愛因斯坦的廣義相對論中提及，物質加速時將產生重力波。LIGO(Laser Interferometer Gravitational-wave Observatory)架設超大型麥克森干涉儀以量測重力波，但其訊號相當微弱，偵測上極為困難，必須先將背景雜訊降低至重力波訊號之下，其中，Coating Brownian noise為首要需降低之雜訊，然而直接量測Coating Brownian noise極為困難，一般均透過量測機械損耗換算求得，故尋找低機械損耗的薄膜材料並降低其損耗為LIGO共同的目標。
　　本實驗使用CVD製程方式沉積非晶矽薄膜，對於製程方式的選取以及材料的選擇有以下幾點理由，製程方面:LIGO的觀測站中，使用直徑35cm的高反射鏡，因此希望尋找大面積且均勻的鍍膜方法，而在現今半導體產業界CVD製程已十分成熟並符合大面積且均勻的要求；材料方面:非晶矽薄膜的折射係數於1550nm波段約3.5，適合做為反射鏡中的高折射係數材料，另一方面，於文獻中可知ion‐beam sputter製程的非晶矽薄膜其機械損耗於低溫時約10-4量級，我們預期相同材料以CVD製程也可得相近的機械損耗。
筆者利用電漿輔助化學氣相沉積法(PECVD)沉積非晶矽薄膜於矽基板時，發現需先沉積二氧化矽(SiO2)作為緩衝層以避免薄膜破裂。二氧化矽與非晶矽薄膜分為光學以及機械損耗兩部分討論，二氧化矽之光學損耗於1550nm波段其光學損耗小於0.000(橢圓儀量測極限);二氧化矽薄膜機械損耗為(4.76±1.16)×10-4，與利用ion beam sputtered所鍍製之二氧化矽相近。利用PECVD沉積溫度於200oC、300oC、400oC之非晶矽薄膜光學損耗於1550nm波段小於0.000，相較LPCVD鍍製之非晶矽薄膜於同波段時為0.001來的小，於TEM下發現LPCVD所沉積之非晶矽薄膜有微結構的出現，這也是沉積溫度較高導致光學損耗較高的結果。非晶矽薄膜機械損耗部分:沉積非晶矽薄膜後損耗低於鍍膜前的異常現象，筆者認為是薄膜應力使基板彎曲，進而降低基板的thermo-elastic loss使原基板總損耗降低，使其出現反轉現象。

According to Einstein’s general theory of relativity, it will produce gravitational wave when a object was accelerated. In order to meaure gravitaitonal wave directly, LIGO set up large-scale Michelson interferometers to observe whether gravitational wave exist or not. But the signal of gravitational wave is so weak to be detected that it must to reduce the background noise below to the gravitational wave signal. One of them, Coating Brownian noise is the urgent problem that is needed to be reduced. However, it’s very difficult to measure coating Brownian noise directly. Fortunately, it shows that coating Brownian noise is propotional to mechanical loss from fluctuation-dissipation theorem. so our goal is to search and investigate the films which behave low mechanical loss and to reduce mechanical loss as possible as we can then use for LIGO application
In this article, CVD process is used for amorphous silicon deposition. There are some advantages that why we choose CVD and this material below. In the aspect of fabrication: CVD process is well-established in semiconductor technologies and it behaves perfect large area (18” wafer) uniformity, this advantage is suitable for LIGO mirrors which size are 35cm diameter. In the aspect of material: Refractive index of amorphous silicon is 3.5 at 1550nm, this high index value makes it desirable for quarter-wave lens coating. On the other hand, mechanical loss of amorphous silicon deposited by ion‐beam sputter is 10-4 order at low temperature in literatures. We expect that mechanical loss of the amorphous silicon films deposited by CVD will be similar low to films deposited by ion‐beam sputter.
In the article, optical loss and mechanical loss of the amorphous silicon films which deposit by different temperatures were measured and analyzed. When utilizing PECVD to deposit amorphous silicon film on silicon wafer directly, it existed some hilllocks on the surface. In order to prevent this phenomenon, a buffer silicon dioxide film was deposited between siliocn wafer and amorphous siliocn film. Finally the surface quality improved.
The stress of amorphous silicon is compressive stress as deposition temperature from 200 oc to 400 oc. Total mechanical loss after coated amorphous silicon is lower than uncoated substrate. This result is similar to the result of high stress SiNx film coated on siliocn cantilever. We think that silicon cantilever is bent by high stress from film and the bending mechanism reduced some part of the mechanical loss of silicon cantilever first(probably thermo-elastic loss). So even after coated the mechanical loss of coated is still lower than unbending siliocn cantilever substrate.

目錄
摘要 I
誌謝 I
圖目錄 V
表目錄 VIII
第一章 導論 1
1-1引言 1
1-2研究動機 3
第二章 非晶矽與二氧化矽薄膜製程 7
2-1基板製作流程 7
2-1.1單晶矽懸臂結構介紹 7
2-1.2矽懸臂基板製作流程 8
2-2電漿輔助化學氣相沉積(PECVD)系統及非晶矽薄膜介紹 10
2-3非晶矽與二氧化矽薄膜製程流程與參數設定 12
2-4 利用二氧化矽薄膜緩衝非晶矽薄膜造成之表面破裂現象 14
第三章 不同沉積溫度下之非晶矽薄膜材料特性 16
3-1量測儀器與原理介紹 16
3-1.1傅立葉轉換紅外線光譜儀(FTIR) 16
3-1.2橢圓偏光儀(Ellipsometer) 18
3-1.4應力量測系統(Stress Measurement System) 22
3-2 量測結果 24
3-2.1非晶矽薄膜之氫含量(CＨ%)比例分析 24
3-2.2非晶矽薄膜之折射係數(Refractive index)與
消光係數(Extinction coefficient) 分析 26
3-2.3非晶矽薄膜之楊氏係數量測分析 28
3-2.4非晶矽薄膜之應力量測分析 30
第四章 非晶矽薄膜之機械損耗特性分析 34
4-1 機械損耗量原理、系統與量測分析 34
4-2非晶矽與二氧化矽薄膜鍍膜前後量測分析 37
第五章 二氧化矽特性分析 44
5-1 二氧化矽薄膜之折射係數(Refractive index)與
消光係數 (Extinction coefficient) 44
5-2 二氧化矽薄膜之楊氏系數(Young’s modulus) 44
5-3二氧化矽薄膜之應力 46
5-4二氧化矽薄膜機械損耗分析 47
第六章 結論與未來展望 50
6-1結論 50
6-2未來展望 52
參考文獻 57

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