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標題: 氮化鎵發光二極體製程簡化之研究
A Study of Chip Process Simplification for GaN Light-Emitting Diodes
作者: 彭繹峰
Peng, Yi-Feng
關鍵字: GaN;氮化鎵;Light-Emitting Diode;Chip Process Simplification;發光二極體;晶粒製程簡化
出版社: 精密工程學系所
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本論文主要是以氮化鎵晶粒製程簡化為主,把原本的四道光罩晶粒製程,減少為三道光罩製程,在四道光罩製程,P、N電極(鈦/金、鈦/鋁)是分別用不同的光罩,蒸鍍不同的金屬。改為三道光罩後,P、N電極(鉻/鉑/金)使用同一道光罩,並蒸鍍相同的金屬,但實驗後發現,鉻和氧銦錫的附著性並不好,經黏貼測試後,發現有電極剝落的情形,所以我們在透明導電層的光罩上,做了個圓孔的設計,這個圓孔的設計可以得到二個優點。首先由於鉻金屬可以蒸鍍在P型氮化鎵上,得到較好的附著性,第二項優點利用鉻和P型氮化鎵無法形成歐姆接觸的特性,迫使電流流向旁側的氧化銦錫,以提高電流擴散的效果增加亮度。電性方面,四道光罩和三道光罩的順向電壓,大約介於3.10~3.17 V,並無太大差異,逆向漏電流都為40 μA,但值得注意的是發光亮度部份,由原本的47 mcd提升到54 mcd,足足增加了有將近15%。二道光罩製程延伸了三道光製程的理念,只是因為透明導電層的圓孔圖形,是用電極的光罩去開的,所以蝕刻完二氧化矽膜及氧化銦錫膜後,必須再做二氧化矽膜的回蝕刻,讓二氧化矽再內縮進去,以增加氧化銦錫和電極的接觸面積,不會造成發光二極體的順向電壓提高,但因製程良率太低,所以還須要繼續研究改善。

The motivation of this thesis is to make a feasibility study of chip process simplification for GaN-based light-emitting diodes (LEDs). Currently, the most popular fabrication method for nitride LEDs is the four mask process, where the p-pad (Ti/Au) and n-pad (Ti/Al) use various masks and metal films. A three-mask chip process was first attempted in this work, where the 3rd mask was designed to evaporate the identical metal films (Cr/Pt/Au) for p- and n-pads. However, it was found that the Cr film showed inferior adhesion property on the ITO current spreading layer (TCL) after the peeling test. In order to overcome this problem, a contact aperture was opened in the mask of ITO layer. This makes Cr directly contact with the p-GaN epilayer and improve the adhesion between p-pad (Cr/Pt/Au) and ITO. Since Cr cannot make a good ohmic contact with p-GaN, the injection current will be forced to flow into the ITO film, resulting in an increase of light output due to the better current spreading. The luminous intensity of the GaN LED increases about 15% from 47 mcd (four masks) to 54 mcd (three masks). Furthermore, the GaN LEDs fabricated by four- and three-mask process shows the same leakage current of 40 μA with a forward voltage (at 20 mA) of 3.10 and 3.17 V, respectively. Finally, a two-mask process was attempted to extend the same concept of the chip process. Here the mask of the contact aperture was replaced by the mask of the LED pad. After etching the SiO2 and ITO in the aperture region, a lateral etch of SiO2 was made to increase the ITO contact area. Although the forward voltage of the GaN LED shows a normal value, the process yield is still low and requires further study.
其他識別: U0005-2807200600083100
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