Showing papers on "Lithography published in 1981"

Fabrication of micro lenses using electron-beam lithography

Abstract: Micro lenses are basic components of micro optics. We have proposed a new fabrication technique for micro lenses that uses electron-beam lithography and have developed an electron-beam lithography system that is specially designed for this purpose. To demonstrate the feasibility of this technique, ordinary-type Fresnel (zone-plate) lenses and a special-type lens for converting an incident Gaussian intensity distribution into a uniform one were designed and fabricated. It was found that these Fresnel (zone-plate) lenses have near-diffraction-limited performance. The fabrication technique and experimental results are discussed.

X‐ray lithography using a pulsed plasma source

Abstract: An imploding gas jet plasma has been developed as a soft x‐ray source for lithographic applications. The plasma is an efficient source of krypton L radiation, which closely matches the wavelength of tungsten anode electron bombardment sources. Resist exposures have been made to evaluate the suitability of the source and determine the filtering requirements necessary to protect the resist. COP resist required 20 shots for a proper exposure; no reciprocity failure was observed with these pulsed, high‐power exposures.

Application of ≊100 Å linewidth structures fabricated by shadowing techniques

Abstract: A variety of shadowing techniques have been developed for fabricating simple structures with lines and spaces in the 100 A linewidth regime. In the basic technique, a smooth vertical step with precisely determined depth is produced in a substrate by reactive ion etching. This step is shadowed at a shallow angle by evaporation in order to deposit material on the vertical wall. The substrate is then etched at normal incidence with an ion beam to remove the thin layer of material outside the step. This leaves a thin rectangular line of material at the step. By alternately evaporating different materials and by adding lithography and etching steps, more complex structures can be made. Applications of these structures in wire grating optical polarizers and the use of long thin wires for studying electron localization are described. Optical polarizers with extinction ratios of nearly 200 to 1 have been made. This demonstrates some of the unique capabilities of the shadowing technique since high quality polarize...

Exposure and development models used in electron beam lithography

Abstract: This review examines exposure and development models which are used in electron beam lithography to predict resist profiles. The following topics are discussed: development models of positive polymeric electron resists, in particular, poly‐methyl‐methacrylate; exposure models based on analytic or Monte Carlo calculations of energy dissipation; comparisons of experimental measurements of linewidth and profile shape and predictions based upon exposure and development models; the dependence of proximity effects on resist and substrate thickness, beam voltage, and substrate material; and finally algorithms used to alter the exposure or pattern shape or both to compensate for proximity effects. The understanding which is gained from the exposure and development models is discussed in terms of fabrication techniques used in electron beam lithography.

Device lithography by selective ion implantation

Abstract: A method is shown whereby implanted ions, for example indium or gallium ions, are used to selectively define a pattern on a material, typically a polymer. The implanted regions react with a plasma (for example, an oxygen plasma) to form a patterned, nonvolatile protective layer (e.g., indium oxide or gallium oxide) on the material. Subsequent etching, which can typically be accomplished by the same plasma, produces a negative tone pattern. Materials other than polymers can be utilized. For example, an indium implant in SiO2 allows direct pattern generation by exposure to a fluorine plasma, without the use of a separate polymeric resist.

Multilevel resist for lithography below 100 nm

Abstract: Features as small as 25 nm have been made with electron-beam lithography using multilevel resists on thick silicon substrates. Liftoff patterning of metal lines and reactive ion etching of silicon have demonstrated the possibility of making device structures with lateral dimensions below 100 nm.

Rotary printing presses with inplace laser impression of printing surface

Abstract: A rotary printing press includes a laser beam imaging device to enable a rotary printing member to be prepared while it is located in the printing press. This arrangement has particular advantages when it is used with a lithographic or a gravure printing press and especially when used as a proofing press for color lithography or color gravure.

Verification of a proximity effect correction program in electron‐beam lithography

Abstract: A new method for computing proximity effect corrections for submicron electron‐beam lithography is introduced It is based on a fast algorithm for shape partitioning to gain better control for resultant exposure intensity distribution across each shape in the pattern By careful investigation of the intrashape and the intershape proximity effects the program supplies a means of controlling the submicron pattern delineation Values for the parameters of the double Gaussian function used in the calculation of the dose variation factors are given for a variety of exposure conditions Results of the application of the program to delineation of submicrometer patterns in PMMA and AZ 1350 resist on silicon substrate are presented

Germanium selenide: A resist for low‐energy ion beam lithography

Abstract: A negative resist consisting of a layer of germanium selenide ∠1800 A thick with a surface layer of silver selenide ∠100 A thick was irradiated with 10 to 38 keV He, N, Ar, and Xe ions. While polymer resists require an incident ion to pass through the entire thickness of the resist film for exposure, germanium selenide films can be exposed with ions which penetrate only the ∠100 A thick silver selenide surface layer. Thus, germanium selenide is an attractive resist system for low energy focused ion beam lithography. Resist sensitivities of ∠1013 to 1015 ions/cm2 were measured. Both nuclear and electronic stopping contribute to exposing the resist. Submicron lines have been produced in germanium selenide with a 20 keV finely focused ion beam.

EL‐3: A high throughput, high resolution e‐beam lithography tool

Abstract: EL‐3 is IBM’s third generation of e‐beam lithography tools developed for the fabrication of semiconductor devices using direct write techniques. The system is designed to operate as a direct write manufacturing tool in a semiconductor factory. EL‐3 has a high throughput capability that is competitive with many optical lithography systems. The system has the capability to cover the lithography requirements at 1 μ and above. In addition, the tool can be operated as a highly effective mask maker. EL‐3 makes use of many of the state of the art techniques associated with electron beam system lithography. These techniques include (1) LEARN calibrated field scan, (2) high current, variable shaped spot, (3) dual channel deflection of large fields and of subfields, (4) high performance handling of large workpieces (6 1/2 in., 163 mm), and (5) Series/ 1 data handling, system control, and automatic operation EL‐3 can expose 30 4 in. (100 mm) wafers per hour at 1.5 μ lithography at 10 μC/cm2 current dose. Four EL‐3 t...

Gold transmission gratings with submicrometer periods and thicknesses ≳0.5 μm

Abstract: Gold gratings with spatial periods of 0.3 and 0.2 μm have been fabricated in thicknesses of 0.6 and 0.25 μm, respectively, and used in x‐ray spectroscopy and spatial‐period‐division. Fabrication techniques included: holographic lithography, shadowing, x‐ray lithography, and gold microplating. Control of linewidth to tolerance of the order of 10 nm has been demonstrated for gratings of 0.2 μm period. A high resolution imaging spectrometer, composed of a 22× Wolter x‐ray microscope in conjunction with a gold transmission grating, was tested. At a wavelength of 0.69 nm, a resolving power, λ/Δλ, of 200 was demonstrated. Resolution in this case was source‐size limited. Gratings of 99.5 nm period were exposed in PMMA by x‐ray (λ = 4.5 nm) spatial‐period‐division.

A multiple-electron-beam exposure system for high-throughput, direct-write submicrometer lithography

Abstract: Scanning-electron-beam lithography has not been generally accepted for the direct writing of patterns on wafers, primarily because of the time required for a single beam to scan a production-sized wafer (100 to 150 mm in diameter). This paper reports progress on a scheme for multiple-beam lithography using an immersion screen lens to overcome the time problem. In this approach, each die of the wafer has its own writing beam. All the beams are scanned and blanked in parallel so that identical patterns are written simultaneously over all dice. A laser interferometer stage under computer control enables dice of large area to be completely covered, despite limitations on the deflection amplitude of the beamlets. It is shown that a 1-min cycle time is practical using PBS resist. Preliminary results from an experimental machine based on these principles are given.

Masked ion‐beam lithography: A feasibility demonstration for submicrometer device fabrication

Abstract: Masked ion‐beam lithography (MIBL) is a high‐resolution pattern‐replication process that offers high throughput capability with submicrometer resolution. In MIBL, a collimated beam of protons is directed through a mask to expose a resist‐covered wafer in proximity to the mask. We report here on four key MIBL technology issues: (1) mask technology, (2) radiation‐damage effects, (3) resist materials, and (4) fabrication of NMOS devices using MIBL. We have established a process for fabricating thin (0.7 μm) silicon‐membrane masks with submicrometer e‐beam‐generated gold absorber patterns. We have evaluated mask‐induced beam scattering (<0.4° for channeled 175‐keV‐protons) and mask in‐plane thermal distortions (<0.1 μm over 1 cm2 for 0.1 W/cm2 beam power) which are the principle factors affecting resolution and throughput. Radiation‐damage effects were studied by simulating MIBL fabrication of MOS test chips. No statistically significant radiation effects were found after annealing at 450°C. We have demonstra...

Silicon-coupled Josephson junctions and super-Schottky diodes with coplanar electrodes

Abstract: Superconducting devices with coplanar electrodes have been fabricated using electron-beam lithography to define the smallest feature. The devices each consist of two Pb-In alloy electrodes, 20 µm wide, deposited on a clean, degenerately doped silicon substrate. The two electrodes are separated by a thin (100-300-nm) gap. Electron-beam lithography is used to define the gap, and sputter etching to remove the underlying alloy film. Depending on the width of the gap and the condition of the metal-semiconductor interface, these devices displayed either Josephson or super-Schottky diode behavior. The Josephson devices show a high degree of robustness and had I_{c}R products in the range 200-800 µV at 4.2 K. The super-Schottky diodes had current sensitivities S in the range 1000-1300 V-1when measured at 4.2 K.

Solid state: Fast electron-beam lithography: High blanking speeds may make this new system a serious challenger in producing submicrometer ICs

Abstract: Electron-beam lithography may become competitive with optical methods for making integrated circuits. The step that could make this possible is an electron-beam lithography system developed at Hewlett-Packard that is potentially many times faster than previous machines for making ICs through direct writing on wafers or generating high-precision masks. The Hewlett-Packard system has a beam spot-corresponding to the smallest pixel that can be written-with a diameter that can be varied from 0.5 to 0.25 μm.

Computer simulations of resist profiles in x‐ray lithography

Abstract: This paper presents a detailed study on computer simulations of resist profiles obtained in x‐ray lithography for exposures made either with synchrotron radiation or with an Al–Kα source. It is assumed, for purposes of the calculations, that the vacuum windows consist of kapton and that silicon is used as the mask material. The influence of edge shape and mask absorber thickness upon the resist structure is of special interest. The other parameters affecting resist profiles, such as Fresnel diffraction (especially in the case of semitransparent absorbers) and photoelectron range, are taken into consideration. In the case of the x‐ray tube, the penumbral blur caused by the finite dimensions of the source spot leads to an additional deterioration of the edge sharpness. For the calculations, the intensity distribution over the spot area was assumed to be uniform (with Gaussian‐shaped edges). The influence of the photoelectron range upon the resist profiles is calculated, using the simple depth‐dose relationship of Gruen. The calculated resist profiles are compared with typical experimental results.

Silicon transfer layer for multilayer resist systems

Abstract: Thin film silicon is found to be a desirable interlayer material for e‐beam lithography with multilayer resist systems. It is easily etched in CF4 plasma (Si/PMMA: 30/1) yet resists O2 reactive ion etch (Si/HPR: 1/300). It is sufficiently conductive to avoid charging effects, both during lithography and SEM inspection. High optical contrast aids in inspection. Monte Carlo calculations show that a 2.5 μm bottom layer of polymer can substantially alleviate the proximity effect, even with an 80 nm Si interlayer. Pattern transfer with less than 100 nm linewidth loss is demonstrated. Lines as narrow as 200 nm in 2 μm of Hunt positive resist were holographically produced.

Fabrication of x‐ray masks using anisotropic etching of (110) Si and shadowing techniques

Abstract: We describe a process for producing x‐ray masks of grating patterns with extremely smooth line edges. The technique developed by Flanders, in which a square‐wave profile relief grating in polyimide is obliquely shadowed with an x‐ray absorber, is followed, except that the original square‐wave structure is produced in (110) silicon by anisotropic chemical etching rather than in SiO2 by reactive ion etching. In this way, significant improvements in edge acuity are achieved because relief grating sidewalls are defined by atomic (111) planes. Holographic lithography is used to expose grating patterns in AZ 1350 over a thin Si3N4 layer on the (110) Si. The Si3N4 is patterned by reactive ion etching and serves as the mask for anisotropically etching the square‐wave‐profile grooves. At the proper crystallographic orientation the groove sidewalls are defined by (111) planes, and groove bottoms are approximately flat. The structure in Si is then transferred to polyimide which is obliquely shadowed and forms the x‐...

Linewidth control in projection lithography using a multilayer resist process

Abstract: Linewidth control using a tri-layer resist system on wafers with topography is investigated. An absorbing dye is incorporated in the bottom layer to improve the usable resolution. Resist patterns of 1-µm lines and spaces over aluminized topography are demonstrated using a projection aligner. The advantages of a multilayer system are investigated using an exposure and development simulation program for optical lithography. The relative contributions of planarization and reflection suppression are discussed.

Extremely low-noise MESFETs fabricated by metal-organic chemical vapour deposition

Abstract: Quarter-micron gate low-noise GaAs MESFETs have been developed by delineating gate electrodes by an electron-beam lithography technique and by using high-purity epiwafers prepared by a metal-organic-chemical vapour deposition (MOCVD) technique. At 18 GHz, a noise figure of 1.75 dB with an associated gain of 8.5 dB and a maximum available gain of 11 dB were obtained at drain currents of 10 mA and 30 mA, respectively. This is the lowest noise figure yet reported for low-noise GaAs MESFETs.

A high‐current, high speed electron beam lithography column

Abstract: The design of a high speed electron‐beam lithography column is described. Designed for use with a high speed raster scan system, the column produces a beam current of 600 nA in an 0.5 μm round spot, and has a deflection field of 5 mm2. The column uses a zirconiated thermal field emission cathode, two magnetic lenses, with an intermediate cross‐over for blanking purposes, and a two‐stage electrostatic deflection system, producing both speed and precision. The column is compatible with a 300 MHz pixel exposure rate and has an accuracy of better than ±0.125 μm (2σ).

Resolution, overlay, and field size for lithography systems

Abstract: Resolution, overlay, and field size limits for UV, X-ray, electron beam, and ion beam lithography are described. The following conclusions emerge in the discussion. 1) At 1-µm linewidth, contrast for optical projection can be higher than that for electron beam. 2) Optical cameras using mirror optics and deep UV radiation can potentially produce linewidths approaching 0.5 µm. 3) For the purpose of comparing the resolution of electron beam and optical exposure, it is useful to define the minimum linewidth as twice the linewidth at which the contrast of the exposure system has fallen to 30 percent. 4) X-ray lithography offers the highest contrast and resist aspect ratio for linewidths above about 0.1 µm, but for dimensions below 0.1 µm, highest aspect ratio is obtained with electron beam. 5) With electron beam exposure on a bulk sample, contrast for a 50-nm linewidth is the same as that for 1-µm linewidth, provided the resist is thin. Higher accelerating voltages make it easier to correct for proximity effects and to maintain resolution with thick resist. 6) Ultimately the range of secondary electrons limits resolution in electron beam lithography, just as the range of photoelectrons limits resolution in X-ray lithography. In both cases, minimum linewidth and spacing in dense patterns is about 20 nm. Resolution with ion beams will probably be about the same because the interaction range of the ions will be similar to the electrons.

Proximity effect correction in electron‐beam lithography

Abstract: Electron‐beam fabrication offers several important advantages for lithography, including a capability of geometries smaller than one micrometer, a high adaptability to automation and the ability to write directly on a Si wafer without the need for a mask. However, for submicron patterns, a proximity effect is observed by the behavior of incident electrons in a resist. In electron‐beam lithography the exposure intensity distribution (hereafter EID) is an essential physical quantity for implementing a proximity effect correction. There are many correction methods and several methods have been tried to correct for practical devices. However, the variation of the EID along the distance into the resist from the surface is neglected, and only a two‐dimensional EID is presented in those articles. The present paper describes experimental and theoretical study on a correction method of the proximity effect which contains the consideration of the three‐dimensional profile of a resist. It has been found from a Monte Carlo simulation that a cross‐sectional profile can be controlled by an additional exposure at the vicinity of a pattern edge. With this method, for example, an undercut resist pattern, which is suitable for a lift‐off process, can be obtained, avoiding as a whole the overdose on a pattern. A 0.5 μm line and space pattern with 1 μm thickness PMMA has been easily obtained, namely, when under‐developed, the wall profile of the resist becomes rather steep, and when properly developed, the profile becomes undercut.

A simple technique for modifying the profile of resist exposed by holographic lithography

Abstract: Holographic lithography is a rapid and convenient method of exposing low distortion periodic and quasi‐periodic patterns over large areas. Spatial periods below 0.2 μm are readily achieved using commercial He:Cd lasers. However, many substrates of interest have significant reflectivity and, because the phase change on reflection is close to π, an intensity minimum occurs at the resist–substrate interface, leading to rounded ’’overcut’’ resist profiles. Such profiles are unsuitable for liftoff and undesirable for anisotropic dry etching. Moreover, the linewidth‐to‐period ratio is difficult to control and exposure latitude is limited. If a dielectric film is placed over a reflecting substrate, the intensity at the resist–dielectric interface can be maximized by proper choice of the optical thickness of the dielectric. We have developed a simple, operational, nondestructive method for precisely determining the angles of laser incidence that correspond to the condition of maximum interface intensity. The meth...

Accelerated particle lithographic processing and articles so produced

Abstract: Ion beam lithography of particular interest in the fabrication of large-scale integrated circuits of unexpectedly increased throughput results from appropriate choice of (a) resist material and (b) ion species. Resist material, generally negative acting, is characterized by electron beam sensitivity inadequate for ordinary commercial electron beam lithography. The relevant characteristic responsible for inadequate electron beam sensitivity is the very characteristic responsible for enhanced ion sensitivity. Ion species, always of atomic number greater than that of proton, are dictated by the observation that sensitivity unexpectedly increases at a greater rate than predictable on traditional bases.

Principles of Optical Lithography

Abstract: Publisher Summary This chapter presents the principles of optical lithography During the process of micro fabrication, fine-line stencil masks are formed using thin photosensitive polymers, called photo resists or resists, which selectively protect an underlying wafer substrate against chemical or physical attack Optical lithography, as the name implies, refers to a means for patterning the resist using actinic radiation in the optical region of the electromagnetic spectrum The information to be replicated is delineated on a thin optically opaque layer supported by a transparent substrate This pattern, called a mask, is transferred or imaged by a lithographic exposure system to form an aerial image, which consists of a spatially dependent light intensity pattern in the vicinity of the wafer The extension of optical lithography to the sub-micrometer realm will require two major developments From the standpoint of the resist, it will require higher-γ systems that can be used at shorter wavelengths From the standpoint of the exposure equipment, it will require small-field systems capable of exposing in the deep UV with a high degree of partial coherence The need for partial coherence will call for very tight manufacturing tolerances to reduce the phase-related aberrations that occur with coherent light and more intense illumination sources to maintain throughput

Electron-beam lithography for small MOSFET's

Abstract: Electron-beam lithography with a novel multilevel resist structure together with two-dimensional process and device modeling and dry processing with reactive sputter etching have been employed to produce silicon-gate NMOS devices with micrometer and submicrometer channel lengths. Results for transistors and ring oscillators are reported.

Vacuum lithography—A completely dry lithography using plasma processing

Abstract: The purpose of this paper is to describe a thoroughly dry lithography using plasma polymerization and plasma etching. The new lithography is named vacuum lithography because all processes are performed at reduced pressures. Resist films were formed in bell-jar-type and argon-flow-type reactors. The controllability of plasma polymerization is discussed with respect to the type of reactor and gas mixture. A pattern was delineated in the resist using an electron beam, and it was developed by plasma etching with a mixture of argon and oxygen. It was found that the quality of the plasma-polymerized resist depends strongly on the polymer structure and on the plasma etching conditions. In this experiment, the recorded values of sensitivity and γ value of plasma-polymerized methyl methacrylate were 700 µC/cm2 and 1, respectively.

X-Ray lithography source tube

Abstract: A composite target cone for use in an X-ray lithography source tube. The composite target cone is multi-layered, having at least an X-ray generating layer formed of platinum, silver, palladium, rhodium, molybdenum, tungsten, silicon, aluminum or copper, and a water-interface layer. The water-interface layer includes a layer of high thermal conductivity material, covered at one side by a layer of high corrosion resistance material and at the other side by a layer of high-melting point material.