Showing papers on "Lithography published in 1989"

Photoreactive Polymers: The Science and Technology of Resists

Abstract: A brief history of resists negative photoresists aspects of photophysics and photochemistry in solid polymers photoinitiated polymerization positive resists based on diazonaphthoquinones the rudiments of imaging science deep-UV lithography electron beam lithography X-ray and ion beam lithographies multilayer techniques and plasma processing.

Oxygen plasma etching for resist stripping and multilayer lithography

Abstract: Oxygen‐based plasmas commonly used in resist stripping and multilayer resist patterning are contrasted to highlight the differences involved in these applications. Mechanisms for polymer etching are reviewed, with particular emphasis on silicon‐containing resists proposed for bilayer lithography. While silicon‐containing materials offer a simpler process than trilayer schemes for improving lithographic resolution, considerable differences in etch behavior among these materials have been observed. Further characterization and fundamental understanding are required before widespread acceptance of silicon‐containing resists is achieved.

Polymer materials for microlithography

Abstract: Since the last review on resist materials for microlithography appeared in the Annual Review of Materials Science (Vol. 6, 1976) (1), astonishing progress has been made in microelectronics, especially in the technology of lithography used to generate high-resolution patterns. In 1976, the state­ of-the-art dynamic random access memory (DRAM) device was capable of storing 4000 bits of data and had minimum features of 5-6 flm. Photo­ lithography was utilized to pattern these devices using either contact print­ ing or, the then relatively new, one-to-one projection printing. Today, devices with one million bits of storage capacity are commercially available with minimum features of 1.0 flm (2). By 1976 standards, it is surprising that photolithography is still the technology used to fabricate micro­ electronic chips. Step-and-repeat 5 or 10 x reduction cameras and highly sophisticated I -toI projection printers are the dominant printing tech­ nologies. There is perhaps no better example than lithography to illustrate the uncertainty associated with predicting technological direction and change. In 1976, it was generally believed (though not by everyone) that photolithography would not be able to produce features smaller than about l.5 flm with high chip yields in a production environment. The current belief is that conventional photolithography will be able to print 0.6-0.8 flm features and will be the dominant technology well into the first half of the 1990s. The same basic positive photoresist, a diazonaphtho­ quinone-novo lac composite, will likely still be the resist of choice. The cost of introducing a new resist material and the cost associated with new hardware are strong driving forces pushing photolithography to its absolute, ultimate limits.

Self-aligned, high resolution resonant dielectric lithography

Abstract: Methods of fabricating electrical contacts on both sides of a thin membrane to form a millimeter wave, self-aligned, opposed gate-source transistor are disclosed. The transistor structure has a subhalf-micron gate, dual-drains placed symmetrically around both sides of the gate, and a source approximately half the length of the gate. The source is directly opposite, and centered under, the gate on the opposite surface of a semiconductor thin film. The gate electrode is fabricated on the first surface of the thin film using conventional single surface lithography, and is used as a conformed mask for the source lithography, thereby self-aligning the source to the gate. The source is formed by resonant dielectric lithography, wherein the gate side of the thin film is irradiated by collimated ultraviolet light to expose a negative resist on the source side with a resolution of less than a wavelength. Lateral diffraction effects affect the relative dimension of the source with respect to the gate. The electron-beam lithographic process utilizes electron scattering in the thin film for the same purpose. This new untraviolet lithography process avoids the need to handle the thin film until after source metallization has been completed.

Conducting polyanilines: Discharge layers for electron‐beam lithography

Abstract: This paper describes the use of electrically conducting polyanilines as discharge layers for electron‐beam (e‐beam) lithography. The emeraldine oxidation state polyaniline is a soluble material which can be doped by various cationic reagents, most commonly protonic acids, to afford conductivity on the order of 10° Ω−1 cm−1. The conducting polyanilines are incorporated as thin interlayers (2000 A) in a multilayer resist system consisting of a planarizing underlayer (2.8 μm) and the imaging resist (1.2 μm) on top. We find that various acid‐treated polyanilines eliminate charging during e‐beam patterning of the resist, i.e., zero pattern displacements are observed as compared to the case where a conducting interlayer is not incorporated into the resist system. In the latter case placement errors greater than 5 μm are observed as a result of charging. A minimum conductivity of 10−4 Ω−1 cm−1 is required for the polyaniline interlayers in order to observe zero pattern displacement. In addition, we have simplifi...

Resolution doubling lithography technique

Abstract: A lithography system is disclosed which is capable of doubling the spatial frequency resolution associated with conventional systems. A spatial filter, positioned to intercept the Fraunhofer diffraction pattern of the mask being exposed, is configured to prevent certain orders of the diffraction pattern (in most causes the O-order and ±2nd, 3rd, . . . orders) from reaching the wafer's surface. The remaining orders reaching the wafer surface (in most cases the ± first-order beams) will produce a cos-type interference pattern with a period half of that if the mask grating were imaged without spatial filtering. Therefore, for a system with a given magnification factor m, a mask grating with a period p will be exposed on the wafer surface as a grating with a period of p'=pm/2. Advantageously, the spatial filtering technique of the present invention allows for a variety of different structures (conventional gratings, chirped and phase-shifted gratings, grids, Fresnel zone plates, etc.), as well as structures of different sizes and orientations, to be included on one mask and transferred to the wafer with a single exposure cycle.

Soft x-ray reduction camera for submicron lithography

Abstract: Soft x-ray projection lithography can be performed using x-ray optical components and spherical imaging lenses (mirrors), which form an x-ray reduction camera. The x-ray reduction is capable of projecting a 5x demagnified image of a mask onto a resist coated wafer using 4.5 nm radiation. The diffraction limited resolution of this design is about 135 nm with a depth of field of about 2.8 microns and a field of view of 0.2 cm 2 . X-ray reflecting masks (patterned x-ray multilayer mirrors) which are fabricated on thick substrates and can be made relatively distortion free are used, with a laser produced plasma for the source. Higher resolution and/or larger areas are possible by varying the optic figures of the components and source characteristics.

Micropatterning of surfaces by excimer laser projection

Abstract: In the coming years, excimer lasers will play two important roles in microelectronic fabrication: as new light sources for submicron photolithography, and for direct surface patterning by ablation or etching. Using this latter application, results are presented for 248 nm excimer laser formation of micron‐sized patterns in several materials by image projection. Photoablation was used to produce patterning in polyimide and a fluorocarbon polymer, while micropatterning by photoetching is demonstrated in copper and silicon using chlorine vapor. The results are discussed both in terms of the optical characteristics of the projection apparatus, and from the point of material response.

Laser scanner for direct writing lithography.

Abstract: A laser scanner and a stepping xy stage have been developed for direct writing lithography in the micron and the submicron range. System design is described and examples of exposed photoresist with a structure size of 1 microm are presented.

X-Y-θ-Z positioning stage

Abstract: A positioning stage is disclosed which achieves high-speed step-and-repeat alignment of a semiconductor wafer to a mask with a full six degrees of freedom. A precision planar translational stage is mounted on a rotating stage to allow a single-laser interferometric system to be utilized to make precise measurements of translational (X and Y) and rotational (θ) positions. The entire X-Y-θ stage system can also be moved vertically in a Z direction, or tilted with respect to the X-Y plane, by independently adjustable flexible mounts. The center of rotation of the rotational stage is on the beam axis, so that registration of the wafer to a mask is simplified. Because the mass of the rotating stage is not moved during high-speed X- and Y-positioning steps, fast response is possible. In lithography applications, one rotational correction at the beginning of the writing procedure suffices for all the chips on the wafer, if all the rows and columns of chips are perfectly straight. Besides its usefulness in lithography with a flood ion beam, the invention is also useful in direct-write electron- or ion-beam lithography systems with focused beams, to obviate the need for high-speed electronic scan rotation.

Polymers in microlithography : materials and processes

Abstract: Polymers in Microlithography: An Overview Bronsted Acid Generation from Triphenylsulfonium Salts in Acid-Catalyzed Photoresist Films Chemically Amplified Resist: Effect of Polymer and Acid Generator Structure Copolymer Approach to Design of Sensitive Deep-UV Resist Systems with High Thermal Stability and Dry Etch Resistance Nonswelling Negative Resists Incorporating Chemical Amplification: Electrophilic Aromatic Substitution Approach Acid-Catalyzed Cross-Linking in Phenolic-Resin-Based Negative Resists New Design for Self-Developing Imaging Systems Based on Thermally Labile Polyformals Polysilanes: Solution Photochemistry and Deep-UV Lithography Syntheses of Base-Soluble Si Polymers and Their Application to Resists Lithographic Evaluation of Phenolic Resin-Dimethyl Soloxane Block Copolymers Preparation of a Novel Silicone-Based Positive Photoresist and Its Application to an Image Reversal Process Photooxidation of Polymers: Application to Dry-Developed Single-Layer Deep-UV Resists Kinetics of Polymer Etching in an Oxygen Glow Discharge Quantitative Analysis of a Laser Interferometer Waveform Obtained During Oxygen Reactive-Ion Etching of Thin Polymer Films Evaluation of Several Organic Materials as Planarizing Layers for Lithographic and Etchback Processing New Negative Deep-UV Resist for KrF Excimer Laser Lithography Characterization of a Thiosulfate Funtionalized Polymer: A Water-Soluble Photosensitive Zwitterion Pyrimidine Derivatives as Lithographic Materials Synthesis of New Metal-Free Diazonium Salts and Their Applications to Microlithography Photobleaching Chemistry of Polymers Containing Anthracenes Lithography and Spectroscopy of Ultrathin Langmuir-Blodgett Polymer Films Dissolution of Phenolic Resins and Their Blends Solvent Concentration Profile of Poly(methyl methacrylate) Dissolving in Methyl Ethyl Ketone: A Fluorescence-Quenching Study Molecular Studies on Laser Ablation Processes of Polymeric Materials by Time-Resolved Luminescence Spectroscopy Mechanism of Polymer Photoablation Explored with a Quartz Crystal Microbalance Mechanism of UV- and VUV-Induced Etching of Poly(methyl methacrylate): Evidence for an Energy-Dependent Reaction

Improvement of defocus tolerance in a half‐micron optical lithography by the focus latitude enhancement exposure method: Simulation and experiment

Abstract: The new method for enhancing the focus latitude in optical lithography, named FLEX (focus latitude enhancement exposure) has been investigated. In FLEX the imaging characteristics are greatly affected by several key parameters such as distance between adjacent focal planes and illuminator coherence factor. The effect of these parameters on optical image characteristics have been examined using computer simulations. The results of the simulations have been verified by applying FLEX to imaging of sub‐half‐micron patterns using a high numerical aperture i‐line stepper. This has confirmed the validity of FLEX in delineating feature sizes in the order of 0.3∼0.5 μm. In particular, the depth of focus for hole patterns is found to be increased more than ten times, if necessary, with no degradation in resolution. However, the high‐contrast resist process is necessary in applying FLEX to patterns like L/S. FLEX will be a great help to future optical lithography with high NA and/or short wavelength optical systems.

Step And Scan: A Systems Overview Of A New Lithography Tool

Abstract: The Micrascan I system, a new 0.5-micron lithography tool, employs a 'step-and-scans concept that combines the virtues of ring-field scanning systems with those of conventional step-and-repeat systems. Individual exposure fields on the wafer are sequentially scanned past the arcuate image field of a catadioptric projection optics system with a 4:1 reduction ratio. The reticle is scanned in precisely coordinated fashion by a separate stage. Exposure illumination is provided by a long-life mercury-xenon arc lamp. The concept enables very large field sizes and high system productivity.

Positive resist image by dry etching: New dry developed positive working system for electron beam and deep ultraviolet lithography

Abstract: A new dry developed high resolution positive working system: positive resist image by dry etching PRIME for e‐beam and deep UV lithography is proposed. This system is derived from photolithographic diffusion enhanced silylating resist diffusion enhanced silylating resist (DESIRE) process. In this report, we present the advantages of a top imaging scheme for e‐beam lithography: forward scattering and proximity effects are considerably minimized. Due to very high contrast (about 6), resolution limits were pushed down to 75 nm lines and spaces in 0.35 μm thick resist; holes of 0.2 μm in 1.2 μm thick resist were obtained. Under deep UV exposure, 0.2 μm lines and spaces in 0.7 μm thick resist were resolved with a mask aligner.

X‐ray lithography: On the path to manufacturing

Abstract: X‐ray lithography has been an active area of research and development for the last 20 years, and recent spectacular results using complete, integrated x‐ray lithography systems have demonstrated, at the research level, the viability of x‐ray lithography, and have shown that x–ray lithography is on the path to manufacturing. This paper presents IBM’s recent successful development of a synchrotron‐radiation‐based x‐ray lithography system. The individual components of the system are described, along with a brief description of available alternate components. Measurements of the lithographic performance of the integrated system are presented, and the use of this system for the fabrication of fully‐scaled 0.5 μm CMOS circuits is described.

Resist technology for deep‐etch synchrotron radiation lithography

Abstract: Preparation de microstructures de dimensions caracteristiques d'un micron et de hauteurs structurales de plusieurs centaines de microns par lithographie de PMMA reticules prepares par polymerisation d'une resine de MMA contenant 1% d'un dimethacrylate reticulant sur une plaque metallique. Le developpement est fait avec des solvants aux parametres de solubilite situes a la limite du domaine de solubilite du PMMA

Adaptive lithography accommodation of tolerances in chip positioning in high density interconnection structures

Abstract: An adaptive lithography technique for use in high density interconnect circuits compensates for displacements of chip contact pads from their ideal location by including chip contact islands in the metallization pattern and positions a via hole connecting the chip contact island to the chip contact pad where it connects to both of them. The result is simplified routing and avoidance of modifications within the metallization pattern itself to accommodate actual chip placements.

Lithography imaging tool and related photolithographic processes

Abstract: An apparatus and method for characterizing lithography imaging to quickly optimize a lithography process is described. The apparatus consists of two lithography masks for use with an optical stepper, ion-beam or x-ray lithography tool. The first mask is used for creating topography on the wafer substrate, and is patterned with groups of large elements arranged in orthogonal and angular directions. The second mask is used for defining a periodic pattern over the large elements. Preferably, the periodic pattern is in the same order of dimension as the critical element on the integrated circuit. A method is provided for characterizing lithography tools which do not have lithography masks such as an electron beam exposure tool.

Step‐and‐scan lithography using reduction optics

Abstract: Scanning 1:1 optical lithography has a long record of success that has been greatly abetted by the relatively straightforward nature of 1:1 ring‐field optics and by the fact that mask and wafer can be mounted to a common scanning carriage. However, as lithography requirements progress into the submicron regime, there is strong motivation to employ reduction optics in order to keep the difficulty of the mask‐making task within reasonable bounds. A new ‘‘step‐and‐scan’’ lithography tool achieves this goal and combines the best features of scanners and steppers by sequentially scanning 20×32.5‐mm subfields. Key features of this system are a ring‐field projection system, with a 4:1 reduction ratio, and a scanning system in which the reticle and wafer are carried by separate stages driven at different but precisely synchronized velocities.

Lithography plates and method and means for imaging them

Abstract: Various lithographic plates suitable for wet or dry lithography are described which are adapted for imaging by spark discharges to the plates. A method and apparatus for imaging those plates are also described.

Electron Beam Lithography And Resist Processing For The Fabrication Of T-Gate Structures

Abstract: This paper will discuss direct-write electron beam lithography and multilayer resist processing for the fabrication of T-shaped gates. Gates whose length at the bottom of the "T" are less than 100 nm have been fabricated by this method using a multilayer of polynethylnethacrylate and lift-off. Because of the large cross-section of the T-gate, the resistance is reduced. The end-to-end resistance of the 100 nm T-shaped lines was less than 25) Ohninin as compered to 2000 Ohm/nin for a 100 nm conventional gate, i.e., an eight-fold decrease. In order to facilitate the fabrication of these gates a series of computer programs were written to simulate the development process in a multilayer of electron resists. These programs are based on a string development model of resist development. They allowed rapid prediction of the resist profiles. As a demonstration of the increased device performance made possible by this prociss, modulation-doped field effect transistors (HOLEY) have been fabricated using these T-gate structures . The extrapolated unity current gain frequency (ft) of these transistors is 113 Gilz.

Wet Chemical Etching for Ultrafine Periodic Structure: Rectangular InP Corrugations of 70 nm Pitch and 100 nm Depth

Abstract: Rectangular corrugations of 70 nm pitch and 100 nm depth were formed on InP using electron beam lithography and two-step wet chemical etching. In electron beam lithography, line distributions were measured to estimate the narrowest possible period, and a fine periodic resist pattern with a 50 nm period was formed. It is pointed out that two-step wet chemical etching with a thin epitaxial mask has the advantage of suppressing the undercut etching because of good adhesion of the epitaxial mask. This etching method was applied to InP etching by HCl utilizing the material-selective and anisotropic properties. Compositions of etchant were optimized to overcome the deformation of mesas in the nanometer range.

Hot-electron-induced instability in 0.5- mu m p-channel MOSFETs patterned using synchrotron X-ray lithography

Abstract: Radiation damage caused by X-ray includes positive oxide charge, neutral traps, and interface states. Although several annealing steps are performed throughout the entire fabrication process, the radiation damage, particularly neutral traps, is not completely annealed out. The hot-electron-induced instability in p-channel MOSFETs is significantly increased due to the enhanced electron trapping in the oxide by residual traps. However, the degradation in n-channel MOSFETs due to channel-hot carriers is not significantly increased by X-ray lithography since n-channel MOSFETs are susceptible to interface state generation by hot carriers but are relatively insensitive to the degradation due to electron trapping. The results suggest that p-channel MOSFETs in addition to n-channel MOSFETs need to be carefully examined for hot carrier-induced instability in CMOS VLSI circuits patterned using X-ray lithography and/or when the radiation damage is incurred in the back-end-of-the-line processing. >

Compound Bragg reflection filters made by spatial frequency doubling lithography

Abstract: A report is presented on the fabrication of complex Bragg filters with resonant wavelengths near 1.55 mu m, patterned by photolithography using a high-resolution deep ultraviolet stepper. The projection of gratings with quarter-micrometer features was made possible by the use of spatial frequency-doubling lithography. A single chip, processed entirely in the silicon facility, was used to demonstrate five Bragg reflectors of different wavelengths, a quarter-wave shifted resonator, broadband stacked filters with as many as 15 uniform Bragg reflector sections of different Bragg wavelengths, and broadband stacked filters containing a passband within the reflection band. The filters exhibited nearly ideal spectral behavior. >

Holograms For Optical Interconnects For Very Large Scale Integrated Circuits Fabricated By Electron-Beam Lithography

Abstract: High performance holograms are a crucial part of realizing the predicted benefits of optical interconnection of electronic circuits. Fabrication of computer-generated holograms using electron-beam lithography provides access to the needed performance but presents new challenges in design, encoding, and data handling. Two holograms are described that represent different approaches in each of these areas. The first hologram connects a single laser source to several widely separated detectors. A paraxial imaging arrangement allows the holographic interferogram to be encoded as concentric circles of a Fresnel zone plate. The second hologram was designed to replace the row address lines on a 1 kbit RAM chip. In this case, broad separation of the sources prohibits use of the paraxial approximation. Instead, a piecewise approximation to the optimal phase function is encoded with a closed-contour fringe-tracing algorithm. Both holograms were evaluated in experimental systems involving photodetectors integrated onto a VLSI circuit chip and a discrete semiconductor laser.

An optical‐heterodyne alignment technique for quarter‐micron x‐ray lithography

Abstract: A new optical‐heterodyne interferometry alignment technique with diffraction gratings is developed for quarter‐micron x‐ray lithography. To obtain detection accuracy as good as a few tens of nanometers, a phase signal is utilized instead of a conventional intensity signal. The relative lateral displacement between mask and wafer is detected by measuring the phase difference between heterodyne beat signals generated by projecting two laser beams from + first‐order and − first‐order diffraction directions on the mask and wafer grating marks. The displacement signal is only slightly influenced by gap variation using symmetric optics. A lateral displacement detection resolution better than 10 nm is obtained by the experimental alignment setup. A nonsymmetric beam from the − third‐order diffraction direction is added to the symmetric beams to detect the gap. The phase difference between two beat signals emitted to the second‐order diffraction direction from the same mask and wafer marks is used as the gap detection signal. The cyclic gap signal makes it possible to set an arbitrary gap. A gap detection resolution of <20 nm is realized. Using this optical‐heterodyne interferometry alignment method, a four‐channel alignment system is developed for synchrotron x‐ray lithography. Six‐axis alignment servo control is established by combining this system with highly accurate stages.

1.55 mu m DFB laser array with lambda /4-shifted first-order gratings fabricated by X-ray lithography

Abstract: First-order grating patterns (λ = 0.24 μm) with λ/4-shift for DFB laser array were successfully fabricated by X-ray lithography. The 20-DFB laser array operated in the single longitudinal mode and the wavelength varied as designed.