Showing papers on "Lithography published in 1991"

Lithography system employing a solid immersion lens

Abstract: A lithography system employing a solid immersion lens having a spherical surface to enhance its resolution is disclosed

Efficient optical elements to generate intensity weighted spot arrays: design and fabrication

Abstract: We report on the design and fabrication of fully 2-D surface relief diffraction elements that can split a single collimated beam into many beams in an arbitrary intensity distribution. These splitters were designed by computer using simulated annealing, and made into phase gratings by electron-beam lithography followed by plasma etching into quartz glass. Both two and four phase level gratings have been fabricated, allowing a wide range of uniform and weighted spot patterns to be generated. These grating elements have a measured diffraction efficiency of over 74%, with the beam intensity ratios accurate to within 1% of their target values.

Resolution limits of optical lithography

Abstract: The development of optical lithography has promoted the development of ultralarge scale integration (ULSI) devices. However, optical lithography is now facing serious obstacles due to the limitations in wavelength. Higher resolution with sufficient depth of focus is the most important requirement for ULSI engineers. To satisfy this requirement, many technologies for resolution improvement and new optical image formation technologies such as phase shifting and focus latitude enhancement exposure (FLEX) are reviewed, and a future perspective on optical lithography is also discussed in this paper.

Three-dimensional microfabrication using synchrotron radiation

Abstract: For fabricating microstructures with extreme structural heights a technology has been developed which is based on deep-etch lithography and subsequent replication processes. A particularly high precision is achieved when the lithographic process is carried out by means of synchrotron radiation. Electroforming and molding processes are used for the replication of microstructures from a large variety of materials. The field of application comprises sensors, electrical and optical microconnectors, components for fluid technology, micromechanical components, microfiltration systems and novel composite materials.

Fabrication of assembled micromechanical components via deep X-ray lithography

Abstract: A variant of deep X-ray lithography, the LIGA process, is described. The fundamental processing sequence has been augmented with a locally defined sacrificial polyimide layer. This requires alignment of the X-ray mask to the optically defined sacrificial pattern via specially developed align-and-clamping jigs. The end results of this process are either fully unsupported metal structures or components which are locally attached to the substrate. Attempts to use this type of processing to produce assembled devices have been successful. Thus, free gears and fully attached shafts have been connected to form a nickel gear box. More complex assembly experiments have been completed successfully and are encouraging enough to pursue this approach further. >

Silicon tip field emission cathode arrays and fabrication thereof

Abstract: Through a silicon fabrication process, an emitter tip array is produced by electron beam or other suitable submicrometer scale lithography for precise location of the emitters. The emitter tips are formed by an oxidation process which ensures accurate and precise formation of tips having uniform radii. The process also utilizes the oxidation step to precisely align gate electrode apertures with respect to corresponding emitter tips so that large arrays can be formed with great accuracy and reliability.

Spatial filtering for depth of focus and resolution enhancement in optical lithography

Abstract: Spatial filtering at the lens pupil can achieve amplitude superposition for multiple images along the light axis and phase control between them. This enhances depth of focus while maintaining high resolution capability in optical lithography. Compared to conventional methods, three times larger depth of focus is expected for hole patterns with 20% improved resolution limit. For general pattern features, a 1.5–1.7 times larger depth of focus is expected at Rayleigh’s resolution limit.

Multiphase printing for E-beam lithography

Abstract: A method for a raster scan particle or light beam lithography system for writing in multiple passes interleaved in such a manner as to achieve a composite result nearly identical to normal single pass raster scan writing with overlapped spots. Multiple pass writing, achieved with little or no degradation or throughput or lithography quality, provides an ideal platform for implementation of known image averaging techniques to improve lithography quality. This technique is combined with the known writing technique of "Virtual Addressing" to improve resolution with little or no degradation of throughput.

Projection electron-beam lithography: A new approach

Abstract: Projection electron‐beam lithography is potentially one of the most attractive techniques available. It offers high resolution, high throughput, and good overlay and registration characteristics. In this paper we discuss some new approaches which seem to offer solutions to problems associated with earlier systems.

Phase-shift mask pattern accuracy requirements and inspection technology

Abstract: Computer simulations and i-line phase shift lithography experiments with programmed 5X phase shift reticle defects were used to investigate the effect of opaque and phase-shift layer defects on sub-half-micron lines. Both the simulations and the experiments show that defects in the phase shift layer print larger than corresponding opaque defects, with 0.3-0.4 micrometers defects affecting sub-half-micron critical dimensions by more than the allowable 10%. Inspection of programmed phase shift defects with a prototype mask inspection system confirmed that the system finds the 0.3-0.4 micrometers phase shift defects critical to sub-half-micron lithography.

Detection and printability of shifter defects in phase-shifting masks

Abstract: Because of the high printability of shifter defects in phase-shifting masks, it is worthwhile to characterize the inspection and printing of the shifter defects. The detectability and printability of shifter defects as a function of size and location have been investigated by experiments and simulation. A test mask with various programmed shifter defects was inspected by means of a die-to-die inspection system and printed in positive resist with an i-line stepper. Corner defects are difficult to detect and have low printability. A defect located in small features has high printability. We have also investigated the detectability and printability of the phase angle defects which have phase angles other than 180°. Defects with 120° to 180° phase angles have high printability. Defects with phase angles below 90° are not printed.

Method and apparatus for fabrication of thin film semiconductor devices using non-planar, exposure beam lithography

Abstract: An apparatus and method for the nonplanar treatment of a volumetric workpiece or substrate utilizing exposure beam lithography are disclosed. The method includes supplying one or more layers of one or more semiconductor materials to surfaces of the substrate, applying a resist over the semiconductor layers, setting the resist, and then directing an exposure beam, such as an electron beam, toward the substrate. The substrate is then moved in at least two degrees freedom of movement, relative to the beam, with one degree of freedom of movement being the rotating of the substrate about an axis generally perpendicular to the beam. The other degree of freedom of movement could be moving the substrate linearly in a direction generally parallel to the axis. By such movement, the resist is exposed to the beam in a predetermined pattern. The exposed resist is then developed and a layer or layers under the exposed resist are etched. The remaining resist is then removed yielding the desired semiconductor device.

Use of a kumakhov lens for x-ray lithography

Abstract: An X-ray lithography device which utilizes a Kumakhov lens is disclosed. This device is capable of using both small area sources and synchrotron sources. This device provides improved X-ray control, precision and accuracy. Also provided is a method of X-ray lithograph which incorporates a Kumakhov lens.

Chromeless phase-shifted masks: a new approach to phase-shifting masks

Abstract: This paper introduces a novel concept, 'chromeless phase-shifting', that eliminates the need for the use of chrome to form patterns in optical lithography. Chromeless phase-shifting uses 180 degree(s) phase-shifters on transparent glass to define patterns. The method relies ont eh destructive interference between phase-shifters and clear areas at the edges of the phase-shifters to define dark or opaque areas on the mask. Gratings sufficiently small will produce sufficient interference to completely inhibit the transmission of light (these gratings are thus named dark-field gratings). The combination of these effects makes is possible to form a wide range of patterns, from line-space patterns to isolated bright or dark areas. In this study, the lithography simulators SPLAT and SAMPLE were used to understand the principles behind this new scheme, and to verify various pattern designs. Simulation and experimental results are presented to demonstrate the concept.

Sub‐30 nm lithography in a negative electron beam resist with a vacuum scanning tunneling microscope

Abstract: We report studies of minimum feature sizes in 50 nm films of the high‐resolution negative electron beam resist, SAL‐601‐ER7 from the Shipley Corporation. Developed linewidths of 27 nm and line spacing of 55 nm, from center to center, were produced by lithography with a vacuum scanning tunneling microscope (STM). In contrast, a minimum linewidth of 95 nm was obtained from exposure with a 17 nm (1/e diameter) 50 kV electron beam. Patterns written in the STM at electron energies down to 15 eV were visible in the developed resist. The limit at 15 eV is related to the operation of the STM and does not represent an exposure threshold energy for the resist.

Fabrication of a planar grating spectrograph by deep-etch lithography with synchrotron radiation

Abstract: A three-layer resist system has been developed which can be used for light guiding. By structuring these layers with deep-etch X-ray lithography, high-precision multimode lightguide components with a relatively low attenuation can be produced. As a first example, a planar grating spectrograph with a self-focusing reflection grating has been fabricated together with fibre-fixing grooves. The spectro-graph shows an excellent dispersion of the light as well as a low cross-talk between the channels.

Three-dimensional resist process simulator PEACE (photo and electron beam lithography analyzing computer engineering system)

Abstract: A three-dimensional topographical simulator PEACE (photo and electron beam lithography analyzing computer engineering system) is discussed One of the difficulties in resist topographical simulation exists due to the three-dimensional resist development algorithm An algorithm based on the cell removal model provides accurate and stable results for the three-dimensional resist development process The program has been adapted to a supercomputer for quick computation The simulator can successfully perform the three-dimensional development in an absolutely stable manner, and good agreement can be obtained with experiments for both photo and electron beam lithography >

Handbook of VLSI microlithography : principles, technology, and applications

Abstract: Issues and Trends Affecting Lithography Tool Selection Strategy Resist Technology u Design, Processing, and Applications Lithography Process Monitoring and Defect Detection Techniques and Tools for Photo Metrology Techniques and Tools for Optical Lithography Microlithography Tool Automation Electron-Beam ULSI Applications Rational Vibration and Structural Dynamics for Lithographic Tool Installations Applications of Ion Microbeams Lithography and Direct Processing X-Ray Lithography Part I Part II Acknowledgment References Index

A new approach to high fidelity e‐beam and ion‐beam lithography based on an in situ global‐fiducial grid

Abstract: The distortion‐free scan field of an electron‐beam or ion‐beam lithography system is generally quite small (∼104×104 beam addresses) and hence to achieve pattern fidelity over large areas laser‐interferometer‐controlled stages are employed. Because the laser interferometer monitors the stage, not the electron or ion beam, beam drift of thermal, mechanical, electrostatic, magnetic, or electronic origin is not accounted for, leading to pattern placement error. To overcome this fundamental problem of ‘‘dead reckoning’’ we propose a new approach in which a global‐fiducial reference grid, which does not disturb the writing process, is put directly on the substrate. The grid is scanned with sufficiently low areal dose that the subsequent pattern development is not adversely affected. This can be achieved by ‘‘sparse sampling’’ of the grid over the entire scan field in conjunction with phase‐locking technqiues in the time domain. In this way one can spatially phase lock the two grids together and thereby ensure ...

Mask fabrication for projection electron-beam lithography incorporating the SCALPEL technique

Abstract: The choice of mask materials and fabrication route for a projection electron‐beam lithography system is subject to a variety of constraints. Some are encountered in most lithographic techniques, while some are unique to the scattering with regular limitation for projection electron lithography SCALPEL technique. We have developed methods for analyzing the performance of potential mask materials and constructions. These have been used to determine the composition of a prototype mask. Results from such a mask are presented.

Mechanistic investigations of nanometer-scale lithography at liquid-covered graphite surfaces

Abstract: Recently, atomic and molecular scale features have been produced on surfaces using scanning tunneling microscopy (STM) methods.‘-’ At room temperature, the smallest permanent lithographic process reported to date involves the formation of -4O-A-diam, =:3-A-deep pits on a highly ordered pyrolytic graphite (HOPG) surface.’ These pits were formed by the application of 3-8 V pulses of 10-100 ps duration, while within tunneling distances. Although a substantial fraction of the STM tips successfully generated hundreds of uniform pits when subjected to constant amplitude and constant duration bias pulses,’ the pulse threshold at which the smallest features were observed varied substantially from tip to tip. Additionally, the lithography process was observed to require a humid atmosphere and to exhibit daily fluctuations in pulse bias versus pit size. In order to elucidate the chemistry of this process, we have performed STM lithography studies of HOPG surfaces in contact with water and other organic liquids. For HOPG in H,O(Z), we have observed a welldefined pulse threshold of (4.0 *0.2)V, which reproducibly yielded 7-A-diam features that apparently protruded from the surface by 2 A. Larger voltage pulses yielded pits (with slightly larger dimensions) that were similar to those produced in air or in humid Nz(g) atmospheres. This work demonstrates that subnanometer scale lithography can be accomplished on graphite at room temperature, and that STM studies can provide mechanistic information regarding the chemistry of the liquid-coated and gas phase lithographic processes. A STM specifically designed for imaging surfaces immersed in liquids was employed for this work.’ Bias pulses with a duration of 20 ps and an amplitude

Optical lithography with chromeless phase-shifted masks

Abstract: Chromeless phase-shifting is a novel concept that completely avoids the use of chrome for pattern formation in optical lithography. This scheme uses 180 degree(s) phase-shifters on transparent glass to define patterns. The method relies on the destructive interference between phase-shifters and clear areas at the edges of the phase-shifters to define dark or opaque areas on the mask. Gratings sufficiently small (named dark-field gratings) will produce sufficient interference to completely inhibit the transmission of light. The combination of these effects makes it possible to form a wide range of patterns, from line-space patterns to isolated bright or dark areas. The lithography simulators SPLAT and SAMPLE were used to understand the principles behind this new scheme, and to verify various pattern designs. Simulation and experimental results are presented to demonstrate the concept.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Characterization of micro-optical components fabricated by deep-etch x-ray lithography

Abstract: Deep-etch x-ray lithography allows the fabrication of micro-optical components with critical lateral dimensions of a few micrometers and structural heights up to several hundred micrometers. Using interferometric methods, the structural tolerances of the side walls of fabricated microstructures are shown to be about 0.3 micrometers per 300 micrometers of structural height. A parallel HeNe laser beam is easily passed through several microprisms, which is evidence for the high precision achievable in positioning micro-optical components on a baseplate. Focussing a light beam by cylinder lenses is also possible. The free two- dimensional shape and the high precision achievable in positioning allow fabrication of micro- optical components with integrated fiber fixing grooves in which multi-mode fibers are precisely positioned. Simple fiber connectors, e.g., fiber forks or Y-couplers, can be achieved. By using a light-guiding resist system, divergence losses can be diminished.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

High‐resolution focused ion beam lithography

Abstract: The resolution and alignment accuracy of FIB lithography is studied for making devices with 0.1 μm dimensions. 0.1‐μm linewidth patterns are successfully fabricated by 260‐keV Be++ FIB for both positive and negative resists. 50‐nm linewidth Novolak based negative resist patterns are fabricated at 1.0×1012 ions/cm2 dose by 260‐keV Be++ FIB. Dot patterns with 0.3 μm diam and high density (108/cm2) are written on a 1×1 cm area in a PMMA resist to demonstrate that FIB lithography can be applied to make practical devices with a large writing area. Moreover, mark detection and overlay accuracy are studied for marks covered with PMMA and CMS resists. Finally, FIB lithography is applied to fabricate 0.1‐μm NMOS gate patterns. The overlay accuracy for hybrid exposure using FIB and an optical stepper is 0.2 μm at 2σ.

New approach to resolution limit and advanced image formation techniques in optical lithography

Abstract: Practical resolution, the minimum feature size with a depth of focus (DOF) required for LSI fabrication process, is analyzed. Dependence of practical resolution on various factors, such as optical system parameters (exposure wavelength lambda , and numerical aperture NA), resist processes, and required DOF, is investigated. It is shown that practical resolution in the sub-halfmicrometer region is not improved, and may even be degraded, with increasing NA. Furthermore, resolution improvement by increasing NA becomes less effective as lambda becomes shorter. This means that the high-resolution capability of high-NA/short-wavelength optics cannot be utilized to create fine-pattern LSIs. In order to overcome this limitation, the effectiveness of advanced image formation techniques, the phase-shifting method and the FLEX method, in practical resolution enhancement is investigated. It is experimentally verified, using a phase-shifting mask and the excimer laser stepper, that a pattern feature size less than 0.2 mu m can be clearly delineated with sufficient focus latitude. These advanced techniques make it possible to overcome the resolution limitation of conventional optical lithography. >

Fabrication of micro-structures using non-planar lithography (NPL)

Abstract: The authors present specific nonplanar lithographic (NPL) techniques for use in fabricating both monolithic micromachines and microcomponents for use in larger systems. The emphasis is on the use of numerically controlled E-beam-based lithography, with the resist exposed over nonplanar surfaces. Previously, nonplanar, optical-mask-based approaches have been used to fabricate devices such as wobble motor rotors, but with less success than the NPL techniques due to depth-of-field problems. The specific focus is on etching cylindrically shaped metal structures which are either (1) homogeneous or (2) layered by successive deposition, masking, and etching. Structures on the order of 80 to 500 microns in diameter have been constructed of either solid metals or sputtered thin metallic layers on quartz shafts. A number of either deep or shallow patterns have been fabricated on and through the structures, with promising results. Examples include helices, longitudinal lines, holes, notches, flexures, barbs, alphanumeric characters, and electrostatic field emitting patterns for use in wobble motors. Efforts are now proceeding toward generating complete systems, including transducers and actuators for industrial and medical applications. >

Nanometer-scale structures and lithography

Abstract: Improved fabrication processes for preparation of nanometer scale structures wherein a polymeric coating is applied to the substrate prior to fabrication are disclosed.

Astigmatism and field curvature from pin-bars

Abstract: Astigmatism and field curvature of lithography lenses can be measured with an error less than 30 nm using an optical microscope and conventional resolution test patterns. A sequence of through-focus images, recorded in positive resist, are examined with an optical microscope to determine the smallest lines remaining after development. It is only necessary to judge existence of lines; no dimensional measurements are required. Imperfections in fabrication and design that limit the resolution of most lithography lenses are easily identified by this new technique. The method for doing the measurements, the analysis, and recent application to characterization of lithography lenses are presented.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.