掺铟二氧化锡薄膜（ITO）的制备及其性质研究
摘要
二氧化锡(SnO2)作为一种典型的n型且有较宽的直接带系的宽禁带金属氧化物半导体材料(Eg=3.6eV),具有稳定的物理化学性质,例如较好的导电性能、光学性能、热稳定性和抗腐蚀性,因此SnO2已被广泛应用于气敏半导体材料、太阳能电池、化学电极、透明导电薄膜等很多领域。因为纯二氧化锡薄膜的电阻率较高,其载流子浓度由氧空位决定,而且难以控制,所以一般都通过用掺杂的方法来降低薄膜的电阻率并使其能够保持良好的光透射率。同时研究也表明,如果在二氧化锡中掺杂一些金属,例如铟、铝等,就可以形成较好的透明薄膜。这些基于二氧化锡的透明薄膜具有良好的光学特性和电学特性,而且有着较好的安全性,并可用于对一些有害气体的监测,是一种价格低廉、性能优良的氧化物半导体薄膜材料。
当前国内外热衷于研究各种不同掺杂物的二氧化锡的性能,例如掺铟的二氧化锡,即所谓的ITO,是目前国内外电子应用中一种非常有用的且比较热门的半导体氧化物材料。ITO有着良好的吸附性,因此在气敏传感器方面占据了越来越重要的地位。目前制备ITO薄膜的方法很多,主要包括：溅射法、蒸发法等,但这些方法需要大型设备的支持,而且价格比较昂贵。本文采用溶胶凝胶法即sol-gel法制备ITO薄膜,并在材料中掺杂了PEG添加剂(聚乙二醇),添加PEG的作用是改善薄膜的表面性能。因为PEG能够在低温时改变材料的性能,在适当条件下对薄膜进行热退火,就可以形成很好的表面结构。该方法简单,成本低廉,各项性能优越。本论文的主要内容如下：
(1)以无水InCl3,SnCl4无机盐和乙酰丙酮,无水乙醇为原料,采用溶胶-凝胶旋涂法,在硅晶片上通过掺杂不同浓度的In制备了高质量的ITO薄膜。此外本文探讨了浓度不同和分子量不同的PEG添加剂对ITO薄膜的影响；并讨论了退火温度,退火时间等对ITO薄膜的影响。我们采用X射线(XRD),扫描电子显微镜(SEM),紫外可见光谱仪等微观分析技术对样品进行了微结构和成分分析,研究表明,PEG的引入带来的好处包括：可以形成多孔薄膜,改善表面平整度,降低薄膜的方块电阻等。
(2)采用氩等离子室温下退火代替传统的热退火法来形成ITO薄膜。通过扫描电子显微镜(SEM),红外分析仪(FTIR),场发射枪扫描电子显微镜(FEGSEM)来探讨等离子体参数对薄膜的表面特性以及纳米结构的影响,例如：等离子体的功率以及作用于薄膜的处理时间。结果表明,采用室温下氩等离子体退火能够形成性能较好的ITO薄膜。
(3)探讨了退火氛围对ITO薄膜的影响。通过扫描电子显微镜(SEM)来研究退火氛围对ITO薄膜表面结构的影响,通过SZT-2四探针测试仪来研究退火氛围对薄膜电阻率的影响。结果表明,退火环境中的含氧量越高,薄膜表面结构越差,其电阻率也越大。
采用掺杂PEG的ITO薄膜具有多孔结构,该结构能够让ITO薄膜成为一种气敏材料。
Tin oxide (SnO2) thin film with a wide direct bandgap (Eg= 3.6eV) is a typical n-type metal-oxide semiconductor with stable physical and chemical properties such as its excellent electrical conductivity, superior optical property, good thermal and anti-corrosion properties. So it is widely used for many purposes such gas-sensing materials, solar cells, chemical electrodes, transparent conductive film, etc. Since the carrier concentration in the SnO2 thin films is decided by oxygen vacancies, the relatively high resistivity is resulted and difficult to be controlled. So SnO2 films doped with metals, such as indium, aluminum, etc. had been used to significantly improve the electrical resistivity and maintain a good optical transmittance.These transparent thin films have not only good optical and electrical properties, but also can be used to as the sensing materials to monitor some harmful gases for its excellent performance.
Indium-doped tin dioxide, known as ITO, is a useful semiconductor oxide in the electronic applications. ITO is also an increasingly important material for the gas sensors application. Lots of techniques had been employed for ITO thin films preparation including:sputtering, evaporation and so on. This paper use sol-gel technique to prepare ITO thin films for gas sensor application. Poly (ethylene glycol) had been used as an additive to improve the quality of ITO thin films. This method is simple, low cost. The main content of this thesis is as below:
(1) Indium-doped tin dioxide (ITO) thin films with various concentration of In have been successfully prepared on silicon wafer by sol-gel spin-coating technique, using C2H5OH, anhydrous SnCl4 and InCl3 as raw materials. In addition, polyethylene glycol (PEG) with different concentrations and molecular weight has been introduced. The influence of the processing paramerters such as the annealing temperature, PEG concentrations, etc on the ITO had been studied. The ITO films were characterized by X-ray (XRD), scanning electron microscopy (SEM), UV-vis spectrometer, etc.The study indicated that the benefits of introduction of PEG include:to form the porous thin films, to improve the surface flatness and to lowering the sheet resistance of the ITO thin films.
(2) Argon plasma calcination had been used instead of the conventional thermal annealing to form the ITO thin films at room temperature. The influence of the plasma parameters such as the plasma power, processing time on the ITO thin film surface properties and nanostructures had been studied and characterized by scanning electron microscopy (SEM), infrared analysis (FTIR), field emission gun scanning electron microscope (FEGSEM). It is demonstrated that with argon plama calcination, ITO thin films with good performance can be fabricated at room temperature.
(3) The influence of the annealing atmosphere on the ITO films was investigated. the structure of ITO films on the different annealing atmosphere were characterized by scanning electron microscopy (SEM) and the films'resistivity were studied by SZT-2 four-probe meter. The results showed that the higher oxygen content in the annealing environment, the worse the film surface structure, the greater the resistivity.
The PEG-doped ITO thin films have the porous structure, which can be used as the gas-sensing material.
当前国内外热衷于研究各种不同掺杂物的二氧化锡的性能,例如掺铟的二氧化锡,即所谓的ITO,是目前国内外电子应用中一种非常有用的且比较热门的半导体氧化物材料。ITO有着良好的吸附性,因此在气敏传感器方面占据了越来越重要的地位。目前制备ITO薄膜的方法很多,主要包括：溅射法、蒸发法等,但这些方法需要大型设备的支持,而且价格比较昂贵。本文采用溶胶凝胶法即sol-gel法制备ITO薄膜,并在材料中掺杂了PEG添加剂(聚乙二醇),添加PEG的作用是改善薄膜的表面性能。因为PEG能够在低温时改变材料的性能,在适当条件下对薄膜进行热退火,就可以形成很好的表面结构。该方法简单,成本低廉,各项性能优越。本论文的主要内容如下：
(1)以无水InCl3,SnCl4无机盐和乙酰丙酮,无水乙醇为原料,采用溶胶-凝胶旋涂法,在硅晶片上通过掺杂不同浓度的In制备了高质量的ITO薄膜。此外本文探讨了浓度不同和分子量不同的PEG添加剂对ITO薄膜的影响；并讨论了退火温度,退火时间等对ITO薄膜的影响。我们采用X射线(XRD),扫描电子显微镜(SEM),紫外可见光谱仪等微观分析技术对样品进行了微结构和成分分析,研究表明,PEG的引入带来的好处包括：可以形成多孔薄膜,改善表面平整度,降低薄膜的方块电阻等。
(2)采用氩等离子室温下退火代替传统的热退火法来形成ITO薄膜。通过扫描电子显微镜(SEM),红外分析仪(FTIR),场发射枪扫描电子显微镜(FEGSEM)来探讨等离子体参数对薄膜的表面特性以及纳米结构的影响,例如：等离子体的功率以及作用于薄膜的处理时间。结果表明,采用室温下氩等离子体退火能够形成性能较好的ITO薄膜。
(3)探讨了退火氛围对ITO薄膜的影响。通过扫描电子显微镜(SEM)来研究退火氛围对ITO薄膜表面结构的影响,通过SZT-2四探针测试仪来研究退火氛围对薄膜电阻率的影响。结果表明,退火环境中的含氧量越高,薄膜表面结构越差,其电阻率也越大。
采用掺杂PEG的ITO薄膜具有多孔结构,该结构能够让ITO薄膜成为一种气敏材料。
Tin oxide (SnO2) thin film with a wide direct bandgap (Eg= 3.6eV) is a typical n-type metal-oxide semiconductor with stable physical and chemical properties such as its excellent electrical conductivity, superior optical property, good thermal and anti-corrosion properties. So it is widely used for many purposes such gas-sensing materials, solar cells, chemical electrodes, transparent conductive film, etc. Since the carrier concentration in the SnO2 thin films is decided by oxygen vacancies, the relatively high resistivity is resulted and difficult to be controlled. So SnO2 films doped with metals, such as indium, aluminum, etc. had been used to significantly improve the electrical resistivity and maintain a good optical transmittance.These transparent thin films have not only good optical and electrical properties, but also can be used to as the sensing materials to monitor some harmful gases for its excellent performance.
Indium-doped tin dioxide, known as ITO, is a useful semiconductor oxide in the electronic applications. ITO is also an increasingly important material for the gas sensors application. Lots of techniques had been employed for ITO thin films preparation including:sputtering, evaporation and so on. This paper use sol-gel technique to prepare ITO thin films for gas sensor application. Poly (ethylene glycol) had been used as an additive to improve the quality of ITO thin films. This method is simple, low cost. The main content of this thesis is as below:
(1) Indium-doped tin dioxide (ITO) thin films with various concentration of In have been successfully prepared on silicon wafer by sol-gel spin-coating technique, using C2H5OH, anhydrous SnCl4 and InCl3 as raw materials. In addition, polyethylene glycol (PEG) with different concentrations and molecular weight has been introduced. The influence of the processing paramerters such as the annealing temperature, PEG concentrations, etc on the ITO had been studied. The ITO films were characterized by X-ray (XRD), scanning electron microscopy (SEM), UV-vis spectrometer, etc.The study indicated that the benefits of introduction of PEG include:to form the porous thin films, to improve the surface flatness and to lowering the sheet resistance of the ITO thin films.
(2) Argon plasma calcination had been used instead of the conventional thermal annealing to form the ITO thin films at room temperature. The influence of the plasma parameters such as the plasma power, processing time on the ITO thin film surface properties and nanostructures had been studied and characterized by scanning electron microscopy (SEM), infrared analysis (FTIR), field emission gun scanning electron microscope (FEGSEM). It is demonstrated that with argon plama calcination, ITO thin films with good performance can be fabricated at room temperature.
(3) The influence of the annealing atmosphere on the ITO films was investigated. the structure of ITO films on the different annealing atmosphere were characterized by scanning electron microscopy (SEM) and the films'resistivity were studied by SZT-2 four-probe meter. The results showed that the higher oxygen content in the annealing environment, the worse the film surface structure, the greater the resistivity.
The PEG-doped ITO thin films have the porous structure, which can be used as the gas-sensing material.
引文
[1]H. Deng, J.M. Hossenlopp, "Combined X-ray Diffraction and Diffuse Reflectance Analysis of Nanocrystalline Mixed Sn (Ⅱ) and Sn (Ⅳ) Oxide Powders ", Journal of Physical Chemistry B,109(1),2005, pp:66-73.
[2]C. Xu, J. Tamaki, N. Miura, N. Yamazoe, "Stabilization of SnO2 ultrafine particles by additives", Journal of Material Science,27(4),1992, pp:963-971.
[3]Bisht H, Eun T, Aegerter A, "Comparison of spray pyrolyzed FTO, ATO and ITO coatings and bent glass substrates", Thin Solid Films,351 (1-2) 1999, pp:109-114.
[4]M.J. Alam and D.C. Cameron, "Optical and electrical properties of transparent conductive ITO thin films deposited by sol-gel process", Thin Solid Films,377-378 (1),2000, pp:455-459.
[5]Choy Siew Fong, "Transparent and conductive multi-component oxide thin films prepared by magnetron sputtering", Master Thesis, National University of Singapore (2001).
[6]Zhi-hua Li, Yu-peng KE and Dong-yan REN,"Effects of heat treatment on morphological, optical and electrical properties of ITO films by sol-gel technique ", Transactions of Nonferrous Metals Society of China,18(2),2008,pp:366-371.
[7]Jiaxiang Liu,Da Wu and Shengnan Zeng, "Influence of temperature and layers on the characterization of ITO films ", Materials Processing Technology,209 (8), 2009,pp:3943-3948.
[8]Bingyan REN,Xiaoping LIU,Minhua WANG and Ying XU,"Preparation and characteristics of indium tin oxide (ITO) thin films at low temperature by r.f. magnetron sputtering ",Rare Metals,25(6),2006,pp:137-140.
[9]Sanchuan Tang,Jisheng Yao,Jian Chen and Jianguo Luo,"Preparation of indium tin oxide (ITO) with a single-phase structure ", Materials Processing Technology,137 (1-3),2003, p:82-85.
[10]M.J. Alam and D.C. Cameron, "Characterization of transparent conductive ITO thin films deposited on titanium dioxide film by a sol-gel process" Surface and Coatings Technology 142-144 (1157),2001,p:776-780.
[11]K. Kajihara and T. Yao, J. Sol-Gel Sci & Tech."Macroporous Morphology of the Titania Films Prepared by a Sol-Gel Dip-Coating Method from the System Containing Poly(ethylene glycol):Effects of Molecular Weight and Dipping Temperature" 19(1-3), 2000, p:219-222.
[12]K. Kajihara and T. Yao, "Macroporous Morphology of the Titania Films Prepared by a Sol-Gel Dip-Coating Method from the System Containing Poly(ethylene glycol). Ⅳ. General Principle of Morphology Formation and Effect of Heat Treatment", J. Sol-Gel Sci & Tech,17(2),2000,p:173-184.
[13]李兴,超大规模集成电路技术基础,电子工业出版社,1999。
[14]J.Zhang, K.H.Au, Z.Q.Zhu, S.O'shea, "Sol-gel preparation of poly(ethylene glycol) doped indium tin oxide thin films for sensing applications",Optical Materials,26(1),2004,pp:47-55.
[15]A.Matsuda,T.Kanzaki,K.Tadanaga,M.Tatsumisago,andT.Minami,"Proton conductivities of sol-gel derived phosphosilicate gels in medium temperature range with low humidity", Solid State Ionics,154-155(2),2002,pp:687-692.
[16]J.M. Harris, J.M. Poly(ethylene glycol) Chemistry:biotechnical and biomedical applications; Plenum Press:New York,1992.
[17]G.S. Devi, T. Hyodo, Y. Shimizu, and M. Egashira, "Synthesis of mesoporous TiO2-based powders and their gas-sensing properties ",Sens & Actua B,87(1),2002,p: 122-129.
[18]V. Bekiari, G. Pistolis, and P. Lianos, "Improvement of the emission properties of sol-gel silica matrices containing Eu3+in the presence of poly(ethylene glycol)-200 ",J Non-Crystall. Sol.,226(1-2]),1998,p:200-204. [27]Masayuki Okuya,Nobuyuki Ito and Katsuyuki Shiozaki,"ITO thin films prepared by a microwave heating",Thin Solid Films,515(24),2007,pp:8656-8659.
[19]J. Watson, K. Ihokura, and G.S.V. Coles, "The tin dioxide gas sensor", Meas. Sci.& Tech.4 (7),1993, p:711-716.
[20]J. Zhang, J.Q. Hu, F.R. Zhu, H. Gong, and S.O. Shea, Sens.& Actuat B, "ITO thin films coated quartz crystal microbalance as gas sensor for NO detection ",87 (1),2002,p: 159-167.
[21]A. Matsuda, Y. Kotani, T. Kogure, M. Tatsumisago, and T. Minami, J. Am. Cerm. Soc.83[1] (2000) 229-232.
[22]J.zhang, K.H.Au, S.Y.Chang,"Investigation of sol-gel derived Indium tin oxide thin films with poly(ethylene glycol) as an additive", Journal of Ceramic Processing Research,5(3),2004,pp:208-213.
[23]S.R. Ramanan."Dip coated ITO thin-films through sol_gel process using metal salts", Thin Solid Films,389 (1-2),2001,p:207.
[24]谷晋骐,朱宣惠,徐明霞,ZY前驱体的拉曼和红外光谱研究,光谱学与光谱分析第16卷,第2期,19-22。
[25]I. Hamberg and C.G. Granqvist, J. Appl. Phys.60 (1986)123-130.
[26]A. Beaurain, D. Luxembourg, C. Dufour, V. Koncar, B. Capoen and M. Bouazaoui,"Effects of annealing temperature and heat-treatment duration on electrical properties of sol-gel derived indium-tin-oxide thin films",Thin Solid Films,516(12),2008,p:4102-4106.
[27]Masatoshi Wakagi, Ken-ichi Chahara, Ken-ichi Onisawa, Yukio Kawakubo, Toshimichi Kichikawa, Tadashi Satoh and Tetsuroh Minemura,"Rapid heat treatment for spin coated ITO films by electron plasma annealing method ",Thin Solid Films,411(1),2002,pp:46-49.
[28]T. Neubert, F. Neumann, K. Schiffmann, P. Willich and A. Hangleiter,"Investigations on oxygen diffusion in annealing processes of non-stoichiometric amorphous indium tin oxide thin films",Thin Solid Films,513(1-2),2006,pp:319-324.
[29]Sung-Jei Hong and Jeong-In Han, Current Applied Physics 6,206(2006),pp:206-210.
[30]Taiki Kawai, Yuki Maekawa and Minoru Kusabiraki, "Plasma treatment of ITO surfaces to improve luminescence characteristics of organic light-emitting devices with dopants ", Surface Science,601(22),2007,p:5276-5279.
[31]J.Y. Park, H. S. Kim, D. H. Lee, K. H. Kwon and G. Y. Yeom,"A study on the etch characteristics of ITO thin film using inductively coupled plasmas", Surface and Coatings Technology,131 (1-3),pp:247-251.
[2]C. Xu, J. Tamaki, N. Miura, N. Yamazoe, "Stabilization of SnO2 ultrafine particles by additives", Journal of Material Science,27(4),1992, pp:963-971.
[3]Bisht H, Eun T, Aegerter A, "Comparison of spray pyrolyzed FTO, ATO and ITO coatings and bent glass substrates", Thin Solid Films,351 (1-2) 1999, pp:109-114.
[4]M.J. Alam and D.C. Cameron, "Optical and electrical properties of transparent conductive ITO thin films deposited by sol-gel process", Thin Solid Films,377-378 (1),2000, pp:455-459.
[5]Choy Siew Fong, "Transparent and conductive multi-component oxide thin films prepared by magnetron sputtering", Master Thesis, National University of Singapore (2001).
[6]Zhi-hua Li, Yu-peng KE and Dong-yan REN,"Effects of heat treatment on morphological, optical and electrical properties of ITO films by sol-gel technique ", Transactions of Nonferrous Metals Society of China,18(2),2008,pp:366-371.
[7]Jiaxiang Liu,Da Wu and Shengnan Zeng, "Influence of temperature and layers on the characterization of ITO films ", Materials Processing Technology,209 (8), 2009,pp:3943-3948.
[8]Bingyan REN,Xiaoping LIU,Minhua WANG and Ying XU,"Preparation and characteristics of indium tin oxide (ITO) thin films at low temperature by r.f. magnetron sputtering ",Rare Metals,25(6),2006,pp:137-140.
[9]Sanchuan Tang,Jisheng Yao,Jian Chen and Jianguo Luo,"Preparation of indium tin oxide (ITO) with a single-phase structure ", Materials Processing Technology,137 (1-3),2003, p:82-85.
[10]M.J. Alam and D.C. Cameron, "Characterization of transparent conductive ITO thin films deposited on titanium dioxide film by a sol-gel process" Surface and Coatings Technology 142-144 (1157),2001,p:776-780.
[11]K. Kajihara and T. Yao, J. Sol-Gel Sci & Tech."Macroporous Morphology of the Titania Films Prepared by a Sol-Gel Dip-Coating Method from the System Containing Poly(ethylene glycol):Effects of Molecular Weight and Dipping Temperature" 19(1-3), 2000, p:219-222.
[12]K. Kajihara and T. Yao, "Macroporous Morphology of the Titania Films Prepared by a Sol-Gel Dip-Coating Method from the System Containing Poly(ethylene glycol). Ⅳ. General Principle of Morphology Formation and Effect of Heat Treatment", J. Sol-Gel Sci & Tech,17(2),2000,p:173-184.
[13]李兴,超大规模集成电路技术基础,电子工业出版社,1999。
[14]J.Zhang, K.H.Au, Z.Q.Zhu, S.O'shea, "Sol-gel preparation of poly(ethylene glycol) doped indium tin oxide thin films for sensing applications",Optical Materials,26(1),2004,pp:47-55.
[15]A.Matsuda,T.Kanzaki,K.Tadanaga,M.Tatsumisago,andT.Minami,"Proton conductivities of sol-gel derived phosphosilicate gels in medium temperature range with low humidity", Solid State Ionics,154-155(2),2002,pp:687-692.
[16]J.M. Harris, J.M. Poly(ethylene glycol) Chemistry:biotechnical and biomedical applications; Plenum Press:New York,1992.
[17]G.S. Devi, T. Hyodo, Y. Shimizu, and M. Egashira, "Synthesis of mesoporous TiO2-based powders and their gas-sensing properties ",Sens & Actua B,87(1),2002,p: 122-129.
[18]V. Bekiari, G. Pistolis, and P. Lianos, "Improvement of the emission properties of sol-gel silica matrices containing Eu3+in the presence of poly(ethylene glycol)-200 ",J Non-Crystall. Sol.,226(1-2]),1998,p:200-204. [27]Masayuki Okuya,Nobuyuki Ito and Katsuyuki Shiozaki,"ITO thin films prepared by a microwave heating",Thin Solid Films,515(24),2007,pp:8656-8659.
[19]J. Watson, K. Ihokura, and G.S.V. Coles, "The tin dioxide gas sensor", Meas. Sci.& Tech.4 (7),1993, p:711-716.
[20]J. Zhang, J.Q. Hu, F.R. Zhu, H. Gong, and S.O. Shea, Sens.& Actuat B, "ITO thin films coated quartz crystal microbalance as gas sensor for NO detection ",87 (1),2002,p: 159-167.
[21]A. Matsuda, Y. Kotani, T. Kogure, M. Tatsumisago, and T. Minami, J. Am. Cerm. Soc.83[1] (2000) 229-232.
[22]J.zhang, K.H.Au, S.Y.Chang,"Investigation of sol-gel derived Indium tin oxide thin films with poly(ethylene glycol) as an additive", Journal of Ceramic Processing Research,5(3),2004,pp:208-213.
[23]S.R. Ramanan."Dip coated ITO thin-films through sol_gel process using metal salts", Thin Solid Films,389 (1-2),2001,p:207.
[24]谷晋骐,朱宣惠,徐明霞,ZY前驱体的拉曼和红外光谱研究,光谱学与光谱分析第16卷,第2期,19-22。
[25]I. Hamberg and C.G. Granqvist, J. Appl. Phys.60 (1986)123-130.
[26]A. Beaurain, D. Luxembourg, C. Dufour, V. Koncar, B. Capoen and M. Bouazaoui,"Effects of annealing temperature and heat-treatment duration on electrical properties of sol-gel derived indium-tin-oxide thin films",Thin Solid Films,516(12),2008,p:4102-4106.
[27]Masatoshi Wakagi, Ken-ichi Chahara, Ken-ichi Onisawa, Yukio Kawakubo, Toshimichi Kichikawa, Tadashi Satoh and Tetsuroh Minemura,"Rapid heat treatment for spin coated ITO films by electron plasma annealing method ",Thin Solid Films,411(1),2002,pp:46-49.
[28]T. Neubert, F. Neumann, K. Schiffmann, P. Willich and A. Hangleiter,"Investigations on oxygen diffusion in annealing processes of non-stoichiometric amorphous indium tin oxide thin films",Thin Solid Films,513(1-2),2006,pp:319-324.
[29]Sung-Jei Hong and Jeong-In Han, Current Applied Physics 6,206(2006),pp:206-210.
[30]Taiki Kawai, Yuki Maekawa and Minoru Kusabiraki, "Plasma treatment of ITO surfaces to improve luminescence characteristics of organic light-emitting devices with dopants ", Surface Science,601(22),2007,p:5276-5279.
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