Showing papers on "Lithography published in 1996"

Imprint Lithography with 25-Nanometer Resolution

Abstract: A high-throughput lithographic method with 25-nanometer resolution and smooth vertical sidewalls is proposed and demonstrated. The technique uses compression molding to create a thickness contrast pattern in a thin resist film carried on a substrate, followed by anisotropic etching to transfer the pattern through the entire resist thickness. Metal patterns with a feature size of 25 nanometers and a period of 70 nanometers were fabricated with the use of resist templates created by imprint lithography in combination with a lift-off process. With further development, imprint lithography should allow fabrication of sub-10-nanometer structures and may become a commercially viable technique for manufacturing integrated circuits and other nanodevices.

Mold‐assisted nanolithography: A process for reliable pattern replication

Abstract: A process for reproducibly and reliably realizing thin‐layer patterning having details with dimensions of 100 nm or even less is described. This process has been called mold lithography. It is a two‐step process: First, a photopolymerization‐replication step is carried out, after which pattern transfer is realized through, e.g., wet or dry etching into the substrate material. We performed a number of elementary experiments to evaluate this process. Processing conditions are given and the obtained results are discussed. The strengths of this process are its simplicity and low cost while maintaining compatibility with (standard) semiconductor‐technology processing.

Ultrahigh resolution of calixarene negative resist in electron beam lithography

Abstract: A nonpolymer material, calixarene derivative (hexaacetate p‐methnylcalix[6]arene) was tested as a high‐resolution negative resist under an electron beam lithography process It showed under 10‐mm resolution with little side roughness and high durability to halide plasma etching A sub‐10‐nm Ge quantum wire was perfectly etched off without defects Such a performance is suitable for nanoscale device processes

Seamless, maskless lithography system using spatial light modulator

Abstract: The invention is a seamless, projection lithography system that eliminates the need for masks through the use of a programmable Spatial Light Modulator (SLM) with high parallel processing power. Illuminating the SLM with a radiation source (1) provides a patterning image of many pixels via a projection system (4) onto a substrate (5). The preferred SLM is a Deformable Micromirror Device (3) for reflective pixel selection using a synchronized pulse laser. An alternative SLM is a Liquid Crystal Light Valve (LCLV) (45) for pass-through pixel selection. Electronic programming enables pixel selection control for error correction of faulty pixel elements. Pixel selection control also provides for negative and positive imaging and for complementary overlapping polygon development for seamless uniform dosage. The invention provides seamless scanning motion by complementary overlap to equalize radiation dosage, to expose a pattern on a large area substrate (5). The invention is suitable for rapid prototyping, flexible manufacturing, and even mask making.

Large‐area achromatic interferometric lithography for 100 nm period gratings and grids

Abstract: Achromatic interferometric lithography is the preferred approach for producing large‐area, spatially coherent 100 nm period gratings and grids. We report on improvements to processes which have enabled exposure areas of ≊10 cm2. In addition, we report on the fabrication of 100 nm period free‐standing gold gratings.

Maskless, reticle-free, lithography

Abstract: A lithography system in which the mask or reticle, which usually carries the pattern to be printed onto a substrate, is replaced by a programmable array of binary (i.e. on/off) light valves or switches which can be programmed to replicate a portion of the pattern each time an illuminating light source is flashed. The pattern of light produced by the programmable array is imaged onto a lithographic substrate which is mounted on a scanning stage as is common in optical lithography. The stage motion and the pattern of light displayed by the programmable array are precisely synchronized with the flashing illumination system so that each flash accurately positions the image of the pattern on the substrate. This is achieved by advancing the pattern held in the programmable array by an amount which corresponds to the travel of the substrate stage each time the light source flashes. In this manner the image is built up of multiple flashes and an isolated defect in the array will only have a small effect on the printed pattern. The method includes projection lithographies using radiation other than optical or ultraviolet light. The programmable array of binary switches would be used to control extreme ultraviolet (EUV), x-ray, or electron, illumination systems, obviating the need for stable, defect free masks for projection EUV, x-ray, or electron, lithographies.

Focused ion beam applications to solid state devices

Abstract: The current state of focused ion beam (FIB) applications in relation to solid state devices is reviewed, and recent use of FIB technology for lithography, etching, deposition, and doping are described. Etching and deposition have become essential processes for failure analysis and for mask repair in silicon ULSL production. Furthermore, the FIB doping technique has been used to fabricate quantum effect devices.

Electrochemically assembled quasi-periodic quantum dot arrays

Abstract: We describe two electrochemical self-assembly processes for producing highly ordered quasi-periodic arrays of quantum dots on a surface. The advantages of these techniques are: (i) they are `gentle' and do not cause radiation damage to nanostructures unlike beam lithography, (ii) they have high throughput and are amenable to mass production unlike direct-write lithography, (iii) structures can be delineated on non-planar substrates, and (iv) the techniques are potentially orders of magnitude cheaper to implement than conventional nanosynthesis. Samples produced by these techniques have been characterized by microscopy, optical and transport measurements, Auger and x-ray. These measurements reveal intriguing properties of the nanostructures. In this paper, we describe our initial results and show the promise of such techniques for low-cost and high-yield nanosynthesis.

Conductive dots, wires, and supertips for field electron emitters produced by electron‐beam induced deposition on samples having increased temperature

Abstract: The procedure for three‐dimensional additive lithography with electron‐beam induced deposition is applied in a scanning electron microscope equipped with an image processor beam control system for lithography. Employing organometallic materials, which contain gold or platinum, quantum dots, resistors, and field emitter tips are deposited. Changing the current, the properties of the deposited nanocrystalline compound materials can be selected to be insulating or conducting. High resolution and high aspect ratio structures are grown with this technique. To find the mechanism responsible for conductivity in the deposited material, resistors are characterized at temperatures ranging from −150 °C to +180 °C. Measurements are performed in a high‐vacuum chamber equipped with a gas cooling system cooled with liquid nitrogen and a resistive heater. Poole–Frenkel plots show that field electron emission and hopping of electrons is the dominant mechanism of conduction. The metal content of the deposits is increased w...

Electron‐beam microcolumns for lithography and related applications

Abstract: Lithography with an array of miniaturized scanning electron‐beam columns presents one of the most promising high‐throughput possibilities for fabrication of devices with feature sizes less than 100 nm. With scanning electron beams no mask is required and the necessary resolution and alignment of overlay structures are realizable. With arrays of microcolumns, the lithography throughput of a single column can be multiplied. The approach can also be used for a number of lithography related applications such as metrology, inspection, testing, etc. We review the status of the microcolumn program and discuss opportunities and challenges of this approach to high‐throughput nanolithography and related applications. Special emphasis is given to lithography in the 100 nm regime.

Fabrication of nano-dot- and nano-ring-arrays by nanosphere lithography

Abstract: We have applied the method of nanosphere lithography to fabricate arrays of nanometer-scale gold and cobalt particles. The individual cobalt particles were found to be in a single domain state as verified by magnetic force microscopy. By tuning the preparation conditions, we also successfully fabricated arrays of mesoscopic gold rings for the first time with potential application for persistent current experiments.

Microcontact printing and pattern transfer using trichlorosilanes on oxide substrates

Abstract: Microcontact printing was used to pattern silicon, aluminum, and titanium substrates using octadecyltrichlorosilane as the ink and an elastomer as the stamp. Patterns were transferred into the substrates using both dry and wet etching. The Al and Ti were etched using an electron cyclotron resonance (ECR) plasma source at low ion energies and low pressure. Silicon was etched in HF to remove the native oxide, followed by KOH. Microcontact printing using OTS ink is a convenient and easy way to pattern both semiconductor and metal surfaces without the extended use of photolithography.

Method for fabrication of close-tolerance lines and sharp emission tips on a semiconductor wafer

Abstract: A method for fabricating submicron lines over a semiconductor material by creating a narrow hard mask over the material using a narrow void-producing process. The narrow void is thus used as a mask to form lines that are narrower than those that can be produced by current lithography techniques. The method can also be used to create sharp emission tips for field effect display devices.

Novel class of low molecular‐weight organic resists for nanometer lithography

Abstract: A novel class of low molecular‐weight organic resist materials for nanometer lithography, 1,3,5‐tris[4‐(4‐toluenesulfonyloxy)phenyl]benzene (TsOTPB) and 4,4′,4″‐tris(allylsuccinimido) triphenylamine (ASITPA), was designed and synthesized. TsOTPB with a glass‐transition temperature (Tg) of 64 °C and ASITPA with a Tg of 80 °C were found to function as positive and negative resists, respectively, enabling the fabrication of 150 and 70 nm line patterns on exposure to an electron beam at 50 keV.

Microlens array imaging system for photolithography

Abstract: Keywords: flat panel displays ; compound eye ; microlenses ; micro-optics ; multi-aperture imaging ; optical images ; photolithography ; photoresists Reference EPFL-ARTICLE-183166 Record created on 2013-01-17, modified on 2017-05-10

Lift-off lithography using an atomic force microscope

Abstract: We present a technique to fabricate nanostructures with an atomic force microscope (AFM). By taking advantage of the AFM tip sharpness, we engrave a narrow furrow in a soft polyimide layer. The furrow is then transferred using dry etching to a thin germanium layer which forms a suspended mask. Metallic layers are then evaporated through this mask. Metallic lines with a 40 nm linewidth and single‐electron transistors have been fabricated. This lift‐off technique can be used on any substrate and allows easy alignment with previously fabricated structures.

Independent parallel lithography using the atomic force microscope

Abstract: The scanning probe microscope ~SPM! has demonstrated itself to be a versatile and effective tool for patterning surfaces at the nanometer scale Two common methods for modifying surfaces using probe microscopes are direct physical patterning and electric field assisted patterning While both methods of surface modification are quite different, they both require that a sharp tip interacts with the surface to be patterned Physical patterning consists of scribing or indenting a sample using the tip of the SPM Jung 1 has used this process to scribe patterns into polymer surfaces, and Mamin 2 has used the physical indentation process in conjunction with laser heating to store 100 nm bits at 100 kHz in a polymer surface This approach has the advantage that the sample is typically much softer and generally unreactive with the tip, thereby reducing tip wear The literature on electrical modification of surfaces with probe microscopes is much more extensive Scanning probe lithography was pioneered by Dagata, 3 who patterned ^111& silicon with the scanning tunneling microscope ~STM!, and Lyding 4 has used this same technique in ultrahigh vacuum ~UHV! to pattern features less than a few nanometers Snow and Campbell have modified this technique and patterned Si 5 and GaAs 6 with the atomic

Magnetic force microscopy of single-domain cobalt dots patterned using interference lithography

Abstract: We have fabricated arrays of Co dots having diameters of 100 nm and 70 nm using interference lithography. The density of these arrays is 7.2/spl times/10/sup 9//in/sup 2/. Magnetic force microscopy measurements indicate that the Co dots are single-domain with moments that can be controlled to point either in-plane or out-of-plane. Interference lithography is a process that is easily scaled to large areas and is potentially capable of high throughput. Large, uniform arrays of single-domain structures are potentially useful for high-density, low-noise data storage.

Fabrication of 3 nm wires using 100 keV electron beam lithography and poly(methyl methacrylate) resist

Abstract: We report the fabrication of 3 nm NiCr wires on a solid silicon substrate. The process uses conventional 100 keV electron beam lithography and poly(methyl methacrylate) resist. The wires consist of short, continuous, lengths of metal that are attached at either end to 20 nm wide wires. Instead of exposing continuous lines in the resist, we blank the beam for several pixels to leave a gap. The resist in the gap is therefore exposed only by the secondary electrons from the neighboring regions that are directly exposed by the beam. The technique is repeatable and we demonstrate that it is possible to make 3 nm features on demand.

A proposal for maskless, zone‐plate‐array nanolithography

Abstract: We propose a novel form of x‐ray projection lithography that: (1) requires no mask, and hence can be considered an x‐ray pattern generator; (2) is, in principle, capable of reaching the limits of the lithographic process. The new scheme utilizes an array of Fresnel zone plates, and matrix‐addressed micromechanical shutters to turn individual x‐ray beamlets on or off in response to commands from a control computer. Zone plate resolution is approximately equal to the minimum zone width, which can approach 10 nm. Zone plates are narrow‐band lensing elements: For a diffraction limited focus, the source bandwidth Δλ/λ should be less than or equal to the reciprocal of the number of zones N. An undulator having Nu magnetic sections emits collimated radiation in a bandwidth Δλ/λ=1/Nu. Nu is usually in the range 35–100. We present a system design based on 25 nm lithographic resolution using λ=4.5 nm. For N=100 the zone‐plate diameter is 10 μm. Each zone plate of the array would be responsible only for exposure wit...

Nonlinear optical properties of photoresists for projection lithography

Abstract: Optical beams are self‐focused and self‐trapped upon initiating crosslinking in photoresists This nonlinear optical phenomenon is apparent only for low average optical intensities and produces index of refraction changes as large as 004 We propose using the self‐focusing and self‐trapping phenomenon in projection photolithography to enhance the resolution and depth of focus

Interferometric lithography of sub‐micrometer sparse hole arrays for field‐emission display applications

Abstract: Interferometric lithography, the use of interactions between coherent laser beams to define sub‐ wavelength patterns, is well adapted to the periodic nature of field‐emitter structures. Techniques to fabricate sparse (hole diameter to pitch ratio of 1:3 or larger) emitter arrays to improve reliability and lifetime are presented. These include: multiple exposures at two different pitches; integration of interferometric and optical imaging lithography; and various multiple beam techniques that both provide a sparse array and result in a two dimensional pattern in a single exposure. Moire alignment techniques are demonstrated to provide a simple process for aligning multiple levels. Manufacturing related issues such as process latitude and photoresist profiles and their suitability for subsequent processing are also discussed. Exposure‐dose process control using latent image monitoring is demonstrated.

Projection lithography system and method using all-reflective optical elements

Abstract: A projection lithographic system that operates within the deep ultraviolet to vacuum ultraviolet region of the spectrum and uses an all-reflective optical arrangement to project a reduced image of a lithographic mask onto a semiconductor wafer. The all-reflective optical arrangement includes from six to eight reflective surfaces wherein each of the reflective surfaces is aspheric, The reflective surfaces are disposed along a common optical axis and are arranged not to interfere with the path of light as the light travel from the lithographic mask to the semiconductor wafer.

General aspheric refractive micro‐optics fabricated by optical lithography using a high energy beam sensitive glass gray‐level mask

Abstract: General aspheric refractive microlens arrays with an almost 100% fill factor are useful in a wide range of applications ranging from display, optoelectronic interconnections, or improving the efficiency of detector arrays to lithography techniques utilizing microlens arrays. In this article a technique will be discussed which allows the microlithographic fabrication of general aspheric non rotationally symmetric refractive lenses with a 100% fill factor. A gray‐level mask based on high energy beam sensitive (HEBS) glass is used to pattern a thick (4–5 micron) photoresist layer. After development, the refractive structure is transferred into the substrate material using a chemically assisted ion beam etching (CAIBE) process. The HEBS‐glass gray‐level mask is generated by a electron‐beam writer, allowing for complete freedom in terms of the shape and location of the lenses.

Diffractive lens fabricated with mostly zeroth-order gratings

Abstract: We demonstrate a spherical diffractive lens fabricated in fused quartz for use at the 632.8-nm wavelength. The lens is constructed by use of a modulated two-dimensional binary grating with a high transmitted zeroth-order efficiency. Rigorous eigenmode analysis is used to correlate the desired phase modulation with the fill factor. Fabrication requires only one lithography step. Using the lens, we were able to image a focal spot with a diffraction-limited spot size (FWHM).

Fabrication of arrays of large step‐free regions on Si(001)

Abstract: In this letter we describe a method for producing large areas of Si(001) surfaces which are (i) free of atomic steps and (ii) arranged in regular patterns on the wafer. The first step is the fabrication of a two‐dimensional grating structure using e‐beam lithography and reactive ion etching. This grating is then annealed within the appropriate temperature window in ultrahigh vacuum to produce the desired array of (001) step‐free regions. We illustrate the success of the method through the use of low‐energy electron microscopy for a few repeat spacings on test structures each extending over a 3×3 mm2 area. Alternative processing steps are discussed as well as application to submicron device technology.

Nanometer‐scale resolution of calixarene negative resist in electron beam lithography

Abstract: New nonpolymer materials, calixarene derivatives were tested as high‐resolution negative resists for use in electron beam lithography. Arrays of 12‐nm‐diam dots with a 25 nm pitch were fabricated easily. The sensitivity of calixarene in terms of area dose ranged from 700 to 7000 μC/cm2, and the required dose for dot fabrication was about 105 electrons/dot. The standard area dose for calixarene is almost 20 times higher than that for polymethyl methacrylate (PMMA), but the electron spot dose for dot fabrication by calixarene is almost the same as that for PMMA and other highly sensitive resists such as SAL (chemically amplified negative resist for electron beam made by Shipley). The electron spot dose for such extremely small dots does not seem to depend on standard area dose, but any resist tends to require the same dose under exposure in a 50 keV electron beam writing system. We propose a qualitative exposure model that suggests a tradeoff of dose and dot size. The calixarene seems to be promising materi...

High resolution electron beam lithography using ZEP-520 and KRS resists at low voltage

Abstract: ZEP‐520 and KRS resist systems have been evaluated as candidates for use in low voltage electron beam lithography. ZEP‐520 is a conventional chain scission resist which has a positive tone for over two orders of magnitude in exposure dose. KRS is a chemically amplified resist which can be easily tone reversed with a sensitivity ∼8 μC/cm2 at 1 keV. Both resist systems are shown to have sensitivities ∼1 μC/cm2 for positive tone area exposures to 1 keV electrons. A decrease in contrast in 50 nm thick resist layers is seen when exposure voltage is lowered from 2 to 1 keV, indicating nonuniform energy deposition over the resist thickness. High resolution single pass lines have been transferred into both Si and SiO2 substrates at both low and high voltages in each resist system without using multilayer resist masks. The ZEP‐520 and KRS resists are shown to have resolutions of 50 and 60 nm, respectively, at 1 kV, within a factor of 2 of their high voltage resolutions under identical development conditions. A cusp shaped etch profile in Si allows high aspect ratio 20 nm wide trenches to be fabricated using these resists on bulk Si. Low voltage exposures have been used to pattern gratings with periods as small as 75 and 100 nm in ZEP‐520 and KRS, respectively. Low voltage exposures on SiO2 show no indications of pattern distortion due to charging or proximity effects.