Electron Beam Microlithography Research Articles

Selective Surface Modification of SiO2−TiO2 Supports with Phosphonic Acids

The selective surface modification by phosphonic acids of SiO2−TiO2 supports at the micrometer and molecular scale was investigated. Under aqueous conditions, phosphonic acids bind to TiO2 and not to SiO2 surfaces. A micropatterned support was prepared by electron beam microlithography and selectivity, of the surface modification was evidenced using scanning Auger electron spectroscopy (SAES). The second support was a mesoporous SiO2−TiO2 mixed oxide (10 mol % Ti) epoxidation catalyst prepared by sol−gel processing. Selectivity was deduced from the decrease of the catalytic activity upon modification and from chemical analysis; bonding modes to the surface were investigated using solid-state 29Si and 31P MAS NMR. The possibility to introduce different organic groups by successive treatments with a phosphonic acid and a silylating agent was illustrated in the case of the mixed oxide.

Electron beam patterning of biomolecules

The patterning of biomolecules on semiconducting surfaces is of central importance in the fabrication of novel biodevices. In the process of patterning, it is required that the biomolecule preserves its properties and the substrate is not damaged by the chemicals, the temperatures or the patterning beams involved in the procedure. Recently, both DUV and electron beam microlithography have been used in order to deposit protein layers in predefined patterns. Various approaches have been used, some involving photoresists. Contrast between exposed and unexposed regions, resolution of adjacent features and sensitivity to dose variation, are the key issues. The approach followed in this paper consists of a direct patterning of a biotin layer, deposited on an amino-silane primed silicon nitride surface, using an electron beam. After irradiation, the surface is covered by bovine serum albumin (BSA), which acts as a blocking material to protect the exposed areas from streptavidin adsorption. Using 20 keV e-beam energy and doses, in the range 100–1000 μC/cm 2, submicrometer dense lines of 1-μm pitch have been obtained. The results have been tested by fluorescence optical microscopy.

Electron beam poling of thin fluoropolymer layers

Electron beam poling by use of a scanning electron microscope was developed and applied to thin polymer layers. The electron beam charging process was studied by measurement of the surface potential, dependent on the acceleration voltage. The induced orientation of CF/sub 2/ dipole groups of the ferroelectric copolymer vinylidene fluoride/trifluoroethylene was detected by means of IR spectroscopy as well as by nonlinear optical methods. Using electron beam microlithography, microscopic polarization structures have been written into thin fluoropolymer layers by means of a direct, computer-controlled writing process; they were read out through potential contrast images as well as by means of SHG (second harmonic generation).

Derivation of the image interaction for non-planar pointed emitter geometries: application to field emission I–V characteristics

Spindt et al. have demonstrated that high density field emitter arrays fabricated using thin-film techniques and electron beam microlithography operate at very low applied voltages, compared with that for conventional etched wire field emission tips. These arrays are capable of operating at effective current densities far higher than can be obtained with etched emitters. The current-voltage curves obtained from Spindt devices generally follow Fowler-Nordheim behavior, but differ dramatically in slope of the F-N curves. It has been suggested that the apparent emitting area per tip is a few atomic sites. By contrast, the data for the etched emitters indicate a much greater emitting area (about 100 atomic sites), from which it is concluded that there are anomalously high fields on Spindt cathodes. This difference was explained by assuming that the emitting atoms form a protuberance on the tip of the cone with a field magnification factor of about 5. Closed form analytical solutions for the image interaction for tips modeled as a cone, paraboloid, hyperboloid, and sphere on cone have been derived. Numerical results show that the classical image interaction for these non-planar emitter geometries is diminished in magnitude relative to the planar image interaction for the same external bias potential. Simple analytic expressions for the image interaction for these non-planar geometries are obtained by fitting of the numerical results. The tunneling barriers have been constructed by adding the image potential for each model of the tip and the corresponding geometrically dependent bias potential. It is found that the bias potentials (fields) for the model emitters significantly modify the shape of the tunneling barriers, and the resulting forms predict a dramatically enhanced current relative to the “classical” Fowler-Nordheim result.

Derivation of the image interaction for non-planar pointed emitter geometries: application to field emission I–V characteristics

Abstract Spindt et al. have demonstrated that high density field emitter arrays fabricated using thin-film techniques and electron beam microlithography operate at very low applied voltages, compared with that for conventional etched wire field emission tips. These arrays are capable of operating at effective current densities far higher than can be obtained with etched emitters. The current-voltage curves obtained from Spindt devices generally follow Fowler-Nordheim behavior, but differ dramatically in slope of the F-N curves. It has been suggested that the apparent emitting area per tip is a few atomic sites. By contrast, the data for the etched emitters indicate a much greater emitting area (about 100 atomic sites), from which it is concluded that there are anomalously high fields on Spindt cathodes. This difference was explained by assuming that the emitting atoms form a protuberance on the tip of the cone with a field magnification factor of about 5. Closed form analytical solutions for the image interaction for tips modeled as a cone, paraboloid, hyperboloid, and sphere on cone have been derived. Numerical results show that the classical image interaction for these non-planar emitter geometries is diminished in magnitude relative to the planar image interaction for the same external bias potential. Simple analytic expressions for the image interaction for these non-planar geometries are obtained by fitting of the numerical results. The tunneling barriers have been constructed by adding the image potential for each model of the tip and the corresponding geometrically dependent bias potential. It is found that the bias potentials (fields) for the model emitters significantly modify the shape of the tunneling barriers, and the resulting forms predict a dramatically enhanced current relative to the “classical” Fowler-Nordheim result.

Custom ICs spread their influence : Roderic Beresford and Harvey J. Hindin. Electronics, 93 (5 May 1982)

The patterning of biomolecules on semiconducting surfaces is of central importance in the fabrication of novel biodevices. In the process of patterning, it is required that the biomolecule preserves its properties and the substrate is not damaged by the chemicals, the temperatures or the patterning beams involved in the procedure. Recently, both DUV and electron beam microlithography have been used in order to deposit protein layers in predefined patterns. Various approaches have been used, some involving photoresists. Contrast between exposed and unexposed regions, resolution of adjacent features and sensitivity to dose variation, are the key issues. The approach followed in this paper consists of a direct patterning of a biotin layer, deposited on an amino-silane primed silicon nitride surface, using an electron beam. After irradiation, the surface is covered by bovine serum albumin (BSA), which acts as a blocking material to protect the exposed areas from streptavidin adsorption. Using 20 keV e-beam energy and doses, in the range 100–1000 μC/cm2, submicrometer dense lines of 1-μm pitch have been obtained. The results have been tested by fluorescence optical microscopy.

Comparison of GaAs device approaches for ultrahigh-speed VLSI : Richard C. Eden. Proc. IEEE70 (1), 5 (1982)

The patterning of biomolecules on semiconducting surfaces is of central importance in the fabrication of novel biodevices. In the process of patterning, it is required that the biomolecule preserves its properties and the substrate is not damaged by the chemicals, the temperatures or the patterning beams involved in the procedure. Recently, both DUV and electron beam microlithography have been used in order to deposit protein layers in predefined patterns. Various approaches have been used, some involving photoresists. Contrast between exposed and unexposed regions, resolution of adjacent features and sensitivity to dose variation, are the key issues. The approach followed in this paper consists of a direct patterning of a biotin layer, deposited on an amino-silane primed silicon nitride surface, using an electron beam. After irradiation, the surface is covered by bovine serum albumin (BSA), which acts as a blocking material to protect the exposed areas from streptavidin adsorption. Using 20 keV e-beam energy and doses, in the range 100–1000 μC/cm2, submicrometer dense lines of 1-μm pitch have been obtained. The results have been tested by fluorescence optical microscopy.

Monemolecular resists: a new class of high resolution resists for electron beam microlithography

Monemolecular resists: a new class of high resolution resists for electron beam microlithography

Polymerized monomolecular layers: A new class of ultrathin resins for microlithography

The potential of photoresists based on monomolecular layers is described. In these organic solid films, polymerization is controlled by the lattice imposed by aliphatic chains, and the low dispersivity of the polymer obtained gives these resists a high contrast ( γ = 1.5). Furthermore, owing to this polymerization control and to a suitable design of the molecules, the sensitivity and contrast of these resists can be varied independently. The ultrathin (30–1000 Å) films of uniform and controllable thickness obtained by this technique make these resists very suitable for low energy electron beam microlithography. Very high resolutions can be achieved by using these films without the need for high contrast; e.g. a 600 Å resolution was obtained on a thick substrate using a monomolecular resist with γ = 0.7.

Monemolecular resists: a new class of high resolution resists for electron beam microlithography : A. Barraud, C. Rosilio and A. Ruaudel-Teixier. Solid St. Technol. p. 120 (August 1979)

Monemolecular resists: a new class of high resolution resists for electron beam microlithography : A. Barraud, C. Rosilio and A. Ruaudel-Teixier. Solid St. Technol. p. 120 (August 1979)

Monomolecular resists—A new approach to high resolution electron beam microlithography

The resist specific properties of ultrathin, very regular films made of monomolecular layers are described. Very high resolution can be achieved in electron beam microlithography, on condition that the resist film is thin enough and the pair thickness-voltage is properly chosen. The contrast of the resin is then unimportant. Ultrathin layers can be achieved by superimposing monomolecular layers, each 30 Å thick. This technique yields compact, uniform, reliable films in the range 30–1000 Å. In these organized crystallized films, polymerization is lattice controlled and stress-limited, and this leads to automatically low-dispersed polymers. This low dispersity gives rise to high contrast. This situation is illustrated by the results obtained from a family of three amphiphilic molecules, one (ω-tricosenoic acid) leading to a linear polymer, and two derivatives of it leading to cross-linked polymers. The exposure curves for these three molecules are given. The position of the funcional groups in the molecules have been chosen in such a way that sensitivity and contrast can be adjusted independently. A sensitivity of 30 μC/cm2 at 5kV together with a contrast value γ of 1.5 have been achieved. Resolution tests have been carried out with the simplest of these molecules. Since its contrast is low (γ=0.7), it has been chosen as an example to show that high resolution can be achieved without high contrast, provided the accelerating voltage is properly adapted to film thinness. Best resolution (600 Å) is obtained at 5 kV, although the spot size is the largest at that voltage. At higher voltages, thickness modulation is no longer 100%. The compactness and the inertness of these films together with their fair protective properties make these ultrathin films suited to electron beam microlithography. This new class of electron resists might bring a new lease of life to microlithography, in the domains500–3000 Å, in the next few years.

Direct wafer exposure

The semiconductor industry is moving towards one and half-micron circuits, always supposing the manufacturing technologies are adequate. This paper examines the merits of photolithography, electron beam microlithography, deep ultra-violet and X-ray microlithography as methods of producing these sub-micron devices.

Physical properties of thin-film field emission cathodes with molybdenum cones

Field emission cathodes fabricated using thin-film techniques and electron beam microlithography are described, together with effects obtained by varying the fabrication parameters. The emission originates from the tip of molybdenum cones that are about 1.5 μm tall with a tip radius around 500 Å. Such cathodes have been produced in closely packed arrays containing 100 and 5000 cones as well as singly. Maximum currents in the range 50–150 μA per cone can be drawn with applied voltages in the range 100–300 V when operated in conventional ion-pumped vacua at pressures of 10−9 Torr or less. In the arrays, current densities (averaged over the array) of above 10 A/cm2 have been demonstrated. Life tests with the 100-cone arrays drawing 2 mA total emission (or 3 A/cm2) have proceeded in excess of 7000 h with about a 10% drop in emission current. Studies are presented of the emission characteristics and current fluctuation phenomena. It is tentatively concluded that the emission arises from only one or a few atomic sites on the cone tips.