藍寶石（Sapphire）為單晶的三氧化二鋁（Al2O3），具有高硬度、高化學穩定性、良好高溫穩定性及優異的光學特性等特點，使其廣泛應用於發光二極體（LED）與半導體基板、光電元件及精密封裝等領域。然而，由於藍寶石高硬度伴隨之高脆性，使得傳統接觸式加工於微鑽孔中面臨容易產生裂紋及工具磨耗等問題，為符合高效率與高精度之製程需求，非接觸式之飛秒雷射精密微鑽孔技術成為極具潛力之替代方案。 本研究以波長1030 nm、脈衝寬度450 fs之飛秒振鏡雷射系統，於試片下表面導入純水進行藍寶石晶圓背向鑽孔研究，目標在於透過將雷射焦點自試片上表面調整至下表面並搭配負離焦策略，將加工模式從由上往下燒蝕轉變為由下往上燒蝕，避免等離子屏蔽效應，從而抑制錐角孔形之生成，獲得孔壁較為垂直之孔洞；並透過液體輔助克服於空氣環境下鑽孔時殘屑排除及再鑄層堆積等問題，提升鑽孔深度與效率。在機制探討方面，本研究利用高速微距攝影技術，於由上往下鑽孔時捕捉到燒蝕羽流引發之等離子屏蔽效應及雷射光束於孔壁之折射與反射現象；並於液體輔助加工中，觀測記錄氣泡之生成潰滅動態及通孔瞬間所噴發之水柱，藉此瞭解加工過程中雷射光、材料與輔助液體三者之交互作用。對於厚度150 μm之藍寶石晶圓，可於0.566秒完成直徑50 μm，粗糙度0.668 μm之通孔。最後使用硫酸與磷酸混合溶液進行濕式蝕刻後處理，進一步去除加工過程因雷射熱影響於孔壁造成的改質區，透過TEM檢測結果證實，蝕刻後孔壁餘剩區域皆呈現排列整齊之藍寶石單晶結構。藉此，本研究成功實現了直徑50 μm，粗糙度0.449 μm，錐角小於1°，深寬比為3之圓形通孔。;Sapphire is the single-crystal form of aluminum oxide (Al₂O₃)， possesses high hardness， excellent chemical stability， good high-temperature stability， and superior optical properties， which have led to its widespread application in light-emitting diodes (LEDs)， semiconductor substrates， optoelectronic components， and precision packaging. However， the high brittleness accompanying the high hardness of sapphire causes conventional contact-based machining to suffer from crack formation and tool wear during micro-drilling. To meet the demands for high-efficiency and high-precision processing， non-contact femtosecond laser precision micro-drilling has emerged as a highly promising alternative. In this study， a femtosecond galvanometer laser system with a wavelength of 1030 nm and a pulse duration of 450 fs was employed to investigate the backside drilling of sapphire wafers， with pure water introduced onto the bottom surface of the specimen. By shifting the laser focal point from the top surface to the bottom surface of the specimen and applying a negative-defocus strategy， the machining mode was transformed from top-down ablation to bottom-up ablation， thereby avoiding the plasma shielding effect， suppressing the formation of tapered hole profiles， and obtaining holes with more vertical sidewalls. Furthermore， the liquid-assisted approach was adopted to overcome the problems of debris removal and recast layer accumulation encountered during drilling in air， thereby enhancing the drilling depth and efficiency. Regarding the mechanism investigation， high-speed micro-photography was utilized to capture， during top-down drilling， the plasma shielding effect induced by the ablation plume as well as the refraction and reflection of the laser beam at the hole wall; in the liquid-assisted process， the formation and collapse dynamics of bubbles and the water jet ejected at the instant of through-hole formation were observed and recorded， thereby elucidating the interactions among the laser beam， the material， and the assisting liquid during machining. For a sapphire wafer with a thickness of 150 μm， a through-hole with a diameter of 50 μm and a roughness of 0.668 μm could be completed within 0.566 seconds. Finally， a wet-etching post-treatment using a mixed solution of sulfuric acid and phosphoric acid was applied to further remove the modified region formed on the hole wall due to laser-induced thermal effects; TEM examination confirmed that the remaining region of the hole wall after etching exhibited a well-ordered single-crystal sapphire structure. Through this approach， this study successfully achieved a circular through-hole with a diameter of 51 μm， a roughness of 0.449 μm， a taper angle of less than 1°， and an aspect ratio of 2.94.
