Feature Size Limit of Liftoff Metallization Technology

The feature size limits for liftoff metallization technology are evaluated both experimentally and by computer simulation following Blech's model. The mechanism producing a smoothly sloped metallization pattern profile was also clarified. The simulation reveals that the average slope angle of the metallization pattern sidewalls is determined by the reverse mask topology, metallization thickness, and the maximum incident angle of the evaporation system used for the metallization deposition. Simulation results showed good coincidence with experimental results. It is shown that the average slope angle can be controlled between 20/spl deg/and 70/spl deg/ with polyimide liftoff technology. Feature size limit, i.e., the minimum pitch of metallization patterns, is determined by the reverse mask topology and the maximum incident angle as well as by mechanical and chemical properties of the polyimide layer, but is independent of metallization thickness. In a sample application of the technology in the fabrication of interconnections on rugged LSI surfaces, the minimum pitch of the polyimide liftoff metallization patterns was estirriated to be 2.6 /spl mu/m.     

Polyimide liftoff technology for high-density LSI metallization

A new liftoff technology, in which a metallization layer can be deposited at high temperatures, is developed to provide two-level highly packed interconnection metallization. A heat-resistant polymide, PIQ^®, is employed as the liftoff layer. The reverse pattern of the metallization is formed by reactive sputter etching of the PIQ layer around a thin Mo mask. After metallization layer deposition, lift-off is carried out by electrolytic etching of the Mo mask, thus removing the layer deposited on PIQ. A higher packing density of interlevel connection is also accomplished by adopting exposed via holes. Utilizing this technology, fine-featured smoothly tapered metallization patterns can be obtained almost irrespective of the underlying topology. The minimum pitches of the first level, second level, and via holes are 5, 7, and 7 µm, respectively. This technology does not appear to be detrimental to bipolar device characteristics. A 4096-bit high-speed bipolar memory LSI with two-level highly packed interconnection metallization was produced experimentally utilizing this liftoff technology.     

The size effect of liftoff metallization of sputtered aluminum films

Liftoff metallization of sputtered aluminum films successfully produces small patterns with tapered sidewalls. In this metallization, a size effect occurs wherein pattern height is influenced by pattern width. This article reports experiments regarding size effect dependences on liftoff parameters of pattern width, film thickness, photoresist thickness, and sputtering argon pressure. The size effect is favorably suppressed by reducting photoresist thickness and sputtering argon pressure. In addition, the effect is discussed by a model taking into account shadowing of sputtered atoms due to photoresist patterns and aluminum film itself deposited on the photoresist patterns.     

在非晶硅上制备角度可控缓坡的方法

介绍了一种利用光的衍射原理制备角度可控缓坡微结构的方法。该方法在光刻步骤中通过调节掩膜板与基片之间的垂直距离来控制光刻胶图形边缘曝光量,光刻显影后得到剖面为正梯形的光刻胶图形,再经过干法刻蚀得到非晶硅的缓坡微结构。结果表明,制备的非晶硅缓坡结构角度（可小于30°）可控,制备方法简单,与半导体工艺兼容,可避免湿法刻蚀带来的过蚀及角度不均匀问题。     

How to design optimal metallization patterns for solar cells

Solar cells have a metallization pattern to collect the current. Generally, simple metallization patterns, such as the H-grid metallization pattern, a cross-hatched pattern or a full metallization, are used. With the widely used technique of screen printing, however, virtually any metallization pattern of any topology can be realized, but the problem is how to design the optimum topology. The paper presents a design method for optimal metallization patterns. Copyright © 1999 John Wiley & Sons, Ltd.     

Direct metallization of gold patterns on polyimide substrate by microcontact printing and selective surface modification

Patterned gold microstructures were fabricated on a polymer substrate by a novel method involving selective electroless plating and microcontact printing. The micro-sized gold patterns were made by the site-selective chemical modification of polyimide substrate films using aqueous potassium hydroxide solution and microcontact printing with a pitch size in the range of 20-200 μm. The base-treated area of the polyimide film became hydrophilic in the regions where the ion-exchange reactions took place for the subsequent metallization. The hydrophilic patterns were sensitized by placing the film in a solution of PdCl₂ and, subsequently, the activated substrate was immersed in an electroless plating solution of Ni and Au to provide well-developed gold patterns on polyimide substrate films.     

Influence of MEEF change on the mask shadowing effect in extreme ultraviolet lithography

The influence of mask error enhancement factor (MEEF) on the mask shadowing effect was investigated for extreme ultraviolet lithography. Imaging properties including horizontal-vertical (H-V) CD (critical dimension) bias and MEEF change through the pitch according to absorber thickness and process condition were studied using aerial image simulation. The mask structure used in this study consisted of tantalum nitride (TaN) absorber and 2 nm ruthenium (Ru) capping layer on the 40 pair of Mo-Si multilayer. As the absorber thickness increased and the pattern pitch decreased, both H-V CD bias and MEEF increased. At the illumination condition of 0.32 numerical aperture (NA), the H-V CD bias variation through the pitch was negligible and slightly increased at 1:1 pitch, while it steeply increased at 1:1.2 and 1:1 pitch for NA of 0.25. The MEEF value was below 1.5 for all calculated absorber thicknesses when the pitch was from 1:1.2 to 1:5, whereas it was 3 with 64 nm thick TaN for 1:1 pitch at vertical pattern. With the increment of absorber thickness, the MEEF difference between the horizontal and vertical pattern increased. We also calculated the H-V overlapping process window (PW) according to TaN thickness using 22 nm 1:1 line and space (L/S) pattern. As absorber thickness decreased, the overlapping zone in the EL of the focus-exposure plots between the horizontal and vertical features increased. Enough image contrast and H-V overlapping PW could be achieved by applying 38 nm thick TaN.     

Ion-beam etched multi-level resist technique for electroplating of submicron gold absorber patterns

A structuring process is developed which enables the fabrication of gold patterns by electroplating with a minimum linewidth of ? 0.3 μm. These patterns are used as mask patterns for X-ray lithography. They can be up to 1.6 μm thick. For this purpose, a resist pattern, which is generated by an electron beam, is transmitted to a multi-layer system by reactive ion-beam etching. The multi-layer system consists of a 2 μm thick polyimide layer, a 70 nm thick aluminum intermediate layer and a 30 nm thick gold passivation layer.With this process, X-ray masks with a polyimide membrane were produced and utilized for exposure to synchrotron radiation.     

亚波长线栅太赫兹偏振分束器的研究

为了提高工作在太赫兹波段偏振分束器的性能,采用激光诱导与化学镀铜的方法在聚酰亚胺衬底上制作了亚波长周期金属线栅太赫兹偏振分束器,并以返波振荡器作为太赫兹辐射源搭建了偏振分束特性测试系统。当入射波频率为340GHz、入射角为45°时,测得在入射波偏振在0°～180°变化过程中,该偏振分束器具有良好的偏振分束特性,透射和反射的消光比分别为27.3dB和10.5dB,插入损耗分别为0.13dB和0.32dB;用太赫兹时域光谱系统测得偏振分束器在0.2THz～1.5THz频域内透射消光比大于18dB。结果表明,测试结果与时域有限元方法模拟结果基本吻合。     

Tapered windows in phosphorus-doped SiO2by ion implantation

Phosphorus-doped SiO2is frequently used as a dielectric coating in silicon integrated circuits. It is important that windows in this dielectric have sufficiently tapered walls so that the subsequent metallization has good step coverage. It is shown here that tapered windows can be made in both Nitrox-deposited ∼ 1-percent phosphorus-doped SiO2and Silox-deposited ∼ 7-percent phosphorus-doped SiO2as well as undoped SiO2by an ion implantation which produces a thin damaged layer at the top of the oxide. The damaged layer etches at a faster rate than the undamaged oxide. This fast-etching layer undercuts the photoresist which serves as the etching mask and results in window walls having slopes in the range of 30-40° with respect to the wafer surface. Tapering windows by ion implantation is a dependable process that gives reproducible results without having to rely on the art of photoresist liftoff methods.     

Nano-scale metallization of Au on flexible polyimide substrate by reversal imprint and lift-off process

The nano-scale metallization of Au on flexible polyimide substrate by reversal imprint and lift-off process was investigated. The nano-scale mold was fabricated; the anti-adhesion property of nanometer-size Si-mold was improved and the surface free energy was calculated with the contact angle measurement. The ∼150 nm width Au nano-wires were successfully fabricated on Si and on flexible polyimide substrate with the proposed process. The PMMA thickness dependent trend with reversal imprinting and Au nano-wires lift-off results were also investigated by SEM analysis.     

基于Berreman 4×4矩阵对胆甾相液晶Bragg反射带宽的模拟研究

利用Berreman 4×4矩阵和Matlab编程模拟了胆甾相液晶的反射光谱,分析了螺旋数(液晶厚度)、基板的折射率、双折射、折射率色散、固定螺距、梯度螺距和入射角等因素对反射光谱带宽的影响。结果表明,要得到理想的Bragg反射带宽,液晶层的厚度即螺旋数N需达到N≥10;基板折射率会影响最大反射率,基板折射率ng与寻常光折射率no相比,ngno时,最大反射率比较低,ng越小越影响明显,当ng≥no时,具有很好的反射率;折射率的色散和大的入射角会使带宽变窄,而大的双折射Δn和螺距P可以得到较宽的反射带宽,但拓宽效果有限。通过梯度螺距的函数表达式,理论模拟了具有螺距梯度的胆甾相液晶的反射带宽,其对于胆甾相液晶宽波反射的实验研究具有一定的意义。     

金属雷电分流条对雷达罩电性能的影响分析

论文建立了天线罩分流条电磁传输研究模型,通过仿真和实验,对比分析了雷电分流条的电磁波传播特性,特别研究了中空十字型和十字型金属分流条的电磁波传输机理,以及金属分流条的材料、长度、宽度、厚度和电磁波不同入射方向对雷达罩电磁波传输性能的影响。研究结果表明:十字型金属雷电分流条对天线罩的电磁传输影响严重,而设计合理的中空十字金属分流条可以有效传输电磁波;另外,金属分流条的厚度和常用金属材料对电磁波传输影响不大,主要影响其导电能力和重量;在保证天线罩雷击安全的前提下,调整金属条长度可以使天线罩电性能达到最佳;金属条的宽度对电磁波传输性能影响明显,宽度越大,天线远场方向图主瓣增益越大;随着入射角的增大,方向图主瓣增益在减小,入射角超过30°时,雷电分流条对天线罩的电磁传输为负影响。     

中波红外集成偏振光栅结构参数对偏振性能影响仿真分析

中红外集成偏振焦平面探测技术将偏振探测技术与中波红外焦平面成像探测技术融合,通过异质集成的方式实现偏振光栅和探测器的单片集成,具有体积小、质量轻,机械稳定性高等优势,可实现多偏振方向的同时成像。像元级的亚波长金属光栅可实现不同偏振方向的高消光比,然而金属材料的选择、光栅的周期、占空比、厚度等参数均会影响偏振探测器的偏振性能。给出了亚波长金属光栅的理论分析,建立了中波红外集成偏振HgCdTe探测器的偏振性能仿真模型,对不同光栅参数对探测器偏振性能影响进行了仿真分析,确定了Al光栅周期200~400 nm,占空比0.5~0.7,厚度＞100 nm的参数选择。仿真分析得到在±14°入射角范围内,偏振消光比变化较小。同时,引入了Si基HgCdTe探测器,仿真分析了SiO₂增透膜厚度对偏振消光比的影响,确定了SiO₂最佳厚度在500 nm附近,对Si基和CdZnTe衬底集成偏振HgCdTe探测器的消光比进行比对,得出了Si基探测器偏振性能更优。仿真结果可为中波红外集成偏振HgCdTe探测器偏振光栅的设计提供理论指导和参考。     

Electrically Tunable Reflective Terahertz Phase Shifter Based on Liquid Crystal

We present a reflective spatial phase shifter which operates at terahertz regime above 325 GHz. The controllable permittivity of the nematic liquid crystals was utilized to realize a tunable terahertz (THz) reflective phase shifter. The reflective characteristics of the terahertz electromagnetic waves and the liquid crystal parameters were calculated and analyzed. We provide the simulation results for the effect of the incident angle of the plane wave on the reflection. The experiment was carried out considering an array consisting of 30?×?30 patch elements, printed on a 20?×?20 mm quartz substrate with 1-mm thickness. The phase shifter provides a tunable phase range of 300° over the frequency range of 325 to 337.6 GHz. The maximum phase shift of 331° is achieved at 330 GHz. The proposed phase shifter is a potential candidate for THz applications, particularly for reconfigurable reflectarrays.     

基于SCKF和姿态估计的SINS/GPS在线对准方法

该文提出了基于平方根容积卡尔曼滤波和初始姿态估计的捷联惯导/全球定位系统组合在线对准法。构建平方根容积卡尔曼滤波器来对初始姿态估计的非线性量测模型进行滤波,估计代表初始姿态转换矩阵的罗德里格参数,并以此求出当前时刻的姿态转换矩阵,从而求出当前时刻准确的姿态。该文分别对制导武器系统和车载系统进行了半实物仿真。仿真结果表明,此方法可在25 s左右完成在线对准。其中短距离制导武器仿真结果航向角及俯仰角误差在0.1°内,横滚角误差在0.3°内;低成本车载导航系统仿真结果航向角误差在0.2°内,俯仰角及横滚角误差在1°内,可满足制导武器及低成本民用车辆的对准需求。     

飞秒激光用超宽带金属介质膜光栅的优化设计和工艺容差分析

基于严格耦合波理论,提出了金属介质膜光栅（MMDG）的带宽评价函数和波长偏离评价函数,并对宽光谱MMDG结构参数进行优化。数值模拟分析表明,当MMDG的槽深为290nm、剩余厚度为10nm、占空比取0．28和入射角为60。时,对以1053nm为中心波长的TE波,其一1级衍射效率优于97％的带宽达到190nm。对结构参数...     

Ohmic contacts to n-type GaN using Pd/Al metallization

Ohmic contacts to n-type GaN grown by metalorganic chemical vapor deposition were formed using a Pd/Al-based metallization. Ohmic contact resistances and specific contact resistances were investigated as a function of rapid thermal annealing temperature, Pd interlayer thickness, and annealing time. As-deposited Pd/AI was found to produce rectifying contacts while the metallization exhibited ohmic characteristics after annealing at temperatures as low as 400°C. A minimum contact resistance of 0.9 ohm-mm (specific contact resistance = 1.2 × 10⁻⁵ ohm-cm²) was obtained upon annealing at 650°C for 30 s. For comparison, Al and Ti/Al contacts were also investigated. Auger electron spectroscopy, secondary ion mass spectrometry, and x-ray diffraction were used to investigate metallurgical reactions.     

Optimization of Material and Process for Fine Pitch LVSoP Technology

For the formation of solder bumps with a fine pitch of 130 μm on a printed circuit board substrate, low‐volume solder on pad (LVSoP) technology using a maskless method is developed for SAC305 solder with a high melting temperature of 220°C. The solder bump maker (SBM) paste and its process are quantitatively optimized to obtain a uniform solder bump height, which is almost equal to the height of the solder resist. For an understanding of chemorheological phenomena of SBM paste, differential scanning calorimetry, viscosity measurement, and physical flowing of SBM paste are precisely characterized and observed during LVSoP processing. The average height of the solder bumps and their maximum and minimum values are 14.7 μm, 18.3 μm, and 12.0 μm, respectively. It is expected that maskless LVSoP technology can be effectively used for a fine‐pitch interconnection of a Cu pillar in the semiconductor packaging field.     

一种仰角可调的变形对数周期天线

设计了一种最大辐射方向仰角可调的缩比变形对数周期天线。对对数周期天线变形,改变天线主体和振子的旋转角,使得该对数周期天线的最大辐射方向在一定范围内连续可调。增加X型反射器,有效改善了前后比,增加了天线增益。这种可调振子旋转角的对数周期天线能够在1~2 GHz实现电压驻波比(VSWR)小于2,俯仰角从25°至90°连续可调。相比传统对数周期天线,该天线除了具备宽带特性外还具备低仰角、俯仰可调等性能。