Microlithographic Techniques Research Articles

Multispectral dielectric microfilter arrays for local resolving color sensors

Dielectric microfilters are designed and developed providing different filter functions on 3-in. substrates. Combining several coating procedures, microlithographic techniques, and dry-etching processes, spectral properties of basic filters are modified within patterns with feature sizes down to 5 µm, resulting in large-area filter patterns (>5 cm2) with multiple spectral characteristics and vertical edge profiles. By applying these techniques within a three-step-iterative procedure red, green, and blue filters (RGB) are arranged edge to edge on one substrate to form a multispectral dielectric microfilter array for use as a key component in a local resolving color sensor. These microfilters are arranged in an array of 19 identical hexagons consisting of three rhombi each. The number of these arrays amounts to 81 on a single 3-in. substrate. A modular setup of a compact local resolving color sensor is presented, consisting of Si p-i -n photoelectric cells, dielectric microfilter arrays, an imaging lens, and a final glass cover plate with an IR-blocking filter.

Poly( p-phenylene vinylene) copolymer patterns prepared via photolithographic techniques

Standard microlithographic techniques can be used for the spatially controlled light-directed synthesis of poly( p-phenylene vinylene) (PPV) block copolymers. Microscalar linear and circular patterns can be prepared in the 25 μm range. The success of the overall procedure rests on the photogeneration of triflic acid from triphenylsulfonium trifluoromethanesulfonate in a poly(9-hydroxy-[2.2]paracyclophan-1-ene) matrix to catalyze the formation of PPV. Absorption and photoluminescence studies were performed to demonstrate the efficiency of the conversion of the precursor polymer to PPV throughout the photolithographic sequence. FT-IR and UV-Vis data are also presented that illustrate how the precursor poly (paracyclophenes) can be patterned for certain block copolymer ratios in the absence of a photoacid generator.

A Biocompatible Interface for the Geometrical Guidance of Central Neuronsin Vitro

Biocompatibility of solid surfaces has become an important concern for interfacing living neurons and designing their circuit geometriesin vitro.In this paper, we report on the use of chemically and geometrically modified substrates for the growth of central nervous system neurons in culture. A glass coverslip modified with a monolayer film of either butyldimethylsilane (BDMS) or aminopropyldimethylsilane (APDMS) was adsorbed with an extracellular matrix protein, laminin. While a physicochemical property of the laminin adsorption was characterized by goniometry, ellipsometry, and fluorescent microscopy, the biocompatible function was examined by growing embryonic hippocampal neurons using a chemically defined culture system. The neurons grown on laminin-adsorbed APDMS surfaces developed a typical morphology of hippocampal neurons with multiple short-branched and single long-branched neurites. The use of BDMS films for laminin adsorption did not significantly affect the longest neuritic length but altered the morphological characteristics by reducing numbers of basal neurites and their branches. Such characteristics were highly dependent on the chemical features of monolayer films where laminin was adsorbed. We have used patterned APDMS monolayer films, fabricated through a microlithographic technique, to preferentially adsorb laminin and to demonstrate the feasible way of geometrically guiding central neuronsin vitro.

Dirac series experiments in 800 T fields: : Innovations for transport measurements

Low-temperature transport measurements in extreme pulsed magnetic fields generated by implosive flux compression techniques are challenging due to the short (micro-second) duration of the pulse, and consequent problems associated with pick-up and eddy current heating arising from the large d B/d t (peak value ∼10 9 T/s). For the `Dirac' series of experiments at Los Alamos, we have developed microlithographic processing techniques to fabricate thin coplanar microwave transmission lines (CTLs) directly onto semiconductor and superconductor samples. The thin metal reduces eddy current heating in the CTLs, allowing measurements at liquid-helium temperatures, while providing excellent electrical coupling to electrons in the sample. For samples with a conducting surface, a thin, robust insulating layer of Si 3N 4 was deposited before the CTLs to provide capacitive coupling.

Micron-Sized Protein Patterning on Diazonaphthoquinone/Novolak Thin Polymeric Films

Protein patterns at 2-μm resolution were surface-printed on the unprofiled surface of diazonaphthoquinone/novolak thin polymeric films through positive-tone and reversed negative-tone lithography. The possible mechanisms responsible for selective protein patterning, that is, (i) linkage of the amino end of the protein to the photoinduced indenecarboxylic acid via NH2-to-COOH cross-linking mediated by carbodiimide, (ii) linkage of the amino end of the protein via in-situ addition to the photoinduced ketene, and (iii) hydrophobic interaction with unexposed surfaces, were assessed through the use of ESCA, contact angle, AFM, and fluorescence microscopy. Of these, the first two mechanisms, in conjunction with diazonaphthoquinone/novolak photopolymers (a class of conventional microlithographic materials) and microlithographic equipment and techniques, can be used for bottom-to-top biomolecular architecture construction. The study proves that photolithographic materials (used for light-assisted selective surface protein attachment) can be easily transferred to bio-microlithography, with potential applications ranging from biodevice fabrication to diagnostic and combinatorial chemistry.

Lateral Separation of Macromolecules and Polyelectrolytes in Microlithographic Arrays

A new approach to separation of a variety of microscopic and mesoscopic objects in dilute solution is presented. The approach takes advantage of unique properties of a specially designed separation device (sieve), which can be built using already developed microlithographic techniques. Because of the broken reflection symmetry in its design, the direction of motion of an object in the sieve varies as a function of its self-diffusion constant, causing separation transverse to its direction of motion. This gives the device some significant and unique advantages over existing fractionation methods based on centrifugation and electrophoresis.

Extending Microcontact Printing as a Microlithographic Technique

This paper describes a number of approaches that have been employed to reduce the size of features of self-assembled monolayers (SAMs) generated using microcontact printing (μCP). In μCP, an elastomeric stamp is used to print patterned SAMs of alkanethiolates on the surfaces of coinage metals and SAMs of alkylsiloxanes on Si/SiO2. It is a convenient technique for generating patterned microstructures with feature sizes ≥ 500 nm. The capability of this technique could be extended to produce features smaller than 500 nm using the following approaches: (1) μCP with mechanical deformation of the elastomeric stampthat is, with lateral compression or uniaxial stretching in the plane of the stamp and with pressure perpendicular to the plane of the stamp; (2) μCP with physical alternation of the elastomeric stampthat is, with a stamp that has been swelled with a solvent or a stamp whose dimensions have been reduced by extraction of an inert filler; (3) μCP with reduction in the size of features resulting from processes taking place on the surfacethat is, lateral reactive spreading of hexadecanethiol on gold; and (4) μCP with multiple impressions on the same surface. The advantages and disadvantages of each approach are evaluated and compared in this paper.

Fabrication of ultra‐high‐resolution three‐color phosphor screens

Abstract— A method for fabricating three‐color phosphor screens with triad pitches of 150 μm and less has been developed. The method combines a modified microlithographic technique with electrophoretic coating of the component phosphors and black‐surround material. Indeed, triad pitches based on 15‐μm color‐line width and 5‐μm spacing between colors have been achieved.

Microlithographic techniques for laser assisted fabrication of bioelectronic devices

Microlithographic techniques are described for the fabrication of removable stencils to be used in micropatterning by laser deposition of organic and biological matter. Patterned layers are shown together with same atomic force microscope preliminary characterization. Also, a lithographically fabricated micron size glucose biosenser is shown, together with first assays of its performance.

Control of the neuronal cell attachment by functionality manipulation of diazo-naphthoquinone/novolak photoresist surface

The surface of the photosensitive Diazo-Naphto-quinone/novolak film was chemically manipulated through UV exposure and subsequent thermal processes to obtain different surface functionalities (DNQ, carboxylic, imidazole, indene, silylated and charged groups) and hydrophobicities. The neuronal cell attachment is sensitive to chemical functionalization, with favourable influence from charged, imidazole and carboxylic groups, while the hydrophobic/hydrophilic balance of the photoresist surface plays at best a secondary role. The microlithographic techniques assessed (standard positive tone, negative and positive tone image reversal, and surface imaging based on silylation) can be used to gain insight into the cell attachment mechanisms. The positive tone DNQ/novolak/imidazole system was found to be a suitable candidate for cell patterning.

Development of Poly(Phenylene)-Based Materials for Thin Film Applications: Optical Waveguides and Low Dielectric Materials

Abstract We have synthesized and evaluated poly(phenylene)-based materials made via spin-coatable polymeric precursors for such thin film applications as optical waveguides and low dielectric materials. Poly(phenylene) precursors were prepared by radical polymerization of cyclohexadiene-1, 2-diol derivatives containing various leaving groups. The precursors were converted into poly(phenylene) either by curing at 300°C or by deep-UV exposure in the presence of a photoacid generator. Poly(phenylene) has a number of desirable properties including good near-IR transmission, low dielectric constant, thermal and environmental stability, low water absorption, and ease of pattern fabrication using microlithographic techniques. Copolymer precursors based on 1,2-diaceto-3,5-cyclohexadiene and styrene derivatives as well as copolymers with Nsubstituted maleimide derivatives were prepared by radical copolymerization. The copolymer precursors were converted into poly(phenylene) copolymers either by annealing at 300°C ...

High field assisted photoemission currents from silicon photocathodes

Silicon photocathodes with arrays of tips have been prepared using microlithographic techniques. Current emission due to field effect has been measured in the case of heavy and weakly doped boron silicon. An argon continuous laser has been used to produce photocurrent. An instantaneous current (600 μA) with a moderate laser power (83 mW) has been produced on weakly doped photocathodes. This current corresponds to an average quantum yield (purely photoelectric) of about 1.7% and a local current density in the range of a few 10 6 A m −2.

Development of a new geometrical form of micropipette: electrical characteristics and an application as a potassium ion selective electrode.

Using a mix of thermal and anodic bonding together with microlithographic techniques, the safe transference of a Si3N4 film with a pore (diameter down to 1 micron) to a glass tube tip (external diameter 800 microns) was accomplished, yielding a new geometrical form of micropipette. Compared with conventional glass micropipettes the device has shown lower resistance, more stable capacitance (independent of the tip immersion depth), tip potential closer to that of a salt bridge, and a simplified filling process. Using this device as a potassium ion selective electrode (ISE), a faster response time ISE was achieved. These features indicate that the new device can advantageously substitute the conventional glass micropipettes when cell impalement is not required.

Development of New Polymeric Materials for Linear Waveguides

AbstractWe have evaluated the use of either poly(phenylene) prepared via spin-coatable polymeric precursors or fluorinated polysilynes for optical waveguides. Poly(phenylene) precursors were converted into poly(phenylene) by either curing at 300 °C or by deep-UV exposure in the presence of a photoacid generator. The poly(phenylene)s have a number of desirable properties for optical waveguide applications including good near IR transmission, low dielectric constant, thermal and environmental stability and ease of pattern fabrication using microlithographic techniques. Copolysilynes were spin-coated onto various types of substrates and then exposed by deep-UV radiation. Upon exposure of deep UV irradiation in the presence of air, they undergo photooxidative crosslinking to give insoluble glass-like materials. This photo-oxidation process is accompanied by a large decrease in refractive index from n=1.61 to n= 1.485. The photooxidation results suggest that their potential applications are as photoresists and optical waveguides.

Detour-phase kinoform interconnects: the concept and fabrication considerations

The concept of detour phase in computer-generated holography is generalized here to specify K-level phasetransmission functions that approximate optimized, periodic Fourier-transform-type carrier-frequency kinoforms. Combined with standard microlithographic techniques, this concept is shown to open up a possibility of generating (using K = 8) fully arbitrary space-invariant holographic interconnects characterized by negligible reconstruction error (<2%) and high diffraction efficiency (75–95%) into the desired pattern.

Thin Film Electrode Arrays for Mapping the Current‐Voltage Distributions in Proton‐Exchange‐Membrane Fuel Cells

An array of reference electrodes was fabricated on a polyperfluorosulfonic acid membrane using microlithographic techniques. This array was used to map the current‐voltage distribution at a proton exchange membrane fuel cell anode. Inhomogeneity in the voltage distribution was attributed to nonuniform humidification of the electrode, resulting in a decrease in half‐cell performance. Details of the fabrication method and the theory behind the array concept are presented.

Microlithographic techniques for high speed GaAs field effect transistors : J. F. Allison, W. H. Chang, L. B. Holdeman and T. Smith. Solid St. Technol., 169 (June 1986)

Microlithographic techniques for high speed GaAs field effect transistors : J. F. Allison, W. H. Chang, L. B. Holdeman and T. Smith. Solid St. Technol., 169 (June 1986)

Micrometer-spaced platinum interdigitated array electrode: fabrication, theory, and initial use

Abstract : An interdigitated array (IDA) electrode composed of 40 pairs of 0.3 micrometers thick Pt fingers 3.5 micrometers wide and separated by 2.5 micrometer gaps of insulating borosilicate glass substrate has been fashioned by a modified microlithographic technique. The two IDA is applied to measurement of redox electron conduction through films of poly-Os(bpy)2 (vpy)2 (C1O4)2, poly-CRu(bpy)2 (vpy)2 (C104)2, and Prussian Blue that had been electrochemically deposited over the Pt fingers and in te insulating gaps. Appropriate theory for using the IDA for this purpose is developed. Electrochemically generated luminescence from solutions of Ru(bpy)3 (2+) is also observed with the IDA. (Author)

Studies of Ag photodoping in GexSe1−x glass using microlithography techniques

Using microlithographic techniques to define the Ag sensitized area, the lateral profile of Ag diffusion in GexSe1−x (x≊0.1) glass is made directly visible with an optical microscope. Experimental measurements have verified that Ag photodoping in Ge0.1Se0.9 glass obeys Fick’s diffusion law with a constant diffusivity. Light absorption in the Ag2Se region has little effect on Ag photodoping. Ag photodoping is caused mainly by light absorption in the Ge0.1Se0.9 near the boundary between the Ag-containing and the non-Ag-doped region. Light absorption in Ge0.1Se0.9 glass has a long range effect which causes Ag photodoping to occur even when light irradiation is away (up to 3 μm) from Ag-containing region.

Automation of analytical isotachophoresis

A review of progress in the field of computer-aided methods for the monitoring of the isotachophoretic separation process and the steady-state zone structure is presented. Sample detection in free solution and the potential utility of three dimensional projections of data from universal and specific detectors are further discussed in the context of a proposed concept of a multicomponent chemical analyzer based on automated analytical isotachophoresis. The analyzer yet to be designed would benefit from favorable scaling laws, which would permit the utilization of microlithographic techniques for its construction. This would lead to miniaturized instrumentation in capillary electrophoresis.