| 摘要: | 自19世紀末期居禮兄弟發現單晶石英之壓電特性以來，由於其出色之物理特性和化學穩定性，使之被廣為應用於頻率震盪元件。藉由單晶種子晶體於高壓釜中進行長晶得以長出高純度及可用體積極高之合成晶體石英(Synthetic Quartz)，並採用具備優異的頻率/溫度特性之AT-CUT晶體切割角度以作為中樞核心之頻率震盪基板。隨著高頻化與高速運算的時代來臨，裝置進一步導向精密微型化趨勢，石英基板微型鑽孔製程成為微米等級佈線之前置作業。然而，單晶石英之硬脆特性，使得傳統接觸式機械加工於微型鑽孔逐漸遇到瓶頸。為符合商業需求，取而代之的是更高效率及高精準性之非接觸式微型加工技術，即超快雷射精密微型鑽孔技術。
本研究以波長515 nm之飛秒振鏡雷射系統，並輔以純水進行石英晶圓背向微鑽孔之特性研究，旨在提升在空氣中雷射微鑽孔的時效、減少孔內表面雷射削除(Ablation)沉積物與雷射加工過程的熱影響區。藉由高速微距攝影技術，本研究同時也觀察雷射石英晶體微鑽孔過程中，等離子體(Plasma)的成形與消散、空化氣泡(Cavitation)及液中水射流(Water jets)等微觀現象，進一步揭示液中超快雷射單晶石英鑽孔過程，光、材料與輔助液體間交互作用現象(Interactions)，藉以說明鑽孔機理並探討輔助液體的功能。實驗結果顯示，相較於空氣中鑽孔，液體輔助，可有效減少雷射削除物的再沉積、縮小熱影響區，同時加快鑽孔速率。對於厚度65 μm石英晶圓，可於0.106秒即完成70 μm直徑通孔。鑽孔後，透過氫氧化鉀(35 wt.% KOH)蝕刻後處理，可達到修整微孔形貌及周圍晶相結構之目的，最終可實現錐度小於1°、粗糙度Ra為0.353 μm之高品質圓孔。透過TEM進行蝕刻前後之微孔熱影響範圍檢測，並得出蝕刻前之孔壁熱影響區範圍呈現次微米等級(≈ 200 nm)，經蝕刻後處理過後則進一步降為45 nm，幾乎僅剩單晶結構存於微孔中。
;Since the discovery of the piezoelectric properties of single-crystal quartz by the Curie brothers in the late 19th century, its excellent physical properties and chemical stability have led to widespread application in frequency oscillation components. High-purity and large-volume synthetic quartz crystals are grown using single-crystal seed crystals in auto-claves, and AT-CUT crystal cutting angles with superior frequency/temperature characteristics are employed to serve as the core frequency oscillation substrate. With the advent of the era of high-frequency and high-speed computing, devices are further trending towards precision miniaturization, making the micro-drilling process of quartz substrates a prerequisite for mi-cron-level wiring. However, the hard and brittle nature of single-crystal quartz poses challeng-es for traditional contact-based mechanical machining in micro-drilling. To meet commercial demands, non-contact micro-machining technology with higher efficiency and precision, spe-cifically ultrafast laser precision micro-drilling technology, has become the alternative.
This study investigates the characteristics of backside micro-drilling of quartz wafers us-ing a femtosecond galvanometer laser system with a wavelength of 515 nm, supplemented by pure water. The aim is to improve the efficiency of laser micro-drilling in air, reduce ablation deposits on the inner surface of the holes, and minimize the heat-affected zone (HAZ) during the laser machining process. Utilizing high-speed micro-photography technology, this study also observes the formation and dissipation of plasma, cavitation bubbles, and water jets dur-ing the laser micro-drilling process of quartz crystals. This further elucidates the interactions between light, material, and the assistant liquid during the ultrafast laser drilling process in water, explaining the drilling mechanism and the function of the auxiliary liquid.
Experimental results indicate that, compared to drilling in air, liquid assistance effective-ly reduces the re-deposition of ablation materials and minimizes the heat-affected zone while accelerating the drilling rate. For a 65 μm thick quartz wafer, a through-hole with a diameter of 70 μm can be completed in 0.106 seconds. After drilling, post-treatment with 35 wt.% KOH etching refines the micro-hole morphology and surrounding crystal structure, ultimately achieving a high-quality round hole with a taper less than 1° and a roughness Ra of 0.353 μm. TEM analysis of the HAZ before and after etching shows that the HAZ on the hole wall is submicron (≈ 200 nm) before etching and further reduced to 45 nm after post-etching treat-ment, leaving almost only the single-crystal structure within the micro-hole. |
