以液相沉積法製作奈米圖形化藍寶石基板成長氮化鎵磊晶層之研究

Abstract

目前圖形化藍寶石基板(PSS)的製作多以標準黃光製程在基板製 作出光罩後，再蝕刻出所需的圖案。然而這種製作方式會受到黃光製 程波長的限制而較難將圖形縮小至微米以下的等級，故本研究提出利 用成本低廉、製程簡單之化學液相沉積法(LPD)製作出奈米圖形化藍 寶石基板，並探討其對於GaN 磊晶品質的影響。 在奈米圖形化藍寶石基板(NPSS)的研究中，本實驗成功地以化學 液相沉積的方法配合濕式蝕刻製作出不同尺寸及種類之NPSS 基板。 相較於傳統平面拋光之c-plane sapphire，XRD 及EPD 等數據顯示在 NPSS 上成長之GaN 磊晶層具有較好的結晶品質。若比較不同蝕刻時 間製作出的奈米圖形基板之磊晶品質則以 NPSS-60 較佳，其原因來 自於NPSS-60 可在降低c-plane 面積的情況下同時提供適當的圖形間 距。保留 NPSS-60 上 c-plane 的 LPD-SiO2 所製作出之 modified NPSS-60 可以更進一步地提昇GaN 磊晶層品質，且根據XRD 及SEM 等數據，顯示圖形上方之SiO2 對於GaN 磊晶成核成長不具有明顯負 面影響。 在奈米圖形化矽氧化層(NPOS)的研究中是以LPD-SiO2 為異質圖 形直接進行磊晶，在此 NPOS 基板上成長之 GaN 磊晶層較在 planar sapphire 上成長者具有更加優良的磊晶品質，此部分的提升可由XRD 及EPD 的數據得到驗證。藉由TEM 分析可觀察到差排彎曲的現象， 顯示此提升應來自於側向磊晶成長面積上升所致。

Fabrication of pattern sapphire substrate(PSS) through a standard photolithography process, which includes mask forming and etching steps, is the major approach to manufacture conventional PSS. However, the resolution limit of photolithography makes nano-sized PSS(NPSS) hard to realize. In this study, chemical liquid-phase deposition(LPD) method is applied to NPSS fabrication and the effect on crystal quality of GaN epitaxial layer brought by NPSS has been discussed. By LPD and wet etching process, NPSS has been successfully fabricated. Compared to GaN grown on planar c-sapphire, the GaN epilayer grown on NPSS has better crystal quality, which is confirmed by the XRD and EPD data. Between NPSS-60 and NPSS-90, the former shows better crystal quality because of its lower c-plane ratio and proper distance between patterns. Modified NPSS, which is fabricated by keeping top LPD-SiO2 on NPSS, can bring further improvement of crystal quality, and the XRD and SEM data shows that the oxide on pattern has no obvious destruction of crystal quality. In ch4, GaN epitaxy directly proceeds on sapphire substrate with LPD-SiO2 pattern. GaN grown on such substrate has better crystal quality. Dislocation bending is observed through TEM analysis, which means the improvement of crystal quality is mainly from increase of lateral growth region.