Low-k Materials Research Articles

Fluorinated intrinsic low-k materials at high frequency with good dielectric performance and excellent hydrophobicity

Through the Grubbs reaction, two fluorinated precursors (M1 and M2) with the thermo-crosslinkable benzocyclobutene (BCB) groups and an unconjugated double bond have been successfully synthesized. The thermally cured products of the precursors exhibit low Dk and Df at a frequency of 10 GHz, as well as excellent hydrophobicity even being immersed in boiling water for 72 h. Among the cured resins, cured M1 exhibits the best comprehensive performance, including a Dk of 2.41, a Df of 1.02 × 10−3, and water uptake (Wa) of 0.013%. For comparison, a control precursor M3 without the unconjugated double bond in the molecular backbones has been also prepared, displaying that the unconjugated double bond has a positive effect on the dielectric and mechanical properties of the resins. Further investigation indicates that cured M1 displays low density than cured M3. This contribution has given an insight to design the intrinsic low-k materials, as well as provided a facile way for the preparation of the materials.

High Thermal Stability and Low Dielectric Constant of BCB Modified Silicone Resins.

Based on the excellent physical properties and flexible molecular modifiability, modified silicone resins have received favorable attention in the field of microelectronics, and recently a number of modified silicone resins have appeared while few breakthroughs have been made in low dielectric constant (low-k) materials field due to the limitations of structure or the curing process. In this work, functional silicone resin with different BCB contents was prepared with two monomers. The resins showed low dielectric constant (k = 2.77 at 10 MHz) and thermal stability (T5% = 495.0 °C) after curing. Significant performance changes were observed with the increase in BCB structural units, and the functional silicone obtained does not require melting and dissolution during processing because of good fluidity at room temperature. Moreover, the mechanical properties of silicone resins can be also controlled by adjusting the BCB content. The obtained silicone resins could be potentially used in the field of electronic packaging materials.

A Study on Fabrication of Mesoporous Silica Nanoparticles Hybrid Polyimide film for Low-k materials

A Study on Fabrication of Mesoporous Silica Nanoparticles Hybrid Polyimide film for Low-k materials

NS-GAAFET Compact Modeling: Technological Challenges in Sub-3-nm Circuit Performance

NanoSheet-Gate-All-Around-FETs (NS-GAAFETs) are commonly recognized as the future technology to push the digital node scaling into the sub-3 nm range. NS-GAAFETs are expected to replace FinFETs in a few years, as they provide highly electrostatic gate control thanks to the GAA structure, with four sides of the NS channel entirely enveloped by the gate. At the same time, the NS rectangular cross-section is demonstrated to be effective in its driving strength thanks to its high saturation current, tunable through the NS width used as a design parameter. In this work, we develop a NS-GAAFET compact model and we use it to link peculiar single-device parameters to digital circuit performance. In particular, we use the well-known BSIM-CMG core solver for multigate transistors as a starting point and develop an ad hoc resistive and capacitive network to model the NS-GAAFET geometrical and physical structure. Then, we employ the developed model to design and optimize a digital inverter and a five-stage ring oscillator, which we use as a performance benchmark for the NS-GAAFET technology. Through Cadence Virtuoso SPICE simulations, we investigate the digital NS-GAAFET performance for both high-performance and low-power nodes, according to the average future node present in the International Roadmap for Devices and Systems. We focus our analysis on the main different technological parameters with regard to FinFET, i.e., the inner and outer spacers. Our results highlight that in future technological nodes, the choice of alternative low-K dielectric materials for the NS spacers will assume increasing importance, being as relevant, or even more relevant, than photolithographic alignment and resolution at the sub-nm scale.

Linker engineering of larger POSS-based ultra-low-k dielectrics toward outstanding comprehensive properties

Low-dielectric-constant (low-k) materials are an indispensable part of microprocessors as they can alleviate electronic crosstalk, charge build-up, and signal propagation delay. However, existing low-k materials usually have k values higher than 2 and inferior thermo-mechanical properties, which restrict the development of microelectronic devices. Although we have recently discovered that larger polyhedral oligomeric silsesquioxanes (POSS) are useful building blocks for fabricating advanced ultra-low-k materials, it remains to be seen whether a POSS cage and linker could be leveraged to tune the structure-property of the materials and create ultra-low-k materials with improved comprehensive properties. Herein, we propose a series of POSS-based hybrid materials (i.e., c-TnPBn and c-TnFn, n = 8, 10, and 12) that consist of distinct POSS cages and linkers. When the linker is kept identical, the gradual enlargement of the POSS cage enhances the porosity/free volume fraction of materials, resulting in quasi-linearly reduced k values for the resulting materials (k = 1.93 for c-T12PB12, 2.14 for c-T12F12). Meanwhile, the materials’ comprehensive properties can be significantly improved by increasing the POSS cage size or varying the linker’s length and type. As a result, ultra-low-k materials with good processability, low surface roughness (< 0.40 nm), excellent thermostability (> 480 °C), mechanical properties (elastic modulus > 2.5 GPa), and hydrophobicity have been obtained, and the low-k values can be maintained under high temperature (e.g., 300 °C) and wet condition. This work reveals the critical contribution of POSS cage size and linker to the structure and properties of POSS-based low-k materials and offers promising materials for the future of the microelectronic industry.

Probing molecular structures at buried solid/solid interfaces involving low-k materials or polymers in situ nondestructively: a review

BackgroundWith the development of three-dimensional (3D) integration technology including extreme ultraviolet (EUV) lithography, more and more buried interfaces are involved in a device. It is important to probe such buried solid/solid interfaces in situ, but due to the lack of appropriate metrology, it is difficult to do so.AimThis review aims to introduce sum frequency generation (SFG) vibrational spectroscopy to researchers and engineers in the research fields related to 3D integration technology including EUV lithography. SFG can probe buried solid/solid interfaces in situ nondestructively.Review ApproachThis review presents the SFG technique and the recent results obtained from SFG studies on a variety of solid/solid interfaces, including porous low-k material/silicon interfaces, plasma treated polymer/epoxy interfaces, flux treated metal/epoxy interfaces, chemical reactions at buried solid/solid interfaces, and structures of buried solid/solid interfaces in multilayered thick device.ConclusionsSFG has been successfully applied to elucidate molecular structures and molecular interactions at buried solid/solid interfaces in situ nondestructively. SFG has great potential to probe buried interfaces in devices based on 3D integration technology.

Tröger’s Base (TB)-Based Polyimides as Promising Heat-Insulating and Low-K Dielectric Materials

The correlations between the molecular structures of four Tröger’s base (TB)-based polyimides (PIs) and two non-TB containing analogues and physical properties including thermal conductivity (λ) and dielectric properties both at low and high frequencies were investigated in detail. The TB-based PI films exhibited low dielectric constants (Dk = 2.25–2.80) at 10 GHz. They possessed much lower λ values (0.035–0.145 W/mK) compared to the commercial PI Kapton (0.240 W/mK). The influences of incorporating TB units into chain backbones on aggregation structures and physical properties of PIs were identified. Incorporating TB units into chain backbones effectively reduced the degree of chain orientation and increased fractional free volume, leading to both low Dk and low λ values for the resulting PI films. Also, introducing TB units enhanced molecular weights, toughness, and glass-transition temperature (Tg) of the resulting PIs. Therefore, the TB-based PIs can be promising heat-insulating and low-k dielectric materials.

Comprehensive Study of the Chemical, Physical, and Structural Evolution of Molecular Layer Deposited Alucone Films during Thermal Processing

Thermal processing of molecular layer deposited (MLD) hybrid inorganic–organic alucone thin films produced porous and low-k materials. Alucone films were deposited by MLD using trimethyl aluminum and ethylene glycol at 120 °C. Changes in the film density and thickness during annealing were monitored using in-situ X-ray reflectivity and were compared to atomic layer deposited (ALD) alumina films. The chemical evolution of the as-deposited and annealed alucone films during post-deposition heating with and without UV was probed using infrared spectroscopy, Rutherford backscattering, nuclear reaction analysis, and 15N spectroscopy, providing a detailed understanding of the induced changes. The concentration of OH groups decreased after depositing 1 nm of alumina capping layer as a barrier to moisture uptake, which also decreased the etch rate in CF4/O2 plasma. The lowest dielectric constant of the processed alucone films (kmin = 4.75) was 25% lower than the lowest values measured in ALD alumina counterparts (kmin = 6.7). Large thickness decreases for alucone films were observed at ∼200 °C of anneal temperatures. Removal of retained organic components by thermal processing of MLD films is demonstrated to be a promising and versatile route to porous thin films for a wide range of applications including low dielectric constant materials.

Fabrication of Ordered Porous Polyimide Films Templated by (AB)m Type of Diblock Copolymer.

Ordered porous polyimide films were fabricated from (AB)m type of diblock copolymer polyimide-b-polystyrene (PI-b-PS). An increase in PS volume fraction (f VPS) is beneficial to decrease the relative dielectric constants and water contact angles of the obtained porous PI films: the relative dielectric constant decreases to 1.89 and water contact angle decreases to 43° when f VPS is 0.36, indicating porous PI films can be used as low-κ material and have good wettability. The solvent uptake of the porous PI films increases with increasing f VPS. A net-like morphology appears when f VPS reaches 0.36. The net-like porous PI film reaches equilibrium uptake of water within approximately 2.5 h, with a final equilibrium uptake ratio of 17.5%, and reaches equilibrium uptake of toluene within approximately 8 h, with a final equilibrium uptake ratio of 15.4%, displaying the highest and fastest solvent uptake compared with other microstructured porous PI films, which is ascribed to the specific characteristic of the interconnecting porous channels derived from the self-assembly of PI-b-PS with f VPS 0.36. Introducing thermally degradable segments to PI-based block copolymer is an effective method to prepare porous PI films and can enhance some of their properties.

Reliability Characteristics of Metal-Insulator-Semiconductor Capacitors with Low-Dielectric-Constant Materials.

In this study, the reliability characteristics of metal-insulator-semiconductor (MIS) capacitor structures with low-dielectric-constant (low-k) materials have been investigated in terms of metal gate area and geometry and thickness of dielectric film effects. Two low-k materials, dense and porous low-k films, were used. Experimental results indicated that the porous low-k films had shorter breakdown times, lower Weibull slope parameters and electric field acceleration factors, and weaker thickness-dependence breakdowns compared to the dense low-k films. Additionally, a larger derivation in dielectric breakdown projection model and a single Weilbull plot of the breakdown time distributions from various areas merging was observed. This study also pointed out that the porous low-k film in the irregular-shaped metal gate MIS capacitor had a larger dielectric breakdown time than that in the square- and circle-shaped samples, which violates the trend of the sustained electric field. As a result, another breakdown mechanism exists in the irregular-shaped sample, which is required to explore in the future work.

A low dielectric constant material synergized by calix[4]arene and benzocyclobutene units

A novel low-kmaterial (Dkis as low as 2.23) was prepared from functionalized 4-tert-butylcalix[4]arene with different numbers of benzocyclobutene (BCB) units (2 or 4) and spacers (–(CH2)3– or –(CH2)6–).

Synthesis of Yttria-Stabilized Zirconia Nanospheres from Zirconium-Based Metal-Organic Frameworks and the Dielectric Properties.

Yttria-stabilized zirconia (YSZ) nanospheres were synthesized by calcination at 900 °C after the adsorption of Y3+ ions into the pores of a zirconium-based metal-organic framework (MOF). The synthesized 3YSZ (zirconia doped with 3 mol% Y2O3), 8YSZ (8 mol% Y2O3), and 30YSZ (30 mol% Y2O3) nanospheres were found to exhibit uniform sizes and shapes. Complex permittivity and complex permeability were carried out in K-band (i.e., 18-26.5 GHz) to determine their suitability for use as low-k materials in 5G communications. The real and imaginary parts of the permittivity of the sintered 3YSZ were determined to be 21.24 and 0.12, respectively, while those of 8YSZ were 22.80 and 0.16, and those of 30YSZ were 7.16 and 0.38. Control of the real part of the permittivity in the sintered YSZ was facilitated by modifying the Y2O3 content, thereby rendering this material an electronic ceramic with potential for use in high-frequency 5G communications due to its excellent mechanical properties, high chemical resistance, and good thermal stability. In particular, it could be employed as an exterior material for electronic communication products requiring the minimization of information loss.

Real-time VUV radiation monitoring in low-pressure hydrogen plasma based on fluorescence of sodium salicylate

Recently, vacuum ultra-violet (VUV) radiation emitted from plasmas has been of particular interest in semiconductor device fabrication because of the effects of its high-energy photons, such as induced damage or curing on low-k materials. Due to the difficulty of implementing conventional spectroscopic methods to monitor VUV radiation with high accuracy and time resolution in current plasma processing equipment, novel monitoring methods must be investigated. Therefore, in this work, we developed a compact VUV radiation monitoring system based on a scintillator, i.e. sodium salicylate (NaSal), for real-time VUV measurements. Compared to conventional VUV spectrometers, the system shows considerable implementation potential thanks to its compact size, higher detection accuracy and high time resolution. VUV radiation emitted by continuous and pulsed hydrogen plasmas generated at low pressure was investigated using the developed system. Using various filters, we were able to compare the VUV photon intensity in different wavelength ranges. It was found that the VUV photon intensity between 115 and 250 nm was about 2.5 times higher than in the region below 115 nm due to intense Lyman-α and molecular radiation, such as Lyman and Werner bands observed in low-pressure hydrogen plasmas.

Design Space Exploration of Interconnect Materials for Cryogenic Operation: Electrical and Thermal Analyses

With Copper (Cu) Interconnects causing performance bottleneck at single nanometer nodes due to increase in resistivity size effects viz., grain boundary scattering and surface scattering, there has always been scavenging for alternate interconnect materials. Although the Cu resistivity value decreases at cryogenic temperature, the problems continue to persist. In this work, we study three alternate interconnect materials specifically for 77K High Performance Compute applications. We select the materials based on their resistivity value at 77K for 7nm node computed using Fuchs-Sondheimer-Mayadas-Shatzkes (FS-MS) models. We analyze the delay of the interconnects, understand repeater insertion as a function of wire length, evaluate repeater count and energy at system level and perform IR drop analysis by showing through detailed analytical models that Ru, Rh and Al can provide appreciable improvements over Cu at 77K. The delay of interconnects reduces by 1-3.75% for Ru, 1.5-7.25% for Rh and 4.4-17.8% for Al across the BEOL stack while repeater counts decrease by 10%, 15% and 37% for Ru, Rh and Al respectively at 77K. We investigate thermal and reliability aspects of interconnect design including electromigration, Joule Heating and maximum allowed current densities again proving that Ru (9%), Rh (18%) and Al (63%) outperform Cu at 77K. Finally, we study the effects of various Low-k dielectric materials on the interconnect capacitance and thermal behavior for Cu as well as three alternate materials noting that, even though thermal conductivity of dielectrics decrease at 77K, the Joule Heating will not be as worse as one might expect.

(Invited) Computational Insights to Dielectric Hybrid Glasses Under Nanoscale Confinement for Next Generation Devices

Low and Ultra-k dielectric organosilicate glasses (OSG) are widely used in device interconnect applications such as shallow trench isolation as insulating units. However, the process of gap filling between conducting units has been challenging. One of the challenges is related to the undesired formation of nanovoids in the low-k dielectric material confined inside the trench geometry. Importantly, the effects of such nanoscale device constraints on the structure and mechanical reliability of low-k dielectric hybrid materials are not very well understood. To close this lack of understanding and guide the related experimental efforts we performed molecular dynamics simulations where we explore the role of the molecular structure and connectivity of different low-k dielectric OSG precursors under nanoscale confinement, and predict the resulting elastic and fracture properties. We demonstrated that hyperconnected OSG precursors with aromatic rings, such as the 1,3,5-benzene molecule, pack more homogenously under confinement leading to smaller nanovoids and better mechanical reliability compared to conventionally bridged OSG precursors, such as the ethylene bridged Et-OCS molecule.

Lattice Thermal Conductivity of MgSiO3 Perovskite and Post-Perovskite under Lower Mantle Conditions Calculated by Deep Potential Molecular Dynamics

Lattice thermal conductivity (κ lat) of MgSiO3 perovskite and post-perovskite is an important parameter for the thermal dynamics in the Earth. Here, we develop a deep potential of density functional theory quality under entire thermodynamic conditions in the lower mantle, and calculate the κ lat by the Green–Kubo relation. Deep potential molecular dynamics captures full-order anharmonicity and considers ill-defined phonons in low-κ lat materials ignored in the phonon gas model. The κ lat shows negative temperature dependence and positive linear pressure dependence. Interestingly, the κ lat undergos an increase at the phase boundary from perovskite to post-perovskite. We demonstrate that, along the geotherm, the κ lat increases by 18.2% at the phase boundary. Our results would be helpful for evaluating Earth’s thermal dynamics and improving the Earth model.

Recent Trends in Copper Metallization

The Cu/low-k damascene process was introduced to alleviate the increase in the RC delay of Al/SiO2 interconnects, but now that the technology generation has reached 1× nm or lower, a number of limitations have become apparent. Due to the integration limit of low-k materials, the increase in the RC delay due to scaling can only be suppressed through metallization. As a result, various metallization methods have been proposed, including traditional barrier/liner thickness scaling, and new materials and integration schemes have been developed. This paper introduces these methods and summarizes the recent trends in metallization. It also includes a brief introduction to the Cu damascene process, an explanation of why the low-k approach faces limitations, and a discussion of the measures of reliability (electromigration and time-dependent dielectric breakdown) that are essential for all validation schemes.

Impact of gate misalignment on the performance of CNTFET: TFET vs MOSFET

CNTFET device structures are gaining more research interest as conventional FET structures are reaching their scaling limits. One of the most crucial effects that could occur in the fabrication on the nanometer scale is the gate misalignment. In this paper, we report on a study of the impact of gate misalignment on the performance of MOSFET and TFET CNT-based device architectures. Given the fact that gate misalignment can occur on any side of the gate, extensive simulations have been carried out to account for the gate misalignment towards the source and the drain sides. We scrutinize how the misalignment influences the device performance parameters like ON-current, subthreshold swing SS, overall gate capacitance and cut-off frequency. Moreover, these “Figure of Merits” are calculated for two cases, one of which uses a single oxide all over the device various regions and the other incorporates a low-k oxide spacer material over the source and the drain regions while a high-k gate oxide material is utilized over the channel region. Simulation results show that MOSFETs are more immune to the fabrication process variations than TFETs.

High-performance and low-dielectric cyanate ester resin optimized by regulating the structure of linear polyhydroxy ether modifier

Cyanate ester resin (CE) is an ideal candidate for low dielectric constant (low-k) materials in the microelectronic industry, however the incoordination among mechanical, thermal and low-k properties greatly restricts their practical applications. Herein, two kinds of fluorinated polyhydroxy ether (PHE) with or without polyhedral oligomeric silsesquioxane (FPHE, FPHE-POSS) were designed and synthesized by regulating the structure of the linear PHE chains, to modify CE resin for elevating its comprehensive performances. Results reveal that FPHE can improve the mechanical properties and reduce the k of CE resin to some extent owing to its weakly polarizable flexible chains. Whereas FPHE-POSS can not only enlarge the optimization effects from FPHE, but also significantly improve thermostability simultaneously due to the extra-contribution of the heat-resistant rigid skeleton (POSS). Especially, FPHE-POSS6/CE possesses lower k values (2.48, 1 MHz), superior impact strength (24.59 kJ/m2, increased by 65.0 %) and higher glass transition temperature (307.6°C, increased by 18.8°C) as compared with pure CE resin. This work proposed a facile strategy to break through the incoordination among dielectric, thermal, and mechanical properties of CE resin via using weak-polarizable and flexible-rigid linear oligomer, which could be a guidance for advanced researches.

Etch Characteristics of Low-K Materials Using CF3I/C4F8/Ar/O2 Inductively Coupled Plasmas

In this study, pulsed CF3I/C4F8/Ar/O2 inductively coupled plasmas have been studied for low-k etching, and the effects of CF3I addition to C4F8/Ar/O2 on the plasma characteristics and etch characteristics of low-k materials were investigated. The increased ratio of CF3I/(CF3I+C4F8) in the gas mixture increased CF3 radicals while decreasing CF2 radicals in the plasma, and which are related to the etching and polymerization, respectively. Therefore, the etch rates of SiCOH increased with increasing the CF3I ratio. However, the etch selectivity over an amorphous carbon layer and photoresist was the highest at the ratio of 0.5 because the CF2/F flux ratio from the plasma and the C/F ratio on the polymer layer were the highest at the CF3I ratio of 0.5. The SiCOH damage was decreased with increasing CF3I ratio and the SiCOH damage appeared to be very low, particularly when the CF3I ratio was ≥0.5 by showing low Si–CH3 bond loss, low F penetration, and a low surface roughness. Therefore, it is believed that, as opposed to the C4F8/Ar/O2 gas mixture only, mixing 50% CF3I into the C4F8/Ar/O2 gas mixtures resulted in not only a high etch selectivity over mask materials, but also a potentially reduced etch damage.