超快雷射雙脈衝與透明材料交互作用之研究-應用於激發探測、精微加工與線上監測

Abstract

近幾年隨著消費性電子產品、5G通訊、醫療器械與電動車產業的突飛猛進，透明材料已逐漸應用在這些領域的產品中，而超快雷射因有超短的脈衝寬度，提供材料冷加工機制，明顯降低加工區域周圍的熱影響區，儼然成為加工透明材料的主流工具之一。 超快雷射製程在透明材料精微加工中，大多伴隨著雷射剝除(Laser ablation)過程。若要加速製程開發速度，優化加工結果，就需了解剝除的加工機制，進而透過光學或製程手法改善剝除加工特性。本論文以超快雷射雙脈衝為光路架構，搭配三種不同光路，研究熔融石英被超快雷射照射產生的暫態破壞機制，改善熔融石英的剝除加工特性，與進行氧化銦錫玻璃的雷射退火線上監測。 本研究首先利用激發-探測原理，搭配800 nm, 170 fs, 1 kHz的激發脈衝與超快連續白光的探測脈衝去探索超快雷射與熔融石英之間的暫態破壞機制。結果發現於460 nm、560 nm、630 nm 三個波長有不同反射強度的光譜訊號。這些訊號與熔融石英被超快雷射激發後，產生的三種缺陷有關，包含Oxygen-deficient center、Peroxy radicals、Nonbridging oxygen hole center (NBOHC)。 接下來使用1064 nm, 10 ps, 100 kHz的雙脈衝進行熔融石英的雷射剝除製程研究。透過改變雙脈衝之間的延遲時間與功率比，來改變雷射對材料的剝除閾值。分析結果得知，當延遲時間為100 ps且功率比為5:5時，可以得到最低的剝除閾值-只有傳統單脈衝剝除閾值的一半。主要是因第一子脈衝照射材料產生的自縛激子種子或缺陷，增加了材料對第二子脈衝吸收率，而使剝除閾值下降。 最後使用800 nm, 100 fs, 80 MHz的激發脈衝搭配800 nm或400 nm的探測脈衝進行氧化銦錫玻璃雷射退火線上監測。研究使用激發脈衝進行雷射退火；在固定的延遲時間下，用單光儀+PD線上量測氧化銦錫玻璃退火處的探測脈衝穿透率。當退火未完成時，探測脈衝的穿透率隨著激發脈衝功率增加成等差級數增加，一旦激發脈衝功率可以對氧化銦錫玻璃產生退火改質，穿透率就會突然性的增加，用此突發訊號作為材料已發生退火改質的判斷。經此線上監測系統確認有改質的玻璃，再使用EBSD量測儀確認氧化銦錫玻璃已發生退火再結晶。

In recent years, transparent materials have been increasingly used in consumer electronics, 5G communications, and medical devices due to their optical clarity, electrical insulation, and mechanical strength. Ultrashort lasers are suitable tools for processing transparent materials from the characteristics of their high peak power and minimum thermal effects. In micro-machining of transparent materials, the ultrashort laser process is mostly accompanied by the mechanism of material ablation. In order to optimize the process results, it is necessary to look into the process of the ablation mechanism, and then improves the laser ablation processing characteristics through optical and/or process methods. In this study, a dual pulse-based optical setup was devised to investigate the interaction between the mechanism of ultrafast laser and fused silica aiming to improve the properties of the ablation processing, and perform in-situ monitoring of ITO glass laser annealing. This study firstly used a pump-probe spectroscopy of a white light beam probe with an 800 fs, 170 fs, 1 kHz femtosecond laser to study the ablation dynamics in fused silica. From the measurements, three characteristic signal bands were found at 460 nm, 560 nm, and 630 nm which are presumemablely related to the defects of fused silica after femtosecond laser irradiation, including the oxygen-deficient center, the peroxy radicals, and the nonbridging oxygen hole center (NBOHC). For the second major part of study, the ablation thresholds of 1064 nm, 10 ps, 100 kHz laser dual pulses in fused silica with different temporal separations and power ratios were investigated. An important result revealed that the lowest damage threshold of the dual-pulse ablation was at a temporal separation of 100 ps and a power ratio of 5:5, and this value was only half of the threshold of the conventional pulse ablation. The underlying physical mechanisms were discussed, and it was found that the first sub-pulses initially excited the electrons of the fused silica and subsequently induced self-trapped exciton seeds or defects generation at 100 ps temporal separations which increased the material absorption of the second sub-pulses and then varied the ablation threshold of the fused silica. A set of pump-probe systems for the in-situ monitoring of femtosecond laser annealing of ITO substrates was established as an extention of applicantion. A pump beam was used as the light source for thermal annealing, and a probe beam was used to in-situ monitor the transmittance variation of ITO. It was found that the pump beam energy was small, the transmittance changed arithmetically, and when the pump beam energy was sufficient to complete the modification of ITO, the transmittance variation rose suddenly and sharply, indicating that the thermal annealing modification had been completed in the irradiated area. An independent verification by the electron backscatter diffraction analysis indicated that the crystallographic directions of ITO after laser annealing were consistent.