Cu Interconnects Research Articles

A Bilevel Multi-Fidelity Polynomial Chaos Approach for the Uncertainty Quantification of MWCNT Interconnect Networks With Variable Imperfect Contact Resistances

With on-chip copper interconnects reaching their performance limits at 22 nanometer technology nodes, multi-walled carbon nanotube (MWCNT) interconnects are projected to replace them below this point. A major aspect of MWCNT interconnect design is to perform uncertainty quantification (UQ) in an efficient yet accurate manner. In this paper, a polynomial chaos (PC) based approach is developed for the UQ of MWCNT interconnect networks under the condition that some shells of each conductor of the network are perfectly contacted while others are imperfectly contacted. The key feature of the proposed approach is the development of a bilevel multi-fidelity algorithm where two different low-fidelity models are combined together. The main outcome of using this bilevel approach is to further reduce the computational time cost of state-of-the-art single level multi-fidelity algorithms, especially in the presence of variable imperfect contact resistances where single level multi-fidelity algorithms fail to provide much speedup over conventional PC approaches. The proposed approach adopts a SPICE hybrid model that combines the features of the equivalent single conductor (ESC) model and the rigorous multiconductor circuit (MCC) model of the MWCNT conductors. Then the low-fidelity ESC model, the intermediate-fidelity hybrid model, and the high-fidelity MCC model are exploited in a bilevel multi-fidelity algorithm for the recovery of the PC metamodel of the interconnect network. This proposed bilevel multi-fidelity algorithm is demonstrably 3-5x more numerically efficient than state-of-the-art single level multi-fidelity algorithms while being even more accurate. Once recovered, the PC metamodel is used to derive all statistical information of the network transient responses.

Integrated Electromagnetic-Thermal Approach to Simulate a GaN-Based Monolithic Half-Bridge for Automotive DC-DC Converter

New technological and packaging solutions are more and more being employed for power semiconductor switches in an automotive environment, especially the SiC- and GaN-based ones. In this framework, new front-end and back-end solutions have been developed, and many more are in the design stage. New and more integrated power devices are useful to guarantee the performances in electric vehicles, in terms of thermal management, size reduction, and low power losses. In this paper, a GaN-based system in package solution is simulated to assess the structure temperature submitted to a Joule heating power loss. The monolithic package solution involves a half-bridge topology, as well as a driver logic. A novel integrated electromagnetic and thermal method, based on finite element simulations, is proposed in this work. More specifically, dynamic electric power losses of the copper interconnections are computed in the first simulation stage, by an electromagnetic model. In the second stage, the obtained losses’ geometrical map is imported in the finite element thermal simulation, and it is considered as the input. Hence, the temperature distribution of the package’s copper traces is computed. The simulation model verifies the proper design of copper traces. The obtained temperature swing avoids any thermal-related reliability bottleneck.

Recent Advances in Electroplating of Through-Hole Copper Interconnection

Recent Advances in Electroplating of Through-Hole Copper Interconnection

Advances in mechanistic understanding of additives for copper electroplating in high-end electronics manufacture

<p indent=0mm>Copper interconnect electroplating is one of the core technologies for the manufacture of high-end electronic devices including but not limited to chips. To promote the development of advanced copper interconnect process, it is necessary to clarify the mechanisms of copper electroplating additives. Herein, we provide a brief overview of the research progress on the interfacial structures and mechanisms of the three types of additives (accelerator, suppressor and leveler) in copper sulfate plating baths from a methodological perspective. Besides, the advantages and limitations of different research methods are discussed and the scientific issues related to the Damascene copper electroplating are summarized, to afford a hint for the further research and development of the additives in advanced chip fabrication.

Investigation of organic additives to regulate growth and signal transmission loss of copper interconnection structure

<p indent=0mm>Signal integrity is severely limited by the copper roughness. Plating solution containing different organic additives could influence the roughness of electroplating copper growth. Molecular simulation and electrochemical tests were used to regulate the competitive adsorption behavior of organic additives on the copper surface and understand the possible mechanism on the difference of copper growth. The results show that the plating solution system containing bis-(sodium sulfopropyl)-disulfide (SPS), ethylene oxide-propylene oxide copolymer (EO/PO) and Janus Green B (JGB) can contribute to the copper growth with smooth surface, leading to insertion loss of <sc>−8.9 dB@20 GHz.</sc> Therefore, organic additives could be used to regulate the low-profile growth of copper interconnection structure and reduce transmission loss to effectively ensure the integrity of high-frequency signal transmission.

All-wet encapsulation and electroless superfilling process for the fabrication of self-assembled-monolayer encapsulated copper interconnects with enhanced electromigration reliability

The continued downscaling of integrated circuits has brought into focus the development of new molecularly thick barrier/capping materials and novel fabrication processes for Cu interconnects with gradually diminished lateral dimensions. Here, an all-wet encapsulation/electroless superfilling process is developed for the first time to lay an amino-based self-assembled monolayer (SAM) all around nanoscaled Cu interconnects embedded in SiO2. Under bias stressing (8.0 × 108–1.6 × 109 A/cm2), premature failure of otherwise identical but bare Cu interconnects occurs within a few seconds. However, SAM-encapsulated Cu interconnects are extremely EM resistant with lifetimes on the order of 103 s under the same rigorous bias stressing. The strengthening mechanism is elucidated experimentally from imaging observations of electric-field induced Cu diffusion routes and theoretically from the prediction of the Black’s equation in terms of EM-induced failure modes.

Evaluation and Reduction of Signal Integrity Issues in Multiwalled Carbon Nanotube On-Chip VLSI Interconnects

Due to advancements in device scaling in very-large-scale integration (VLSI) technology, signal integrity (SI) issues play a major role to determining the performance of on-chip interconnects in high-speed digital circuits. The main SI issues are delays, peak voltage noise effects, crosstalk, and timing uncertainties. Here, the SI issues of the coupled multi-walled carbon nanotube (MWCNT) on-chip interconnects are evaluated with and without the effect of shielding technique and compared to the copper interconnects. The MWCNT exhibits an average of 47.9% smaller propagation delays than Cu in dynamic crosstalk conditions. Further, for crosstalk reduction, the active shielding (AS) and passive shielding (PS) techniques are proposed. With the AS and PS techniques, the MWCNT interconnects experience a decreased delay by 46.8% and 30.15% compared to without shielding technique, respectively. Moreover, the AS exhibits smaller crosstalk effects than the PS technique due to its input switching activities on shielded lines. In addition, the quality of the signal (QoS) and Intersymbol interference (ISI) noise effects of coupled MWCNT interconnect with and without shielding is evaluated. Finally, to improve the QoS and reduce the ISI effects, the decision feedback equalizer with the least mean square adaptive algorithm is implemented at the receiver end.

Experimental and theoretical investigation on the inhibition performance of disulfide derivatives on cobalt corrosion in alkaline medium

Cobalt, as the barrier layer material for 14 nm copper interconnection, has been widely applied owing to its superior characteristics of low resistivity, excellent adhesion performance and blocking properties for copper. Most of the preciously developed cobalt corrosion inhibitors under weak alkaline condition are toxic, low water solubility, and limited to traditional experimental research. In this work, 3,3-dithiodipropionic acid (DDA), 2,2-dibenzamidodiphenyl disulfide (DPD) as potential corrosion inhibitors for cobalt in NH4Cl and H2O2 media under alkaline environment were investigated. Electrochemical experiments, surface morphology characterization, quantum chemical calculation and molecular dynamic simulation were combined to analyze the corrosion inhibition ability and mechanism. The experimental and theoretical results present that these disulfide derivatives can inhibit the corrosion behavior of cobalt surface effectively in ammonium-based aqueous solutions. When the concentration of inhibitors was 0.5 wt%, the corrosion inhibition efficiency of DDA, DPD reach up to 92.9%, 91.41%, respectively. Their favorable capability is attributed to the dense adsorption films following the Langmuir adsorption isotherm. Besides, these two inhibitors show excellent performance of galvanic corrosion inhibition at the Co/Cu interface, which is consistent with the shift tendency simulations for binding to Co/Cu substrates. The results of water solubility and toxicity tests indicate that DDA is more suitable for industrial applications.

Progress of Microstructure and Texture of High Purity Tantalum Sputtering Target

In recent years, the IC (integrated circuit) industry has developed rapidly and the chip process technology has developed in the direction of higher density. Because of its good chemical stability, tantalum is used as a sputtering coating material for the diffusion barrier in the copper interconnect process. The uniform microstructure of the tantalum target directly affects the sputtering performance. The fabrication of high-quality thin films requires the tantalum target to have fine and uniform crystal grains and random grain orientation distribution. However, due to the characteristics of tantalum, it is easy to form a microstructure with {100} (&lt;100&gt;//ND) orientation on the surface and {111} (&lt;111&gt;//ND) orientation on the core during cold working. During the fabrication of thin films, the sputtering rate varies with the thickness of the target, which affects the sputtering stability. To provide ideas for improving the uniformity of the microstructure of the tantalum target, this article reviews the preparation processes that affect the grain orientation and size of the high-purity tantalum target, including forging methods, rolling methods, recrystallization annealing, etc., analyze the law of texture evolution of tantalum and introduction the research status of cold working and recrystallization.

Hexagonal Boron Nitride: Mitigation of Electromigration in Metal Interconnects via Hexagonal Boron Nitride as an Ångström‐Thin Passivation Layer (Adv. Electron. Mater. 6/2021)

Ångström-thin hexagonal boron nitride (hBN) is a highly promising barrier/liner dielectric material for passivating electrical interconnects in ultra-scaled integrated circuits (ICs). In article number 2100002, Michael Cai Wang and co-workers present a novel approach to mitigating electromigration in nanoscale copper interconnects. Significant improvements in the breakdown current density and operating lifetime are observed in hBN-passivated copper interconnects, paving the way for further single-nanometer node scaling of semiconductor and ICs manufacturing

The Influence of Leveler on the Impurity Behavior of Electroplated Cu Films During Laser Annealing

Leveler is one of the key factors for the fabrication of electroplated Cu with superior electrical properties in Cu interconnect metallization. Rarely notice has been paid on the influence of leveler on the impurity behavior of electroplated Cu during recrystallization. In this study, the impacts of five different levelers on the impurity behavior during recrystallization of the electrochemical deposited Cu films are studied in terms of microstructure and electrochemical behavior. Five levelers perform differences in molecular types and inhibition ability on Cu deposition. The former will affect the initial impurity content of the original crystal, while the latter is directly related to the amount of impurity diffusion during recrystallization. This study shows the direct evidence that two factors affect the impurity behavior of the electroplated Cu films during laser annealing and thus affect the resistance performance. We find that the films obtained by using leveler that has a reasonable inhibitory ability and incorporates the lowest initial impurity content shows the largest resistance drop during recrystallization. We believe the findings are meaningful for the selection of levelers to improve electrical property in the metallization of electroplated copper interconnects.

A comprehensive comparative study of the performance of carbon‐ and copper‐based interconnects in ultra‐large‐scale integrated circuits

AbstractContinuous increase of transistor count in ultra‐large‐scale integrated (ULSI) circuits demands denser interconnection networks to guarantee normal operation. As the distances between adjacent interconnect lines shrinks, severe crosstalk effects appear. New interconnect materials and technologies are proposed to alleviate deteriorating crosstalk effects and maintain overall circuit performance at a desirable level. Carbon‐based materials including carbon nanotubes (CNTs) and graphene nanoribbons (GNRs) are among promising candidate materials to replace copper in future ULSI interconnects. In this work, carbon‐based interconnects including multiwall carbon nanotubes (MWCNTs) and multilayer graphene nanoribbons (MLGNRs), both horizontal (HMLGNRs) and vertical (VMLGNRs), are compared with traditional copper interconnects in terms of crosstalk delay and noise. Due to lower surface roughness, boron nitride (BN) is considered as substrate material for carbon‐based interconnects. To obtain more accurate and reliable results, layer number dependence of dielectric constant of BN multilayers and surface roughness dependence of the resistivity of HMLGNR interconnects are considered. The role of interconnect length, line spacing, and interlayer distance (substrate thickness) in crosstalk delay and noise of coupled carbon‐ and Cu‐based interconnect lines is investigated. It is shown that VMLGNR interconnects with perfect GNR edges exhibit the least crosstalk delay while MWCNT interconnects show far less crosstalk noise than other materials.

Direct Imaging of Integrated Circuits in CPU with 60 nm Super-Resolution Optical Microscope.

Far-field super-resolution optical microscopies have achieved incredible success in life science for visualization of vital nanostructures organized in single cells. However, such resolution power has been much less extended to material science for inspection of human-made ultrafine nanostructures, simply because the current super-resolution optical microscopies modalities are rarely applicable to nonfluorescent samples or unlabeled systems. Here, we report an antiphase demodulation pump-probe (DPP) super-resolution microscope for direct optical inspection of integrated circuits (ICs) with a lateral resolution down to 60 nm. Because of the strong pump-probe (PP) signal from copper, we performed label-free super-resolution imaging of multilayered copper interconnects on a small central processing unit (CPU) chip. The label-free super-resolution DPP optical microscopy opens possibilities for easy, fast, and large-scale electronic inspection in the whole pipeline chain for designing and manufacturing ICs.

Mitigation of Electromigration in Metal Interconnects via Hexagonal Boron Nitride as an Ångström‐Thin Passivation Layer

AbstractElectromigration in metal interconnects remains a significant challenge in the continued scaling of integrated circuits towards ever‐smaller single‐nanometer nodes. Conventional damascene architectures of barrier/liner layers and conducting metal cause inevitable compromises between device performance and feature dimensions. In contrast to contemporary barrier/liner materials (e.g., Co, Ta, and Ru), an ultrathin passivation layer that can effectively mitigate electromigration is needed. At the ultimate atomically‐thin limit, 2D materials are promising candidates given their exceptional mechanical properties and impermeability. Here, a facile and effective approach is presented to mitigating electromigration in copper (Cu) interconnects via passivation with insulating monolayer 2D hexagonal boron nitride (hBN). The hBN‐passivated Cu interconnects, compared to otherwise identical but bare Cu interconnects, exhibit on average a &gt;20% higher breakdown current density and a &gt;2600% longer lifetime (at a high current density of 5.4 × 107 A cm−2). Post‐mortem metrology elucidates uniform conformal contact between the hBN‐passivated Cu interface and common failure features due to electromigration.

High electrical conductivity and breakdown current density of individual monolayer Ti3C2Tx MXene flakes

High electrical conductivity and breakdown current density of individual monolayer Ti3C2Tx MXene flakes

Effect of UV Radiation on Oxidation for Ru CMP

As feature size continue to decrease, traditional copper (Cu) interconnections will encounter many problems. Ruthenium (Ru) is selected as a barrier material and even a future interconnection metal material because of its many advantages. However, due to its high hardness and chemical inertness, Ru is difficult to be removed during chemical mechanical polishing (CMP). In this study, the effect of UV-activated potassium persulfate (K2S2O8) on the removal rate of Ru CMP was studied. X-ray photoelectron spectroscopy (XPS) combined with electrochemistry is used to study the removal mechanism and chemical reactions. The results show that ultraviolet rays can enhance the chemical action in the CMP process and change the removal rate. Under the condition of 80 mM, the promotion rate is about 28.01%. When the particle diameter increases to 80 nm, the removal rate is also significantly increased by about 26.36%. Mechanism analysis shows that, on the one hand, it is affected by diffusion-control. On the other hand, the surface RuO3 and K2S2O8 undergo a Fenton-like reaction under UV conditions, which makes the Ru surface loose and porous (Rq = 0.533 nm), so it is easier to remove under mechanical action.

Surface Analysis of TMCTS-Based SiOC(H) Low-k Dielectrics in Post-Etch Strip of ACL Hardmask.

The miniaturization of devices requires the introduction of a high aspect ratio through patterning in the Damascene copper interconnect process. The high aspect ratio etch process employs hardmasks, such as amorphous carbon, that can withstand high-powered plasma exposure. When an etch hardmask is removed after patterning, the properties of the underlying film can be altered by the effect of plasma exposure during the strip process. In this study, surface properties of SiOC(H) are investigated after an amorphous carbon strip with O2/Ar plasma. Since the low-k film of SiOC(H) structure shows characteristics according to the Si-O internal bonding structure, the Si-O bonding ratio of the ring, network and cage structure was analyzed through Fourier-transform infrared (FT-IR) analysis to measure changes in thin film properties. X-ray photoelectron spectroscopy (XPS) was also used to add reliability to the SiOC(H) film structure. In addition, the end point of the strip process was obtained using an optical emission spectroscopy sensor and variations in thin film characteristics over the plasma exposure time were analyzed. These results revealed the structural modification of the SiCO(H) thin film in the post-etch strip of the amorphous carbon layer (ACL) hardmask.

Impurity diffusion behavior study of electroplated copper films annealed by linear shaping laser mobile scanning system

Impurities due to additives in electroplated copper interconnects diffuse during grain growth. High-resolution electron backscatter diffraction and TOF-SIMS (Time-of-flight secondary ion mass spectrometer) results reveal that the electroplated copper films after laser annealing by linear shaping laser mobile scanning system (LALS) have higher recrystallization fraction and less impurity content than traditional thermal annealing. Impurity diffusion behavior and grain boundary migration are inseparable. The effect of LALS on the impurity diffusion of electroplated Cu films is the result of the introduced local temperature gradient, which works collaboratively on the thermodynamics and kinetics of grain boundary migration. And the amount of impurity diffusion is related to the proportion of different species of impurities. The findings are meaningful for the metallization of electroplated copper interconnects.

Effect of EDTA-based alkaline cleaning solution on TAZ removal in post CMP cleaning of copper interconnection

1,2,4-triazole (TAZ) has been proved to be an alternative to Benzotriazole (BTA) as an corrosion inhibitor in chemical mechanical polishing (CMP) of multilayer copper interconnection for integrated circuit. It has also become the main object to be removed in post CMP cleaning. In this paper, a new type of alkaline cleaning solution based on EDTA was proposed to remove TAZ on copper surface. The optimal concentration ratio and pH value of the alkaline cleaning solution were explored using electrochemical measurement, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) and scanning electron microscopy (SEM). When the components of the cleaning solution were 25mg/L ethylenediaminetetraacetic acid (EDTA) and 600mg/L dodecylbenzene sulfonic acid (LABSA) (pH = 10.6), the Cu-1,2,4-trazole compounds formed by TAZ contamination on the copper surface can be effectively removed. Density Functional Theory (DFT) was used to confirm that EDTA could break the bond of Cu-1,2,4-triazole through the strong interaction between O16、H2、H36 and copper surface. No corrosion was observed on the cleaned copper surface and surface roughness was lower, which indicated that the cleaning solution was suitable for the removal of TAZ on copper surface.

Novel Circuit Model of Multi-walled CNT Bundle Interconnects Using Multi-valued Ternary Logic

This research paper presents a novel circuit modeling and analysis of ternary logic for MWCNT bundle interconnects with active shielding under the influence of temperature variations. The far end crosstalk-induced noise and propagation delay of MWCNT bundle interconnects has been analyzed with and without the effect of shielding. A standard ternary inverter (STI) driver model is used to obtain the ternary logic at output. The temperature-dependent analysis is also carried out at different temperatures such as 300, 400 and 500 K. The temperature-dependent comparative analysis for MWCNT bundle, SWCNT bundle and copper interconnects with and without shielding is also performed. It has been observed that MWCNT bundle with active shielding outperforms the SWCNT and Cu by 75.7% and 84.4%, respectively. Similarly, the power dissipation is substantially reduced in the case of MWCNT bundle with respect to the Cu and SWCNT interconnects. It is also reported that the noise margin is marginally stable in ternary interconnects under the influence of temperature variation.