氢化非晶硅TFT器件电学特性漂移的研究与改善
|
摘要
氢化非晶硅薄膜晶体管(Hydrogenated Amorphous Silicon Thin Film Transistor, a-Si:H TFT)作为目前平板显示技术中成熟应用的电子器件,以其在大面积面板生产上的高均一性,低成本等优势,成为当前应用最为广泛的一种薄膜晶体管。在采用a-Si:H TFT器件来驱动有机发光二极管OLED (Organic Light-Emitting Diode器件)生产大面积基板OLED显示产品时有着无可比拟的成本优势,具有重大的意义,但同时也存在a-Si:H TFT器件电学特性漂移,有效迁移率低等问题。本文以提高a-Si:H TFT器件可靠性为目的,探索了a-Si:HTFT器件电学特性漂移的物理机制,提出物理模型,并在此基础上设计进行了两个实验对a-Si:H TFT器件电学特性漂移进行改善。
在本文中在TFT Id-Vg特性,C-V特性测试分析基础上,提出了一个a-Si:HTFT器件电学特性漂移的物理模型,认为在a-Si:H TFT器件中,非晶硅薄膜界面及其内部晶粒间界处,由于缺陷的影响存在大量的处于应力状态下的弱Si-Si键,在a-Si:H TFT器件工作状态下,即处于栅压偏置状态下,该部分弱Si-Si键会断裂形成新的界面态,所新产生的界面态缺陷能级,导致了a-Si:H TFT器件电学特性的漂移。
基于所提出的电学特性漂移理论模型,确定以改善氢化非晶硅中的弱Si-Si键的密度为主要的实验方向,设计了两个实验改善方案,用以确认弱Si-Si键对TFT在负栅压偏置下电学特性漂移的影响。具体是针对减少a-Si：H与SiN：H界面弱Si-Si键,设计了a-Si背沟道反应离子刻蚀后退火实验；针对减少a-Si内部Si-Si键,设计了减少a-Si等离子增强化学气相淀积成膜厚度的实验。
从实验结果上看,所得到的结果是与文中所提的理论模型相一致的,进一步确认了弱Si-Si键的密度是影响TFT电学特性漂移的主要因素,且相对于a-Si:H内部的弱Si-Si键,a-Si：H与SiN：H界面处的弱Si-Si键对氢化非晶硅TFT电学特性漂移起主导影响作用。
最后本文明确了,a-Si：H与SiN：H界面膜质的改善是改善a-Si:H TFT器件电学特性漂移的关键,而实验中所采用的快速热退火工艺,能够有效改善a-Si:H与SiN：H界面膜质,为氢化非晶硅TFT电学特性漂移的改善在大规模实际生产制程的运用上提出了一个可行有效的方向。
Hydrogenated Amorphous Silicon Thin Film Transistor (a-Si:H TFT) technology is mature and widely applies to produce active matrix display devices because of its excellent process uniformity and low fabrication costs in large area glass substrate production. So that it makes sense to introduce a-Si:H TFT which used widely in liquid crystal Display (LCD) to drive organic light emitting diode (OLED) devices. While the disadvantages of a-Si:H TFT such as shift of electrical character, lower effective mobility are need to be solved in order to drive OLED well.
An a-Si:H TFT electrical character degradation physical model was proposed in this thesis, which is based on the test and analysis of a-Si:H TFT Id-Vg curve and C-V curve. The model believe that the extra interface state caused by weak Si-Si bond breaking determine the degradation degree of a-Si:H TFT electrical character.
To decrease the defect state in the interface between SiN:H and a-Si:H, a rapid thermal anneal process after back channel reactive ion etching experiment is proposed. To decrease the state in the boundary of grain inside the a-Si:H, a thinning a-Si:H film layer experiment is proposed.
The a-Si:H TFT electrical character degradation physical model is supported by the experiment result. That the weak Si-Si bond breaking is main cause of the a-Si:H TFT electrical character degradation is confirmed again. Furthermore compare to the grain boundary defect state the interface state between SiN:H and a-Si:H seem to be dominating. the model and the experiment result are useful to the TFT design and production process.
在本文中在TFT Id-Vg特性,C-V特性测试分析基础上,提出了一个a-Si:HTFT器件电学特性漂移的物理模型,认为在a-Si:H TFT器件中,非晶硅薄膜界面及其内部晶粒间界处,由于缺陷的影响存在大量的处于应力状态下的弱Si-Si键,在a-Si:H TFT器件工作状态下,即处于栅压偏置状态下,该部分弱Si-Si键会断裂形成新的界面态,所新产生的界面态缺陷能级,导致了a-Si:H TFT器件电学特性的漂移。
基于所提出的电学特性漂移理论模型,确定以改善氢化非晶硅中的弱Si-Si键的密度为主要的实验方向,设计了两个实验改善方案,用以确认弱Si-Si键对TFT在负栅压偏置下电学特性漂移的影响。具体是针对减少a-Si：H与SiN：H界面弱Si-Si键,设计了a-Si背沟道反应离子刻蚀后退火实验；针对减少a-Si内部Si-Si键,设计了减少a-Si等离子增强化学气相淀积成膜厚度的实验。
从实验结果上看,所得到的结果是与文中所提的理论模型相一致的,进一步确认了弱Si-Si键的密度是影响TFT电学特性漂移的主要因素,且相对于a-Si:H内部的弱Si-Si键,a-Si：H与SiN：H界面处的弱Si-Si键对氢化非晶硅TFT电学特性漂移起主导影响作用。
最后本文明确了,a-Si：H与SiN：H界面膜质的改善是改善a-Si:H TFT器件电学特性漂移的关键,而实验中所采用的快速热退火工艺,能够有效改善a-Si:H与SiN：H界面膜质,为氢化非晶硅TFT电学特性漂移的改善在大规模实际生产制程的运用上提出了一个可行有效的方向。
Hydrogenated Amorphous Silicon Thin Film Transistor (a-Si:H TFT) technology is mature and widely applies to produce active matrix display devices because of its excellent process uniformity and low fabrication costs in large area glass substrate production. So that it makes sense to introduce a-Si:H TFT which used widely in liquid crystal Display (LCD) to drive organic light emitting diode (OLED) devices. While the disadvantages of a-Si:H TFT such as shift of electrical character, lower effective mobility are need to be solved in order to drive OLED well.
An a-Si:H TFT electrical character degradation physical model was proposed in this thesis, which is based on the test and analysis of a-Si:H TFT Id-Vg curve and C-V curve. The model believe that the extra interface state caused by weak Si-Si bond breaking determine the degradation degree of a-Si:H TFT electrical character.
To decrease the defect state in the interface between SiN:H and a-Si:H, a rapid thermal anneal process after back channel reactive ion etching experiment is proposed. To decrease the state in the boundary of grain inside the a-Si:H, a thinning a-Si:H film layer experiment is proposed.
The a-Si:H TFT electrical character degradation physical model is supported by the experiment result. That the weak Si-Si bond breaking is main cause of the a-Si:H TFT electrical character degradation is confirmed again. Furthermore compare to the grain boundary defect state the interface state between SiN:H and a-Si:H seem to be dominating. the model and the experiment result are useful to the TFT design and production process.
引文
[1]戴亚祥,TFT-LCD面板的驱动与设计密码,台湾五南文化事业出版公司,P51
[2]S. M. Venugopal, D. R. Allee, Integrated a-Si:H source drivers for 4 inch QVGA electrophoretic display on flexible, Journal of Display Technology, vol. 3(1),2007, pp 57-63.
[3]T. C. Huang, H. Y. Tseng, C. P. Kung, el at, Reliability analysis for flexible electronics:case study of integrated a-Si:H TFT scan driver,
[4]. M. J. Powell, C. van Berkel, A. R. Franklin, S. C. Deane, and W. I. Milne, "Defect pool in amorphous-silicon thin-film transistors," Phys. Rev. B, vol.45, no.8, pp.4160-4170, Feb.1992.
[5]M. J. Powell, Analysis of field-effect-conductance measurements on amorphoussemiconductors, Philos. Mag. B, vol.43, no.1, pp.93-103, Jan.1981.
[6]R. A. Street and K. Winer, Defect equilibria in undoped a-SiH, Phys. Rev. B, vol.40, no.9, pp.6236-6249, Sep.1989.
[7]Peyman Servati and Arokia Nathan, Modeling of the Reverse Characteristics of a-Si:H TFTs, IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL.49, NO.5, MAY 2002, IEEE
[8]孙以材,半导体测试技术,冶金工业出版社,1984,Pages 420-424
[9]张少强、徐重阳等,有源层厚度对非晶硅薄膜晶体管特性的影响,J.Huazhong U niv. of Sci.& Tech., Nov.1996
[10]T. Tiedje and A. Rose, A physical interpretation of dispersive transport in disordered semiconductors, Solid State Commun,1980, 37:49-52.
[11]Morell, G.;Katiyar, R. S. Weisz, S. Z. el at, Raman study of the network disorder in sputtered and glow discharge a-Si:H films, Journal of Applied Physics, Volume:78 Issue:8
[12]Akira Sasanoa, Haruo Matsumarua, Yoshiyuki Kanekoa and Toshihisa Tsukadaa Phosphorus diffusion effect on off-current of a-Si thin film transistors, Journal of Non-Crystalline SolidsVolumes 97-98, Part 2,2 December 1987, Pages 1295-1298
[13]谷至华,薄膜晶体管(TFT)阵列制造技术,复旦大学出版社,2007年9月第一版。
[14]Chung Yi, Shi-Woo Rhee, Sae-Hwan Park and Jin-Ho Ju, Effect of Back-Channel Plasma Etching on the Leakage Current of a-Si:H Thin Film Transistors, Jpn. J. Appl. Phys.39 (2000) pp.1051-1053
[15]丁晖、徐重阳等,PECVD a-Si:H薄膜对TFT有源矩阵性能的影响及其淀积工艺研究,光电子技术,vol 17,No.1
[16]Rohatgi A and Jeong JW. High-efficiency Screen-printed Silicon Ribbon Solar Cells by Effective Defect Passivation and Rapid Thermal Processing. Applied Physics Letters,2003 82:224.
[2]S. M. Venugopal, D. R. Allee, Integrated a-Si:H source drivers for 4 inch QVGA electrophoretic display on flexible, Journal of Display Technology, vol. 3(1),2007, pp 57-63.
[3]T. C. Huang, H. Y. Tseng, C. P. Kung, el at, Reliability analysis for flexible electronics:case study of integrated a-Si:H TFT scan driver,
[4]. M. J. Powell, C. van Berkel, A. R. Franklin, S. C. Deane, and W. I. Milne, "Defect pool in amorphous-silicon thin-film transistors," Phys. Rev. B, vol.45, no.8, pp.4160-4170, Feb.1992.
[5]M. J. Powell, Analysis of field-effect-conductance measurements on amorphoussemiconductors, Philos. Mag. B, vol.43, no.1, pp.93-103, Jan.1981.
[6]R. A. Street and K. Winer, Defect equilibria in undoped a-SiH, Phys. Rev. B, vol.40, no.9, pp.6236-6249, Sep.1989.
[7]Peyman Servati and Arokia Nathan, Modeling of the Reverse Characteristics of a-Si:H TFTs, IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL.49, NO.5, MAY 2002, IEEE
[8]孙以材,半导体测试技术,冶金工业出版社,1984,Pages 420-424
[9]张少强、徐重阳等,有源层厚度对非晶硅薄膜晶体管特性的影响,J.Huazhong U niv. of Sci.& Tech., Nov.1996
[10]T. Tiedje and A. Rose, A physical interpretation of dispersive transport in disordered semiconductors, Solid State Commun,1980, 37:49-52.
[11]Morell, G.;Katiyar, R. S. Weisz, S. Z. el at, Raman study of the network disorder in sputtered and glow discharge a-Si:H films, Journal of Applied Physics, Volume:78 Issue:8
[12]Akira Sasanoa, Haruo Matsumarua, Yoshiyuki Kanekoa and Toshihisa Tsukadaa Phosphorus diffusion effect on off-current of a-Si thin film transistors, Journal of Non-Crystalline SolidsVolumes 97-98, Part 2,2 December 1987, Pages 1295-1298
[13]谷至华,薄膜晶体管(TFT)阵列制造技术,复旦大学出版社,2007年9月第一版。
[14]Chung Yi, Shi-Woo Rhee, Sae-Hwan Park and Jin-Ho Ju, Effect of Back-Channel Plasma Etching on the Leakage Current of a-Si:H Thin Film Transistors, Jpn. J. Appl. Phys.39 (2000) pp.1051-1053
[15]丁晖、徐重阳等,PECVD a-Si:H薄膜对TFT有源矩阵性能的影响及其淀积工艺研究,光电子技术,vol 17,No.1
[16]Rohatgi A and Jeong JW. High-efficiency Screen-printed Silicon Ribbon Solar Cells by Effective Defect Passivation and Rapid Thermal Processing. Applied Physics Letters,2003 82:224.