以水熱法製作非極性氧化鋅及其應用

Abstract

本論文主要研究為製作出非極性氧化鋅。為了克服氮化鎵具有的Quantum Confined Stark Effect (QCSE)，而選用非極性氧化鋅作為氮化鎵與基板的中間層。在論文中，我們採用一種簡便且無汙染的溶液製程-水熱法，去製作非極性氧化鋅。藉由掃描式電子顯微鏡觀察氧化鋅成長結構，並透過X光繞射儀來判斷氧化鋅是否具有良好的非極性取向。首先，我們利用曝光顯影的製程，製作出週期排列的矽蝕刻槽，並透過溶膠凝膠法和水熱法成長氧化鋅。 為了去除蝕刻槽外極性氧化鋅，我們採取金屬剝離法，金屬層採用金。先在蝕刻槽上鍍金，並旋塗氧化鋅種子層，再以水熱法成長氧化鋅，並浸泡於三碘化鉀溶液中，去除金層，並順帶移除槽外極性氧化鋅。然而，金與三碘化鉀溶液的接觸面積極少，使得金無法被完全移除，造成部分極性氧化鋅殘留。故針對金屬剝離法進行改良，原先是先鍍金，再旋轉塗佈種子層，而改良後的製程則改為先塗種子層再鍍金。此方式具有兩個優點:其一，槽外的氧化鋅成長在金層上，故會成長出倒柱，倒柱間的空隙能增加金與三碘化鉀溶液的接觸面積，提高除金效率；其二，槽內的側壁表面為氧化鋅種子層，而底部是金，氧化鋅會優先於種子層上成長，故只會成長出水平方向的氧化鋅。但改良的金屬剝離法仍具有一些缺點。其一，當水熱法的成長時間超過3小時，倒柱排列太過密集，而無法移除；其二，為了接合槽內水平方向的氧化鋅，採用二次除金的方式，但成長的氧化鋅具有尖塔的結構，須再以RIE沿著鉛直方向進行蝕刻，鉛直方向的蝕刻無法大面積生產，使得此技術應用性不大。最後，改以電感耦合式乾蝕刻法去製作整面的非極性氧化鋅。首先，藉由ICP-RIE去除槽外氧化鋅，並量測XRD頻譜，觀察到明顯的a-ZnO晶相，接著再以RIE蝕刻Si層，使得槽內的氧化鋅裸露出來，再以水熱法填滿為整面，最後以ICP-RIE蝕刻上層氧化鋅，得到整面的非極性氧化鋅。接著，於玻璃上以相同方式製作整面非極性氧化鋅。此方式能完全不以磊晶的方式，而以低成本及簡便的方式製作整面非極性氧化鋅，並製作成氧化鋅薄膜電晶體，其場效載子遷移率約為4.269 cm2/V-s。

The study of this thesis is to fabricate nonpolar zinc oxide (ZnO). To avoid quantum confined Stark effect (QCSE), we choose nonpolar ZnO as the intermediate layer between GaN and a substrate. In this thesis, we use a convenient solution process that is hydrothermal method to grow nonpolar ZnO. By using scanning electron microscopy (SEM) to observe the structure of ZnO. X-ray diffraction (XRD) is adopted to confirm whether ZnO has nonpolar orientation. We first fabricate a periodic array of Si etching grooves. Sol-gel and hydrothermal method are used to grow ZnO on Si etching grooves. After removing the gold layer and the polar ZnO in the same time, we present the ZnO with nonpolar face on the top. However, the contact area between the gold layer and three potassium iodine solution is little. Part of gold layer still remains on the sample. Therefore, an improved method is proposed. The original method is to deposit gold layer first. The improved method is to spin coat ZnO seed layer first. Then, to deposit the gold layer. It is two advanages. One, inverted column is grown outside the grooves. The more interspace higher the rate of removing gold. The other, seed layer is coated on the sidewall of the grooves, and the gold layer is deposited on the bottom. The only horizontal ZnO is growed. However, it is two shortcomings of the modified method. First, when the growth time of hydrothermal method is higher than 3 hours, the inverted column will not be lift off. Second, twice removing gold process is adopted to merge the ZnO in the grooves. Minaret structure of ZnO appear. Therefore, reactive ion etching (RIE) is used to remove minaret structure along the vertical direction. It is unable to achieve large area of production. Fianally, inductively-coupled plasma reactive ion etching (ICP-RIE) is used to remove ZnO outside the grooves. It appear apparent crystalline phase of a-ZnO from XRD measurement. RIE is used to etch Si. Hydrothermal method is adopted to fill the whole plane. After c-plane ZnO is removed by ICP-RIE, the whole plane nonpolar ZnO is completed. Also, the whole plane nonpolar ZnO is completed on glass substrate. Without the epitaxy process, the more convenient method is adopted to fabricate nonpolar ZnO of whole plane. Also, ZnO thin film transistor is finished. The field effect mobility is 4.269 cm2/V-s.