無光罩藍寶石基材蝕刻及其在發光二極體之運用研究

Study of Mask-free Wet Etching on Sapphire Substrate and Its Application on Light Emitting Diodes

陳怡如(Yi-ju Chen)

指導教授 ： 劉正毓

國立中央大學/工學院/化學工程與材料工程學系/博士(2011年)

摘要

本論文研究不同酸蝕液(純磷酸、純硫酸和混酸H3PO4/H2SO4)在藍寶石基材上的蝕刻反應，其中混酸在310 ℃下可得到最快得蝕刻速度(1.5 μ/min) ，相較下，純硫酸的蝕刻速度則相當緩慢。 有趣的是，雖然硫酸蝕刻藍寶石基材的速度相當緩慢，但卻可以在其上形成，和藍寶石基材晶格結構相異的四面金字塔的圖案化藍寶石基材，不需要任何微影製程。 在本文裡，我們探討金字塔在藍寶石基材上形成的機制，及不同蝕刻時間、溫度下對金字塔角度變化的影響。並建立隨蝕刻時間變化其金字塔形成的模型。 我們將其應用在氮化鎵藍光發光二極體的薄膜成長，並利用XRD及PL證實氮化銦鎵薄膜沉積在此金字塔圖案化藍寶石基材相較於磊在平的藍寶石基材有更佳的薄膜品質，且在LED晶片的光強上有37 %的增益。 並利用垂直式LED結構搭配模擬結果推測37 %的增益裡有5.7 %是來自於薄膜品質的改善(即IQE增益)。 其餘的增益則為來自於圖案化的結構，破壞了全反射效應使光可以被散射而逃脫出來。 接著我們利用不同蝕刻溫度及蝕刻時間，得到不同圖案及不同覆蓋率的圖案化藍寶石基材，並探討不同圖案及覆蓋率間對薄膜品質及光取出效益的影響(LEE)。 從結果中顯示當圖案覆蓋率達39%時，缺陷密度相較於氮化鎵成長在平的藍寶石基材減少了一半。 但是隨覆蓋率再增加，缺陷密度並沒因為側向成長區域增加而有更多的減少。 而在光的表現上，光的外部取出效率(LEE)也並非成正比的增加。 當覆蓋率大於於39 %時，光取出效率隨著覆蓋率增加的效用趨緩，直到圖案的覆蓋率高於67 %時，光取出效率才有再明顯的增加。

關鍵字

溼式蝕刻 ； 垂直式發光二極體 ； 圖案化藍寶石基材 ； 發光二極體

並列摘要

Chemical wet-etching on c-plane sapphire wafers by three etching solutions (H3PO4, H2SO4 and H3PO4/H2SO4 mixing solution) were studied. Among these etching agents, the mixing H3PO4/H2SO4 solution has the fastest etching rate (1.5 µm/min.). Interestingly, we found that H2SO4 does not etch the c-plane sapphire wafer in thickness, instead, a facet pyramidal pattern formed on the c-plane sapphire wafer which was formed by the etched products. GaN LED expitaxial structure was grown on the sapphire wafer with the pyramidal pattern and the standard flat sapphire wafer. XRD and PL measurement show that the pyramidal pattern on the sapphire wafer improved crystalline quality but augmented the compressive stress level in the GaN LED epi-layer. The horizontal LED chips fabricated on the pyramidal-patterned sapphire wafer has a larger light out-put than that of the LED chips fabricated on the standard flat sapphire wafer by 35 %. Beside, the IQE was evidenced to get improvement about 5.7% when pattern coverage increasing from 13.6 % to 53.8% when n-pss wafer was applied into thin-GaN LED structure. .
Also, various pyramidal pattern coverage is processed on patterned sapphire substrates by mask-free wet-etching process. Internal quantum efficiency and light extraction efficiency of GaN epitaxial layers grown on patterned sapphire substrates with different pattern coverage were studied. Internal quantum efficiency can be enhanced in the initial increase of pattern coverage. As pattern coverage over 39%, the effectiveness of the pattern on enhancing internal quantum efficiency is drenched. The light extraction efficiency increases with pattern coverage less than 39 % and over 67%. As the pattern coverage in between 39% ~ 67%, the light extraction efficiency is very similar.

並列關鍵字

Thin-GaN LED ； pattern sapphire substrate ； light emitting diodes

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