雷射干涉重力波天文台(Laser Interferometer Gravitational-Wave Observatory, LIGO)利用大型麥克森干涉儀偵測重力波訊號，由於重力波的訊號十分微弱，所以降低探測儀的雜訊提高靈敏度是目前主要的研究重點。其中主要雜訊來源之一為高反射鏡的薄膜熱擾動雜訊(Coating Brownian noise)，該不易量測，可藉由量測與其成正比之機械損耗來判斷。此外，做為高反射鏡的材料也要考量其光學特性，因此本實驗室致力於開發低機械損耗與低光學吸收之薄膜材料。
本研究首先分析以Standard PECVD製程鍍製之高氮的SiN0.87H0.93與低氮的SiN0.40H0.79薄膜於退火後的材料之光學特性，結果顯示材料的光學吸收分別與N-H鍵以及矽懸鍵呈現正相關。而後為了獲得更佳的光學吸收與機械損耗，利用NH3-free PECVD製程鍍製具有很少N-H鍵的氮化矽薄膜材料，且藉由調製SiH4、N2的流量與RF Power鍍製參數，找出光學吸收與機械損耗表現相對較佳的氮化矽薄膜。
在先前的研究中，本實驗室所開發之高反射鏡SiN0.40H0.79/SiO2堆疊膜的機械損耗已優於目前LIGO所使用之Ti:Ta2O5/SiO2堆疊膜。而本研究中最佳的氮化矽材料，SiN0.33H0.58，相較於SiN0.40H0.79薄膜擁有較低的光學吸收，並具有高達2.68的折射係數；低溫機械損耗落在5×〖10〗^(-5) ~ 8×〖10〗^(-5) (10K~120K) 且沒有loss peak，該損耗比SiN0.40H0.79¬薄膜下降了兩至三倍。因為SiN0.33H0.58有著更低的光學吸收、機械損耗以及高折射係數，故可以被期待做為下世代低溫重力波探測儀的高反射鏡材料。

Laser Interferometer Gravitational-Wave Observatory (LIGO) detects gravity wave signals by a large Michelson interferometer. Owing to the weak gravity wave signals, how to reduce the noise and to boost the sensitivity of the gravitational wave detector is critical. One of the main noises is the coating Brownian noise, which is directly related to the mechanical loss. In addition, the optical absorption of the coatings should be low. Therefore, the development of low mechanical loss and low optical absorption materials is the main task of this thesis.
In this thesis, the optical properties of SiN0.87H0.93 and SiN0.40H0.79 films deposited by the standard PECVD process before and after annealing were analyzed. We found that the cryogenic mechanical loss and the optical absorption were positively correlated with the concentration of N-H bonds and the silicon dangling bonds in the films. Therefore, we tried a NH3-free PECVD process with optimal parameters (SiH4, N2 flow and RF Power) and expecting that the N-H bond and hence the optical absorption and mechanical loss could be reduced.
The best NH3-free silicon nitride film in this study, SiN0.33H0.58, showed lower optical absorption, 1.21x10-5, than SiN0.40H0.79 films, 1.51x10-5, and a refractive index of up to 2.68. Furthermore, mechanical loss of the SiN0.33H0.58 in cryogenic temperature (10 K to 120 K) varied from 5 × 10-5 to 8 × 10-5, which was two to three times lower than that of the SiN0.40H0.79. There was no distinct cryogenic loss peak as well. It was reported previously that the SiN0.40H0.79/SiO2 high-reflector QW coatings has promising thermal noise characteristics and optical absorption. The result of this thesis showed that the SiN0.33H0.58 film would out-perform the SiN0.40H0.79 when incorporated into the QW stack with the SiO2 for the next-generation cryogenic gravitational wave detector.

[1] A. Einstein, Die grundlage der allgemeinen relativitätstheorie, Annalen der Physik, 49, 769 (1916)
[2] B. P. Abbott et al., Observation of Gravitational Waves from a Binary Black Hole Merger, PRL, 116, 061102 (2016)
[3] B. P. Abbott et al., GW151226: Observation of Gravitational Waves from a 22-Solar-Mass Binary Black Hole Coalescence, Phys. Rev. Lett. 116, 241103 (2016).
[4] B. P. Abbott et al., GW170104: Observation of a 50-Solar-Mass Binary Black Hole Coalescence at Redshift 0.2, Phys. Rev. Lett. 118, 221101 (2017).
[5] B. P. Abbott et al., GW170814: A Three-Detector Observation of Gravitational Waves from a Binary Black Hole Coalescence, Phys. Rev. Lett. 119, 141101 (2017).
[6] B. P. Abbott et al., GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral, Phys. Rev. Lett. 119, 161101 (2017).
[7] LIGO Scientific Collaboration, Instrument Science White Paper 2018, LIGO Document: LIGO-T1800133 (2018)
[8] H. B. Callen, T. A. Weltont. Irreversibility and generalized noise. Phys. Rev., Jul. 83,34-40 (1951)
[9] R. F. Greene, H. B. Callen. On the formalism of thermodynamic fluctuation theory. Phys. Rev., 83: 1231-1235 (1951)
[10] H. B. Callen, R. F. Greene, On a theorem of irreversible thermodynamics., Phys. Rev. 86,702-710 (1952)
[11] I. W. Martin et al., Effect of heat treatment on mechanical dissipation in Ta2O5 coatings, Class. Quantum Grav., 27, 225020 (2010)
[12] I. W. Martin et al., Low temperature mechanical dissipation of an ion-beam sputtered silica film, Class. Quantum Grav., 31, 035019 (2014)
[13] H.W. Pan et al., Silicon nitride films fabricated by a plasma-enhanced chemical vapor deposition method for coatings of the laser interferometer gravitational wave detector, Phys. Rev. D, 97, 022004 (2018)
[14] L.A. Chang, Annealing effect on the optical and mechanical properties of nitrogen-rich silicon nitride film fabricated by plasma enhance chemical vapor deposition, Master thesis, National Tsing Hua University (2018)
[15] T. Liu, Study of annealing effect on the optical properties and the room temperature mechanical loss of the silicon-rich silicon nitride films deposited with PECVD, Master thesis, National Tsing Hua University (2018)
[16] K. Wörhoff et al., Plasma enhanced chemical vapor deposition silicon oxynitride optimized for application in integrated optics, Sensors and Actuators 74 9–12, (1999)
[17] H. Albers et al, Reduction of hydrogen induced losses in PECVD-SiO¬xNy optical waveguides in the near infrared, IEEE-LEOS 2, 88-89 (1995)
[18] E. A. Douglas et al., Effect of precursors on propagation loss for plasma-enhanced chemical vapor deposition of SiNx:H waveguides, Optical Materials Express, (2016)
[19] R. Birney et al., Amorphous Silicon with Extremely Low Absorption: Beating Thermal Noise in Gravitational Astronomy, Phys. Rev. Lett. 121, 191101 (2018)
[20] Warren B. Jackson et al., Direct measurement of gap-state absorption in hydrogenated amorphous silicon by photothermal deflection spectroscopy, Phys. Rev. B, (1980)
[21] H.C. Chen, Annealing effect on the room temperature mechanical loss of the silicon nitride films deposited with PECVD on silicon cantilever, Master thesis, National Tsing Hua University (2017)
[22] F. Mandl et al., Statistical Physics (2nd Edition), John Wiley & Sons, (2008)
[23] H.D. Young, R.A. Freedman, University Physics – With Modern Physics (12th Edition), Addison-Wesley (2008)
[24]G.R. Eaton et al., Quantitative EPR, Springer (2010)
[25]J. Möser et al., Using rapid-scan EPR to improve the detection limit of quantitative EPR by more than one order of magnitude, Journal of Magnetic Resonance 281 (2017)
[26] G.E. Jellison et al., Spectroscopic ellipsometry characterization of thin-film silicon nitride, Thin Solid Films, 313-314, 193-197 (1998)
[27] G.E. Jellison, Jr et al., Parameterization of the optical functions of amorphous materials in the interband region, Appl. Phys. Lett., 69, 371 (1996)
[28] J.W. Lee et al., Bond density and physicochemical properties of a hydrogenated silicon nitride film, J. Phys. Chrm. Solids Vol. 56. No. 2, pp. 293-299., (1995)
[29] Christoph Boehmea et al., Dissociation reactions of hydrogen in remote plasma-enhanced chemical-vapor-deposition silicon nitride, J. Vac. Sci. Technol. A 19, (2001)
[30] Z. Lu et al., Fourier transform infrared study of rapid thermal annealing of aSi:N:H(D) films prepared by remote plasma enhanced chemical vapor deposition, Journal of Vacuum Science & Technology A 13, 607 (1995)
[31] A. zelenina, silicon nanocrystals in various dielectric matrices: structural and optical properties, (2015)
[32] L. Cai, A. Rohatgi, D. Yang, and M. A. El-Sayed, Effects of rapid thermal anneal on refractive index and hydrogen content of plasma enhanced chemical vapor deposited silicon nitride films, American Institute of Physics, (1996)
[33] N. Kang, Photothermal common-path interferometry system setup and study of the optical absorption of the silicon nitride film deposited by PECVD method, Master thesis, National Tsing Hua University (2017)
[34] https://www.corning.com/
[35]E.A. Douglas et al., Effect of precursors on propagation loss for PECVD of SiNx H waveguides, Optical Material Express,Vol. 6, No 9 (2016)
[36]T.D. Bucio et al., Material and optical properties of low-temperature, Applied Physics, 50 025106 (2017)
[37]R. Bousbilh et al., Silicon lifetime enhancement by SiNx H anti-reflective coating deposed by PECVD(SiH4 N2), Solar Energy, 86 1300-1305 (2012)
[38] S. M. Sze, VLSI technology: McGraw-Hill New York, (1988)
[39] D. L. Smith et al., Mechanism of SiNxHy deposition from N2-SiH4 plasma, Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, vol. 8, pp. 551 (1990)
[40] C. Iliescu, F. E. H. Tay, and J. Wei, Low stress PECVD-SiNx layers at high deposition rates using high power and high frequency for MEMS applications, Journal of Micromechanics and Microengineering, vol. 16, pp. 869 (2006)
[41] K. B. Sundaram, R. E. Sah, H. Baumann, K. Balachandran, and R. M. Todi, Wet etching studies of silicon nitride thin films deposited by electron cyclotron resonance (ECR) plasma enhanced chemical vapor deposition, Microelectronic Engineering, vol. 70, pp. 109 (2003)
[42]P. W. Bohn and R. C. Manz, a multiresponse factorial study of reactor parameters in plasma-enhanced CVD growth of amorphous-silicon nitride, Journal of the Electrochemical Society, vol. 132, pp. 1981 (1985)
[43] D. L. Smith, Thin-film deposition: principles and practice: McGraw-Hill Professional, (1995)
[44] E. A. Taft, Characterization of Silicon Nitride Films. J. Electrochem. Soc., 118, 1341-1346 (1971)
[45] S. Hasegawa et al., Connection between Si-N and Si-H Vibrational Properties in Amorphous SiNx: H Films. Philos. Mag. B, 59, 365−375 (1989)
[46] M. H. Srodsky et al., Infrared and Raman spectra of the silicon-hydrogen bonds in amorphous silicon prepared by glow discharge and sputtering, Phys. Rev. B, 16, 8 (1977)
[47] H. Shanks et al., Infrared Spectrum and Structure of Hydrogenated Amorphous Silicon, Phys. Status Solidi, 100, 43 (1980)
[48] C. J. Fang et al., The hydrogen content of a-Ge:H and a-Si:H as determined by ir spectroscopy, gas evolution and nuclear reaction techniques, Journal of Non-Crystalline Solids, 35-36, 255-260 (1980)
[49] A. Morimoto et al., Properties of Hydrogenated Amorphous Si-N Prepared by Various Methods, Jpn. J. Appl. Phys., 24, 1394, (1985)
[50] M. Sato et al., Low-temperature-deposited insulating films of silicon nitride by reactive sputtering and plasma enhanced CVD Comparison of characteristics, Jpn. J. Appl. Phys., 55, 04EC05 (2016)
[51] W.C. Oliver, G.M. Pharr, An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments, J. Mater. Res., 7, 6 (1992)
[52] X. Li, B. Bhushan, A review of nanoindentation continuous stiffness measurement technique and its applications, Materials Characterization, 48, 1 (2002)
[53] C. Lee, Study of the material properties and the mechanical loss of the silicon nitride film deposited by PECVD method on silicon cantilever for laser interference gravitational wave detector application, Master thesis, National Tsing Hua University (2013)
[54] W. Y. Wang., Study of mechanical vibration and loss of silicon cantilever for development of the high-reflection mirror in the laser interference gravitational wave detector. Master thesis, National Tsing Hua University (2013)
[55] S. T. Thornton, J. B. Marion. Classical dynamics of particles and systems. Brooks Cole, 5: 109-121 (2003)
[56] T. Makino and M. Maeda, Bonds and Defects in Plasma-Deposited Silicon Nitride Using SiH4-NH3-Ar Mixture, Jpn. J. Appl. Phys. 25, 1300 (1986).
[57]T. Makino, Journal of the Electrochemistry Society 130 450-5 (1983)
[58] H. Shanks, et al. Infrared Spectrum and Structure of Hydrogenated Amorphous Silicon.Phys. Stauts Solidi B 100, 43 (1980)
[59] J. Oul, Setup of room temperature mechanical loss measurement and preliminary measurement results on fused silica and silicon cantilevers, Master thesis, National Tsing Hua University (2012)
[60] M. Wu, Room Temperature Mechanical Loss of SiN0.40/SiO2 Quarter-wave Stacks Deposited by Plasma Enhanced Chemical Vapor Deposition Method, Master thesis, National Tsing Hua University (2017)
[61] C. Cheng, Cryogenic mechanical loss measurement system setup and annealing effect on the mechanical loss of the nano-layer coatings, Master thesis, National Tsing Hua University (2015)
[62] H.W. Pan et al., Silicon nitride films fabricated by a plasma-enhanced chemical vapor deposition method for coatings of the laser interferometer gravitational wave detector, Phys. Rev. D.97.022004 (2018)
[63] L. C. Kuo, H.W. Pan, H. Wu, H. Y. Ho, and S. Chao, LIGO Report No. LIGO-G1700301 (2017)
[64] H.W. Pan et al., Silicon nitride and silica quarter-wave stacks for low-thermal-noise mirror coatings, Phys. Rev. D, 98 102001 (2018)
[65] Alex Amato et al., Defects on Coatings and Correlations, LVC meeting (2019)
[66] J. Steinlechner et al., Silicon for Test Masses - Optical Absorption of Coatings and Substrates, Institute for Gravitational Research, University of Glasgow (2015)
[67] X. Jiang et al., a-SiNx H-based ultra-low power resistive random access memory with tunable Si dangling bond conduction paths, scientific reports, 5 15762 (2015)