronics Letters, vol. 40, no.12, 2004
【3】 Z. H. Feng, Y. G. Zhou, S. J. Cai, and Kei May Lau, “Enhanced thermal stability of the two-dimensional electron gas in GaN/AlGaN/GaN heterostructures by Si3N4 strain solidification,” Appl. Phys. Lett., vol. 85, no. 22, pp.5248-5250, 2004
【4】 V. Adivarahan, G. Simin, J. W. Yang, A. Lunev, M. AsifKhan, N. Pala, M. Shur, and R. Gaska, “SiO2 passivatedlateral geometry GaN transparent Schottky-barrier detectors,” Appl. Phys. Lett., vol. 77, no.6, pp.863-865, 2000
【5】 L. H. Peng, C. W. Chuang, J. K. Ho, C. N. Huang, and C. Y. Chen, “Deep ultra violet enhanced wet chemical etching of gallium nitride,” Appl. Phys. Lett., vol. 72, no.8, pp.939-941, 1998
【6】 C. T. Lee, H. Y. Lee, and H. W. Chen, “GaN MOS device using SiO2/Ga2O3 insulator grown by photoelectrochemical oxidation method,” IEEE Electron Devices Letters, vol.24, no.2 , pp.54-56, 2003
【7】 J. W. Johnson, B. Luo, F. Ren, B. P. Gila, W. Krishnamoorthy,
C. R. Abernathy, S. J. Pearton, J. I. Chyi, T. E. Nee, C. M. Lee,
and C.C. Chuo, “Gd2O3/GaN metal-oxide-semiconductor field-effect transistor,” Appl. Phys. Lett., vol. 77, no. 20,
pp.3230-3232, 2000
【8】 L. W. Tu, W. C. Kuo, K. H. Lee, P. H. Tsao, C. M. Lai, A. K. Chu, and J. K. Sheu, “High-dielectric-constant Ta2O5 n-GaN metal-oxide-semiconductor structure,” Appl. Phys. Lett., vol. 77, no. 23, pp.3788-3790, 2000
【9】 T. Kazuhiro , T. Takayuki, K. Shigefusa, ” Infrared lattice absorption in wurtzite GaN,’’ Jpn. J. Appl. Phys, vol. 38 , pp.151-153, 1999
【10】Y. Nakano, and T. Jimbo, “Interface properties of thermally oxidized n-GaN metal-oxide-semiconductor capacitors,” Appl. Phys. Lett., vol. 82, no. 2, pp.218-220, 2003
【11】S. D. Wolter, B. P. Luther, D. L. Waltemyer, C. Onneby, S. E. Mohney, and R. J. Molnar, “X-ray photoelectron spectroscopy and x-ray diffraction study of the thermal oxide on gallium nitride,” Appl. Phys. Lett., vol. 70, no. 16, pp.2156-2158, 1997
【12】C. C. Tang, Y. Bando, and Z. W. Liu, “Thermal oxidation of gallium nitride nanowires,” Appl. Phys. Lett., vol. 83, no. 15, pp.3177-3179, 2003
【13】 吳昌崙, 張景學,“半導體製造技術第二版,” 新文京開發出版股份有限公司, 2003
【14】 C. Youysey, I. Adesida , L.T. Romano, and G. Bulman, “Smooth
n-type GaN surface by photoenhanced wet etching,” Appl.
Phys. Lett., vol.72, pp.560-562, 1997
【15】T. Rotter, D. Mistele, F. Fedler, J. Aderhold, J. Graul, and M.Heuken, “Photoinduced oxide film for mation on n-type GaN surfaces using alkaline solution,” Appl. Phys. Lett., vol.76, no.26, pp.3923-3925, 2000
【16】E. H. Chen, D. T. Mclnturff, T. P. Chin, M. R. Melloch and J. M. Woodall, “Use of annealed low-temperature grown GaAs as a selective photo etch stop Layer,” Appl. Phys. Lett., vol.68, pp.1678-1680, 1996
【17】李世鴻, “半導體物理與元件,” 台商圖書有限公司, 2003
【18】J. E. Borton, C. Cai and M. I. Nathan, P. Chow, J. M. VanHove, A. Wowchak, and H. Morkoc, “Bias-assisted photoelectrochemical etching of p-GaN at 300K,” Appl. Phys. Lett., vol. 77, no.8, pp.1227-1229, 2000
【19】J. W. Seo, C. S. Oh, H. S. Jeong, J. W. Yang, K. Y. Lim, C. J. Yoon, and H. J. Lee, “Bias-assisted photoelectrochemical oxidation of n-GaN in H2O,” Appl. Phys. Lett., vol. 81, no.6, pp.1029-1031, 2002
【20】B. Van Daele, G. Van Tendeloo, W. Ruythooren, J. Derluyn, and M. Germain, “The role of Al on ohmic contact formation on n-type GaN and AlGaN/GaN,” Appl. Phys. Lett., vol. 87, pp.061905, 2005
【21】 L. H. Peng, C. H. Liao, Y. C. Hsu, C. S. Jong, C. N. Huang, J. K. Ho, C. C. Chiu, and C. Y. Chen, “Photoenhanced wet oxidation of gallium nitride,” Appl. Phys. Lett., vol. 76, no.4, pp. 511-513, 2000
【22】B. P. Gila, K. N. Lee, W. Johnson, F. Ren, C. R. Abemathy, and
S. J. Pearton, “A comparsion of gallium gadolinium oxide
and gadolinium oxide for use as dielectrics in GaN MOSFETs,” IEEE Electrics Devices , pp.182-191, 2000
【23】A. Castaldini, A. Cavallini, and L. Polenta, ”Role of edge dislocations in enhancing the yellow luminescence of n-type GaN,” Appl. Phys. Lett., vol. 88, pp.122105, 2006
【24】C. F. Lin, Z. J. Yang, J. H. Zheng, and J. J. Dai, “Enhanced light output in nitride-based light emitting diodes by roughening the mesa sidewall,” Appl. Phys. Lett., vol.87, pp. 2038-2040, 2005
【25】Z. Z. Chen, Z. X. Qin, C. Y. Hu, X. D. Hu, T. J. Yu, Y. Z. Tong, and G. Y. Zhang, “Ohmic contact formation of Ti/Al/Ni/Au to n-GaN by two-step annealing method,” Materials Science and Engineering, vol.111, pp.36-39, 2004
【26】C. T. Lee, H. W. Chen, and H. Y. Lee, “Metal oxide semiconductor devices using Ga2O3 dielectrics n-type GaN,” Appl. Phys. Lett., vol. 82, no.24, pp.4304-4306, 2003