| 摘要: | 藍寶石（Sapphire）是單晶的三氧化二鋁（Al2O3），擁有優異的物理性質和高化學穩定性，包括高硬度、高耐磨性、優越的熱傳導性、高溫度穩定性、高透光性，以及抗強酸鹼耐腐蝕等特點。在長晶應用上，它與氮化鎵（GaN）之間的晶格常數匹配度高，並具有出色的高溫穩定性，因此成為LED長晶的重要基板。此外，藍寶石的高硬度、耐磨性和優越的熱傳導性，也使其它成為一個理想的氮化矽（Silicon nitride，Si3N4）替代材料，可用於製作高密度探針卡（Probe card）。
然而，藍寶石的高硬脆特性，也使它的微精密加工(Micromachining)充滿挑戰性，特別是傳統的機械式加工在製作應用於探針卡、邊長數十微米的方形通孔時，已達極限。目前超快雷射的非線性吸收特性與極小的加工熱影響區(Heat affected zone, HAZ)，被視為是一種極有潛力應用於藍寶石微尺寸加工的工具。本研究旨在開發超快雷射加工技術在藍寶石基板上製作低錐度、低圓角的方形通孔。在實驗中選用厚度為110微米的藍寶石基板，使用波長為515 nm、脈衝週期為300 fs的飛秒雷射進行加工。在研究中，首先嘗試了三種不同環境下的加工方式，包括在空氣中加工、將試片直接浸入水中加工以及將基板下表面浸入水中加工，比較、探討此三種加工方式的優劣。配合基板下表面浸入水中加工方式，本研究提出兩階段式加工策略: 以基板下方作為起點，首先由下而上進行加工；然後，再切換為由上而下的方式進行加工，藉此獲得無裂紋、錐度良好的方形通孔。最後，使用硫酸和磷酸的混合溶液，進一步去除凝固的再鑄層以及堆積殘渣，從而成功實現了邊長為52 µm、錐角為0⁰，深寬比為2.12的方形通孔。
;Sapphire is a single crystal aluminum oxide (Al2O3), exhibiting exceptional physical properties and high chemical stability, including high hardness, wear resistance, excellent thermal conductivity, temperature stability, high transparency, and corrosion resistance against strong acids and alkalis. In crystal growth applications, its high lattice constant matching with gallium nitride (GaN) and outstanding high temperature stability make it a crucial substrate for LED crystal growth. Additionally, the high hardness, wear resistance, and excellent thermal conductivity of sapphire position it as a promising alternative to silicon nitride (Si3N4) for high-density probe card substrates.
However, the high hardness and brittleness of sapphire pose challenges in micro-precision machining, especially when traditional mechanical machining reaches its limits in creating square micro-holes with side lengths in the tens of micrometers for applications like probe cards. Currently, the nonlinear absorption characteristics of ultrafast lasers and their minimal heat-affected zones (HAZ) are considered highly promising for micro-scale sapphire processing. This study aims to develop ultrafast laser machining techniques for creating low-taper, low-rounded square micro-holes on sapphire substrates. In the experiments, a 110-micrometer thick sapphire substrate was taken, and machining was performed using a femtosecond laser with a wavelength of 515 nm and a pulse duration of 300 fs. Three different machining environments were explored, including air, direct immersion in water, and immersion of the substrate′s bottom surface in water, with a comparative analysis of their advantages and disadvantages. The study proposes a two-stage machining strategy, starting from the bottom of the substrate with an upward process and then switching to a downward process, to obtain square micro-holes with no cracks and well-defined taper angles. Finally, a mixed solution of sulfuric acid and phosphoric acid was used to further remove solidified recast layers and accumulated residues, successfully achieving square micro-holes with side lengths of 52 µm, a taper angle of 0⁰, and an aspect ratio of 2.12. |
