Enhanced adhesion buffer layer for deep x-ray lithography using hard x rays

Carlo, Francesco De; Song, J.J.; Mancini, Derrick C.

doi:10.1116/1.590492

Cited by 9 publications

(5 citation statements)

References 8 publications

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“…Microstructured polymer films on optical or metal surfaces facilitate the formation of array layouts of sensor chips. , Poly(methyl methacrylate) (PMMA) is commonly used as high-resolution resist for electron beam lithography as well as for X-ray and UV microlithography. PMMA forms homogeneous films and is known for its good optical homogeneity, negligible swelling in water, and its good adhesion to oxides and metals. , Due to its biocompatibility, PMMA is widely used as a material for medical implants. , …”

Section: Introductionmentioning

confidence: 99%

Characterization of Metal-Supported Poly(methyl methacrylate) Microstructures by FTIR Imaging Spectroscopy

2006

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Thin microstructured poly(methyl methacrylate) (PMMA) films may be used as scaffolds for biosensor arrays. Microstructured pores form miniaturized vessels, each constituting an individual reaction vessel or detector element. Arrays of micropores with diameters between 2 and 80 microm were prepared in thin PMMA films on gold by optical lithography. Laterally resolved chemical information for microstructured PMMA films on a gold substrate was obtained by FTIR spectroscopic imaging. The carbonyl band was used to characterize the microstructure. Spectroscopic results indicate small amounts of PMMA residues inside the pores. A downshift of 5 cm(-1) compared to the position of the PMMA bulk carbonyl band indicates interactions of the PMMA residue with the gold substrate. Additional small bands are observed which indicate the formation of carboxylate during PMMA microstructuring. Three possible types of strong PMMA-gold interactions are discussed. All strong PMMA-gold interactions involve carbonyl or carboxyl oxygen.

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Section: Introductionmentioning

confidence: 99%

Characterization of Metal-Supported Poly(methyl methacrylate) Microstructures by FTIR Imaging Spectroscopy

2006

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“…Feature tolerances and the minimum feature size producible by LIGA are limited by many considerations. Most of these, including beam divergence [4,5], fluorescence radiation [4][5][6][7][8][9], mask thermal deformations [10], development conditions [8,11], feature loss of adhesion [7,8,[12][13][14] and PMMA swelling [15][16][17], are practical limitations amenable to improvement through optimization, innovation and determined process engineering. In contrast, fundamental limitations are beyond our control as they arise from physical phenomena inherent to x-ray lithography.…”

Section: Introductionmentioning

confidence: 99%

Fundamental limitations of LIGA x-ray lithography: sidewall offset, slope and minimum feature size

Griffiths¹

2004

J. Micromech. Microeng.

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and numerical methods are used to examine photoelectron d ,oses and th ieir effect on the dimensions of features produced by deep x-ray lithography. New analytical models describing electron doses are presented and used to compute dose distributions for several feature geometries. The history of development and final feature dimensions are also computed, taking into account the dose field, dissolution kinetics based on measured development rates, and the transport of PMMA fragments away from the dissolution front. We find that sidewall offsets, sidewall slope and producible feature sizes all exhibit at least practical minima and that these minima represent fundamental limitations of the LIGA process. The minimum values under optimum conditions are insensitive to the synchrotron spectrum, but depend strongly on resist thickness. This dependence on thickness is well approximated by simple analytical expressions describing the minimum offset, minimum sidewall slope, minimum producible size of positive and negative features, maximum aspect ratio and minimum radius of inside and outside corners.

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“…Using a different approach, De Carlo et al solved the problem of high interface doses by incorporating a polymer buffer layer between the metallic surface and the resist [21][22][23]. The thin buffer layer, insoluble in developer and not degraded by radiation, absorbs electrons emitted by the metal before they reach the resist.…”

Section: Past Researchmentioning

confidence: 99%

Resist substrate studies for LIGA microfabrication with application to a new anodized aluminum substrate

Griffiths¹,

Losey²,

Hachman³

et al. 2005

J. Micromech. Microeng.

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Resist substrates used in the LIGA process must provide high initial bond strength between the substrate and resist, little degradation of the bond strength during x-ray exposure, acceptable undercut rates during development and a surface enabling good electrodeposition of metals. Additionally, they should produce little fluorescence radiation and give small secondary doses in bright regions of the resist at the substrate interface. To develop a new substrate satisfying all these requirements, we have investigated secondary resist doses due to electrons and fluorescence, resist adhesion before exposure, loss of fine features during extended development and the nucleation and adhesion of electrodeposits for various substrate materials. The result of these studies is a new anodized aluminum substrate and accompanying methods for resist bonding and electrodeposition. We demonstrate the successful use of this substrate through all process steps and establish its capabilities via the fabrication of isolated resist features down to 6 µm, feature aspect ratios up to 280 and electroformed nickel structures at heights of 190 to 1400 µm. The minimum mask absorber thickness required for this new substrate ranges from 7 to 15 µm depending on the resist thickness.

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Enhanced adhesion buffer layer for deep x-ray lithography using hard x rays

Cited by 9 publications

References 8 publications

Characterization of Metal-Supported Poly(methyl methacrylate) Microstructures by FTIR Imaging Spectroscopy

Characterization of Metal-Supported Poly(methyl methacrylate) Microstructures by FTIR Imaging Spectroscopy

Fundamental limitations of LIGA x-ray lithography: sidewall offset, slope and minimum feature size

Resist substrate studies for LIGA microfabrication with application to a new anodized aluminum substrate

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