Fabrication and analysis of MEMS resonator

本論文所製作之薄膜體聲波振器由Al/ZnO/Al/Si3N4等不同之薄膜組成，沉積在矽基板(100)上，先利用低壓化學氣相沉積法在矽晶圓兩邊沉積低應力之氮化矽薄膜，一面用來當作薄膜體聲波共振器之支撐層，另一面用來當作氫氧化鉀蝕刻之防護罩，在壓電能作用區下方製作出腔體(cavity)，再利用射頻磁控濺鍍法濺鍍壓電層氧化鋅，上下電極使用熱蒸鍍法沉積製作，最後再使用反應式離子蝕刻將腔體內之殘餘矽基板去除，讓共振器下方形成晶界與空氣之介面。 利用X光繞射儀(X-Ray Diffraction, XRD)、掃描式電子顯微鏡(Scanning Electron Microscopy, SEM)，針對壓電層氧化鋅作檢測，可發現此薄膜具有C軸(002)之擇優取向，及良好之圓柱狀結構。 最後完成的薄膜體聲波共振器元件之壓電能做作用面積為200×200 μm2，由壓電層氧化鋅、支撐層氮化矽和上下電極鋁所構成，厚度分別為1.54μm、0.2μm、0.1μm、0.1μm。經模擬計算結果，共振頻率為1.86GHz；量測結果為1.27GHz。而實驗結果與討論可提供實驗室一個有價值的參考在未來發展薄膜體聲波共振器之相關研究上。In this thesis, the Film Bulk Acoustic Resonator (FBAR) has been fabricated by stacking various layers of Al/ZnO/Al/Si3N4 on a silicon substrate (100). The low-stress silicon nitride films were deposited on both side of the substrate by Low-pressure chemical vapor deposition (LPCVD). The upper Si3N4 layer served as a support membrane for the FBAR cantilever, while the bottom layer acted as an etching mask and selectively etched in a KOH (potassium hydroxide) wet etching process to create a cavity under the piezoelectric-active area. The piezoelectric zinc oxide (ZnO) thin film was deposited by reactive RF magnetron sputtering. The bottom and top electrodes are deposited by using thermal evaporation. The underside of the residual silicon was then removed using reactive ion etching (RIE) etching process to create a cavity under the piezoelectric-active area to form a crystal/air interface beneath the resonator. The ZnO film was investigated using x-ray diffractometer (XRD) and scanning electron microscopy (SEM) techniques. The ZnO film showed strongly preferred orientation towards the c-axis, well-textured columnar structure. The FBAR device piezoelectric-active area was 200×200 μm2 which consisted the ZnO film, low-stress Si3N4 membrane, top and bottom Al electrodes with thicknesses of 1.54μm, 0.2μm, 0.1μm, and 0.1μm, respectively. Simulated resonant frequency is 1.86GHz, and measured one is 1.27GHz. The experimental results provided a valuable reference for the future development of FBAR.中文摘要.............................................i 英文摘要.............................................ii 目錄.................................................iv 圖目錄...............................................vii 表目錄...............................................x 第一章 導論.........................................1 1.1文獻回顧..........................................1 1.2研究動機與目的....................................4 1.3論文架構..........................................5 第二章 原理.........................................6 2.1 聲波運動方程式...................................6 2.2 壓電效應及方程式.................................8 2.2.1正逆壓電效應................................9 2.2.2壓電方程式..................................9 2.3 薄膜體聲波共振器原理.............................11 2.3.1體聲波技術之關鍵參數........................12 2.4 等效電路原理.....................................14 2.4.1 Mason等效電路..............................14 2.4.2傳輸矩陣法..................................17 2.5 電漿理論.........................................21 2.6 薄膜成長原理.....................................23 2.6.1 薄膜表面及截面結構.........................24 2.6.2 氧化鋅薄膜結構與特性.......................24 2.6.3 低壓化學氣相沉積(LPCVD).......... .........25 2.6.4 電漿輔助化學氣相沉積(PECVD)................25 2.6.5 射頻磁控濺鍍系統...........................25 2.7 蝕刻原理.........................................26 2.7.1 氫氧化鉀(KOH)濕蝕刻........................27 2.7.2 反應式離子蝕刻(RIE)........................27 2.8 量測方法.........................................27 2.8.1 掃描式電子顯微鏡分(SEM)....................28 2.8.2 X光繞射分析(XRD)..........................28 第三章 元件製程步驟與光罩設計.......................29 3.1 製程步驟.........................................29 3.2 元件光罩設計.....................................31 第四章 實驗結果與討論...............................32 4.1 黃光製程參數測試.................................32 4.1.1 光阻塗佈參數測試...........................32 4.1.2 曝光顯影參數測試...........................33 4.2 共振器腔體蝕刻...................................34 4.2.1 氫氧化鉀腔體濕蝕刻濕蝕刻...................35 4.2.2 反應式離子蝕刻殘餘矽基板...................36 4.3 薄膜沉積.........................................36 4.3.1 下電極鋁薄膜蒸鍍...........................37 4.3.2 壓電層氧化鋅薄膜濺鍍.......................37 4.3.3 上電極鋁薄膜蒸鍍...........................39 4.4 共振器結構特徵分析...............................40 4.4.1 表面輪廓儀析厚度量測.......................40 4.4.2 壓電層截面、上視圖與矽基板腔體圖...........40 4.4.3 壓電層結晶取向檢測.........................41 4.5 共振器電性量測與模擬分析.........................41 第五章 結論.........................................43 參考文獻.............................................8