Fabrication of buried microfluidic channels with observation windows using femtosecond laser photoablation and parylene-C coating

• Published in: Microfluidics and nanofluidics Vol. 22; no. 9; pp. 1 - 7
• Main Authors: Gablech, Imrich, Somer, Jakub, Fohlerová, Zdenka, Svatoš, Vojtěch, Pekárek, Jan, Kurdík, Stanislav, Feng, Jianguo, Fecko, Peter, Podešva, Pavel, Hubálek, Jaromír, Neužil, Pavel
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.09.2018; Springer Nature B.V
• Subjects: Ambient temperature; Analytical Chemistry; Biomedical Engineering and Bioengineering; Buried structures; Channels; Electronic devices; Engineering; Engineering Fluid Dynamics; Etching; Fabrication; Fluorescein; Forming; Laser ablation; Lasers; Metal oxide semiconductors; Metals; Methods; MOS devices; Nanotechnology and Microengineering; Removal; Semiconductor devices; Semiconductors; Short Communication; Silicon; Silicon substrates; Silicon wafers; Temperature; Trenches; Vapors; Xenon; CMOS Camera; Deep Reactive Ion Etching (DRIE); Parylene Layer; Buried Channel; Segmented Flow
• ISSN: 1613-4982; 1613-4990
• DOI: 10.1007/s10404-018-2125-6

We developed an advanced method for fabricating microfluidic structures comprising channels and inputs/outputs buried within a silicon wafer based on single level lithography. We etched trenches into a silicon substrate, covered these trenches with parylene-C, and selectively opened their bottoms using femtosecond laser photoablation, forming channels and inputs/outputs by isotropic etching of silicon by xenon difluoride vapors. We subsequently sealed the channels with a second parylene-C layer. Unlike in previously published works, this entire process is conducted at ambient temperature to allow for integration with complementary metal oxide semiconductor devices for smart readout electronics. We also demonstrated a method of chip cryo-cleaving with parylene presence that allows for monitoring of the process development. We also created an observation window for in situ visualization inside the opaque silicon substrate by forming a hole in the parylene layer at the silicon backside and with local silicon removal by xenon difluoride vapor etching. We verified the microfluidic chip performance by forming a segmented flow of a fluorescein solution in an oil stream. This proposed technique provides opportunities for forming simple microfluidic systems with buried channels at ambient temperature.