Showing papers on "Lithography published in 1992"

Using light as a lens for submicron, neutral-atom lithography.

Abstract: We show that light can be used as a lens to focus a collimated neutral atomic beam to submicron dimensions during deposition onto a substrate. We have used an optical standing wave at 589 nm as an array of cylindrical lenses to focus a perpendicular sodium beam into a grating on a substrate, with a periodicity of 294.3\ifmmode\pm\else\textpm\fi{}0.3 nm. This result is the first direct evidence of submicron focusing of atoms by light, and represents a fundamentally new scheme for submicron lithography.

Nanometer-scale lithography using the atomic force microscope

Abstract: We demonstrate a new use of the atomic force microscope (AFM) for nanometer‐scale lithography on ultrathin films of poly(methylmethacrylate) (PMMA). The PMMA films were chemically modified as both positive and negative resists due to energy transfer from a highly localized electron source provided by metallized AFM tips. We were able to fabricate a line pattern with 68 nm line periodicity with about 35 nm line widths.

Method for fine-line interferometric lithography

Abstract: In microelectronic processing, the method of producing complex, two-dimensional patterns on a photosensitive layer with dimensions in the extreme submicron range. A photosensitive layer is first exposed to two beams of coherent radiation to form an image of a first interference pattern on the surface of the layer. The layer is subsequently exposed to one or more interference pattern(s) that differ from the first interference pattern in some way, such as by varying the incident angle of the beams, the optical intensity, the periodicity, rotational orientation, translational position, by using complex amplitude or phase masks in one or both of the coherent beams, or a combination of the above. Desired regions of the complex pattern thus produced are isolated with a further exposure of the photosensitive layer using any conventional lithography.

Two-photon lithography for microelectronic application

Abstract: Two-photon excitation in laser scanning photolithography allows exposure of patterns not possible with conventional one-photon direct writing. In our experiments two red photons from a highly focused subpicosecond colliding pulse mode-locked dye laser are simultaneously absorbed by initiator molecules to affect a photochemical reaction that is normally driven by single-photon absorption using ultraviolet light. The quadratic dependence of the two-photon absorption rate on the incident intensity confines excitation to a submicron focal volume. By scanning this volume in a 3-d pattern through a thick layer of photoresist it is possible to expose arbitrary three dimensionally defined regions. Preliminary results showing half micron wide trenches of very high aspect ratio, and resist structures with undercutting edges, all produced with only a single development step, demonstrate. the potential utility of two-photon excitation in microfabrication.

Fabrication of 0.2 µm Fine Patterns Using Optical Projection Lithography with an Oil Immersion Lens

Abstract: Fine patterns are fabricated by using optical projection lithography with both an oil immersion lens of NA=1.25 and a conventional single-layer resist. Chlorobenzene soak is used in order to remove the immersion oil and to improve the side wall profile of the resist patterns. Some samples are lightly etched by O2 plasmas in order to remove a residual resist at the bottom of the resist patterns. Finally, it is found that a 0.18 µm fine resist pattern with a good edge definition can be fabricated. Al line and space pattern with a width of about 0.21 µm is also fabricated by lift-off technique.

1/8 μm optical lithography

Abstract: The critical bottleneck to extending optical lithography down to the 1/8 μm level is the performance of the projection optics. The Markle–Dyson configuration is virtually free of all geometric and chromatic aberrations. A prototype system has been constructed and characterized. The system uses 248 nm light from a mercury arc lamp at a numerical aperture of 0.7. 0.25 μm resolution has been demonstrated with non phase shifting masks: using phase shifting Levenson‐type masks, a grating consisting of 0.125 μm lines and spaces has been printed. Two possible extensions of the existing design are proposed which would allow general 1/8 μm geometries to be patterned. The first is a 0.7 numerical aperture (NA) system working at a wavelength of 157 nm, and the second is a 1.05 NA immersion system working at 193 nm. At these high NAs the depth‐of‐focus (DOF) of the image becomes very small if a clear aperture is used. However, if the aperture is apodized, the DOF can be increased considerably, and a procedure for opt...

Arrayed miniature electron beam columns for high throughput sub-100 nm lithography

Abstract: In recent years, considerable progress has been made on an approach based on a novel concept which combines scanning tunneling microscope, microfabricated lenses, and field emission technologies to achieve microminiaturized low‐voltage electron beam columns with performance surpassing the conventional column. High throughput lithography is a potentially very important application for these microfabricated columns which measure only millimeters in dimensions. This is to be achieved using an array of these minicolumns in parallel in a multibeam mode with one or more columns per chip. The low‐voltage operation is attractive because proximity effect corrections may not need to be applied. In addition, an arrayed microcolumn system also has the potential of reducing the cost of the overall system through the compaction of the mechanical system. The throughout advantages for such an arrayed system based on different beam forming optics and pattern generation approaches will be discussed. In addition to lithography, a wide range of other applications for such an arrayed system such as testing, metrology, storage, etc., can also be considered.

Hybrid integration of semiconductor lasers with Si-based single-mode ridge waveguides

Abstract: Hybridization is a convenient way for providing silicon-based integrated optical circuits with a laser source. An entirely passive alignment technique exclusively based on the high precision obtainable by lithography and by semiconductor processes was examined. A novel way of cleaving the laser chips by self-aligned cleaving grooves was employed. It resulted in 15.5-dB coupling losses between the laser diode and the single-mode buried ridge waveguide. >

Fabrication of high depth-to-width aspect ratio microstructures

Abstract: It is reported that a 3-D fabrication process, based on sputtering of a thin-film plating base, on conventional UV lithography, and on electrochemical deposition of gold, makes microstructures of considerable height and resolution possible. The thin-film formation and the lithographic process are outlined, particular attention being paid to layer deposition and structure printing. The present resolution limit is about 4.5 mu m for a 30- mu m-thick resist. Much thicker layers (80 mu m) can be printed with reduced resolution. The results are discussed and process characteristics relevant in various applications are considered. >

Direct-to-press imaging system for use in lithographic printing

Abstract: A direct-to-press imaging system for use in lithographic printing wherein a master-image printing cylinder is used with separate application of ink and water onto its surface to enable repetitive conveyance of image-formatted ink films onto substrates for printing purposes. The imaging system includes a master-image printing cylinder adapted for receiving a hydrophilic coating layer on its surface and a device for laying down a uniform layer of hydrophilic material on the surface of this cylinder. An apparatus is also provided for applying oleophilic material in image-formatted patterns on top of the layer of hydrophilic material on the master-image printing cylinder to form a printing structure having separate hydrophilic and oleophilic areas of the format to be printed. Further, a mechanism is provided for removing the printing structure including both the hydrophilic and oleophilic materials from the surface of the master-image printing cylinder so that a new printing structure corresponding to a new image to be printed can be formed on the master-image printing cylinder.

The physics of submicron lithography

Abstract: Forming Electron Beams of Submicron Cross Section. The Physics of the Interactions Between Fast Electrons and Matter. The Physics of Ion Beam Lithography. The Physics of X-Ray Microlithography. Optical Lithography. Proceedures for Processing Exposed Resist Films and Resist Mask Topography. Index.

Subhalf-micron lithography system with phase-shifting effect

Abstract: We propose in this paper a new imaging technology for the 64M DRAM, named "CQUEST” (Canon Ql/adrupole Effect for Stepper Technology). CQUEST is derived from the mathematical analysis of the partial coherence theory1. It can provide almost the same effects with conventional masks as those that result using phase shift masks. Therefore, it is a promising candidate for next generation lithography. Simulation and some experimental results will be shown to substantiate the above. As shown in the results, the 64M DRAM process can be achieved with the existing i-line technology.

Characterization of near‐field holography grating masks for optoelectronics fabricated by electron beam lithography

Abstract: Direct write e‐beam lithography and reactive ion etching was used to fabricate square‐wave gratings in quartz substrates which serve as pure phase masks in the near‐field holographic printing of gratings. This method of fabricating these masks extends the flexibility of the printing technique by allowing both abrupt phase shifts as well as multiple grating pitches to be simultaneously printed from a single contact mask. Grating masks with periods in the 235–250 nm range have been produced and measured to be within 0.15 nm of the design period. Transmitted and diffracted beam powers have also been measured for various duty cycles and etch depths and are shown to be important parameters for ‘‘balancing’’ these interfering beams. Simple scalar diffraction modeling is used to qualitatively examine the dependence of diffraction on grating parameters, but the need for a more comprehensive modeling is illustrated. Prototype masks have been used to produce grating patterns on InP substrates using two different ul...

Nanolithography and its prospects as a manufacturing technology

Abstract: The resolution requirements for nanolithography can be satisfied; both devices and small‐scale circuits with features well below 100 nm have been fabricated. However other requirements such as adequate throughput (about 1 cm2/s) and a precision on feature edge placement of the order of 10 nm over 20 mm remain as serious challenges. Evolving technology may allow us to extend present‐day technology such as deep ultraviolet lithography towards 100 nm feature sizes. But to go below that size radically new approaches will probably be needed. Examples include x‐ray printing and some form of adaptive alignment in which relative distortion between mask and wafer is tracked.

Patterning Characteristics of a Chemically-Amplified Negative Resist in Synchrotron Radiation Lithography

Abstract: To explore the applicability of synchrotron radiation X-ray lithography for fabricating sub-quartermicron devices, we investigate the patterning characteristics of the chemically-amplified negative resist SAL601-ER7. Since these characteristics depend strongly on the conditions of the chemical amplification process, the effects of post-exposure baking and developing conditions on sensitivity and resolution are examined. The resolution-limiting factors are investigated, revealing that pattern collapse during the development process and fog caused by Fresnel diffraction, photo-electron scattering, and acid diffusion in the resist determine the resolution and the maximum aspect ratio of the lines and spaces pattern. Using the model of a swaying beam supported at one end, it is shown that pattern collapse depends on the resist pattern's flexural stiffness. Patterning stability, which depends on the delay time between exposure and baking, is also discussed.

Application of blind method to phase-shifting lithography

Abstract: A blind mask and a simplified-blind (S-blind) mask proposed for phase shifting lithography are discussed. They both have very simple structures. Both the blind and S-blind methods are very effective in solving the bridging problem in single-layer-shifter phase-shifting lithography. These phase-shifting methods are suitable for 0.3- mu m lithography for the manufacture of 64-Mb DRAMs. >

Electron‐beam lithography with the scanning tunneling microscope

Abstract: The scanning tunneling microscope (STM), operated in vacuum in the field emission mode, has been used in lithographic studies of the resist SAL‐601 from Shipley. Patterns have been written by raising the tip–sample voltage above −12 V while operating the STM in the constant current mode. Resist films, 50 nm thick, have been patterned and the pattern transferred into the GaAs substrate by reactive ion etching. The variation of feature size with applied dose and tip–sample bias voltage has been studied. Comparisons have been made to lithography with a 10 nm, 50 kV electron e‐beam in a JEOL JBX‐5DII in the same resist thickness films. In all cases the resist films were processed in the standard fashion before and after exposure. The STM can write smaller minimum features sizes and has a greater process latitude. Proximity effects are absent due to the reduced scattering range of the low energy primary electrons. However, the writing speed is slower, being limited by the response of the piezoelectric scanner....

Confined etchant layer technique for two-dimensional lithography at high resolution using electrochemical scanning tunnelling microscopy

Abstract: In order to realize two-dimensional lithography at high resolution (several tens of nanometres), a new approach to the lithography of a fine pattern using a confined etchant layer technique (CELT) in an electrochemical system is presented. A mould plate of conductive material with a high-resolution line pattern (which can be prepared with the aid of e.g. electron beams) is used instead of the tip in scanning tunnelling microscopy (STM). The etchant species is generated at the surface of the mould plate by electrochemical photochemical or photoelectrochemical methods, then diffuses away from the surface of the mould plate. The key feature of CELT is the design of a chemical reaction which rapidly destroys the etchant (e.g. within microseconds on average) following its generation. Therefore, the gradient of the concentration of etchant can be greatly enhanced and the thickness of the diffusion layer can be greatly decreased to several tens of nanometres. Thus, the etchant layer is confined and its outer boundary can essentially retain the fine structure of the pattern of the mould plate. Then the substrate to be corroded is adjusted by ECSTM to approach the mould plate within several tens of nanometres and the corroded pattern can retain the fine structure giving a resolution of several tens of nanometres.

High-efficiency continuous surface-relief gratings for two-dimensional array generation.

Abstract: Continuous surface-relief phase gratings for two-dimensional (2-D) array generation have been realized by laser-beam writing lithography For a 9 × 9 fan-out element, a diffraction efficiency of 94% and a uniformity of better than ±8% have been achieved These are, to our knowledge, the best published results for 2-D surface-relief fan-out elements Separable and nonseparable solutions for the design of 2-D fan-out elements are discussed

Broad band optical reduction system using matched multiple refractive element materials

Abstract: A broad band catadioptric optical reduction system using refractive elements made of different types of glass matched for color correction over a broad band width. A combination of fused silica and crown glass is used. An aspheric mirror is used for improved aberration correction. The optical system is adapted for use in lithography for semiconductor manufacturing in the I-line and is capable of 0.5 micron resolution at a wavelength of 365 nanometers.

Low voltage alternative for electron beam lithography

Abstract: The current trend in electron beam lithography for patterning submicron features is towards the use of higher beam voltages (20–100 keV). Among the problems often perceived to be associated with the use of low voltages are the poorer resolution, the lower brightness, and the greater sensitivity to electric and magnetic interference. Both by simulation and by experiment at 2 kV it is shown: (1) features of less than 100 nm are clearly resolved in resist of about the same thickness; (2) such features are clearly resolved in both sparse and dense pattern; (3) such features in sparse and dense areas are clearly resolved over a twofold range of exposure doses; (4) such delineation is largely independent of substrate material; (5) there is no evidence of alternating‐current magnetic interference; (6) the lower beam brightness at low voltages is compensated by the increased sensitivity of resists to lower energy electrons. The remaining concerns about low voltage lithography are the reliability of resist with an imaging layer less than 100 nm thick and the extent and effect of charging of such a resist.

Diamond membranes for X-ray lithography

Abstract: A substantially compressive stress-free, pinholes free, and defects free continuous polycrystalline diamond membrane for an x-ray lithography mask is produced by placing a prepared substrate (22) into a hot filament chemical vapor deposition reaction chamber (100), pre-heating the substrate to 400 °C-650 °C in the presence of an inert gas, heating the substrate to 650 °C-700 °C in the presence of hydrogen and carbon compounds (61), and chemically vapor depositing a polycrystalline diamond membrane onto the substrate.

Laser-produced plasmas for soft x-ray projection lithography

Abstract: Laser‐produced plasmas are one of the most likely sources to be used for soft x‐ray projection lithography The characteristics of these sources are described in terms of the expected radiation efficiency within the illumination bandwidth of a lithographic system Measurements of the plasma particulate emission are described and techniques for interdicting this emission before it reaches the illumination optics are discussed The laser requirements are obtained for a lithographic system producing a wafer rate of 60, 6 in wafers per hour

Low‐voltage electron beam lithography

Abstract: The use of low‐voltage electron beam lithography to reduce proximity effects, improve throughput, and reduce substrate damage caused to underlying materials has been investigated. Various films of PMMA were exposed with a field emission scanning electron microscope adapted with blanking capability and a 16 bit resolution beam control package. The exposure voltages used were from 1 to 15 keV with probe sizes of ≤150 to ≤70 A, respectively. The dose latitude or working dose range was determined for each voltage on film thicknesses of 0.05, 0.18, and 0.38 μm poly(methylmethacrylate). Optimum beam voltage for a particular thickness which maximizes the energy deposited within the resist has been approximated using Monte Carlo modeling and verified experimentally. Atomic force microscopy showed that at lower voltages the dose required to properly expose a feature is relatively low and as beam voltage increases, the dose required to expose a given area increases. This data also verifies the fact that if the expo...

Projection type x-ray lithography apparatus

Abstract: Reduction projection type X-ray lithography with an exposing beam wavelength of 40-150 10⁻¹⁰ m (40-150 A), which is longer than in conventional 1:1 proximity exposure, has a high-vacuum space. This would reduce wafer (10) replacement work efficiency and contaminate optical mirrors (4, 5, 6, 7) with substances released by a resist decomposed during exposure except for separating an optical system chamber (2) and a wafer exposing chamber (13) by a differential pumping section (8) and a thin-film window (9A). Wafer exposure is under atmospheric pressure, improving productivity, accuracy of exposure and longevity of the optical devices (4, 5, 6, 7).

X-ray projection lithography camera

Abstract: Optimum solutions for three-mirror lenses for projection lithography cameras using X-ray radiation to image a mask on a wafer are represented as single points within regions of two-dimensional magnification space defined by the magnification of a convex mirror as one coordinate and the ratio of the magnifications of a pair of concave mirrors optically on opposite sides of the convex mirror as another coordinate. Lenses within region 30, 50, and preferably within region 40, 60, of such magnification space represent potential solutions that are optimizable by standard computer optical design programs and techniques to achieve extremely low distortion lenses having a resolution of about 0.1 micron or less.

High performance optical lithography using a separated light source

Abstract: In projection lithography systems with fly’s‐eye elements, a virtual source is created as an array of approximately mutually incoherent point sources. This article describes light amplitude and phase simulations for an image of a mask illuminated by a point source. This article discusses the dependence on the point‐source location for a plane perpendicular to the optical axis. An image projected by a separated light source, rather than a ring‐shaped light source, improves due to interference effects between multiple apertures is shown. Resolution of 0.25 μm equal lines and spaces was improved experimentally at a wavelength of 365 nm and a numerical aperture of 0.54. Also, how an isolated pattern image can be improved theoretically using an optimally separated light source is shown.

A 0.72 mu m/sup 2/ recessed STC (RSTC) technology for 256 Mbit DRAMs using quarter-micron phase-shift lithography

Abstract: A recessed stacked capacitor (RSTC) structure to achieve both fine-pattern delineation and high cell capacitance is presented. Using a RSTC structure, an experimental memory array with 0.25 mu m phase-shift lithography and CVD-W plate technology has been fabricated. A 25-fF/cell capacitance was obtained in a 0.72 mu m/sup 2/ cell. >