Improving resolution in photolithography with a phase-shifting mask

The phase-shifting mask consists of a normal transmission mask that has been coated with a transparent layer patterned to ensure that the optical phases of nearest apertures are opposite. Destructive interference between waves from adjacent apertures cancels some diffraction effects and increases the spatial resolution with which such patterns can be projected. A simple theory predicts a near doubling of resolution for illumination with partial incoherence σ < 0.3, and substantial improvements in resolution for σ < 0.7. Initial results obtained with a phase-shifting mask patterned with typical device structures by electron-beam lithography and exposed using a Mann 4800 10X tool reveals a 40-percent increase in usuable resolution with some structures printed at a resolution of 1000 lines/mm. Phase-shifting mask structures can be used to facilitate proximity printing with larger gaps between mask and wafer. Theory indicates that the increase in resolution is accompanied by a minimal decrease in depth of focus. Thus the phase-shifting mask may be the most desirable device for enhancing optical lithography resolution in the VLSI/VHSIC era.     

New concept for applying edge line phase-shifting masks to arbitrary mask layouts

This paper explains the principle of a method which avoids printing of phantom resist lines due to undesired intensity minima appearing on Cr-less edge line phase-shifting masks. The method combines principles of grey-tone lithography and attenuated phase-shifting masks to give, what we call, a Cr-Less Attenuated Phase-shifting mask (CLAP). Rules for generating a CLAP design and a paradigm setup of a CLAP mask are presented. The capabilities and possible limitations of the CLAP method based on simulated results for a standard wafer stepper setup using the SOLID lithography simulator are being assessed.     

Electroprinting tubes and their applications to television facsimile

This paper describes two types of electroprinting tubes, one of which has been applied to television facsimile. The electrostatic printing tube and fiber-optics printing tube have a resolution of 8 lines/mm and 15 lines/mm, and a writing speed of 200 m/s and 1700 m/s, respectively. The electron scanning method utilizing the fiber-optics printing tube showed good results in experimental television facsimile.     

焊膏印刷不良与漏板

焊膏印刷工序中的关键部件漏板对印刷质量有很深的影响。不同加工方法做成的板带有不同的特点，也存在不同的不良隐患。改进后的增加聚四氟乙烯的金属漏板和激元漏板，在性能方面达到了新的水平。     

Inkjet printed copper source/drain metallization for amorphoussilicon thin-film transistors

Source/drain metallization to amorphous silicon thin-film transistors has been made by inkjet printing. Contact pads of a metal organic copper precursor were inkjet printed, and then converted to copper metal at a maximum process temperature of 200°C. The copper contacts were used as the mask for back-channel etch. Laser printed toner was used for all other mask levels in a photoresist-free fabrication process. The inkjet printing of copper contacts represents a further step toward an all-printed thin-film transistor technology     

HV‐SoP Technology for Maskless Fine‐Pitch Bumping Process

Recently, we have witnessed the gradual miniaturization of electronic devices. In miniaturized devices, flip‐chip bonding has become a necessity over other bonding methods. For the electrical connections in miniaturized devices, fine‐pitch solder bumping has been widely studied. In this study, high‐volume solder‐on‐pad (HV‐SoP) technology was developed using a novel maskless printing method. For the new SoP process, we used a special material called a solder bump maker (SBM). Using an SBM, which consists of resin and solder powder, uniform bumps can easily be made without a mask. To optimize the height of solder bumps, various conditions such as the mask design, oxygen concentration, and processing method are controlled. In this study, a double printing method, which is a modification of a general single printing method, is suggested. The average, maximum, and minimum obtained heights of solder bumps are 28.3 μm, 31.7 μm, and 26.3 μm, respectively. It is expected that the HV‐SoP process will reduce the costs for solder bumping and will be used for electrical interconnections in fine‐pitch flip‐chip bonding.     

Direct gravure printing (DGP) method for printing fine-line electrical circuits on ceramics

The tendency toward higher packing densities and higher frequencies for telecommunication devices based on ceramic technology requires smaller dimensions for electrical wiring. Electrical thick-film circuits for ceramic and LTCC-substrates have, up to now, been printed with screen printing, where the printing lines width limit is about 125 /spl mu/m in mass production. A silicone polymer direct gravure printing (Si-DGP) process has been developed to perform smaller dimensions, down to 20 /spl mu/m lines width, for electrical circuitry. In the DGP process, the conductor paste is doctored to the grooves of the gravure and then it is pressed against the substrate. The paste is, thus, printed directly onto the substrate from the patterned gravure. The results showed that, using the DGP process, it was possible to print conductor lines down to 20 /spl mu/m in width. It was also noted that a 100% transfer of paste from the grooves of the gravure could be obtained with commercial pastes using the silicone polymer gravure. A dried thickness of up to 28 /spl mu/m was measured for the narrowest lines. Also conductor lines printed by the Si-DGP method were embedded inside LTCC-module.     

Photolithographic linewidth control

A simple model for the image formation process in photoresist is proposed based on Fresnel diffraction from the edge of a mask feature. It is shown theoretically and verified experimentally that the dimensional difference between a clear mask feature and its image in photoresist is given by aL^½[ ln (Ei) - ln (ET) + ln (K) ] where a and K are constants peculiar to the exposure optics, L is the separation between mask and silicon wafer, Eiis the exposure energy, and ETis the effective exposure energy threshold of the photoresist. The model is used to show the existence of "optimum" exposure ratios Ei/ETwhich minimize image variability in hard-, soft-, and near-contact printing. Control of this exposure ratio is found to be the key to successful use of off-contact printing. Based on this model, a photolithographic process control system is outlined in which exposure tool operation and photoresist processing parameters are characterized and monitored with a single silicon wafer. The system is equally applicable to photomask fabrication.     

Models for characterizing phase-shift defects in optical projectionprinting

An algebraic model is developed for characterizing the printability, inspection, and repair of phase-shift defects in optical projection printing. Phase-shift defects are particularly difficult to characterize because of the many parameters associated with the exposure tool and with the attenuating phase shift mask (PSM) pattern. Furthermore, the parameters change during inspection of the attenuating PSM because the mask is examined under illumination conditions which differ from the exposure illumination. An algebraic model which encompasses this large set of variables is derived by considering the electric fields under the mask to be a combination of the electric fields from the feature and defect. These fields are then combined according to the mutual coherence function for the mask illumination. A notable difficulty is the relative phase shift due to defocus between large and small features. The model is shown to be valid for defects up to 0.35 λ/NA by comparison to SPLAT. Experimental verification is made for defects impacting a 6% transmitting PSM for 0.35-μm features at i-line. The reliability of the model is illustrated by giving rules of thumb for defect printing in attenuating PSM's     

Aligned double exposure in deep X-ray lithography

Deep X-ray lithography with synchrotron radiation is a powerful tool to generate threedimensional microstructures with high aspect ratios. In order to complement and enhance the normal shadow printing with methods to generate true threedimensional structures, we investigated the aligned multiple exposure process to produce step-like LIGA structures also involving the sacrificial layer technique to obtain movable structures. Irradiations have been performed utilizing a newly developed X-ray Scanner (JENOPTIK GmbH) with internal optical alignment system.

Multiple exposure requires the alignment of mask and substrate. We used silicon nitride mask membranes with 10 μm thick gold absorber patterns, which show excellent transmission in the visible light range for alignment purposes and good X-ray transparency in the hard X-ray regime.

The first results of double exposure experiments obtained with the scanner prototype are promising. With the exception of a systematic error an alignment accuracy of σ_x = 0.26 μm and σ_y = 0.4 μm (standard deviation) has been achieved. Present work concentrates on the improvement of the adjustment system.

All the exposures have been carried out at the BESSY wavelength shifter (Berlin/Germany).     

A study of projected optical images for typical IC mask patterns illuminated by partially coherent light

Optical projection printing using partially coherent illumination is simulated for one micrometer and half micrometer objects representative of typical mask patterns such as contact holes, rectangular bars and openings, intersections of perpendicular lines, and adjacent lines of unequal lengths. The image intensity distributions in absorptionless photoresists on nonreflective substrates are plotted as sets of constant intensity contours. For each pattern and illumination, an exposure-defocus (E-D) diagram is generated by evaluating the combined exposure and defocus tolerance yielding linewidths within ±2.5 percent of the mask linewidth. Besides comparing the image and ED margins of different object shapes and sizes, the effects of high versus low degrees of coherence, single versus dual wavelength, as well as long-wavelength high NA versus short-wavelength low NA were studied using the 1-µm rectangular opening.     

The absorption ink transfer mechanism of gravure offset printing for electronic circuitry

The gravure offset method has been developed toward an industrially viable printing technique for electronic circuitry. In order to obtain the optimum ink resin for printing lines of required thickness (>5 /spl mu/m) of narrow lines (down to 25 /spl mu/m), several ink resin systems have been assessed in previous studies by the authors. The best printed results were obtained with a novel ink using a hydrocarbon resin. This ink did not comply with the traditional ink transfer mechanism based on evaporation of the solvent, but with a postulated new "absorption mechanism.".     

A new patterning process concept for large-area transistor circuitfabrication without using an optical mask aligner

A new concept to produce large thin film transistor liquid crystal displays (TFT-LCD's) without using an optical mask aligner is proposed which emphasizes patterning technology. Some experimental thin film transistors (TFT's) are fabricated according to the concept and operated like conventional transistors fabricated by using an optical mask aligner. The concept includes improvement of printing technology and development of a double-layer resist method. The latter method employs a printed ink pattern and a photoresist. This prevents contamination of thin films by metal impurities which affect electrical characteristics of the TFT's. A special gravure offset printing technology is proposed, composed of a large thixotropy valued UV ink, and a fine, precision etched glass intaglio. The experimental TFT's, with a designed minimum gate length of 10 μm, have comparable electric characteristics to those of conventional poly-Si TFT's     

Masked ion beam lithography for proximity printing

Optical and X-Ray proximity printing systems are resolution limited by diffraction and beam dispersion. Parallel dispersion free ion beam systems are therefore ideal to transfer stencil mask patterns onto all sorts of nonideal substrates. A feasibility study was performed with the existing Alpha ion projector of the Society for the Advancements of Microelectronics in Austria operated in the MIBL (Masked Ion Beam Lithography) mode with ≈ 10×10 mm² exposure field. Structures as small as 0.2 μm in diameter could be transfered even with a gap of 1 mm between stencil mask and substrate. The widening of resist lines with 10% increase in dose was evaluated to be 14 nm for 2800 μm gap and 4 nm for 300 μm gap. This excellent exposure latitude favourably compares with synchrotron based X-ray lithography, where a widening of 20 nm with 10% overexposure has been reported for a 40 μm gap, and 10 nm for 10 μm gap. Promising applications of the MIBL technique include the fabrication of flat panel displays based on vacuum electronics (field emitter displays), surface acoustic wave and microoptic devices and - in combination with reactive ion etching - the fabrication of micro electro mechanical systems (MEMS). Prospects for MIBL steppers of printing fields > 100×100 mm² are discussed.     

Study of bending reliability and electrical properties of platinum lines on flexible polyimide substrates

We have experimentally studied the variation in electrical resistance of flexible platinum lines patterned on polyimide foil when they are subjected to circular bending constraints. The lines were patterned by means of standard photolithography and sputtering deposition. Two different photolithography masks were used for comparative evaluation: an un-expensive transparency mask and a standard chromium mask. Measurements of the temperature coefficient of resistance (TCR) and time stability of the resistance have been acquired for lines bent down to 1.25 mm radius of curvature on a customized bending setup, showing good reliability results. The robustness of the lines has been also assessed by registering their change in resistance while bending at different radii of curvature. The lines showed reliability issues for radii of curvature below 1.25 mm, presenting a resistance variation of 19% for transparency mask-fabricated lines and 9% for chromium mask-fabricated lines. The worse reliability performances of transparency mask lines, compared to the chromium mask ones, was found to be due to their imperfect edges, which promoted the formation and propagation of cracks during bending. The results of the experiments in this work permitted to compare the performances of flexible conductive lines with different geometry and fabricated with two different masks, establishing quantitative and qualitative bending limits for their appropriate operation in flexible electronics systems.     

A review of mask errors on a variety of pattern generators

The question of how mask dimensional errors impact yield is becoming increasingly critical to VLSI manufacturing. Both the magnitude and the spatial correlation of CD and registration errors are believed important to this issue. As part of a program to characterize these errors, we have had one identical test mask made on 6 different state-of-the-art mask pattern generators with widely different architectures. The test mask provides information on both registration and feature-size errors in both x- and y-directions, and does so over distances of several centimeters with spacing between measurements as small as 1 μm. More than 100000 data points have been collected from these test plates using a LMS2000 optical metrology system, and are analyzed in the spatial frequency domain where error contributors as small as 1 nm can be identified. All systems were found to have similar characteristics in that most error contributors occur at a number of machine-specific spatial frequencies correlated to the particular architecture and printing strategy of the machine. Comparison of raster to vector machines show that vector machines tend to have more periodic error contributors, especially in the high spatial frequency range, which is consistent with the more complex writing fields used to achieve higher throughput     

石墨烯微纳结构加工技术的研究进展

简单介绍了石墨烯独特的光电子性质,说明实现其在光电子器件中应用的有效方法是进行微纳加工。接下来对主要的石墨烯微纳加工技术——掩膜光刻、转移压印以及激光直写和干涉进行详细阐述,通过实例对每种加工技术的关键步骤和特点进行说明,并分析比较了不同加工技术的优缺点。然后对近期出现的转移压印辅助光刻和飞秒直写辅助转移压印技术的加工流程进行详细介绍,阐述将两种加工技术相结合应用于石墨烯微纳结构加工的优势。最后,简单展望了石墨烯微纳加工未来的发展趋势,指出需进一步研究的问题,对如何更好地实现石墨烯微纳结构的加工提出一些建议。     

数字喷墨打印技术在PCB抗蚀层制作中的初步研究

随着数字喷墨打印设备和纳米油墨的不断发展,喷墨打印技术在PCB制作中得到了越来越广泛的应用。目前市场上主要包括三个方面的应用：抗蚀层、字符、阻焊。文章通过市场调研,成本评估和工艺能力评估重点研究了喷墨打印技术在线路抗蚀层制作中的应用。结果发现喷墨打印技术相对于传统的线路制作工艺具有一定的成本优势和线路制作能力。     

用光学制版设备制作1μm光掩模版

本文研究了用常规光学制版设备制作微细线条光掩模的加工技术,分析了精缩机,初缩版(原版)、化学处理、工艺环境在1μm光掩模版制作中的作用和要求。研制结果表明,采用反差大、过渡区小的初缩版,在严格聚焦的情况下进行分步精缩制版,精确控制显影和腐蚀时间,就能够制作出1μm条宽的光掩模版。