Characterization of masking layers for deep wet etching of glass in an improved HF/HCl solution

This paper describes the main protocols that are used for fabricating microfluidic devices from glass and silicon. Methods for micropatterning glass and silicon are surveyed, and their limitations are discussed. Bonding methods that can be used for joining these materials are summarized and key process parameters are indicated. The paper also outlines techniques for forming electrical connections between microfluidic devices and external circuits. A framework is proposed for the synthesis of a complete glass/silicon device fabrication flow. I. WHY USE SILICON AND GLASS IN MICRO-AND NANO-FLUIDIC APPLICATIONS?Micro-and nano-fluidic technology continues to be embraced by biologists, 1-3 chemists, 4 and engineers throughout academia and industry. As its applications have expanded, there has been an explosion in the range of materials and processes used to fabricate these devices. The earliest microfluidic devices (e.g., gas 5 and liquid 6 chromatography devices) were made from silicon and glass and borrowed processes directly from semiconductor and microelectromechanical systems (MEMS) manufacturing. 7 Now, however, many researchers have moved away from silicon and glass, and instead use cast elastomers such as polydimethylsiloxane (PDMS)-which is ideal for swift prototyping-or thermoplastic polymers, which can be hot-embossed or injection-molded and are well suited to inexpensive manufacturing. Yet, there remain many applications where glass and silicon offer advantages over polymeric materials. In this paper, we highlight these advantages and offer a framework for selecting fabrication processes when using silicon and glass. A. The dominance of soft lithographyOver the last decade, PDMS has become virtually the default material for forming microfluidic devices, 8 because of the sheer ease with which it can be cast on to a micro-scale mould and then strongly bonded to glass. 9 The elastomeric nature of the material has been exploited to integrate fluidic valves and pumps on-chip and has simplified the production of multi-layer devices because the soft layers readily conform to each other. 10,11 Yet, the low stiffness (usually <1 MPa) of PDMS relative to amorphous thermoplastics, silicon, and glass has its own a) Authors to whom correspondence should be addressed. Electronic addresses: ciliescu@ibn.a-star.edu.sg and hkt@ntu.edu.sg. 6, 016505 (2012) drawbacks. High aspect-ratio channels are notoriously difficult to fabricate in PDMS because of their propensity to collapse. 12 Moreover, difficulties in automating the handling of such a soft material have hampered efforts to scale up PDMS device manufacturing. Meanwhile, PDMS's high oxygen and water permeabilities have proved both a blessing and a curse in different applications.The hydrophobic nature of PDMS can be an important consideration for some biological applications. In drug screening applications, for example, hydrophobic drugs as well as metabolites (urea or albumin) can be absorbed into the device's material due to hydrophobic--hydrophobic interaction...

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“…To remove any insoluble products, HCl (Ref. 46) or H 3 PO 4 (Ref. 47) can be added to the etching solution.…”

Section: Wet Etchingmentioning

confidence: 99%

A practical guide for the fabrication of microfluidic devices using glass and silicon

Iliescu¹,

Taylor²,

Avram³

et al. 2012

Biomicrofluidics

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310

207

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“…To achieve a better Al stripping during wet etching after the RIE, it is advised to do an oxidization step using O 2 plasma, which creates Al 2 O 3 . However as the use of O 2 plasma without adding SF 6 creates a rough surface for glassy carbon; this step has been put aside. …”

Section: Glassy Carbon Plasma Etching Using An Aluminium or A Titaniumentioning

confidence: 99%

“…Kuhnke et al have made a comparison between direct laser micromachining and reactive ion etching (RIE) [28], and Youn et al and Takahashi et al have investigated focused ion beam, nano/femtosecond-pulsed laser, excimer laser and dicing techniques [24,[30][31][32]. Dry etching of glassy carbon which results in a smooth surface quality has been highlighted by combining SF 6 /O 2 during the RIE process [33,34].…”

mentioning

confidence: 99%

Wafer-level microstructuring of glassy carbon

Hans

Prater

Kilchoer

et al. 2014

Advanced Fabrication Technologies for Micro/Nano Optics and Photonics VII

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Glassy carbon is used nowadays for a variety of applications because of its mechanical strength, thermal stability and non-sticking adhesion properties. One application is glass molding that allows to realize high resolution diffractive optical elements on large areas and at affordable price appropriate for mass production. We study glassy carbon microstructuring for future precision compression molding of low and high glass-transition temperature. For applications in optics the uniformity, surface roughness, edge definition and lateral resolution are very important parameters for a stamp and the final product. We study different methods of microstructuring of glassy carbon by etching and milling. Reactive ion etching with different protection layers such as photoresists, aluminium and titanium hard masks have been performed and will be compare with Ion beam etching. We comment on the quality of the structure definition and give process details as well as drawbacks for the different methods. In our fabrications we were able to realize optically flat diffractive structures with slope angles of 80° at typical feature sizes of 5 micron and 700 nm depth qualified for high precision glass molding.

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“…Wet etching processes using hydrofluoric acid or potassium hydroxide solutions are conventionally available in the fabrication of microchannels. [12][13][14][15] However, wet etching processes often generate undesired over-etching or etching defects arising from the difficulty in controlling the solution composition and reaction times, and is also tainted by the formation of non-rectangular shapes due to isotropic etching and low aspect ratios (usually lower than 1.0). Moreover, such strong acidic solutions are toxic and not environmentally friendly.…”

Section: Introductionmentioning

confidence: 99%