次微米尺度圖案藍寶石基板製備與光學特性研究

Fabrication of Nano-Scale Patterned Sapphire Substrate and the Optical Properties

陳志源(Chih-Yuan Chen) ； 洪偉中(Wei-Chung Hung) ； 柯文政(Wen-Cheng Ke)

《臺灣鑛業》 67卷1期 (2015/03) Pp. 55-61

摘要

本實驗使用陽極氧化處理技術，在藍寶石基板上製備次微米尺度圖案，並成功在次微米尺度圖案藍寶石基板上成長高材料品質之氮化鎵薄膜。關鍵製程步驟簡述如下：（1）以電子束蒸鍍系統在藍寶石基板上蒸鍍厚度為600 nm（Al）／100 nm（Ti）之鈦鋁膜，（2）在15℃、0.3M草酸溶液中施加80V電壓進行陽極氧化處理，形成孔洞直徑約100 nm之陽極氧化鋁圖案，（3）以感應電漿耦合活性離子蝕刻（ICP-RIE）在適當蝕刻條件下，將陽極氧化鋁圖案轉移至藍寶石基板上，（4）清洗藍寶石基板，完成磊晶等級（Epi-ready）之次微米尺度圖案藍寶石基板，（5）以有機金屬氣相沉積系統（MOCVD）在次微米尺度圖案藍寶石基板上成長高材料品質氮化鎵薄膜。本研究中利用草酸電解溶液製備之陽極氧化鋁遮罩，其遮罩孔洞平均直徑約100奈米。並藉由感應耦合電漿活性離子蝕刻（ICP-RIE）時間控制次微米圖案藍寶石基板的圖案深度，實驗資料顯示蝕刻時間在600秒時圖案深度可達200奈米。此外，由原子力顯微影像圖觀察成長於次微米圖案藍寶石基板之3 μm氮化鎵薄膜，表面為階層狀（step-flow）形貌且表面粗糙度Rrms約為0.7nm。進一步利用X光繞射儀分析（002）與（102）面譜圖，經由半高寬計算得知，貫穿型差排密度可降低至1.1×10^8cm^(-2)。霍爾量測結果顯示，載子遷移率可從101cm^2/Vs提升至243cm^2/Vs。由掃描式電子影像側視圖觀察發現GaN薄膜與次微米圖案基板介面存在孔洞，顯示在GaN薄膜成長初期階段具側向成長機制，故可以有效提升GaN薄膜材料品質。

關鍵字

次微米圖案藍寶石基板 ； 陽極氧化鋁 ； 氮化鎵薄膜

並列摘要

This study presents the structure and optoelectronic properties of GaN thin films grown on the nano-patterned sapphire substrate (NPSS). The anodic aluminum oxide (AAO) template was used as an etching mask for preparing NPSS. The key processes including: (1)deposit 600-nm-thick Al films/100-nm-thick Ti films on the bare sapphire substrate by e-beam evaporation system, (2) anodic treated in oxalic or phosphoric acid solution to form the different average diameter of AAO template, (3) transfer AAO template pattern to bare sapphire substrate by ICP-RIE dry etching technique, (4) remove the residual AAO template by acid solution then finish the fabrication of NPSS, and (5) deposit a 3-μm-thick GaN thin films on NPSS by metal organic chemical vapor deposition system. The average diameter of sub-micro patterned sapphire substrate about ~100 nm and ~200 nm respectively for the samples used oxalic and phosphoric acid treated AAO etching mask. The pattern depth of NPSS is controlled by the ICP-RIE etching time. The SEM cross-section view indicated the pattern depth of NPSS is about ~200 nm. The surface of GaN/oxalic treated NPSS shows the step-flow morphology with roughness R_(rms) of ~0.7 nm which confirmed by AFM measurement. The edge dislocation density estimated by the full width at half maximum value of (002)(102) X-ray diffraction spectra decreased from 1.1×10^8 cm^(-2) for GaN/bare sapphire substrate to 2.4×10^8 cm^(-2) for GaN/oxalic treated NPSS. The Hall measurement shows the carrier mobility can be increased from 101 cm^2/Vs to 243 cm^2/Vs for GaN/oxalic treated NPSS. The empty patterned hole between the oxalic treated NPSS and GaN thin films indicated that the lateral growth mechanism dominate the early growth stage. The low density dislocation density of GaN thin films can be achieved by using a high aspect ratio of NPSS.

並列關鍵字

nano-patterned sapphire substrate ； anodic aluminium oxide ； GaN thin films