Showing papers on "Lithography published in 1988"

X‐ray lithography

Abstract: X‐ray lithography with wavelengths between 0.2 and 5 nm provides both high‐structural resolution as good as 0.1 μm and a wide scope of advantages for the application in circuit production. Examples for this better process performance compared to optical techniques are: lower particle and dust sensitivity, applicability of simple single‐layer resist technique, high depth of focus without any influence of substrate material and chip topography, and presumably, the highest throughput of all lithography methods which are able to go into the submicron range. However, the introduction of x‐ray lithography into the semiconductor production means a revolutionary change of production technology. This begins with a completely different mask technology which makes, for example, the classical separation of mask substrate fabrication from pattern generation by different manufacturers very problematical and ends with the necessity to introduce x‐ray lithography in relatively large production capacity units consisting of a larger number of x‐ray steppers. The latter is caused by the fact that a storage ring—even in the smallest version, e.g., COSY (Kompakt Speicherring fur Synchrotronstrahlung)—has to supply up to 10 x‐ray steppers with light in order to clearly beat the optical techniques with respect to throughput and lower cost level. To prove such statements in pilot production lines, the necessary tools and components for x‐ray lithography are already or will be available for the first time on a commercial basis in the very near future. Especially steppers, sources, and resists with satisfying specifications have been announced by a growing number of vendors. The most critical problem at present is the mask technology and the tools for defect elimination. However, with the existing technologies, the requirements for 0.5‐μm‐design rules will be met very soon on a pilot scale.

Soft x‐ray projection lithography using an x‐ray reduction camera

Abstract: Soft x‐ray projection lithography can now be realized with recent developments in x‐ray optics. Using new x‐ray optical components and spherical imaging optics, we have designed an x‐ray reduction camera which is capable of projecting with soft x‐ray radiation, a 5× demagnified image of a mask onto a resist coated wafer. The resolution of this design is ∼100 nm with a depth of focus of ±5.6 μm and a 0.5‐cm‐diam image field. We use x‐ray reflecting masks (patterned x‐ray multilayer mirrors) which are fabricated on thick substrates and can be made relatively distortion free. Our design uses a laser produced plasma for the x‐ray source. Better resolution and/or larger areas are possible with improvements in optic figures and source characteristics.

Lift‐off metallization using poly(methyl methacrylate) exposed with a scanning tunneling microscope

Abstract: The scanning tunneling microscope (STM) is a unique tool for ultrahigh resolution, ultralow voltage electron beam lithography. In a previous paper we described the formation of metallic patterns by a ‘‘contamination’’ process followed by sputter etching. Here we report the formation of 22‐nm‐wide metal lines by STM exposure of poly(methyl methacrylate) (PMMA) resist followed by liftoff. Resist exposure and liftoff have also been achieved with reverse polarity, where the electrons are emitted from the resist sample and accelerated towards the tip. Results include the first working device made with a STM, a thin‐film resistor 2 μ long and 120 nm in width. In addition to lithographic applications, studying resists in this regime may offer new insights on the chemical process of resist exposure and the role played by secondary electrons in exposing resist. Our results indicate that PMMA only works as a negative resist for energies above 25 eV; below this value it appears that the electrons cannot cause suffic...

Plasma focus x‐ray source for lithography

Abstract: A bright and reliable x‐ray source for lithography has been developed using plasma focus. Discharge with constant pressure gas, one of the features of plasma focus, makes the x‐ray source system simple and lengthens lifetime. A fine ceramic insulator made of alumina in place of a conventional Pyrex glass insulator improves system reliability. The system operates for more than 105 discharges without maintenance. The lifetime of the system is ten times longer than that of a conventional plasma focus device. The resolution of a pattern printed by multishot exposure depends not only on the diameter of pinched plasma but also on the variation of source position. A new spherical electrode surrounding the plasma‐focusing space is added to stabilize the location of the spot on the axis by eddy currents which exert the Lorentz force on the plasma. The spot position deviation has become negligibly small as compared with the pinched plasma diameter. The x‐ray source size for neon is 1 mm in diameter and 10 mm in len...

Deep-submicrometer MOS device fabrication using a photoresist-ashing technique

Abstract: A photoresist-ashing process has been developed which, when used in conjunction with conventional g-line optical lithography, permits the controlled definition of deep-submicrometer features. The ultrafine lines were obtained by calibrated ashing of the lithographically defined features in oxygen plasma. The technique has been successfully used to fabricate MOSFETs with effective channel length as small as 0.15 mu m that show excellent characteristics. An NMOS ring oscillator with 0.2- mu m devices has been fabricated with a room-temperature propagation delay of 22 ps/stage. Studies indicate that the thinning is both reproducible and uniform so that it should be usable in circuit as well as device fabrication. Since most polymer-based resist materials are etchable with an oxygen plasma, the basic technique could be extended to supplement other lithographic processes, including e-beam and X-ray processes, for fabricating both silicon and nonsilicon devices and circuits. >

A review of excimer laser projection lithography

Abstract: Excimer‐laser projection lithography now appears to be in a position to extend production optical techniques to dimensions approaching 0.25 μm. Such methods could well be the basis for the bulk of the advanced manufacturing capability in microelectronics over the next decade. This technology is reviewed with an eye to the state of the art and to the optical‐, resist‐, and materials‐engineering issues that it presents.

LIGA process: sensor construction techniques via X-ray lithography

Abstract: The LIGA (from the German Lithographie, Galvanoformung, Abformung) method, based on deep-etch X-ray lithography, electroforming and molding processes, is described. This microfabrication technique makes it possible to generate devices with minimal lateral dimensions in the micrometer range and structural heights of several hundred micrometers from metallic and plastic materials. In contrast to orientation-dependent etching of monocrystalline silicon, there are no restrictions on the cross-sectional shape of the microstructures. Various concepts of sensors for measuring vibration, acceleration, position, spectral distribution, radiation, composition of mixtures, etc. are presented. >

Laser plasma x‐ray sources for microlithography

Abstract: A plasma produced by laser irradiation of solid targets is a promising candidate as an efficient x‐ray lithography source. In order to design a practical laser created x‐ray source, it is necessary to study the factors affecting the x‐ray emission. For this purpose, we investigate both theoretically and experimentally the influence of the laser target parameters on the x‐ray emission in different spectral ranges for two laser wavelengths (λ=1.06 μm, λ=0.26 μm). From these results and considering mask transmission, resist sensitivities, and wafer throughput, we establish the characteristics of the laser required as an x‐ray lithography source with performance acceptable for industrial applications.

Requirements on resist layers in deep‐etch synchrotron radiation lithography

Abstract: To fabricate microstructures with heights of several hundred micrometers and great aspect ratios by the LIGA (German acronym for LIthographie, Galvanoformung, Abformtechnik) process thick poly(methylmethacrylate) (PMMA) resist layers are produced on a metallic base plate. The requirements these resist layers must fulfill are reported. It is shown that it is possible to achieve defect‐free structuring with high accuracy using cross‐linked PMMA with little content of residual monomer. Good adherence of microstructures with extremely small diameters, even on polished surfaces, is achieved by using an internal coupling agent which establishes a chemical bond between the substrate surface and the PMMA layer. By modifying the resist composition requirements dependent on product specifications can be fulfilled.

Progress in deep‐etch synchrotron radiation lithography

Abstract: The recent progress in the development of the lithographic processes within the LIGA technique is reported, which is based on deep‐etch synchrotron radiation lithography, electroforming, and molding processes (in German: lithografie, galvanoformung, abformung). Mask blanks for high‐contrast x‐ray masks for 0.2 nm wavelength are fabricated from titanium and beryllium membranes produced by physical vapor deposition techniques. Absorber patterns on these masks can be produced by 50‐keV electron‐beam pattern generation in 3–5‐μm‐thick polymethylmethacrylate (PMMA) resists, because the use of beryllium strongly reduces the otherwise marked influence of electrons backscattered from the substrates on the resist profiles. To comply with the requirements of deep‐etch lithography cross‐linked PMMA resists and suitable multicomponent developers have been formulated. The casting resin‐based resists are polymerized directly on the substrate which results in extremely low internal stresses to prevent stress corrosion of the resist structure during development.

Understanding Focus Effects In Submicron Optical Lithography

Abstract: In the age of submicron optical lithography, focus has become a critical process parameter. Each decrease in minimum feature size is accompanied by a corresponding decrease in depth-of-focus (DOF). Sources of focus errors, such as wafer warpage, topography, and the thickness of the photoresist, however, are not being reduced in proportion to the DOF. Thus, the effects of focus on the practical resolution capabilities of a lithographic tool are becoming increasingly important.

Proposal for a new submicron dimension reference for an electron beam metrology system

Abstract: A new submicron level reference for an electron beam metrology system is proposed. This reference is a fine rectangular‐profile diffraction grating fabricated by laser interferometer lithography and anisotropic chemical etching of (110) crystalline silicon. The pitch size of the grating is derived from the wavelength of the laser and the angle of incidence of the holographic lithography. The optical diffraction measurement absolutely assures accurate grating pitch size. The measurement error is estimated to be smaller than 0.001 μm. A deep lamellar grating fabricated by anisotropic chemical etching of (110)Si generates a stable and high‐contrast secondary electron signal in an electron beam metrology system. Reference pitch size measurement by optical diffraction and by the electron beam metrology system assures that the pitch size error is smaller than 0.02 μm.

High-resolution focused ion beam lithography

Abstract: The resolution of focused ion beam (FIB) lithography has been studied by proximity effect measurement and fine pattern fabrication. In the proximity effect measurement, a 0.1 μm line pattern, according to the gap between square and line patterns, could be achieved. Moreover, 0.1 μm line and space poly(methylmethacrylate) patterns and 0.1 μm linewidth novolak based negative resist could be fabricated at 1×1013 and 2×1012 ions/cm2 dose by 260 keV Be++ FIB with 0.1 μm beam diameter, respectively.

Manufacture of semiconductor device

Abstract: PURPOSE:To obtain interconnection layers for a Schottky barrier diode which are so smoothened that they are hardly disconnected while shortening a period of time required for producing such interconnection layers by reducing a number of lithography processes and opening a plurality of contact holes simultaneously. CONSTITUTION:An insulating film 2, an N type conducting layer 4, a P type conducting layer 5 and a field insulating film 3 are formed on a lowly doped N-type silicon substrate 1. The film 3 between the layers 4 and 5 is removed by lithography and contact holes 7a and 7b are opened simultaneously. The surface of the film 3 on the side faces of the holes 7a, 7b is smoothened by heat treatment at a high temperature. Then, a polycrystalline silicon film 6 and a nitride film 8 are formed and the film 8 located on a Schottky barrier diode region is removed by lithography. The layer 6 is then oxidized by heat oxidation to form an oxide film 11. The oxide film 11 is then etched off so that the surface of the substrate 1 is exposed. The film 8 is also removed and Al interconnection layers 9 are formed. ln this manner, the contact holes can be opened simultaneously prior to formation of the layer 6 by a reduced number of lithography processes, namely two lithography processes. Further, since the side walls of the contact holes are smoothened, the interconnection layers which are hardly disconnected can be obtained in a short-period of time.

Achromatic holographic lithography in the deep ultraviolet

Abstract: Holographic lithography, in which the interference pattern of two coherent waves is used to expose a resist film, is the preferred technique for producing large‐area gratings with low distortion. The spatial period of a pattern produced by holographic lithography is directly proportional to the wavelength of the radiation and inversely proportional to the sine of one‐half the angle between the incoming beams. To expose gratings with periods ≊100 nm (50‐nm‐nominal linewidth) the source wavelength must be ≊200 nm. Since coherent deep‐ultraviolet sources are not readily available, we have investigated an achromatic holographic configuration which permits the use of incoherent sources (e.g., CdXe arc lamp) or short‐coherence‐length (≊10 μm) excimer lasers. The configuration consists of two gratings, one acting as a beamsplitter, the other as a recombiner. The beam from the source is split into plus and minus first‐order beams by the beamsplitter grating, and the zero order is subsequently blocked. The plus an...

Image Quality Enhancements For Raster Scan Lithography

Abstract: Raster scan lithography systems, such as scanned-laser and most E-beam mask writers, produce images through a mosaic of discrete picture elements (pixels). Image qualities of the printed mask (or wafer) are governed by the interplay of several printing variables, including size and shape of the writing spot, pitch and orientation of the pixel grid, relative intensities of pixels, and exposure characteristics of the resist. We will review the theoretical foundations of raster imaging and show how these variables affect several key measures of lithographic image quality, including minimum feature size, edge placement resolution and accuracy, dimensional uniformity, and edge roughness. We will present three quality enhancement techniques and compare their performances to that provided by a basic raster printing scheme where pixels of binary (on or off) values are printed on a cartesian grid. The first technique involves rotating the printing grid 45 degrees to the main axis of the data coordinate system. We will demonstrate that, for lithographic images where most edges are parallel to the data axes, this grid provides 41% more addressable edge positions than a non-rotated grid with the same pixel density. The second technique, adapted from computer-graphics "antialiasing" applications, involves modulating the intensity of pixels along the edges of features to finely control the shape of the aerial image. This provides a vernier mechanism for the placement of exposed edges between grid locations and results in finer effective addressability and smoother edges. Third, we will review how multiple pass printing (a.k.a. vote-taking) reduces random errors, and show how it also reduces systematic errors when certain printing parameters are alternated between passes. Finally, we will present a single printing strategy in which all three techniques are combined to yield high accuracy, high-resolution images with economic use of printing pixels.

Method of forming an ink image and printing the formed image

Abstract: The present invention provides a method of forming an ink image with a thermo-sensitive ink by using a printing plate that is used in dry lithographic printing, and printing the ink image onto an object. An ink remover is placed via a thermo-sensitive ink layer that is in a heated state on a printing surface of a printing plate having a part receptive to ink and a part capable of repelling ink. The printing plate and the ink remover are separated after they are cooled so that the ink layer on the part capable of repelling ink is transferred to the ink remover. The ink image obtained on the printing plate or the ink remover is transferred to an object. According to this method, printing that does not require maintenance that has been essential to conventional dry lithographic printing becomes possible.

Method and apparatus for low-energy scanning electron beam lithography

Abstract: An electron sensitive surface is patternized treated to a high resolution pattern of low-energy electrons without any need to do focussing by emitting the low-energy electrons from a pointed electrode and positioning the apex of the pointed electron emitting source suitably close to the surface being treated.

Quantitative analysis of resolution and stability in nanometer electron beam lithography

Abstract: A technique for the measurement of the beam diameter and the positional stability of an electron beam with respect to the substrate using an anisotropically etched silicon edge is described. Measurements are done either in a scanning beam mode to measure the beam diameter or in a stationary beam mode to measure beam positional noise. This technique has been used for a quantitative analysis of the resolution and stability in a 8‐nm spot size electron beam lithography system. The detection limit of the beam position stability measurements is <0.1 nm. Applications for the measurement of mechanical vibrations and acoustical noise, deflection amplifier noise, magnetic interference, and eddy currents in magnetic deflection systems are discussed.

X-ray lithography with a Ag-Se/Ge-Se inorganic resist using synchrotron radiation

Abstract: A Ag‐Se/Ge‐Se inorganic resist is applied in x‐ray lithography using synchrotron radiation (SR). Usable sensitivity of 0.3–3 times that of a polymethylmethacrylate (PMMA) resist and high contrast (γ∼3.5) are obtained through SR exposures. By utilizing the fringes of masked SR flux caused by Fresnel diffraction, 500‐A‐wide fine lines are formed by using x rays of 2–10 A in wavelength. It is determined that a high‐density resist, such as a Ag‐Se/Ge‐Se inorganic resist, is favorable for forming micropatterns using x rays because of the short ranges of the electrons generated by the x rays in the resist.

Quantitative evaluation of shape of image on photoresist of square apertures

Abstract: Simulation of images of two-dimensional structures in optical lithography is considered to have become quite important with the patterning of near-micrometer geometries in complex structures encountered in VLSI. Here, the results are presented of theoretical computations performed to calculate the aerial image of square apertures in a projection system using a partially coherent light source. The resist has been modeled by its sensitivity curve in order to compute the image profile on the resist after development. A figure of merit (FOM) has been proposed that quantifies the shape of the aerial as well as the resist image. Such an FOM has been proposed that can be used very effectively to optimize a lithographic process. >

Ultrathin semiconductor layer masks for high vacuum focused Ga ion beam lithography

Abstract: The application of thin semiconductor layers as etch masks for high vacuum lithography is described. Heteroepitaxial layers of In0.53Ga0.47As or InP, as thin as 30 A, were grown by molecular beam epitaxy and patterned using a focused beam of Ga ions. The Ga ion beam exposure is very rapid, since only a small amount of the mask material needs to be removed, and readily produces features with submicron sizes. The patterned thin layer can then be used as a mask for deep, material selective etching. The feasibility of selective dry etching of InP based compounds is discussed. This combination of molecular beam epitaxy and efficient precision patterning techniques is expected to result in a new flexibility in design and fabrication of semiconductor devices.

Creating And Observing Surface Features With A Scanning Tunneling Microscope

Abstract: Scanning Tunneling Microscopy (STM) can be used to perform lithography on a surface and to image the results of lithography performed using other techniques. We have imaged a 1 nm structure created with the STM on graphite, a 300 nm structure electrodeposited with the STM on gold, and a gold diffraction grating created using a diamond scribe. In addition we present atomic resolution images of graphite showing a surface reconstruction.

Nanometer lithography for III–V semiconductor wires using chloromethylated poly‐α‐methylstyrene resist

Abstract: Chloromethylated poly‐α‐methylstyrene negative resist was investigated for its suitability in the fabrication of nanometer structures for optical studies. Investigating the photoluminescence efficiency of etched GaAs/AlGaAs wires we find a steep decrease with decreasing wire width, whereas for InGaAs/InP the decrease is much smaller. The difference in the behavior of the material systems can be explained by the effectiveness of surface recombination.

Understanding Focus Effects In Submicrometer Optical Lithography

Abstract: A new approach for characterizing resolution and depth of focus (DOF) in optical microlithography is introduced. By examination of the interaction of the aerial image with the photoresist process, a metric of image quality is defined. The variation of this metric with feature size and defocus can be used to measure the resolution and DOF. The effects of various imaging parameters on DOF can then be determined. To further study focus effects in submicrometer imaging, the lithography simulation program PROLITH (the positive resist optical lithography model) is modi­ fied to account for defocus within the photoresist film. Subject terms: microlithography; depth of focus; resolution; lithography simula­ tion.

Method for sloping the profile of an opening in resist

Abstract: A lithography method for forming an opening in a resist layer with a sloped profile is disclosed which requires no additional processing steps or equipment. A scattering element, for example a ground glass diffuser, is placed in the optical path of radiation passing through a standard lithography apparatus. The scattering element modifies the radiation passing through the lithography apparatus with the result that the developed resist profile exhibits sloped edges. The slope modification can be conveniently changed by exchanging the optical scattering element used.

Dot lithography for zero-dimensional quantum wells using focused ion beams

Abstract: A 50‐keV focused Ga+ beam formed in a two‐lens microprobe column with prefinal lens deflection was used to expose dot arrays in a negative‐acting bilevel resist. Dot arrays 600×600 μm with 600‐A‐diam resist posts on 0.6‐μm centers (incorporating 1024×1024 dots) were fabricated with ion exposure times of 18 s (beam dwell times of 16 μs/post). By reducing the beam dwell time by a factor of 2, roughly 300‐A‐diam posts were fabricated. Since the ions stop in the bottom resist layer and do not enter the substrate, the optical properties of underlying material should not be altered by damage from the exposure process.

Soft X-ray dosimetry and its application on the lithography beamline at SSRL

Abstract: We describe simple methods of soft X-ray dosimetry (1000–3000 eV) for synchrotron based X-ray lithography. These methods are generally applicable to other synchrotron installations and possibly to so-called “stand alone” X-ray sources. A double crystal monochromator of synthetic multilayer crystals was used to obtain narrow band X-rays for energy-dependent measurements. The quantum efficiency of a stainless steel vacuum photocathode is shown to be well modeled by a simple power law, and its use in measuring the quantum efficiency of semiconductor diodes is described. The photocathode modeling is used in conjunction with the monochromator to demonstrate that resist sensitivity depends uniquely on absorbed dose density. The validity of the modeling is discussed, and the limitations of each type of detector are outlined. Suggestions are made for the application of these inexpensive detectors to real time source calibration in practical X-ray lithography equipment.

Nanowriter: A new high‐voltage electron beam lithography system for nanometer‐scale fabrication

Abstract: A new high‐voltage electron beam lithography system, Nanowriter, has been designed and constructed to give a large scan field size without compromising the ability to write nanometer‐scale structures. Nanowriter comprises a 100‐kV LaB6 electron gun with a zoom condenser arrangement consisting of two condenser lenses which are used to provide a system demagnification of up to 10 000 times. To combine a very small on‐axis spot diameter of 4 nm and a large scanned field of 250×250 μm without dynamic correction, a newly developed swinging objective immersion lens (SOIL) concept based on variable axis immersion lens (VAIL) and swinging objective lens (SOL) has been utilized. The SOIL used here has four advantages: first, it is possible to reduce the working distance, thereby decreasing spherical aberration; second, the scanned field is increased without significantly increasing deflection aberrations; third, it permits easy alignment of the column, and fourth, an inherent attribute of the SOIL is the shielding...