Owing to recent interest in the production of flexible devices, it is necessary to develop a more convenient approach in which silicon (Si) thin film transistors (TFTs) are fabricated directly onto the flexible substrates at low substrate temperatures. Unfortunately, the physical limitations of conventional plasma-enhanced chemical vapor deposition (PECVD) under low pressures becomes a critical obstacle. In this study, Si film deposition using PECVD under atmospheric pressure excited by very high-frequency electrical power was investigated to overcome this issue. Tetramethylsilane [Si(CH₃)₄] is used as a source gas that is much safer than silane (SiH₄) gas. We investigated the effects of the reactive gas concentration and specific energy (the ratio of input power to unit volume of the reaction gas) on carbon incorporation into the resultant films. Based on the results, we discuss the possibility of forming Si films with sufficiently low carbon content, which is applicable to Si TFTs.

1. [1] H. E. Lee et al., “Micro light-emitting diodes for display and flexible biomedical applications,” Adv. Funct. Mater., Vol.29, Issue 24, 1808075, 2019. https://doi.org/10.1002/adfm.201808075
2. [2] T. Horii, T. Fujie, and K. Fukuda, “Flexible thin-film device for powering soft robots,” J. Robot. Mechatron., Vol.34, No.2, pp. 227-230, 2022. https://doi.org/10.20965/jrm.2022.p0227
3. [3] M. T. Shoani, M. N. Ribuan, and A. A. M. Faudzi, “Design, fabrication, and performance analysis of a vertically suspended soft manipulator,” Int. J. Automation Technol., Vol.15, No.5, pp. 696-705, 2021. https://doi.org/10.20965/ijat.2021.p0696
4. [4] C. Feng et al., “A flexible a-sic-based neural interface utilizing pyrolyzed-photoresist film (C) active sites,” Micromachines, Vol.12, No.7, 821, 2021. https://doi.org/10.3390/mi12070821
5. [5] H.-P. Phan et al., “Long-lived, transferred crystalline silicon carbide nanomembranes for implantable flexible electronics,” ACS Nano, Vol.13, No.10, pp. 11572-11581, 2019. https://doi.org/10.1021/acsnano.9b05168.
6. [6] T. Akagi, S. Dohta, H. Kuno, and A. Fukuhara, “Development of flexible sensors for measuring human motion and displacement of novel flexible pneumatic actuator,” Int. J. Automation Technol., Vol.5, No.5, pp. 621-628, 2011. https://doi.org/10.20965/ijat.2011.p0621
7. [7] I. C. Hwang et al., “Effective Photon Management of Non-Surface-Textured Flexible Thin Crystalline Silicon Solar Cells,” Cell Reports Physical Science, Vol.1, Issue 11, 100242, 2020. https://doi.org/10.1016/j.xcrp.2020.100242
8. [8] V. Babu et al., “Improved stability of inverted and flexible perovskite solar cells with carbon electrode,” ACS Appl. Energy Mater., Vol.3, Issue 6, pp. 5126-5134, 2020. https://doi.org/10.1021/acsaem.0c00702
9. [9] J. S. Cho et al., “Wide-bandgap nanocrystalline silicon-carbon alloys for photovoltaic applications,” Solar Energy Materials and Solar Cells, Vol.182, pp. 220-227, 2018. https://doi.org/10.1016/j.solmat.2018.03.035
10. [10] M. J. M. Hosseini and R. A. Nawrocki, “A review of the progress of thin-film transistors and their technologies for flexible electronics,” Micromachines, Vol.12, No.6, 655, pp. 1-19, 2021. https://doi.org/10.3390/mi12060655
11. [11] H. Kakiuchi, H. Ohmi, and K. Yasutake, “Pulsed very high-frequency plasma-enhanced chemical vapor deposition of silicon films for low-temperature (120°C) thin film transistors,” J. Phys. D: Appl. Phys., Vol.53, No.41, 415201, 2020. https://doi.org/10.1088/1361-6463/ab9919
12. [12] H. Kakiuchi, H. Ohmi, R. Inudzuka, K. Ouchi, and K. Yasutake, “Enhancement of film-forming reaction for microcrystalline Si growth in atmospheric-pressure plasma using porous carbon electrode,” J. of Applied Physics, Vol.104, Issue 5, 053522, 2008. https://doi.org/10.1063/1.2975978
13. [13] H. Kakiuchi et al., “Characterization of Si and SiOx films deposited in very high-frequency excited atmospheric-pressure plasma and their application to bottom-gate thin film transistors,” Phys. Status Solidi A, Vol.212, No.7, pp. 1571-1577, 2015. https://doi.org/10.1002/pssa.201532328
14. [14] H. Kakiuchi, H. Ohmi, and K. Yasutake, “Controllability of structural and electrical properties of silicon films grown in atmospheric-pressure very high-frequency plasma,” J. Phys. D: Appl. Phys., Vol.51, No.35, 355203, 2018. https://doi.org/10.1088/1361-6463/aad47c
15. [15] H. Kakiuchi, H. Ohmi, and K. Yasutake, “Atmospheric-pressure low-temperature plasma processes for thin film deposition,” J. Vac. Sci. Technol. A, Vol.32, Issue 3, 030801, 2014. https://doi.org/10.1116/1.4828369
16. [16] P. Vavia, R. d’Agostino, and F. Fracassi, “Plasma and surface diagnostics in PECVD from silicon containing organic monomers,” Pure & Appl. Chern., Vol.66, No.6, pp. 1373-1380, 1994. https://doi.org/10.1351/pac199466061373
17. [17] Yu. M. Rumyantsev et al., “Synthesis and properties of thin films formed by vapor deposition from tetramethylsilane in a radio-frequency inductively coupled plasma discharge,” Glass Physics and Chemistry, Vol.44, No.3, pp. 174-182, 2018. https://doi.org/10.1134/S1087659618030124
18. [18] C. C. Chiang et al., “Physical and barrier properties of plasma-enhanced chemical vapor deposited α-SiC:H films from trimethylsilane and tetramethylsilane,” Jpn. J. Appl. Phys., Vol.42, pp. 4273-4277, 2003. https://doi.org/10.1143/JJAP.42.4273
19. [19] T. Unold and J. D. Cohen, “Enhancement of light-induced degradation in hydrogenated amorphous silicon due to carbon impurities,” Appl. Phys. Lett., Vol.58, Issue 7, pp. 723-725, 1991. https://doi.org/10.1063/1.104527
20. [20] C. H. Wu, K. M. Chang, Y. M. Chen, Y. X. Zhang, and Y. H. Tan, “Study of in-situ hydrogen plasma treatment on InGaZnO with atmospheric pressure-plasma enhanced chemical vapor deposition,” J. Nanosci. Nanotechnol., Vol.19, No.4, pp. 2310-2313, 2019. https://doi.org/10.1166/jnn.2019.15997
21. [21] H. Kakiuchi, H. Ohmi, R. Nakamura, M. Aketa, and K. Yasutake, “Structural characterization of polycrystalline 3C–SiC films prepared at high rates by atmospheric pressure plasma chemical vapor deposition using monomethylsilane,” Japanese J. of Applied Physics, Vol.45, No.10S, pp. 8381-8387, 2006. https://doi.org/10.1143/JJAP.45.8381
22. [22] H. Kakiuchi et al., “Effect of hydrogen on the structure of high-rate deposited SiC on Si by atmospheric pressure plasma chemical vapor deposition using high-power-density condition,” Thin Solid Films, Vol.496, Issue 2, pp. 259-265, 2006. https://doi.org/10.1016/j.tsf.2005.08.338
23. [23] W. C. Steele, L. D. Nichols, and F. G. A. Stone, “The determination of silicon-carbon and silicon-hydrogen bond dissociation energies by electron impact,” J. Am. Chem. Soc., Vol.84, Issue 23, pp. 4441-4445, 1962. https://doi.org/10.1021/ja00882a014
24. [24] J. A. Dean, “Lange’s Handbook of Chemistry, 15th Edition,” McGraw-Hill, Inc., pp. 329-341, 1999.
25. [25] B. Ruscic, “Active thermochemical tables: sequential bond dissociation enthalpies of methane, ethane, and methanol and the related thermochemistry,” J. Phys. Chem. A, Vol.119, Issue 28, pp. 7075-7950, 2015. https://doi.org/10.1021/acs.jpca.5b01346
26. [26] A. U. Haq, P. Lucke, J. Benedikt, P. Maguire, and D. Mariotti, “Dissociation of tetramethylsilane for the growth of SiC nanocrystals by atmospheric pressure microplasma,” Plasma Process Polym., Vol.17, Issue 5, e19002435, 2021. https://doi.org/10.1002/ppap.201900243
27. [27] H. Kakiuchi, H. Ohmi, and K. Yasutake, “Gas-phase kinetics in atmospheric-pressure plasma-enhanced chemical vapor deposition of silicon films,” J. Appl. Phys., Vol.130, Issue 5, 053307, pp. 1-12, 2021. https://doi.org/10.1063/5.0057951
28. [28] S. Mukhopadhyay, S. C. Saha, and S. Ray, “Role of substrate temperature on the properties of microcrystalline silicon thin films,” Jpn. J. Appl. Phys., Vol.40, pp. 6284-6289, 2001. https://doi.org/10.1143/JJAP.40.6284
29. [29] G. Ambrosone et al., “Structural and optical properties of hydrogenated amorphous silicon-carbon alloys grown by plasmaenhanced chemical vapour deposition at various rf powers,” Philosophical Magazine B, Vol.82, No.1, pp. 35-46, 2002. https://doi.org/10.1080/13642810208211214
30. [30] J. L. C. Fonseca, D. C. Apperley, and J. P. S. Badyal, “Plasma polymerization of tetramethylsilane,” Chem. Mater., Vol.5, pp. 1676-1682, 1993. https://doi.org/10.1021/cm00035a015
31. [31] H. Ito et al., “Fabrication of amorphous silicon carbide films from decomposition of tetramethylsilane using ECR plasma of Ar,” J. of Physics: Conf. Series, Vol.441, 012039, 2013. https://doi.org/10.1088/1742-6596/441/1/012039
32. [32] A. Wada et al., “Local structural analysis of a-SiCx:H films formed by decomposition of tetramethylsilane in microwave discharge flow of Ar,” Diamond & Related Materials, Vol.20, Issue 3, pp. 364-367, 2011. https://doi.org/10.1016/j.diamond.2011.01.020
33. [33] E. Ermakova et al., “Controlling of chemical bonding structure, wettability, optical characteristics of SiCN:H (SiC:H) films produced by PECVD using tetramethylsilane and ammonia mixture,” Coatings, Vol.13, No.2, 310, 2023. https://doi.org/10.3390/coatings13020310