結合光輔助濕式蝕刻和誘發耦合電漿蝕刻之後的氮化鎵蕭基特性之研究

Abstract

此論文探討在經過光輔助濕式蝕刻(PEC)結合誘發耦合電漿蝕刻(ICP)後的AlGaN 和GaN的蕭基特性。所使用的氮化鎵晶體是以低壓有機金屬化學氣相磊晶法成長在Al2O3基板上。光輔助濕式蝕刻使用KOH蝕刻液並予以100mW/cm2 的汞燈照光，ICP的反應氣體則是Cl2和N2。蕭基金屬使用Ni/Au (100nm/100nm) 而歐姆金屬則使用Al (100nm)。 一般而言，氮化鎵在ICP中的蝕刻率為300nm/min、粗糙度為1.7nmm。而在濕式蝕刻中，蝕刻速率為0.64nm/min、粗糙度為0.32nm。乾式蝕刻的蝕刻率快很多，但相對的也會比較粗糙。 在600W ICP 蝕刻300秒後，氮化鎵蕭基的理想因子(n)為1.57，能障高為0.65eV，崩潰電壓為0.75V。然而在ICP 蝕刻後再加上光輔助濕式蝕刻30分鐘，可以得到蕭基理想因子降為1.11，能障高升高到0.78eV，且崩潰電壓升高為3.8V。此電性的改善可解釋為濕式蝕刻移除了ICP蝕刻造成的損壞結構。 整體而言，結合乾室與濕式蝕刻可以兼顧高蝕刻速率又可以得到較小損壞的表面。

GaN and AlGaN Schottky contact characteristics after hybrid photo-enhanced wet etch and Inductively coupled plasma etch (ICP) is studied. KOH solution and 100mW/cm2 UV illumination by Hg arc lamp was used for photo-enhanced wet etch. Gas mixture of Cl2 and N2 was used for ICP etch. The Schottky metal used in this study is Ni/Au (100nm/100nm) and the Ohmic metal used is Al (100nm). Typical etch rates are 0.64 nm/min and 300nm/min with a roughness of 0.32nm and 1.70nm for wet and dry etch respectively. The ICP process etches more rapidly but the etched surfaces are rougher when compared to the wet-etch process. After ICP etch at 600 watt for 300sec, the GaN schottky diode for example has an ideality factor n=1.57 and the barrier height □B=0.65 eV ,and breakdown voltage VB=0.75V. However, for the ICP etched sample followed by photo-enhanced wet chemical etch for 30mins, the sample has an ideality factor n=1.11, and the barrier height □B=0.78 eV, and the breakdown voltage VB is recovered to 3.8V. The study indicates that the wet chemical etch can remove the damage caused by ICP etch. Overall, the hybrid dry/wet etch process is a high etch rate process and cause very low damages on the etched surface.