Effect of Al trace dimension on electromigration failure time of flip-chip solder joints

The effect of Al-trace dimension on electromigration of flip-chip solder joints was investigated. The Al trace dimension was found to have a significant influence on the electromigration failure time. When joints with Al traces 100 μm wide were stressed by 1.0 A at 100°C, failure times were 35 h, 1,700 h, and >3,000 h for joints with Al traces that were 2,550 μm, 1,700 μm, and 850 μm long, respectively. Solder joints with Al traces 40 μm wide and 2,550 μm long failed instantly at 0.6 A. The Joule heating effect was found to be responsible for the huge difference in failure time.     

The influence of addition elements on the early resistance changes observed during electromigration testing of Al metal lines

This paper provides a critical review on early resistance changes observed during electromigration testing of Al, AlSi and AlSiCu metal lines. At present, high resolution in situ electrical resistance measurements are widely accepted as a valuable tool for the study of electromigration. It will be shown however that the results of these measurements should be interpreted with care. It will indeed be shown that, particularly for Si and/or Cu alloyed metallizations, an early resistance change measurement (during electromigration) can contain information that has no link with the damage induced by the electromigration process. A number of disturbing factors will be identified, which are all induced by temperature driven processes. The first type of disturbance is well known: the immediate change of the measured resistance with temperature steps and fluctuations (thermometer effect). The second type of disturbance is not so widely recognised. It is induced by time dependent changes that are observed over an extended period of time, following a preceding temperature step. Two types of disturbing contributions to resistance changes of this second type are identified, which will be denoted as irreversible changes and reversible changes. The irreversible resistance changes are usually observed during the first annealing of the metal line. The reversible changes are typically detected at the start of an electromigration measurement, when the current stress is switched on. It is shown that both the reversible and irreversible changes are caused by precipitation/dissolution reactions of addition elements. It is also shown that the often observed parabolic initial resistance increase that is detected at the start of electromigration experiments should be attributed to the time dependent, reversible dissolution of the addition element(s). Comparable experiments, executed however at a much reduced current level so that no Joule heating takes place, and hence no reversible processes are initiated, show that the kinetics of the purely electron-wind induced resistance changes are completely different: instead of a parabolic initial increase, an incubation time can be observed during the first stage of the measurement.     

Computational analysis of the interfacial effect on electromigration in flip chip solder joints

Recent experiments have shown failure in flip chip micro solder joints induced by electromigration. This paper proposes a three-dimensional computational model to simulate the evolution of micro and sub-micro scale solder joints due to electromigration induced diffusion. The evolving morphology of the solder joint related with multiple mechanisms causes a computational challenge. This is addressed by employing a diffuse interface model with multiple concentrations. To efficiently resolve complications, a semi-implicit Fourier spectral scheme and a biconjugate-gradient method are adopted. Results have demonstrated rich dynamics and solder breakage at the interface on the cathode side. Furthermore, the effect of the designed interface region on the reliability of solder joints has been investigated with the developed model.     

A study of the influence of inter-metal dielectrics on electromigration performance

The relative electromigration performance of test structures with a common Ti/TiN-Al-1% Cu-TiN metallization scheme and with three different inter-metal-dielectric (IMD) layers is compared. Differences in lifetimes are observed which are attributable to the influences of the different IMD layers. The IMD layers in question are (a) polyimide, (b) a flexible inorganic dielectric layer, and (c) a rigid inorganic dielectric layer. A matrix of conventional electromigration tests has been carried out. The possible influence of stress migration is investigated and an explanation for the relative behaviour is proposed.     

Effects of Mg additions on the electromigration behavior of Al thin film conductors

Aluminum thin film conductors containing Mg alloying additions have been tested for electromigration failure by formation of electrically open circuits. The test conditions were either 2 × 10⁶ A/cm² or 4 × 10⁶ A/cm² for the current density, and either 175 or 225°C for the temperature. The median lifetimes were found to increase with increasing Mg concentrations up to the highest concentration tested, about 6%. With polycrystalline films the maximum increase in lifetime resulting from Mg additions corresponds to a factor of about 100, as compared to pure Al films. This is about equal to previously reported results obtained with Cu additions. The increase in lifetime has been shown to result from a decrease in the rate of grain boundary diffusion for the Al atoms. Magnesium atoms diffuse at approximately the same rate as Al atoms. Thus the mechanism of failure formation in Al films containing Mg is thought to be different than in Al-Cu films, where Cu atoms diffuse faster than Al atoms and failure ensues upon local Cu depletion.     

Electromigration resistance and long term stability of textured silver thin films on LTCC

Silver (Ag) is regarded as advanced material for metallization purposes in microelectronic devices because of its high conductivity and its enhanced electromigration resistance. Besides the typical use of silicon based substrate materials for device fabrication, thin film metallization on ceramic and glass-ceramic LTCC (low temperature co-fired ceramics) substrates gets more and more into focus as only thin film technology can provide the required lateral resolutions of structures in the μm-range needed for e.g. high frequency applications. Therefore, the reliability of Ag thin films is investigated under accelerated aging conditions, utilizing test structure which consists of 5 parallel lines stressed with current densities up to 1.5 × 10⁷ A cm⁻² at temperatures ranging from room-temperature up to 300 °C. To detect the degradation via the temporal characteristics of the current signal a constant voltage is applied taking the overall resistance of the test structure into account. The mean time to failure of the Ag metallization substantially depends on the degree of (1 1 1)-orientation which, in turn, is strongly affected by the plasma power P_P during deposition. Therefore, Ag thin films deposited at P_P = 1000 W feature a 7 times higher reliability than those deposited at P_P = 100 W. Due to the enhanced stability of grains being (1 1 1)-oriented in textured thin films the material transport predominantly occurs along grain boundaries, whereas in Ag films without a (1 1 1)-orientation volume-related diffusion effects dominate due to the lower stability of these grains.     

CMOS工艺氧化膜完整性的评估

提出了用阵列电容来监测氧化层的完整性。分析表明,从多个子列的氧化层电容漏电合格率的曲线可以求出氧化层完整性的表征因子Ｅ值（每个缺陷包含的单元数）。     

激光-电阻复合焊接铝合金T型接头工艺及性能

采用激光-电阻复合焊接方法进行铝合金T型接头焊接工艺试验,对激光-电阻复合焊接过程中的主要焊接工艺参数:滚轮电极形状、电流大小和激光功率对焊缝成形及接头性能的影响进行分析,并优化工艺参数以获得良好的焊缝成形和优质焊接接头.试验结果表明:采用弧形端面滚轮电极,在合适的电流和激光功率参数条件下,激光-电阻复合焊接T型接头不仅可以降低接头搭接面的间隙,而且改善焊缝成形,增加搭接面的焊缝宽度,使T型接头的拉伸剪切栽荷与单独激光焊接相比得到显著提高.激光-电阻复合焊接有效改善了激光焊接存在的一些不足,拓展了激光焊接的工业应用范围.     

Effect of mechanical process parameters on friction behavior and material removal during sapphire chemical mechanical polishing

The effect of mechanical process parameters such as down force and rotation speed on friction behavior and material removal rate (MRR) was investigated during chemical mechanical polishing (CMP) of sapphire substrate. It was found that the increase in both rotation speed and down force can enhance the MRR and friction force almost linearly depends on the down force and rotation speed. The coefficient of friction (COF) decreases with increasing rotation speed under a fixed down force but keeps constant regardless of variation in down force under a fixed rotation speed. Moreover, the relationship between friction force and MRR was obtained. MRR was proportional to friction force with increasing down force whereas converse proportional to that with increasing the rotation speed. In addition, MRR data are fitted to the Preston equation in the sapphire CMP.     

Interconnect reliability - A study of the effect of dimensional and porosity scaling

A number of challenges linked to the reliability characterization of downscaled back-end-of-line copper/low-k interconnects are covered. Concerning copper reliability, it is shown using early data on 30 nm ½pitch that advanced barrier/seed/plating options can counteract models that predict decreased electromigration performance in smaller dimensions. Regarding stress-induced voiding, it is discussed that porosity scaling negatively influences metal degradation due to increased stress gradients. Also, since copper degradation during high temperature storage tests is driven by different failure mechanisms, it is argued that tests at a wide range of temperatures are needed to characterize stress-induced voiding in copper/low-k systems at normal operating conditions. In addition, it is suggested that the current knowledge on the dependence of interconnect pitches and dielectric porosity on stress in copper lines needs to be taken into account when building finite element models of copper/low-k stacks. This is motivated by highlighting results of our recent study where the copper strain is varied for different copper dimensions and pattern densities. Finally, because the reliability margin of time dependent dielectric breakdown of scaled intermetal dielectrics becomes smaller, it is put forward that understanding the low voltage behaviour of time dependent dielectric breakdown becomes indispensable. A case study using fully passivated MOS capacitors without metallic barrier between the copper and the dielectric is detailed out and differences in current versus time behaviour and distributional shapes between low and high fields are highlighted.     

三种胍盐对低磨料浓度碱性阻挡层抛光液性能的影响

The influence of three kinds of guanidinium salt on the removal rate selectivity of different materials was studied during the barrier chemical mechanical polishing(CMP) process at first.The three kinds of guanidine saltguanidine hydrochloride,guanidine nitrate and guanidine carbonate.Then we compared the effect of the three kinds of guanidine salt on the dishing,erosion and surface roughness value.In the end,the reaction mechanism was studied through electrochemical analysis.All the results indicate that there is a better performance of the slurry with guanidine hydrochloride than the slurries with the other two kinds of guanidine salt.It effectively improved the removal rate selectivity and the surface roughness under the premise of low abrasive concentration and low polishing pressure,which is good for the optimization of the alkaline slurry for the barrier CMP process.     

Effects of deposition conditions of Al and Ti underlayer on electromigration reliability for deep-submicron interconnect metallization

We have studied the effects of Ti underlayer (collimated Ti vs. standard Ti) and Al deposition power (12 KW vs. 6 KW) on the electromigration (EM) lifetime of bottom-Ti/Al-0.5wt.%Cu/Ti/TiN-top stack. The (002) texture of standard Ti (s-Ti) was stronger than that of collimated Ti (c-Ti). The Al stack prepared with s-Ti underlayer, which had the stronger Al (111) texture and more uniform grain size distribution, showed better EM lifetime than the same with c-Ti underlayer, independent of the Al deposition power. The Al stack prepared with an Al deposition power of 6 KW was also found to show better EM lifetime than the same with a 12 KW deposition power, independent of the type of Ti underlayer. Longer deposition time for low power sputtering resulted in the stronger Al (111) texture, larger median grain size, and more uniform Ti−Al reaction layer. Finally, the effects of Ti underlayer and Al deposition power on the EM lifetime of Al-0.5%Cu films could be well explained by the grain size distribution and Al (111) texture, which is closely related to the underlying-Ti (002) texture.     

Study of the electroluminescent properties of crystalline silicon wafers in devices based on junctions of indium-doped zinc oxide and porous silicon

In this study we obtained electroluminescent devices (ELD) based on junctions of indium doped zinc oxide (ZnO:In) and porous silicon layers (PSL). The PSL were obtained by electrochemical etching with different types and resistivities of silicon wafers. In the visible part of the electromagnetic spectrum, the porous silicon (PS) exhibits photoluminescence (PL) that is centered around 680 nm. Once the devices were obtained, they were optically and electrically characterized. The PSL were coated with ZnO:In film, which was gotten by the ultrasonic spray pyrolysis technique (USP). When the devices were electrically polarized they showed optical response in the regions corresponding to the visible and infrared band of the electromagnetic spectrum. The observed electroluminescence (EL) in the visible region goes from 400 to 750 nm and the corresponding emission of the infrared part is around 750–1150 nm. The devices presented luminescent spots on the surface which were visible to the naked eye. The analysis of the results shows that the emission source in the visible part is attributed to the filaments present in the PS, and also to the ZnO:In films and the emission in the infrared part is associated to the silicon substrate. The electrical characterization was carried out by current–voltage curves (I–V) that show in the devices a rectifying behavior.     

Effect of multistep annealing on mechanical and surface properties of electroplated Cu thin films

Electroplated (EP) Cu films demonstrate a microstructural transition at room temperature, known as self-annealing, that involves grain growth and texture changes. In this paper, we have investigated the annealing behavior of EP Cu films grown on a Cu seed layer deposited on top of a TaN barrier layer. A grazing incident x-ray diffraction (GIXRD) pattern shows stronger x-ray reflections form Cu (111) and (220) planes but weaker reflections from (200), (311), and (222) planes in all the EP Cu samples. Nanoindentation was performed on all the samples using the continuous stiffness measurement technique. The elastic modulus varied from 121 GPa to 132 GPa, while the hardness varied from 1 GPa to 1.3 GPa, depending on the annealing conditions. The surface morphology and roughness of the Cu films were characterized using atomic force microscopy (AFM). The tribological properties of the copper films were measured using the Bench Top chemical mechanical polishing (CMP) tester (CETR, Inc., Campbell, CA). Nanoindentation was performed on the samples after CMP, and an increase in hardness and modulus was observed. This may be attributed to the work hardening of the Cu films during CMP.     

包裹A1_2O_3对BaTiO_3基陶瓷性能的影响

采用固相法制备掺杂有稀土元素Nd和Y的BaTiO3基陶瓷粉体,在该粉体表面包裹A12O3。研究了包裹A12O3对BaTiO3基陶瓷的微观结构、微观形貌、介电性能、击穿电压和介电非线性的影响。结果表明:包裹A12O3后,BaTiO3基陶瓷的相对介电常数达到4000,绝缘电阻率达到1011?.cm,耐压提高到20×103V/mm,介电非线性得到改善,有望在储能领域中得到应用。     

The properties of aluminum, platinum silicide and copper based contacts for silicon high-power devices

Electrical, thermo-electrical and thermo-mechanical properties were compared for PtSi, aluminum (Al, PtSi-Al, PtSi-AlCuSi, PtSi-TiW-AlCuSi), and copper based contacts (TiW-Ni-Cu, TiW-Ni-Cu-Ni-Au, PtSi-TiW-Ni-Cu, PtSi-TiW-Ni-Cu-Ni-Au). High-power 2.5 kV/150 A P-i-N diode with both lapped and etched anode surface was used to characterize the performance of the contacts in the conditions of free floating silicon in pressed package. The devices with PtSi contacts have the lowest forward voltage drop, but do not survive the operation in pressed package under thermal cycling. The copper based contacts with PtSi layer give lower voltage drop and better thermo-mechanical ruggedness compared to that of aluminum. These features are conserved even with passivation against corrosion using Ni-Au. The contacts without the PtSi layer have high voltage drop and fail under thermal cycling. The composition of the contact layer is shown to influence the thermal behavior of device voltage drop. The crossing point current is found to decrease with increasing contact layer thickness. The lowest magnitude gives the aluminum contact.     

Optoelectronic properties of expanding thermal plasma deposited textured zinc oxide: Effect of aluminum doping

Aluminum-doped zinc oxide films exhibiting a rough surface morphology are deposited on glass substrates utilizing expanding thermal plasma. Spectroscopic ellipsometry is used to evaluate optical and electronic film properties. The presence of aluminum donors in doped films is confirmed by a shift in the zinc oxide bandgap energy from 3.32 to 3.65 eV. In combination with transmission reflection measurements in the visible and NIR ranges, charge carrier densities, optical mobilities, and film resistivities have been obtained from the free carrier absorption. Film resistivities are consistent with direct measurements, values as low as 6.0×10⁻⁴ ω cm have been obtained. The interdependence of electrical conductivity, film composition, and film morphology is addressed.     

Nanotwin formation and its physical properties and effect on reliability of copper interconnects

Ultra-fine grained copper with a large amount of nano-scale twin boundaries has high mechanical strength and maintains normal electrical conductivity. The combination of these properties may lead to promising applications in future Si microelectronic technology, especially as interconnect material for air-gap and free-standing copper technologies. Based on first principles calculations of total energy and in-situ stress measurements, high stress followed by stress relaxation during the Cu film deposition seems to have contributed to nanotwin formation. Nanoindentation studies have shown a larger hardness for copper with a higher nanotwin density. The effect of Cu nanotwin boundaries on grain growth was investigated by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The presence of a high density of nanotwin boundaries may improve the reliability of Cu interconnects.     

Microstructure and properties of aluminum contacts formed on GaAs(100) by low pressure chemical vapor deposition with dimethylethylamine alane source

We report on a low pressure chemical vapor deposition of metallic thin aluminum films on GaAs (001) with a dimethylethylamine alane (DMEAA) source and H₂ as a carrier gas. The deposition temperatures varied in the range 130–360°C. Integrated volumes for Al (111), (100), (110)R, and (110) grains were estimated by the x-ray diffraction technique and the growth temperature values preferred for every type of grains were observed. The experimentally observed dominance of Al(110)R over Al(110), irrespective of the substrate miscut direction, supports the GaAs(100) inner anisotropy effect on the Al grain orientation. Electrical resistivity was 5 ·cm for the best Al films. The Schottky barrier heights were near a 0.7 eV level and the ideality factor n=1.1. Nonalloyed ohmic contacts were fabricated on an n-type GaAs epitaxial layer with an additional set of Si-layers near the Al/GaAs interface. Specific contact resistance, c=7 cm², was measured. Best contacts were obtained at a deposition temperature lower than 250°C.     

pH值对铌酸锂晶片抛光速率及抛光表面的影响

采用化学机械抛光方法,自制碱性抛光液对铌酸锂晶片进行抛光,通过试验得出适宜铌酸锂晶片抛光的pH值,配合压力、流量等外界参数可以得到较高的表面质量和较快抛光速率.分析了铌酸锂晶片在碱性条件下的去除机理和抛光液的pH值及抛光液中各个组分对抛光速率和表面质量的影响.