雷射干涉重力波偵測天文台(LIGO)利用大型麥克森干涉儀偵測重力波，由於重力波訊號相當微弱又容易受到各種雜訊干擾，所以必須降低環境雜訊以提高重力波探測系統的靈敏度。反射鏡薄膜材料的熱擾動雜訊為影響系統的雜訊來源之一，根據fluctuation-dissipation theorem得知此雜訊與材料之機械損耗成正比。此外做為光學應用之高反射鏡薄膜也必須擁有良好的光學性質，因此研發低機械損耗且光學特性良好之薄膜材料為本實驗室的主要研究方向。
首先本實驗室已經利用PECVD鍍製出具備高折射率以及低溫機械損耗較低且平坦之氮化矽薄膜SiN0.33H0.58；低折射率方面已經鍍製出改善SiO2低溫機械損耗有峰值缺點之氮氧化矽薄膜SiO0.85N0.27H0.45，不過該材料有著較高的矽懸鍵。本研究以三種方式嘗試減少氮氧化矽薄膜之矽懸鍵，使氮氧化矽薄膜之光學吸收能夠進一步降低。
本研究三種方式分別為:1.固定N2O/SiH4流量比，調整氣體通量、2.補氫退火、3.純氮退火。第一種方式在氣體通量增加時，讓腔體內原子碰撞機率增加，使懸鍵不易產生，不過在減少矽懸鍵的同時，折射率也同時上升，能隙也同時下降，因此光學吸收降低效果不佳，與SiN0.33H0.58¬做高反射鏡堆疊會讓總厚度增加，使機械損耗上升。第二種補氫退火，能夠將氫擴散至薄膜內部與懸鍵相互結合，使懸鍵減少，光學吸收也因此降低，在長時間退火下，能夠持續減少矽懸鍵，且折射率不會有太大的變化，在補氫退火6小時後，1064nm之光學吸收從2×10-6降至8×10-7，降了60%；1550nm之光學吸收從8.5×10-6降至4.9×10-6，降低43%，1950nm之光學吸收則從9.5×10-6降至7.9×10-6，降低17%。第三種純氮退火使懸鍵與懸鍵相互結合，使矽懸鍵減少，該方式在長時間退火下無法持續降低矽懸鍵，因此改善光學吸收之效果並不如補氫退火。所以如果要降低薄膜中的矽懸鍵，補氫退火是一個不錯的方式，而且並不會對薄膜造成其他負面影響。

Laser Interferometer Gravitational-Wave Observatory (LIGO) uses the large Michelson interferometer to observe the gravitational wave directly. Due to the signal of the gravitational wave is quite weak and is impacted by various noise easily, it is important that increasing the sensitivity of the detector by reducing the environmental noise. The coating Brownian noise which is contributed from the materials coated on the high-refractive mirror is one of the noise types influencing the measuring systems. According to the fluctuation-dissipation theorem, the coating Brownian noise is proportional to the mechanical loss of the materials. Additionally, the coating materials of the high-refractive mirror must have excellent optical characteristics. Therefore, we have been dedicated to developing thin-film materials with low mechanical loss and outstanding optical properties.
Our group developed NH3-free silicon nitride thin film, SiN0.33H0.58, which had a high refractive index and low cryogenic loss without loss peak；we also developed silicon oxynitride thin film, SiO0.85N0.27H0.45, which had lower refractive index and cryogenic loss was lower than SiO2, but dangling bond was not low enough. So, this research tried three way to reduce dangling bond of silicon oxynitride.
First way, fixed N2O/SiH4 flow rate, and adjust gas flow. With increasing the gas(N2O、SiH4) flow, the dangling bond would reduce, but refractive index was increase. Energy gap was lower. Therefore, optical absorption had no better reduction. Second way, H2 annealing. This way was the best in the three ways. With H2 annealing, H2 can diffuse in the thin film, and combine with dangling bond. Under long-term H2 annealing, dangling bond will been decreased continuously, so the optical absorption had a better reduction. Optical absorption in 1064nm reduce from 2×10-6 to 8×10-7；Optical absorption in 1550nm reduce from 8.5×10-6 to 4.9×10-6, Optical absorption in 1950nm reduce from 9.5×10-6 to 7.9×10-6. Third way was N2 annealing. This way did not better than H2 annealing. Because this way made dangling bond to combine with each other. Under long-term N2 annealing, dangling can’t be continuously reduced, so decreasing optical absorption by N2 annealing was not better than H2 annealing.

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