自十九世紀末居禮兄弟發現單晶石英之壓電特性以來，石英因其優異之物理特性與化學穩定性，長期被廣泛應用於頻率振盪元件。藉由單晶種子於高壓釜中長晶，可獲得高純度且可用體積大之合成石英（Synthetic Quartz），並採用具備優異頻率/溫度特性之 AT-CUT 切割角度作為頻率振盪基板之核心。隨著高頻化與高速運算時代之來臨，元件持續朝精密微型化發展，石英基板之微型鑽孔製程已成為微米等級佈線之關鍵前置作業。然而，單晶石英之硬脆特性使傳統接觸式機械加工於微孔製程逐漸遭遇崩裂與精度之瓶頸，因而需以更高效率及高精度之非接觸式超快雷射精密微鑽孔技術取而代之。 本研究以波長1030 nm之Satsuma X-50飛秒雷射系統，採用MHz 叢發模式（Burst Mode）搭配固定焦點之由下而上（Bottom-up）單點鑽孔策略，於純空氣環境中進行 AT-cut 單晶石英晶圓（厚度80 μm）之微孔加工特性研究。本研究藉由高速微距攝影技術，完整觀測微孔逆向燒蝕之動態過程，揭示燒蝕前緣自底面起始、沿光軸逆向推進、貫穿與壓力釋放，以至孔壁修整與順向排屑之完整時序演化，並與傳統 Top-down 配置進行對比，闡明 Bottom-up 配置在避免電漿屏蔽與維持排屑路徑暢通上之機制優勢。實驗進一步指出，在子脈衝能量密度（1.08 J/cm²）低於單晶石英單脈衝燒蝕閾值之條件下，MHz叢發模式之子脈衝間熱累積效應為驅動逆向燒蝕之關鍵機制。 實驗結果顯示，於原始參數（平均功率 46.8 W、叢發脈衝數 180、加工時間 1 ms）下，可於單晶石英中形成準直度優異之微孔，其錐角僅約 0.16°。該微孔之深寬比可達約 8，且加工時間僅需 300 μs 即可完成貫穿，展現本製程於加工效率與孔型品質上之優勢。經氫氧化鉀（35 wt.% KOH）蝕刻後處理後，孔壁之重鑄層與熔融碎屑獲得選擇性移除，微孔錐角進一步降至0.08°，孔壁最大高度粗糙度Rz由3.313 μm降至1.986 μm。透過聚焦離子束（FIB）製備試片並以穿透式電子顯微鏡（TEM）搭配選區電子繞射（SAED）進行檢測，確認蝕刻前孔壁前緣之雷射熱影響區為厚度約700 nm 至1 μm 之非晶態改質層，且晶格損傷並未大範圍擴散至基材深處，經 KOH 蝕刻後處理後則大幅縮減至約 150 nm，使孔壁更接近原始單晶結構。此外，本研究進一步將相同製程應用於厚度 100 μm 之單晶石英，成功以陣列形式完成微孔加工，且深寬比可提升至約10，驗證了該製程於不同晶圓厚度下之適用性。本研究證實，於純空氣環境下，MHz 叢發模式之 Bottom-up 鑽孔搭配適當之蝕刻後處理，即可獲得高品質之單晶石英微孔。;Since the Curie brothers discovered the piezoelectric properties of single-crystal quartz in the late nineteenth century， quartz has been widely used in frequency-control devices owing to its excellent physical properties and chemical stability. High-purity synthetic quartz of large usable volume can be grown from single-crystal seeds in an autoclave， and the AT-cut orientation， which offers superior frequency–temperature characteristics， serves as the core substrate for frequency oscillation. With the advent of higher operating frequencies and high-speed computing， devices continue to advance toward precision miniaturization， making the micro-drilling of quartz substrates a key preliminary step for micron-scale interconnection. However， the hard and brittle nature of single-crystal quartz causes conventional contact-based mechanical machining to encounter limitations of edge chipping and precision in micro-hole fabrication， prompting a shift toward non-contact ultrafast-laser precision micro-drilling， which offers higher efficiency and accuracy. In this study， AT-cut single-crystal quartz wafers (80 μm thick) were micro-drilled in an ambient-air environment using a Satsuma X-50 femtosecond laser system at a wavelength of 1030 nm， employing an MHz burst mode combined with a fixed-focus， bottom-up single-point percussion drilling strategy. Using high-speed macro photography， the complete dynamic process of reverse ablation was observed， revealing the full temporal evolution of the ablation front—from initiation at the bottom surface， upward propagation along the optical axis， breakthrough and pressure release， to wall refinement and forward debris ejection. A comparison with the conventional top-down configuration clarifies the mechanistic advantages of the bottom-up scheme in avoiding plasma shielding and maintaining an unobstructed debris-ejection path. The results further reveal that， under a sub-pulse fluence (1.08 J/cm²) below the single-pulse ablation threshold of single-crystal quartz， the inter-pulse heat-accumulation effect of the MHz burst mode is the key mechanism driving reverse ablation. Experimental results show that， under the baseline parameters (average power 46.8 W， 180 pulses per burst， processing time 1 ms)， micro-holes with excellent straightness were formed in single-crystal quartz， with a taper angle of only approximately 0.16°. The micro-holes reached an aspect ratio of about 8， and through-hole formation was achieved in as little as 300 μs， demonstrating the advantages of this process in both machining efficiency and hole quality. After post-processing by potassium hydroxide (35 wt.% KOH) wet etching， the recast layer and resolidified debris on the hole wall were selectively removed， the taper angle was further reduced to 0.08°， and the maximum-height roughness Rz of the hole wall decreased from 3.313 μm to 1.986 μm. Through focused ion beam (FIB) sample preparation followed by transmission electron microscopy (TEM) with selected-area electron diffraction (SAED)， the laser heat-affected zone at the hole-wall front before etching was confirmed to be an amorphous modified layer approximately 700 nm to 1 μm in thickness， with lattice damage not extending extensively into the bulk substrate; after KOH post-processing， this layer was substantially reduced to about 150 nm， bringing the hole wall closer to its original single-crystal structure. Furthermore， the same process was applied to 100 μm-thick single-crystal quartz， successfully producing micro-hole arrays with an aspect ratio of up to about 10， validating the applicability of the process across different wafer thicknesses. This study demonstrates that， in an ambient-air environment， bottom-up drilling in MHz burst mode combined with appropriate post-processing can produce high-quality single-crystal quartz micro-holes.
