以光輔助電化學技術剝離藍寶石基板供垂直型發光二極體製作

Abstract

在本論文中，我們展示了利用光輔助電化學蝕刻法來實現一個低成本，大面積且有效率剝離藍寶石基板的方法。首先，我們製作一維條紋狀溝槽結構的圖案化藍寶石基板，然後，在長晶的過程中，這些溝槽可以保留並且形成通道。光輔助電化學電解質溶液則可以順著通道流入並且蝕刻氮化鎵層的底部，進而將氮化鎵和藍寶石基板分離。配合元件隔離步驟，利用光輔助電化學來剝離四分之一晶圓大小的圖案化藍寶石基板只需要八分鐘。剝離後，將樣品研磨至n-型氮化鎵層，即可製作垂直式發光二極體，在本研究中，我們也比較了垂直式發光二極體和傳統側向式發光二極體的各項特性。 此外，我們藉由調整長晶參數，來消除原本在成長時所產生的縫隙並且進一步改善晶體品質。同時我們利用非破壞性的光學同調斷層掃描技術來檢測在氮化鎵層下方是否確實產生通道。接下來，我們利用氙氣燈做為光輔助電化學蝕刻的光源，配合元件隔離步驟，成功將一整片兩吋的藍寶石基板剝離。為了更進一步提升剝離基板的效率，我們成功地製作了二維結構的圖案化藍寶石基板，並且在其上成長氮化鎵層時保留底下的通道。我們利用一個紫外光發光二極體陣列作為光源，在沒使用元件隔離步驟之條件下，也成功剝離了一整片兩吋大小的二維圖案化藍寶石基板。

In this dissertation, a low-cost large-area effective sapphire substrate liftoff method based on the photoelectrochemical (PEC) etching technique is demonstrated. By preparing patterned sapphire substrate (PSS) with 1-D periodic grooves and an epitaxial structure with the grooves preserved to form tunnels, PEC electrolyte can flow along the tunnels to etch the bottom of the GaN layer for separating the PSS from the wafer-bonded epitaxial layer. Assisted by the device isolation procedure, the PSS liftoff of a quarter-wafer sample can be completed in 8 min. After a smoothing process of the exposed N-face surface after liftoff, a vertical light-emitting diode (LED) is fabricated for comparing its characteristics with those of a conventional LED. In addition, we further optimize the growth condition to eliminate the formation of the slits during the growth and also improve the crystal quality. Then, the technique of optical coherence tomography is introduced for noninvasive testing of the PSS grooves beneath of nitride epitaxial layer. Next, the PEC liftoff of a 2-inch full-wafer sample with the device isolation procedure is demonstrated based on the illumination of a xenon lamp. To increase the PEC liftoff speed, the fabrication of 2-D PSS and its successful nitride overgrowth are demonstrated. Finally, the full-wafer PEC liftoff of 2-D PSS without the device isolation procedure is implemented based on the illumination of a UV LED array.