| dc.description.abstract | 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. | en_US |