由於磊晶條件之限制，目前氮化鎵發光二極體(GaN light emitting diode, GaN LED)使用藍寶石(sapphire)做為基板材料，然藍寶石其導熱性極差，嚴重影響發光二極體之發光效率。為了改善此問題，將藍寶石移除並使用其他導熱性較佳之材料做為基板，為較常見之解決方法。藍寶石基板移除方法中，雷射剝離(laser lift-off)方法為最方便且最有效率之方法。雷射高溫使氮化鎵產生熱分解(thermal decomposition)進而使藍寶石與氮化鎵分離。
發光二極體晶圓由材料磊晶或沉積而成，若各材料間生長溫度差異過大，回到室溫之後，會因材料間熱膨脹係數(coefficient of thermal expansion, CTE)不匹配而導致晶圓產生翹曲現象，將造成後段製程的困難。另外，雷射剝離時因藍寶石與氮化鎵間之應力受到釋放，不同的剝離方法將產生不同的力學行為，進而影響晶圓翹曲量。本論文利用有限元素法(finite element method, FEM)套裝軟體ANSYS®進行雷射熱傳以及晶圓翹曲之分析。
首先將建立兩吋晶圓之熱傳模型以模擬雷射剝離後之溫度場。藉由等效之熱通量載荷模擬雷射，並以雷射剝離實驗量測之溫度場結果，與有限元素之數值結果相對照，證明雷射等效熱通量之正確性。
本研究進一步為了解晶圓翹曲的力學特性，研究雷射剝離過程及材料厚度，對氮化鎵發光二極體晶圓翹曲之影響。利用製程模擬使模型具有製程後因熱膨脹係數不匹配所造成之應力，並分別以二維及三維模型，分析不同剝離方法對翹曲量之影響。以ANSYS®內溫度-熱應力耦合系統將熱傳模型之溫度結果帶入結構分析進行計算，結果顯示雷射所造成之內部高溫對剝離後翹曲值影響甚小。利用晶圓翹曲為二次多項式曲線之關係，兩吋晶圓之翹曲可由較小半徑模型之翹曲求得，以節省計算時間。由三維模型可觀察不同剝離路徑對翹曲量之影響，使用螺旋線剝離路徑約可使翹曲量下降7.7%。最後，根據本論文的研究，希望找出減少發光二極體晶圓翹曲之最佳製程方法，作為後續研究之依據。

GaN light emitting diodes (LED) are often grown on sapphire substrates due to the restriction of epitaxy condition. The low thermal conductivity of sapphire causes the efficiency of LED to seriously degrade. In order to solve this problem, sapphire substrates must be removed and other substrate materials with better thermal conductivity must be utilized. Among the sapphire lift-off methods, the laser lift-off is the most convenient and efficient method. The high temperature caused by the laser decomposes GaN at the GaN/sapphire interface, thus allowing the sapphire substrate to be removed.
The LED wafers are comprised of different materials created by decomposition and epitaxy. If the differences of growth temperature between materials are large, then a coefficient of thermal expansion (CTE) mismatch between materials will lead wafer warpage after it returns to room temperature. Otherwise, the laser tacjectory may influence stress distribution between the free and still attached parts of the wafer and therefore has an effect on mechanics behavior and wafer warpage. In this thesis, the finite element method (FEM) software, ANSYS®, is employeed to analyze the laser thermal conductivity and wafer warpage behavior.
First, for the thermal analysis, a 2” wafer model is established to simulate the temrperature field after the laser lift-off process. The laser is applied through an equivalent heat flux, and the results are then compared with experiment data to prove the feasibility of equivalent heat flux.
To understand the mechanics of wafer warpage, research is performed on the effect of the lift-off procedure and material thickness on wafer warpage. The initial stress of wafer from the manufacturing process is calculated using process modeling. The effect of the lift-off procedure on warpage is simulated using 2-D and 3-D models, respectively. Using the structure-thermal couple system of ANSYS®, the former results of the thermal analysis are substituted into the structure analysis and the rising temperature by the laser, which showed less effect on wafer warpage. The wafer warpage curve is 2nd order polynomial, therefore the warpage results of a 2” wafer can be calculated from smaller models to reduce calculation time. Different warpages from various lift-off procedures can be observed using the 3-D structure model. Moreover, a lift-off with a spiral trajectory can reduce the warpage by 7.7%. Finally, from this research, the best lift-off procedure can be indentified, and this study is expected to become a reference for future research.

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