Analysis of laser metal-cut energy process window

Metal fuses for laser redundant links have been used for years in laser repair application. Nonetheless, reliability problems have occurred for laser metal cut structures, such as the material leftover remaining at the bottom of the cut site or the formation of a lower corner crack. In this paper, a special finite element Two-Stage Laser Cut Simulation Model (TSLCSM) is proposed to study the cut process. Compared with other simulation methods for similar purposes, the proposed model not only includes the stress-relief effect caused by cracking and breakthrough of passivation caused by upper corner cracks, but it also explains the laser-cut mechanism ignoring the metal underlayer. It proves earlier experimental results that a laser-energy window exists for each cut structure under a specified laser pulse. Different laser cut structures and different laser parameters are considered in the simulation, and useful guidelines are obtained for a maximum laser-energy process window. Experimental observations consistent with simulation results show that the differential between upper corner stress and lower corner stress is temporarily dependent on the passivation breakthrough caused by upper corner cracks. Also, it is shown that lower corner cracks can be formed at much lower laser energies than previously expected     

Polarization Effect in Laser Processing of Fine Pitch Link Structures for Advanced Memory Designs

Metal fuses for laser redundant links have been widely used for years in laser repair application to enhance yield. Shrinking design rules in IC fabrication have necessitated decreased fuse pitches in the redundancy circuitry. Current infrared lasers are facing the 2 $mu{hbox{m}}$ pitch barrier due to the diffraction limited spot size and depth of focus capabilities. In this paper, we present experimental results showing how we have achieved successful laser cut processes of future metal fuse structures down to 1.0 $mu{hbox{m}}$ pitch using a combination of the small spot of short wavelength laser and the polarization effect to tightly pitched neighbor structures. Inline polarization with link length minimizes the adjacent link damages and thus improves the energy process window for robust cutting. Electrical measurement data of metal link structures with various pitches, metal width and top passivation thicknesses shows the importance of controlling of top oxide thickness on the fine pitch structure. This enabling technology provides a viable production solution for laser fuse processing down to 45-nm node technology and below.      

Scalability study of laser-induced vertical make-link structure

The scalability of a direct metal-to-metal connection between two different levels of metallizations has been extrapolated to be compatible with modern semiconductor fabrication technology. A simple equation to evaluate the scalability was formulated based on focused ion beam (FIR) cross-sectional images of larger link structures with various sizes. With a 0.6-μm-thick metal 1 line and a 0.5-μm-thick interlevel dielectric (ILD), a width of less than 0.5 μm is evaluated to be possible for the metal 1 line. Two limitations exist in the process of scaled-down link structures, which are the ratio of the thickness of ILD to the thickness of the metal 1 line, t_ILD/t _m, and the quality of laser beam parameters including the spot size and positioning error. However, modern processing technologies and advanced laser processing systems are considered to allow the scalability of a vertical make-link structure. Two layouts of two-level interconnects were designed with increased interconnect densities with a 1-μm pitch of a 0.5-μm-wide metal 1 line. These results demonstrate the application of commercially viable vertical linking technology to very large-scale integration (VLSI) applications     

Laser link cutting for memory chip repair

Link processing with individual laser pulses has become an industry standard process in IC memory chip manufacturing. It is gaining wide acceptance in analog chip reprogramming and tuning as well. Traditional laser processing, using the standard output of Nd:YAG at 1.064-/spl mu/m and Nd:YLF at 1.047-/spl mu/m laser wavelengths, works well for polysilicon links but is not satisfactory for metal links. This paper describes the physics modeling and computer simulation of the laser link process and a new technique of using 1.3-/spl mu/m laser wavelength for the process. While light absorption of link materials at 1.064-, 1.047-, and 1.3-/spl mu/m wavelengths are relatively the same, the absorption of a Si substrate at 1.3 /spl mu/m is considerably less. The improved absorption contrast between the link material and silicon substrate at 1.3-/spl mu/m delivers a much wider laser process window. Both simulation and experimental results are given and discussed. A brief introduction of another new technique, which uses UV laser pulses for link processing, is given. This UV laser process delivers a laser beam spot size much smaller than 1.5 /spl mu/m.     

脉冲激光干扰面阵CCD成像系统的实验研究

为了研究脉冲激光对面阵CCD的干扰效果,采用近场模拟实验的方法,设计了重复频率脉冲激光干扰CCD成像器件近场实验。当CCD器件表面接收激光功率密度达到2.97mJ/cm2时,观察和记录了CCD器件串音饱和现象;当CCD摄像机电子快门打开时,除发射窗口有激光光斑图像外,激光脉冲在激光器出光口竖直方向也会形成偏离出光口位置的漂移光斑图像。分析了CCD摄像机电子快门作用机理及图像信号转移方式机理,并对光斑漂移现象给出了合理解释。结果表明,重复频率脉冲激光可使CCD图像上出现漂移光斑而对图像形成干扰。这为重频脉冲激光干扰CCD的研究提供了理论基础和初步实验验证。     

重复激光脉冲作用下薄膜损伤演化规律研究

为了深入研究重复激光脉冲的能量效应对光学薄膜的烧蚀机理,采用实验观测与热力学分析相结合的方法进行了研究。通过观察光学薄膜烧蚀形貌随入射激光脉冲数量增加发生改变的典型形貌特征,分析了激光与等离子体相互作用的热力学过程,得到了在激光重复脉冲作用下光学薄膜的损伤特性及其演化规律。结果表明,薄膜在重复脉冲作用下,其表面会变得粗糙,这会大大增加对激光的吸收效应,从而加速了薄膜的破坏,最终被完全去除而露出基底;同时,烧蚀物会在热膨胀作用下向激光作用区域外扩散,在激光烧蚀中心区域外进行沉积,而形成更大范围的污染。由于激光光强为高斯分布,重复脉冲作用的效应主要是对在光束中心区域的薄膜进行集中烧蚀,会不断增加烧蚀的损伤程度,而对烧蚀面积的增加效应极为有限。这一研究结果为重复激光脉冲对薄膜烧蚀机理的建立提供了参考。     

Laser linking of metal interconnects: analysis and designconsiderations

Lateral connections between adjacent lines of metallization have been developed in order to achieve high density linking for customization in programmable gate arrays and for additive redundancy in restructurable integrated circuits. Links were formed by focusing a pulsed laser between two same-level aluminum lines. The mechanism of link formation appears to be the nucleation of a fissure, induced by the thermal expansion mismatch between the metallization and the surrounding dielectric (SiO₂) and passivation layer (Si₃N₄); molten aluminum fills the crack. Numerical simulation by the finite element method was carried out using a plane strain model. The probable path for the link-forming fissure, as predicted by the model on the premise that the local maximum tensile stress determines cracking, is shown to be consistent with experimental observations. Parametric analyses were performed to gain insights into the linking processes. It is found that damage in the passivation can be avoided by increasing the thickness of the dielectric between the aluminum and the passivation. Reducing the spacing between the metal lines increases the chance of successfully forming the link. Under certain conditions, the linking propensity can also be increased by reducing the metal width. In addition, the link is much easier to form when symmetric laser heating between the two metal lines can be achieved. These findings can be directly applied to improving the design of the laser linking processes and devices     

激光选区熔化/干式铣削复合加工实验研究

为研究激光选区熔化增材与干式铣削减材复合加工中的工艺交互作用对零件成形质量的影响,以316L奥氏体不锈钢粉末为研究对象,分别采用单一增材工艺和“增材-减材”交替复合加工工艺制备试样,分析成形区的致密度、残余应力。实验结果表明,在制件致密度和残余应力方面,以上两种加工方法均受到激光能量密度的影响且规律相似。此外,复合加工中的铣削减材工艺会对成形样件的致密度和残余应力造成影响,在激光能量密度设置为100J·mm-3和125J·mm-3时,铣削减材工艺可以明显提高致密度并降低残余应力水平。     

Reliability of laser-induced metallic vertical links

A new method has been proposed to form electrical connections vertically between two levels of metallization by using a commercial pulsed IR laser system. Samples were stressed at accelerated current densities and temperatures. The failure activation energy has been found to be about 0.66 eV, from which electromigration is identified as a main failure mode. The extrapolated mean time to failure (MTTF) at room temperature and accelerated current density of 3 MA/cm² is about 38 years. The dependence of MTTF on laser energy has also been obtained, showing agreement with the resistance dependence on laser energy. Focused ion beam (FIB) cross sections suggest that the laser process-induced voids in the lower line limit the lifetime of links. Furthermore, a modified structure is proposed to improve the electromigration reliability. From the reliability point of view, this study shows that the laser-induced vertical link has sufficient reliability for practical implementation     

Drainage ratio impact on void creation in gold interconnect

This articles details investigation into metal voiding observed on electroplated gold interconnect during high temperature wafer-scale bake. The test structures and methodology to measure this effect are discussed in detail. Various factors affecting a metal voiding phenomenon were examined and measured. A drainage ratio is defined to quantify the effects of test structure layout proportions on gold void formation. Different metal formulations were also investigated to better comprehend the influence of metal composition on gold void formation. Furthermore the effect of temperature on void formation was studied and an activation energy of 2.0 eV was estimated for this phenomena. Several methods are proposed to minimize any reliability impact from this phenomenon.     

金属板料激光冲击成形技术研究

本文首次提出利用激光冲击波进行金属板料成形的新技术——金属板料的激光冲击成形,分析了其成形机理和特点。利用脉冲能量为1030J、脉宽为20ns的高功率Nd:Glass激光器,对金属板料进行了激光冲击成形的实验研究,探讨了激光参数、约束边界条件等对板料成形的影响。结果表明:在单次激光冲击下,随激光能量的增加,板料成形量随之增大,顶部曲率半径减小;随约束孔径的增加,板料成形量和顶部曲率半径都随之增加;在成形区凸面顶部为残余压缩应力-301MPa～-28MPa,而在成形凹面顶部因板料厚度的不同而呈现为残余压缩应力或拉伸应力。通过选择不同的激光参数和约束条件可以获得所需的工件轮廓形状和表面残余应力性质,为大面积板料的无模激光冲击成形技术的研究提供了依据。     

激光直接金属沉积工艺能效的田口试验研究

为了研究金属激光直接沉积工艺过程中工艺参量对工艺能效的影响,采用自主研发的HCX60五轴激光复合制造机床开展工艺能效田口试验,并对其结果进行了信噪比分析、极差分析以及方差分析,得到激光功率、送粉量、扫描速率、提升量以及搭接率对工艺能效的影响主次关系,提出了工艺因素优化组合。结果表明,送粉量对工艺能效的影响最为显著,最佳参量组合为激光功率P=500W,送粉量f=28g/min,扫描速率v=600mm/min,提升量h=0.6mm和搭接率λ=30%。这为研究增材制造工艺参量对工艺能效的作用及影响规律提供了理论借鉴和实验基础。     

Frequency tuning of a CW atomic iodine laser via the Zeeman effect

A continuously operating, C₃F₇I photolytic 1.315-μm atomic iodine laser has been used to make the first precise observations of frequency tuning of an atomic iodine laser by means of the Zeeman effect. Application of a uniform magnetic field to the gain region of the photolytic iodine laser causes the laser to operate at different frequencies as a function of the strength of the applied field and the polarization of the laser. With the light polarized perpendicular to the applied magnetic field by means of Brewster output windows, the laser could be tuned to frequencies near the 3-4, 2-2, and 3-3 zero-field transitions of the hyperfine spectrum of atomic iodine. With the light polarized parallel to the applied magnetic field the laser could be tuned to two frequencies bracketing the 3-4 zero-field transition and one frequency near the 2-2 transition. Measurements show close agreement between the observed frequency behavior and theoretical models     

强激光辐照7075铝合金热响应与材料尺度律关系研究

为了明确金属板受激光辐照产生的热响应与材料尺度律之间的关系。采用数值模拟和实验相结合的研究方法,开展了不同尺度律下7075铝合金板在波长为1064 nm的连续波激光辐照下的热响应研究。首先利用COMSOL有限元软件建立了金属板在连续激光辐照下的数值模型,得到不同尺度律的铝合金板的温升过程;之后开展同尺寸实验验证,对比数值仿真数据。研究结果表明:在等效时间内,不同尺度律模型温升过程一致;实验数据与仿真结果趋势相似,各尺度律下仿真与实验相对误差均小于17 %。该研究结果对于强激光辐照效应的应用与研究具有一定价值。     

Al-Mg-Sc合金板料激光冲击成形的有限元分析

激光冲击板料变形是利用高能脉冲激光和材料相互作用诱导的高幅冲击波的力效应使板料产生塑性变形的新型激光加工技术。基于激光冲击成形原理,建立了有限元模型,利用有限元分析软件MSC.Marc,对激光冲击载荷下Al-Mg-Sc板料成形过程进行模拟。结果表明:仿真结果与实验结果取得了良好的一致性,随着激光能量的增大,变形量增大;当激光能量大于30J时,板料最大变形量随着约束孔径的增大而增大,当激光能量小于30J时,板料最大变形量随着约束孔径的减小而增大,在距冲击中心9mm附近和冲击中心处,属于易破裂区域,距冲击中心3mm附近,应力值也比较大。     

304不锈钢板料激光热应力成形试验研究

通过改变激光功率、扫描速度、光斑直径、扫描次数及板料宽度对2 mm厚度的AISI304不锈钢板料进行激光热应力弯曲试验, 分析了各工艺参数对弯曲角度的影响规律, 对工件表面烧蚀情况进行评价, 并对板料金相组织进行观察分析。试验结果表明: 在试验参数范围内激光扫描次数、光斑直径、扫描速度和板料宽度对弯曲角度呈近似线性规律, 而激光功率对弯曲角度的影响不呈线性规律; 较大的面能量密度产生较大的弯曲角度。可通过工艺参数的合理组合在保证板料表面质量的前提下采用较大的面能量密度进行扫描以提高弯曲变形的效率。以上研究为精确控制板料激光弯曲成形奠定基础。     

Asymmetric quantum well broadband thyristor laser

A broadband thyristor laser based on InGaAs/GaAs asymmetric quantum well (AQW) is fabricated by metal organic chemical vapor deposition (MOCVD). The 3-μm-wide Fabry-Perot (FP) ridge-waveguide laser shows an S-shape I-V characteristic and exhibits a flat-topped broadband optical spectrum coverage of ~27 nm (Δ_-10 dB) at a center wavelength of~1090 nm with a total output power of 137 mW under pulsed operation. The AQW structure was carefully designed to establish multiple energy states within, in order to broaden the gain spectrum. An obvious blue shift emission, which is not generally acquired in QW laser diodes, is observed in the broadening process of the optical spectrum as the injection current increases. This blue shift spectrum broadening is considered to result from the prominent band-filling effect enhanced by the multiple energy states of the AQW structure, as well as the optical feedback effect contributed by the thyristor laser structure.     

A new generation of power lateral and vertical floating islands MOS structures

In this paper, new vertical and lateral MOS structures are proposed, in which P⁺ layers called floating islands are located in the drift region. These new structures, called “FLIMOS” (floating islands metal–oxide semiconductor) transistors, are based on the FLI–diode concept in which the voltage handling capability is obtained by many PN junctions in series instead of the conventional diode, where the breakdown voltage is supported by only one PN junction. In the medium voltage range (200–1000 V), the on-state performance of vertical FLIMOSFET is strongly improved when compared to the conventional MOSFET. For instance, for a 900-V vertical FLIMOSFET, a reduction of the specific on-resistance of about 70% relative to the conventional structure and of 40% relative to the silicon limit is observed. But for a 180-V lateral FLIMOSFET, a reduction of 28% relative to the conventional structure is observed, which is not a very significant improvement when compared to medium voltage vertical devices.     

The Geoscience Laser Altimetry/Ranging System

The Geoscience Laser Altimetry/Ranging System (GLARS) is a planned highly precise laser distance-measuring system to be used for geoscience measurements requiring extremely accurate geodetic observations from a space platform. The system combines the attributes of a pointable laser ranging system making observations to retroreflectors placed on the ground with those of a nadir-looking laser altimeter making height observations to ground, ice sheet, and oceanic surfaces. In the ranging mode, centimeter-level precise baseline and station coordinate determinations will be made on grids consisting of 100 to 200 targets separated by distances from a few tens of kilometers to about 1000 km. These measurements will be used for studies of seismic zone crustal deformations and tectonic plate motions. Ranging measurements will also be made to a coarser, but globally distributed, array of retroreflectors for both precise geodetic and orbit determination applications. In the altimetric mode, relative height determinations will be obtained with approximately decimeter vertical precision and 70-100-m horizontal resolution. Altimetric profiles consisting of nearly contiguous spots will be available when the system is operated at 40 pulses per second. The height data will be used to study surface topography and roughness, ice sheet and lava flow thickness, and ocean dynamics. Waveform digitization will provide a measure of the vertical extent of topography within each footprint.     

Improvement of hot carrier reliability with deuterium anneals formanufacturing multilevel metal/dielectric MOS systems

This paper discusses new experimental findings critical for process integration of deuterium post-metal anneals to improve channel hot carrier reliability in manufacturing multilevel metal CMOS integrated circuits. Detailed account of the deuterium process optimization experiments varying temperature, time, and ambient is given. Specifically, the first demonstration of the large hydrogen/deuterium isotope effect for multilevel metal/dielectric MOS systems is reported. Previous accounts of the isotope effect had been limited to CMOS structures with one-level of dielectric/metal and to about a 10 fold improvement in reliability. Deuterium, instead of hydrogen is introduced via an optimized post-metal anneal process to achieve a 50-100 fold improvement in transistor channel hot carrier lifetime. The benefits of the deuterium anneal are still observed even if the post-metal anneal is followed by the final SiN cap wafer passivation process. It is concluded that the deuterium post-metal anneal process is suitable for manufacturing high performance CMOS products and fully compatible with traditional integrated circuit processes