Fabrication of graphite masks for deep and ultradeep x-ray lithography

Desta, Yohannes M.; Aigeldinger, Georg; Zanca, Kevin J.; Coane, P.; Goettert, Jost; Murphy, Michael C.

doi:10.1117/12.395599

Cited by 11 publications

(12 citation statements)

References 7 publications

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“…A mold insert for hot embossing was produced using the LIGA process. [43][44][45] The mold insert was used to hot emboss several microfluidic channels in polycarbonate substrates (Goodfellow, UK) using a PHI (City of Industry, CA) press equipped with a vacuum chamber. Inspection of SEM micrographs indicated that the sidewalls of the embossed channels were straight and smooth and contained the insert-defined channel width and height indicating minimal replication errors.…”

Section: Experimental Methods Cfpcr Device and Apparatusmentioning

confidence: 99%

Rapid PCR in a continuous flow device

et al. 2004

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Continuous flow polymerase chain reaction (CFPCR) devices are compact reactors suitable for microfabrication and the rapid amplification of target DNAs. For a given reactor design, the amplification time can be reduced simply by increasing the flow velocity through the isothermal zones of the device; for flow velocities near the design value, the PCR cocktail reaches thermal equilibrium at each zone quickly, so that near ideal temperature profiles can be obtained. However, at high flow velocities there are penalties of an increased pressure drop and a reduced residence time in each temperature zone for the DNA/reagent mixture, that potentially affect amplification efficiency. This study was carried out to evaluate the thermal and biochemical effects of high flow velocities in a spiral, 20 cycle CFPCR device. Finite element analysis (FEA) was used to determine the steady-state temperature distribution along the micro-channel and the temperature of the DNA/reagent mixture in each temperature zone as a function of linear velocity. The critical transition was between the denaturation (95 uC) and renaturation (55 uC-68 uC) zones; above 6 mm s 21 the fluid in a passively-cooled channel could not be reduced to the desired temperature and the duration of the temperature transition between zones increased with increased velocity. The amplification performance of the CFPCR as a function of linear velocity was assessed using 500 and 997 base pair (bp) fragments from l-DNA. Amplifications at velocities ranging from 1 mm s 21 to 20 mm s 21 were investigated. The 500 bp fragment could be observed in a total reaction time of 1.7 min (5.2 s cycle 21) and the 997 bp fragment could be detected in 3.2 min (9.7 s cycle 21 ). The longer amplification time required for detection of the 997 bp fragment was due to the device being operated at its enzyme kinetic limit (i.e., Taq polymerase deoxynucleotide incorporation rate).

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Section: Experimental Methods Cfpcr Device and Apparatusmentioning

confidence: 99%

Rapid PCR in a continuous flow device

et al. 2004

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“…Carbon is a promising material, because it is conducting, generally inexpensive and non-toxic. Vitreous carbon was an interesting candidate over graphite, because it is known from earlier work that the graphite material used for mask substrates increases the surface sidewall roughness in the PMMA mold significantly, by an order of magnitude and vitreous carbon does not seem to do so (Desta et al 2000;Scheunemann et al 2003). Figure 6 shows a typical resist sidewall resulting from using graphite as a mask substrate compared to the same sidewall using a thin titanium mask ubstrate in Fig.…”

Section: Examples and Calculationsmentioning

confidence: 97%

“…Beryllium can be used as a mask material at thicknesses of hundreds of micrometers but the toxicity of the oxide requires special handling considerations and the material is relatively expensive (Toxicological Profile for Beryllium and Update 1993). Graphite substrates are commonly used for low cost masks since the substrate can be hundreds of micrometers thick, the material is readily available, and the conductivity of graphite facilitates electroplating of the gold absorber Desta et al 2000). However, microstructures made using graphite masks have striations on the microstructure sidewalls and sidewall surface roughness an order of magnitude higher than those made with titanium masks .…”

Section: Introductionmentioning

confidence: 99%

“…However, microstructures made using graphite masks have striations on the microstructure sidewalls and sidewall surface roughness an order of magnitude higher than those made with titanium masks . Scattering from the graphite matter has been proposed as a mechanism for the formation of the striations (Desta et al 2000). Silicon has been used as a mask material since it is widely available, mechanically robust, and inexpensive.…”

Section: Introductionmentioning

confidence: 99%

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Influence of mask substrate materials on resist sidewall roughness in deep X-ray lithography

et al. 2007

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Absorption of X-rays in deep X-ray lithography masks can significantly increase exposure time, harden the X-ray spectrum and lead to heating and distortion of the mask. To reduce the impact of such absorption, we have evaluated low atomic mass (low-z) materials that allow the utilization of thick substrates (>100 lm) for reliable mask fabrication. Various forms of graphite, vitreous carbon (VC), boron nitride and beryllium were chosen for testing. Transmission tests were conducted to evaluate resulting surface roughness in the X-ray resist sidewalls. We found that VC, beryllium and pyrolytic graphite all have minimal effect on the resist sidewall surface roughness; however, graphite and boron nitride both significantly increase the roughness to about 300 nm RMS. We could show that this increase in surface roughness is directly related to the crystal structure of these materials. From the tests conducted, VC proves a promising mask substrate, superior to the more expensive and hazardous beryllium that is commonly used for thick high precision masks. VC has been successfully employed as a mask substrate and corresponding resist structures are introduced.

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“…Although there are inorganic materials, such as Si [13], SiC [14], and SiN [15], that are used on masks, and they are excellent in their dimensional stability and chemical resistance, but forming a thin layer on them is relatively a difficult task. In addition, an X-ray mask with a graphite membrane, of which the thermal resistance is same as that of an inorganic material, has also been made [16]. In the case of absorber materials, an Au [17] absorber, which can easily be manufactured by electroplating, has been employed by many researchers.…”

Section: Introductionmentioning

confidence: 99%

Performance of SU-8 Membrane Suitable for Deep X-Ray Grayscale Lithography

Mekaru

2015

Micromachines

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Abstract:In combination with tapered-trench-etching of Si and SU-8 photoresist, a grayscale mask for deep X-ray lithography was fabricated and passed a 10-times-exposure test. The performance of the X-ray grayscale mask was evaluated using the TERAS synchrotron radiation facility at the National Institute of Advanced Industrial Science and Technology (AIST). Although the SU-8 before photo-curing has been evaluated as a negative-tone photoresist for ultraviolet (UV) and X-ray lithographies, the characteristic of the SU-8 after photo-curing has not been investigated. A polymethyl methacrylate (PMMA) sheet was irradiated by a synchrotron radiation through an X-ray mask, and relationships between the dose energy and exposure depth, and between the dose energy and dimensional transition, were investigated. Using such a technique, the shape of a 26-μm-high Si absorber was transformed into the shape of a PMMA microneedle with a height of 76 μm, and done with a high contrast. Although during the fabrication process of the X-ray mask a 100-μm-pattern-pitch (by design) was enlarged to 120 μm. However, with an increase in an integrated dose energy this number decreased to 99 μm. These results show that the X-ray grayscale mask has many practical applications. In this paper, the author reports on the evaluation results of SU-8 when used as a membrane material for an X-ray mask.

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Fabrication of graphite masks for deep and ultradeep x-ray lithography

Cited by 11 publications

References 7 publications

Rapid PCR in a continuous flow device

Rapid PCR in a continuous flow device

Influence of mask substrate materials on resist sidewall roughness in deep X-ray lithography

Performance of SU-8 Membrane Suitable for Deep X-Ray Grayscale Lithography

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