With design rules for integrated circuits attaining the_submicron range and current lithography techniques being pushed to their limits, the need for new lithography tools has become acute. A candidate for this is an X-ray stepper wilich provides high resolution with process latitude as well as high throughput. This paper will describe such a stepper.
A new interferometric optical-heterodyne method has been developed for detection of displacement between a mask and a wafer. This method uses three symmetrically-arranged gratings and detects the displacement from the phases of beat signals. Using a 0.76-μm-period-grating system and a He-Ne transverse-mode Zeeman laser( wave length = 0.6328 μm ), sensitivity better than 1° /0.01 μm was obtained and displacement smaller than 5nm was detected independently of the mask-wafer gap variations. With this method, a prototype alignment system having vertical mask and wafer stages was constructed for synchrotron x-ray lithography. The alignment accuracy better than 0.01 μm was achieved. Effects of several factors ( dimension of grating, resist coating, etc. ) influencing the alignment accuracy are discussed.
This paper deals with the development of an X-ray stepper mask technology based on a rigid SiC.-membrane and a stress compensated W-absorber system. The SiC-mask blanks are being fabricated using batch processes like CVD-deposition and selective thin etching. As a result of extensive process optimization the polycristalline membranes can be fabricated with a smooth surface (< 40 nm) and a Young's modulus as high as the bulk value (4.6*10 11 N/m 2). Membranes of 2.7 μm in thickness are being prepared routinely with excellent transparency for synchrotron and optical radiation. For a high X-ray absorption and low thermal expansion sputter deposited tungsten has been applied. Ihe proposed stress compensating technique enables absorber stresses of less than 1*107 N/m , resulting in a mask distortion of < 100 nm. Precise sub-0.5-micron pattern with steep profiles have been generated by use of e-beam lithography and RIE techniques. High doses SOR experiments indicate an excellent long-term stability of SiC-W-masks.
A novel X-ray mask fabrication process, which is as simple as that used for conventional photomasks, has been developed. Several step and repeat X-ray lithography masks with SIN, membranes, which are stretched over rectangular rigid Si-frames, are fabricated from the same large wafer. Transparent window formations fot several tens of X-ray mask substrates are carried out simultaneously, by etching the (100) oriented Si wafers in KOH solution using no protection. V-grooves with (111) plane side walls, for dividing individual wafers into individual X-ray mask substrates, are simultaneously formed by the unisotropic etching. X-ray absorber patterns are fabricated on the SiNv membrane with rf-sputtered tungsten, by the subtractive method. Employing the present method, SIN, mask blanks, with less than 0.3μm warpage across a 26mm square window, have been fabricat&I with several tens of times higher throughput than can be achieved by the conventional process.
We present a new model capable of fully describing the image formation in X-ray Lithography with a Synchrotron Radiation source. All the relevant effects, such as beam size, scanning, transmittivity and reflectivity are included. The model itself can be used to predict the achievable resolution for a given process. It is applied to the discussion of a particular process, based on Hewlett Packard mask technology and using one of the Center beamlines, for which we show that resolution in the sub-0.25 micron region can be easily achieved. Solutions to the problem of anamorphicity are presented, as well a discussion of the optimum configuration for scanning.
We have demonstrated that high-intensity soft x rays (900 eV to 3 keV) from transition radiation can be generated by passing moderate-energy (17 to 109 MeV) electron beams through targets consisting of thin (1 pm) multiple foils of beryllium and aluminum. We measured the absolute photon flux from five foil targets using a 44-pA, 109-MeV-elec-tron beam, and estimated the photon flux by exposing 4" silicon wafers coated with PGMA photoresist. All previous measurements of photon production used photon-counting methods. We destructively tested foils at high-average cur-rents for the first time. We exposed photoresist using a mask to produce a soft-x-ray lithograph. This research constitutes the first use of transition radiation as a source of soft x rays for lithography. These results indicate that moderate-energy linacs with transition radiators offer an alternative method of high power production of soft x rays for lithography. The radiation produced is at least three orders of magnitude brighter on a per-electron basis than synchrotron radiation. Storage rings have higher average beam currents than linacs; however, with a 10-2 difference in average currents, our experiments show that transition radiation will have the same average flux. Small, inexpensive accelerators such as one-klystron linacs can produce the required beam energies needed and would be less expensive than larger synchrotron sources. The Lawrence Livermore National Laboratory's (LLNL) electron-positron linac was used in a series of short experi-ments (two 8-hr. shifts) to show feasibility. The foils were located in the accelerator cave in a direct line with the linac primary beamline. Immediately downstream from the foils, the electron beam was deflected into a beam-monitoring system. The lithography station and photon detectors were located 6.4 m downstream of the foils. The silicon wafers were partially shielded from other ionizing radiation produced in the accelerator cave. The soft-x-ray radiation was emitted in a cone of apex angle ± 5 mrad, with a diameter at the wafer of approximately 10 cm. The average power at the silicon wafer was 0.28 mw using the 44-pA beam. The x-ray flux produced a smooth exposure of the resist, result-ing in the "doughnut" pattern that is characteristic of the transition-radiation cone. No attempt was made to determine the optimum exposure time during these runs, and the wafers were left in the photon beam for time periods between 1 to 2 hrs.
For the replication of submicron patterns with high throughput and high overlay accuracy, an x-ray stepper with a plasma source has been developed. The maintenance interval of the gas-puff z-pinch plasma source is 100 times better than that of the previous plasma source. The improvement is achieved by reducing electrode consumption and devising a new plasma remover. A single grating and double-pitch dual grating technique has been developed to align wafer to mask. The gap and lateral displacement between mask and wafer are detected by utilizing +1st-order diffraction light intensities. Their detection resolutions are less than 0.01pm. By combining this detection system with the conventional stages, an absolute gap accuracy of ±0.3μm and a lateral alignment servo accuracy of ±0.02μm have been achieved. Using this new x-ray stepper with the plasma source, a 0.3pm pattern has been replicated accurately in a maximum field of 30x3Omm at a throughput of 20 wafers per hour.
A hybrid e-beam/deep-UV lithography (a D2ED process) and its application for GaAs FET's are described. A D2 ED process consists of Deep UV exposure and Development in MIBK (methyl isobutyl ketone) for less critical features, and E-beam exposure and Development in IPA (isopropyl alcohol) for critical fine features. E-beam exposure is performed at one pixel per minimum linewidth. A higher throughput and better linewidth control are obtained by using a D ED process. A high overlay accuracy is obtained by use of tungsten registration marks and D2ED processes for the source/drain and gate levels in GaAs FET's.
This paper describes an innovative photolithographic method for the fabrication of 1/4 micrometer gates in gallium arsenide Metal-Semiconductor Field Effect Transistors (GaAs MESFETs). The method utilizes image reversal technology, in which negative polarity images are produced in positive diazide photoresists. This work describes improvements obtained using ammonia as the image reversal catalyst over work previously described which used imidazole . The ammonia based image reversal process is characterized with respect to sensitivity to several process parameters and uniformity of the resultant linewidth. The linewidth uniformity attained using this process is + 0.03 micrometer over a 50 mm diameter wafer and is currently used to fabricate 1/4 micrometer gate MESFETs on gallium arsenide.
Recent advances in optical lithography driven by the use of mid-UV radiation (365/313 nm) require resists optimized to operate effectively at these wavelengths. New positive resist formulations have been developed to meet this need. DYNALITH resists X-1608 and X-1605 display enhanced sensitivity toward mid-UV exposure. Comparison data vs. standard and deep UV resists are presented. A variety of exposure modes, including projection and contact, have been investigated. DYNALITH Positive Resist X-1608 is based on a novolac and 2,1,4 quinone diazides which are optimized for resist performance. This new resist 11.as sensitivity which is improved over standard resists in mid-UV exposures. Sensitivity of 30-70 mJ/cm is demonstrated at 313 nm and 365 nm. X-1608 mid-UV resist demonstrates submicron imaging capability with high contrast and wide process windows. DYNALITH Positive Resist X-1605 is based on a novolac and the more standard 2,1,5 quinone diazide. This resist formulation provides an overhung or reentrant sidewall profile with the use of standard processing steps. The absence of the necessity of a chlorobenzene soak coupled with the appearance of sidewall profiles as displayed indicates the X-1605 resist to have application for metal lift off processing. The suitability of consistent resist sidewall profiles for metal lift off provides an application for X-1605 resist in GaAs lithography. A control of the degree of curvature and overhang displayed by the resist profiles relative to formulation is described. Process stability of soft bake and exposure is presented for DYNALITH X-1608 on mid-UV projection aligners. Dry etch data relating resists X-1608 and X-1605 to standard resists is presented. Statistical process control (SPC) is an important control method as production requirements shrink to the one micron regime. The use of process control (X) and range charts (R) generated for coating DYNALITH X-1608 resist is presented. SEM photos characterizing the resists and certain process latitudes are presented. Analytical techniques, such as GPC and C13 NMR, assisted the characterization of structure/performance relationships.
Proc. SPIE 0773, Direct-Write Electron Beam Lithography For Integrated Circuits: Submicron Image Reversal Process Of Novolac-Diazo Resist And Its Stability Towards Composite Metallization In Bipolar Gate Arrays For Vlsi, 0000 (30 June 1987); https://doi.org/10.1117/12.940356
Considerable effort has recently been directed at the development of direct write electron beam lithography techniques for the fabrication of custom gate arrays with the submicron design rules. Advantages include quick turn around time for prototype circuits as well as the elimination of the mask fabrication cost. In this paper, a lithographic technique for the patterning of submicron dimensions using an image reversal process and its process stability for the layered structures of TiW/A1-2% Cu interconnect metallization in a double metal technology for the prototyping of bipolar gate arrays, are described. This image reversal process for AZ1470 photoresist differs from that of Oldham and Heike (reference number 6) in that an extra edge exposure of electron dose is given to the resist to create electron density difference between exposed and unexposed areas and also to achieve vertical sidewall of the resist profile. The various processing parameters are optimized to obtain 90Ã‚Â° sidewall of the resist profile with 0.25pm gate metal features, with high contrast and high aspect ratio. Resolution between 1.0pm and 2.0pm (1.0pm lines and 1.5pm spaces) on TiW/A1-2% Cu electrode metallization patterns were obtained in lithographic evaluation of this image reversal process for the fabrication of bipolar gate arrays. Such resulting patterns have the following characteristics: no notching or necking of the pattern, reduced proximity effect with no feature biasing needed, higher etch resistance of novolac resist, higher speed of electron beam exposure, and compatibility of the resist and equipment for standard processing. Isolated gate features as small as 0.25pm and 1.0pm lines and 1.5pm spaces on metallization patterns in prototyping for bipolar gate arrays have been realized by this lithographic process using direct write electron beam technique.
Tri-layer resist technique has been developed for volume production of VLIs to achieve 0.8 um line and space pattern using an NA 0.35 stepper. The 0.8 um feature process was done mostly by optimizing normality of developer for top-layer resist. Obtained resolution dep ends strongly on normality of the developer. The lower normality gives much wider latitude to CD control. Possibility of application of tri-layer resist process whose struc,ture con-sists of top-layer resist, middle-layer silicon resin, and underlayer resist was examined.
In response to a study conducted at Perkin-Elmer ALO, which showed that surface anomalies present on PBS-coated masks prior to exposure were responsible for more than 50 percent of the chrome spot defects observed on the finished masks, Perkin-Elmer EBT initiated a study focusing on the causes of the defects found in the original materials. This study found that chemical oxidation, not foreign particulate contamination, was the major cause of the discrete defects found on PBS films. Elemental analysis of the small defects on fresh PBS-coated quartz masks with a scanning electron microscope, energy-dispersive x-ray analysis, and Auger spectroscopy showed that 66 percent of the defects contained little or no elemental contamination other than excess oxygen. X-ray photoelectron spectroscopy and small-spot refective infrared analysis of larger oxidized defects on older plates and of defects induced by known initiators of oxidation in polymers yielded information on chemical functional groups in the defects. This information confirmed the finding that oxidation was responsible for the changes observed in discrete areas. Oxidation changes the physical and chemical properties of the reacting area and produces an embedded particle or pinhole that causes a chrome spot or pinhole defect in the finished mask. Perkin-Elmer EBT has matched chrome spot defects that are images of known oxidized areas on PBS films with chrome spot defects detected by a KLA on finished production masks at Perkin-Elmer ALO. That similar defects have been observed on PMMA, EBR-9, and several kinds of AZ optical resists allows us to predict that oxidation of resists increases defect densities in all types of microlithography. The mechanisms of oxidation that result in discrete defects are described, and ways of reducing or eliminating such defects are discussed.
The characteristics of a photomask repaired with a focused ion beam (FIB) are described. The edge-placement accuracy of the repair is +0.1 um, while the edge roughness is almost negligible for both clear and opaque repairs. Less than 3% of the repair sites are captured on an automatic photomask inspection system. Correlation between linewidth measurements on the photomask and wafers printed on a projection aligner show that variations of the line-edge are well within the +0.1 um placement accuracy of the FIB repair system. This means that truly zero-defect plates are possible with repair CD's the same as the lithography CD's.
Based on our present understanding of the recent progress in optical technology, it appears that wafer steppers will be applicable for the production line up to 16M DRAM having 0.5 μm design rule or so. From this point of view, we have concluded that E-beam system promising the production of high quality reticles is mandatory necessary in the field. For the back-ground mentioned above, Toshiba has developed the new conceptual E-beam system designated EBM-160/80. This paper describes the design concept and system outline on EBM-160/80. The most essential requirements of this type of system, such as raster scan, round Gaussian beam and continuous moving stage, are to make CD increment smaller, simultaneously to get high production throughput and reasonable accuracy. Employing high speed bit data generating processor (HBG), we have completed high production throughput E-beam system which means throughput free from reticle pattern complexity. As a result, it takes about 40 min. at 0.25 μm address size or 250 min. at 0.1 pm address size for 5X, approx. 80 mm x 90 mm reticle with several millions of pattern. EBM-160/80 has capability to produce high quality reticle for up to 16M DRAM. In order to realize enough accuracy, the new technologies have been developed and integrated. As a result, we could achieve our accuracy target, butting accuracy 0.05 pm, CD control 0.1 μm, overlay accuracy 0.1 pm, scan linearity 0.05 μm.
A technique to evaluate the X-ray intensity distribution on the wafer in an X-ray lithography system equipped with a conventional X-ray source with a Pd target was devised. A practical formula for the Pd L X-ray production efficiency, including parameters such as the incident electron beam energy, its incident angle, and the X-ray take-off angle was derived to develop a method of simulating the X-ray intensity distribution on the wafer. This simulation includes realistic factors such as the target shape, the profile and direction of the electron beam, and the X-ray absorption by the window and mask membrane. A good agreement between the calculated and the measured X-ray intensity distributions obtained in the application of this technique to a cone shaped target verified the usefulness of the technique in the design of Pd X-ray sources.
Boron nitride membranes (produced through chemical vapor deposition of diborane and ammonia) have been exposed to synchrotron radiation and have showed severe degradation in optical properties after absorbing doses on the order of 200kJ/cm3. Damage kinetics are described as well as measurements made to identify the damage mechanism. Preliminary results on associated mechanical damage are also presented. Boron nitride membranes (produced through the pyrolysis of borazine), silicon nitride and silicon membranes exposed and tested in the same manner showed no such degradation.
The x-ray lithographic performance of a new, experimental negative acting, single level resist has been investigated. Unlike other negative x-ray resists, which are solvent developed, the new resist is developed with aqueous base. This results in very low image swelling and allows high resolution, high aspect ratio, negative resist images to be obtained with a conventional palladium anode x-ray source of wavelength 4.37 A. The x-ray sensitivity of the resist to Pd x-rays is about 40 mJ/cm2, sufficient to allow a throughput of 5 to 10 wafer levels per hour , when used in conjunction with an x-ray stepper powered by a conventional, fixed anode, 6kW x-ray source. Using this production oriented x-ray stepper and suitable x-ray masks, submicron resolution is demonstrated in single level resist layers of 1 to 2 pm thickness over various substrates and topographies. Dry etch resistance under Si, poly Si and Al etching conditions is evaluated. Thermal stability and DUV hardening characteristics are also investigated. The speed and excellent processing characteristics of the resist make it very attractive for hybrid x-ray/optical lithography applications, using conventional x-ray lithography systems.
The recent resurgence of interest in Wafer Scale Integration (WSI) is driven by a requirement for dense multilayer interconnect at wiring capacities far in excess of that which is achievable in ceramic hybrid packages. All of the problems associated with achieving satisfactory yield in such structures must now be reexamined to see whether the current technology is capable of achieving what has proven so elusive in the past. One of the relevant technologies is direct write electron beam lithography. Initially. efforts are being directed at fabricating wire at rather large dimensions (5-10 pm) with similar wire separations. At these dimensions. good clean room practices should be adequate to fabricate about 20-70 meters of fault-free wire on 97% of the wafers. However. longer wire lengths encounter some defects with higher probability. The IBM EL-2 electron beam lithography system available at the Rensselaer Center for Integrated Electronics is capable of achieving discretionary wafer wide wire patterning because it can be used in direct write to wafer mode with excellent registration and low stitching error. The availability of this tool eliminates the cost of plate making and permits the use of adaptive wafer wire rework for repair. In this paper we examine some of the strategies and technical issues associated with E-Beam patterning of wafer length interconnections.
E-Beam resists such as PBS have been used successfully by the mask making industry for many years, however, PBS suffers from a few major disadvantages. These disadvantages include safety issues stemming from solvent processing, lack of latitude, particularly with respect to humidity during development, poor plasma durability and a long, many step process which increases the probability of added defects. This paper describes a process developed to utilize MP 2400-17 optical photoresist for electron beam mask lithography and presents production results achieved. The benefits of optical photoresist over conventional positive EB resists are aqueous processing, wide and controllable process latitude, plasma durability, increased resolution and lower achievable defect densities. In addition, E-Beam exposed optical photo resists can be processed to produce a high resolution negative image, potentially replacing COP. One major drawback is decreased exposure sensitivity. Although the required multi-write scans increase total write time, the averaging effect of multiple exposures do produce superior line edge definition and resolution for a given address unit size. An analysis is presented demonstrating that the reduced process time and complexity, coupled with increased yield, can more than offset the cost of increased write time.
We recently reported on a proximity, flood exposure process using pulsed electron beams.1 We showed replication of 0.5 um feature sizes from an electron transmitting stencil mask on to 3 um PMMA film via 28 KV pulsed electron beams produced in air and helium at 50 mTorr. In this paper, we describe the direct patterning of a commercial polyimide spin coated on a silicon wafer and cured at 100°C by exposure to 28 KV pulsed electron beams (current pulse duration 500 nsec, FWHM and 100 pulses) produced in 50 mTorr air and helium. The exposed region of polyimide cross-linked and the region covered by the 7 um line on the electron microscope grid used as stencil mask was unaffected. Patterning was completed by wet development in N-methylpyrolidone at 21°C for 15 secs. We present developed thickness vs exposure characteristics and SEM photographs of developed patterns.
Proximity correction in electron beam lithography is essential to obtain the best performance in the submicron regime. Several parameters are required to achieve good correction and their interaction is complex. This paper describes the use of response surface analysis to optimize those parameters values. The effect of individual parameters as well as the result of optimized parameters will be shown for the case of e-beam exposed optical positive resist.
An electrical tester has been designed for measuring proximity effect in e-beam lithography. The tester consists of a clover-shaped van der Pauw resistor for sheet resistance measurement, a four-terminal resistor for linewidth measurement, and a second four-terminal resistor of identical width but with adjacent bars for evaluating changes due to proximity exposure. The test chip is composed of a set of testers with various combinations of linewidth, bar size, and intermediate space, ranging in dimension from 0.5 μm to 10 μm. Computer software has been developed to interface a commercial computer to the wafer prober for fully automated data acquisition, statistical analysis, and graphic display. The test system yields very high precision in both the sheet resistance (3 a < 1% of nominal) and electrical linewidth (3 a < 0.01 μm). The accuracy of the linewidth data has been verified by SEM measurements. The chip can serve as a general purpose metrology tool to evaluate the efficacy of different proximity correction techniques in e-beam lithography, to complement SEM linewidth measurements which suffer from profile and threshold dependence especially for non-vertical sidewalls, and to monitor linewidth control for submicron process development. Using an e-beam exposure tool at 20kV, the chip has been delineated in GMC, a negative imaging resist, in a trilevel resist structure, on substrates of tantalum silicide and aluminum. These substrates correspond to the GATE and the METAL level substrates in a MOS integrated circuit. In addition, it has been delineated in chromium, a typical photomask substrate, using single layer resist. The extent of proximity exposure effect on each of these substrates is reported. Linewidth deviations of 0.1 μm or greater are observed for near-micron equal line and space patterns. In addition, proximity exposure increases with incident exposure dose and the atomic number of the substrate. On the basis of these results, VLSI layout constraints arising from e-beam proximity exposure are identified.
Recent results in the development of positive and negative resist processes for use with the AEBLE-150 electron beam lithography system are discussed, detailing techniques used for the evaluation and modeling of resist performance. Specific results for RD-2000N, a negative resist available commercially from the Hitachi Corporation, are presented demonstrating processes suitable for use with the AEBLE-150 for feature sizes below 0.5μm. In addition, results of processes with high resolution imaging in thick layers of PMMA are presented.
We present a description of our second generation micromachining system. This machine has been developed at AT&T Bell Laboratories for applications including photomask repair, integrated circuit modification, and fabrication of integrated optical structures. The architecture incorporates many of the features and capabilities found separately in other systems, in a unique combination with emphasis on flexibility and ease of operation. The hardware features a 30 KeV Gallium beam with a one millimeter deflection field and 250 mm by 300 mm stage travel. Provisions have been made for secondary electron and ion imaging, charge neutralization, gas phase material deposition and secondary ion mass spectroscopy (SIMS).
A novolac resin resist (ONPR-800) is exposed to 50 keV Ga focused ion beam (FIB) to create a fine line pattern by a self-development process. A dose dependence of the self-developed depth shows a rapid increase at some critical dose of about 3x10 -2 C/cm 2 . Furthermore, it is found out that the shape of the groove is considerably affected by the tensile force in the resist film. We can obtain grooves with the width of 40 nm and the aspect ratio of 40 by eliminating the stress. Gold line pattern of a 0.1 μm width is successfully produced by electroplating into the self-developed resist pattern.
The use of focused-ion-beam (FIB) technology for the repair of masks and for the modification of integrated circuits is discussed. The processes required for these two applications are similar and can thus be implemented by similar systems. Focused-ion-beam sputtering and focused-ion-beam induced deposition results are presented which show the usefulness of FIB techniques for repair applications.
Wafer scale interconnections offer an approach for improved wiring in ultrahigh speed digital systems. Conventional packaging introduces excessive parasitics such as coupling, stray inductance and capacitance, and excessive delay. Fabrication of large amounts of wafer scale wiring (hundreds of meters of wiring) will require automated inspection and repair strategies. The focused ion beam (FIB) is uniquely suited to some of these tasks. In this paper, a high yield lift-off process is employed to fabricate the wafer wire. Residual defects in this process have been categorized and found amenable to detection and repair by using the ion milling capabilities of the focused ion beam. However, special steps are required to enhance the milling rates. Secondary electron imaging permits the inspection of surface defects, but precautions must be taken to neutralize charge build-up on insulators.
Focused ion beam systems for mask repair have been built by several companies. These systems differ from each other in beam optics design (one or two lens systems) and various mechanical and electrical aspects, but all use the same Gallium ion beam from an "elemental" ion source to effect repairs at the mask surface. The disadvantage of this approach is an inherent inability to select an ion beam optimized for each task required in mask repair and the problems associated with "gallium staining" of the mask substrate. We report on an advanced focused ion beam mask repair system under development that combines a mass separator with two lenses in the ion optics. Significant advantages result from this design when used with "alloy" vs "elemental" liquid metal ion sources. For each task, the mass analyser selects the most suitable ion species from the beam emitted by the source. A beam of ions having a low sputter rate is used during imaging and critical dimension measurements, minimizing damage to the mask and eliminating "gallium staining". During repair, a beam of ions selected for the task being performed is used to optimize the defect repair process. The ion beam spot size in the NanoFix is changeable in size from 100 nanometers to 500 nanometers, with the beam voltage being variable from 4 kV to 60 kV. The x-y stage has travel for the repair of seven inch mask plates. The target and optical chambers are differentially pumped with high speed vacuum pumps allowing ion-beam-assisted chemical vapor deposition in the target chamber while maintaining a low pressure in the optical chamber. The design, performance, and additional advantages of the NanoFix in mask repair applications are described for a simple to use and reliable machine for the production environment.
The potential of excimer laser lithography was studied by using a newly developed KrF excimer laser exposure system which employed an achromatic lens of 0.37 NA. As a result, a resolution limit of 0.3 μm was achieved by the use of PMGI resist on a tri-level structure. However, for the case of resist exposure on a bare Si wafer, the resist film remailed locally in layers along the nodes of the standing waves, and fine pattern could not be obtained. This phenomenon is called spotted development in this paper. The spotted development, which is due to strong standing waves within the resist film, was successfully solved by the use of new resist process technologies such as a bias exposure method and excimer laser image reversal process.
An electron beam lithography system has been developed for research and development of fine structure advanced devices. The system is capable of 0.1 um resolution, 0.04 um stitching accuracy, 0.04 um overlay accuracy and 1 wafer/hr throughput. One of key technologies used in this system is a variable gaussian optics and a pattern edging-process. This makes it possible to realize ten times higher throughput than the conventional fixed gaussian beam method and provide a simple means of proximity correction.
The focused ion beam (FIB) technology has various applications such as microfabrication and micromachining. Two FIB systems, JIBL-106S and JIBL-150, which can perform pattern writing using pattern data from a CAD system have been developed. Both systems have the ability to produce actual devices. Using the FIB systems, various experiments have been performed, and some of the resutls have offered new fabrication processes of semiconductor devices.
Intense soft x-ray generation in 1.05, 0.53, 0.26μm laser-produced plasmas has been investigated for the photon energies of 0.15 to 3keV. X-ray spectra and conversion efficiency are obtained as a function of atomic number. We find a parameter range of the target and laser conditions which allows us to achieve an adequate throughput of the exposure for x-ray lithography. X-ray lithography experiments using laser plasma x ray are presented. The facility consisting of a laser system and several exposure stations is proposed. Finally we propose the use of liquid or solid cryogenic targets of xenon or krypton to avoid the deposition of the target material. A preliminary experimental result and target schemes are presented.
The design parameters of a compact synchrotron radiation (SR)ring dedicated to industrial X-ray lithography are discussed. Further studies have been continued for making the SR ring and its injector smaller to complete a practical SR system. The Electrotechnical Laboratory and Sumitomo Electric Industries, Ltd. jointly completed a conventional compact test ring "NIJI-1 (rainbow-1 in English)" and succeeded in SR generation on February 1986. Presented here are useful results indispensable for the development of a compact SR system.