Low Dielectric Constant Materials Research Articles

Effect of NH3/N2 ratio in plasma treatment on porous low dielectric constant SiCOH materials

This study investigates the effect of the NH3/N2 ratio in plasma treatment on the physical and electrical properties as well as the reliability characteristics of porous low-k films. All of the plasma treatments resulted in the formation of a thin and modified layer on the surface of porous low-k films, and the properties of this modified layer were influenced by the NH3/N2 ratio in the plasma. Experimental results indicated that pure N2 gas plasma treatment formed an amide-like/ nitride-like layer on the surface, which apparently leads to a higher increase in the dielectric constant. Plasma treatment with a mixture of NH3/N2 gas induced more moisture uptake on the surface of the low-k dielectric, degrading the electrical performance and reliability. Among all plasma treatment with NH3/N2 mixed gas, that with pure NH3 gas yielded low-k dielectrics with the worse electrical and reliability characteristics.

Borazine-containing arylacetylene resin as low dielectric constant materials

A novel borazine-containing arylacetylene resin (PBZA) has been synthesized in high yield through condensation reaction between B,B′,B″-trichloroborazine and arylacetylene Grignard reagent, which are potential candidates as low dielectric constant material for microelectronic packaging and also radio and microwave frequency substrate. The PBZA is a brown viscous liquid and soluble in a variety of common solvents. PBZA could be cured by polymerization of alkynyl groups to form organic–inorganic hybrid structure containing borazine ring and aromatic rings with exothermic polymerization temperature in the 190–250 °C range and the structure exhibits great dependence on the substituent on borazine in PBZA. The cured PBZA exhibits high thermal stability with char yield up to nearly 80% at 1000 °C and great chemical stability. Especially, the cured PBZA shows low dielectric constant (ca. 2.7) and extremely low dielectric loss (<0.002). The cured PBZA under higer annealing temperatures exhibits lower dielectric constant and dielectric loss.

Growth and characterization of NixZn1−xSO4·7H2O single crystals

NiSO4·7H2O (morenosite) and ZnSO4·7H2O (goslarite) are hydrogen bonded crystals having wide applications in various fields. In an attempt to understand the formation and properties of mixed crystals based on NiSO4·7H2O and ZnSO4·7H2O, we have grown by the free evaporation method at room temperature and characterized NixZn1−xSO4·7H2O single crystals (with x having the values 0.0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0). The grown crystals were characterized chemically and structurally by carrying out density, X-ray powder diffraction, and atomic absorption and Fourier transform infrared spectral measurements. The grown crystals exhibit good optical transparency in the wavelength range 210–1100nm. The second harmonic generation measurements indicate a maximum efficiency for the mixed crystal with x=0.5. Results of microhardness measurements follow the normal indentation size effect. Electrical (AC and DC) measurements indicate that the grown crystals exhibit a normal dielectric behavior and the electrical conduction is understood to be due to the protonic movement. The present study indicates that the mixed crystals with x=0.2 and 0.5 are not only promising nonlinear optical materials but also useful as low dielectric constant materials.

Investigation of O2 and SF6 plasma interactions on thermally stable damage resistant poly phenyl-methyl silsesquioxane low-k films

The need for improved device performance has led the microelectronics industry to consider alternate materials to use as interlayer dielectrics. Thermally stable low dielectric constant (low-k) materials, with minimal dielectric constant variation during plasma exposure are essential for microelectronic applications. Here we report on the deposition and characterisation of low-k poly phenyl-methyl silsesquioxane films having less k-variation upon interaction with O2 and SF6 plasmas compared to the other reported silsesquioxane materials. Structural transformation and thermal stability of the films during annealing was studied using Fourier transform infrared spectroscopy (FTIR). Even though significant removal of the film occurred with SF6 plasma exposure, no considerable variation of the k-value was observed with both O2 and SF6 plasma exposures. X-ray photoelectron spectroscopic (XPS) analysis was used to investigate the surface modification of the films resulting from plasma exposure. The higher dielectric stability is due to the insignificant moisture intake of the films after plasma treatment which is clear from the FTIR and XPS analysis.

Prospects for dielectric constant reduction in integrated circuits interconnects

ABSTRACTTo improve the integrated circuits’ performance and continue the downscaling of dimensions, it is necessary to use low dielectric constant materials as interconnects insulators. Current porous SiCOH low-k dielectrics are now reaching their limits since their porosity enables the diffusion of species that modify the inner surface of the pores. To further reduce the dielectric constant, it is necessary to change paradigm in interconnects fabrication. In this paper, we discuss the most promising innovations in terms of process, materials and architectures to reduce the interconnects insulators dielectric constant.

Simulations of electrical asymmetry effect on N2-H2 capacitively coupled plasma by particle-in-cell/Monte Carlo model

A N2-H2 capacitively coupled rf discharge has potential applications in etching of organic low dielectric constant (low-k) material for microelectronics technology. In this paper, we investigate the characteristic and electrical asymmetry effect (EAE) on the N2-H2 capacitively coupled plasma used for low-k material etching by particle-in-cell/Monte Carlo (PIC/MC) model, in which the two frequency sources of 13.56 MHz and 27.12 MHz are applied separately to the two electrodes in geometrically in symmetry. It is found that the plasma density profiles, the ion flux density profiles and the energy distribution of ion bombarding electrodes can be changed by adjusting the phase angle θ between the two harmonics. When the phase angle θ is 0°, the density of primary ion (H3+) near low frequencie electrode (LFE) (wafer) is smallest, whereas flux and average energy of ion (H+, H3+, H2+) bombarding LFE are biggest; if the phase angle θ is tuned from 0° to 90°, the dc self-bias increases almost linearly from -103 V to 106 V, ion flux bombarding the LFE decreases by ±18%, the maximum of the ion bombarding energy at the LFE decreases by a factor of 2.5. For the N2-H2 capacitively coupled rf discharge, for the case of two frequencies (13.56 MHz/27.12 MHz) applied separately to the two electrodes, can realize separate control of ion energy and flux via the EAE, and is generally in qualitative agreement with experimental and modeling investigation on the Ar and O2 plasma for a dual-frequency voltage source of 13.56 MHz and 27.12 MHz is applied to the powered electrode. This work supplies a references basis for experimental research and technology that the EAE on the H2-N2 plasmas is used for organic low-k material etching process.

Complete Elemental Analysis of Low-k a-SiC:H Thin Films by Transmission FTIR Spectroscopy

Fourier transform infrared (FTIR) spectroscopy is a popular technique for qualitatively investigating the chemical bonding of low dielectric constant (low-k) materials utilized in nanoelectronic Cu interconnects. However, quantitative FTIR analysis of low-k materials with widely varying stoichiometry has proven challenging due to numerous optical interference effects, variations in IR absorption strength with optical constants, and a negligible IR activity for homopolar bonds. In this paper, these challenges are overcome to demonstrate full elemental composition analysis by applying multivariate partial least squares (PLS) modeling to the true IR absorbance spectra obtained using previously described methods for eliminating optical interference effects from thin film FTIR spectra. To demonstrate the validity of this approach, transmission FTIR spectra were collected from a series of low-k a-SiC:H thin films with hydrogen content ranging from 25–60%. The elemental concentrations determined from PLS analysis of the corrected low-k a-SiC:H FTIR spectra were found to be in agreement to within ±5% of results obtained from independent nuclear reaction analysis and Rutherford backscattering measurements. These results demonstrate a clear path for establishing transmission FTIR as a quantitative metrology for full compositional analysis (elemental and chemical bond) for a wide range of thin film materials.

Study of Wet Surface Activation Routes to Enable the Deposition of Monomolecular Organic Thin Films on k 2.0 Porous Dielectrics

This paper explores the effects of different wet surface treatments on low dielectric constant (low-k) materials and the consequences for the growth behavior of self-assembled monolayers (SAMs) from 11-cyanoundecyltrichlorosilane precursor on these modified substrates. Hydrofluoric acid (HF), tetramethylammonium hydroxyde (TMAH) and sulfuric peroxide mixture (SPM) treatments were performed on SiCOH low-k films to modify their chemical surface groups. Transmission FTIR and water contact angle analysis showed that the SPM and TMAH treatments changed the hydrophobic surface completely into a hydrophilic surface, while the HF changed it only partially. In particular, low-k surface hydrophilicity, thickness loss and refractive index increase associated with the TMAH activation are reported as a function of TMAH concentration, contact time and temperature. The density of the SAM molecules deposited from the vapor phase and their penetration degree in the bulk of the low-k films were found to be proportional to the density and depth of the hydroxyl groups created during the wet pre-activation, respectively. In a subsequent step, an HfO2 Atomic Layer Deposition was applied on top of the SAMs. The film stacks were exhaustively characterized after each step in terms of k damage and pore sealing by ellipsometric porosimetry, and Rutherford Backscattering Spectroscopy.

Polymethyl methacrylate (PMMA)–bismuth ferrite (BFO) nanocomposite: low loss and high dielectric constant materials with perceptible magnetic properties

Herein, poly(methyl methacrylate)-bismuth ferrite (PMMA-BFO) nanocomposites were successfully prepared by an in situ polymerization method for the first time. Initially, the as prepared bismuth ferrite (BFO) nanoparticles were dispersed in the monomer, (methyl methacrylate) by sonication. Benzoyl peroxide was used to initiate the polymerization reaction in ethyl acetate medium. The nanocomposite films were subjected to X-ray diffraction analysis (XRD), (1)H NMR, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), thermogravimetric analysis (TGA), infrared spectroscopy (IR), dielectric and magnetic characterizations. The dielectric measurement of the nanocomposites was investigated at a frequency range of 10 Hz to 1 MHz. It was found that the nanocomposites not only showed a significantly increased value of the dielectric constant with an increase in the loading percentage of BFO as compared to pure PMMA, but also exhibited low dielectric loss values over a wide range of frequencies. The values of the dielectric constant and dielectric loss of the PMMA-BFO5 (5% BFO loading) sample at 1 kHz frequency was found be ~14 and 0.037. The variation of the ferromagnetic response of the nanocomposite was consistent with the varying volume percentage of the nanoparticles. The remnant magnetization (Mr) and saturation magnetization (Ms) values of the composites were found to be enhanced by increasing the loading percentage of BFO. The value of Ms for PMMA-BFO5 was found to be ~6 emu g(-1). The prima facie observations suggest that the nanocomposite is a potential candidate for application in high dielectric constant capacitors. Significantly, based on its magnetic properties the composite will also be useful for use in hard disk components.

DIELECTRIC PROPERTIES OF PURE AND NI2+ DOPED GLYCINE SODIUM SULFATE CRYSTALS

Pure and Ni 2+ added glycine sodium sulfate (GSS) single crystals were grown by the slow evaporation technique and c haracterized chemically, structurally, thermally, optically, mec hanically and electrically. Effect of Ni 2+ addition as an impurity on the properties of GSS has also been investigated. All the six crystal s grown exhibit normal dielectric behavior and are found to be thermally stable up to 250˚C, NLO active and mechanically soft. The Ni 2+ addition is found to increase the dielectric param eters. The low dielectric constant values observed for pure GSS indicate that GSS is not only a promising NLO material but also a low dielectric constant value dielectric material.

Effect of magnesium additive on structure and properties of Al2O3–B2O3–SiO2 glass system

Printed wiring board is an important component of electronic devices. Low dielectric constant materials are expected to reduce the time delay of signal propaganda and dielectric loss. E-glass fibre as reinforcing material of printed wiring board does not meet the requirements. To reduce the operating temperature of glass, bivalent metal oxides must be introduced, often at the expense of dielectric properties. Aluminoborosilicate glass is a typical glass system with low dielectric constant. Al2O3–B2O3–SiO2 glasses that replaced Al2O3 by MgO were melted, and their microstructure, some physical properties and chemical durability were investigated. In addition, the role of Al2O3 in borosilicate glasses was investigated. The glass system was characterised with lower dielectric constant (4·8–5·7) and loss tangent (10−3) at 1 MHz. By replacing Al2O3 with MgO, the density and viscosity–temperature characteristic points of the studied glasses showed a decreasing tendency. The average dissolution rate of the studied glasses was <4·51×10−8 g cm−2 min−1. When the molar ratio of RO/Al2O3 is >2·5 (R = Ca2+, Mg2+), the trivalent, tetrahedral [BO4] and [AlO4] network units increased at the same time as indicated by infrared spectra. The paper has designed a group of glasses that has both satisfactory processing properties and dielectric properties. The present glass system could substitute E-glass and be a possible candidate for many applications.

Detection of surface electronic defect states in low and high-k dielectrics using reflection electron energy loss spectroscopy

Abstract

Atomic Layer Deposition of TiO2 on Surface Modified Nanoporous Low-k Films

This paper explores the effects of different plasma treatments on low dielectric constant (low-k) materials and the consequences for the growth behavior of atomic layer deposition (ALD) on these modified substrates. An O2 and a He/H2 plasma treatment were performed on SiCOH low-k films to modify their chemical surface groups. Transmission FTIR and water contact angle (WCA) analysis showed that the O2 plasma changed the hydrophobic surface completely into a hydrophilic surface, while the He/H2 plasma changed it only partially. In a next step, in situ X-ray fluorescence (XRF), ellipsometric porosimetry (EP), and Rutherford backscattering spectroscopy (RBS) were used to characterize ALD growth of TiO2 on these substrates. The initial growth of TiO2 was found to be inhibited in the original low-k film containing only Si-CH3 surface groups, while immediate growth was observed in the hydrophilic O2 plasma treated film. The latter film was uniformly filled with TiO2 after 8 ALD cycles, while pore filling was delayed to 17 ALD cycles in the hydrophobic film. For the He/H2 plasma treated film, containing both Si-OH and Si-CH3 groups, the in situ XRF data showed that TiO2 could no longer be deposited in the He/H2 plasma treated film after 8 ALD cycles, while EP measurements revealed a remaining porosity. This can be explained by the faster deposition of TiO2 in the hydrophilic top part of the film than in the hydrophobic bulk which leaves the bulk porous, as confirmed by RBS depth profiling. The outcome of this research is not only of interest for the development of advanced interconnects in ULSI technology, but also demonstrates that ALD combined with RBS analysis is a handy approach to analyze the modifications induced by a plasma treatment on a nanoporous thin film.

Effect of moisture on electrical properties and reliability of low dielectric constant materials

The effect of absorbed moisture on the electrical characteristics and reliability of low dielectric constant materials (low-k) was investigated in this study. The experimental results reveal that porous low-k dielectrics absorb more moisture than dense low-k dielectrics. This absorbed moisture degrades the electrical performance and reliability of both classes of low-k dielectrics. Annealing at a higher temperature of 400°C is required to decompose the physically-adsorbed moisture and thereby restore reliability performance. However, the chemically-adsorbed moisture seems to be difficult to remove by annealing at 400°C, causing a degraded TDDB performance.

Electrical properties of hollow glass particle filled vinyl ester matrix syntactic foams

Low dielectric constant materials play a key role in modern electronics. In this regard, hollow particle reinforced polymer matrix composites called syntactic foams may be useful due to their low and tailored dielectric constant. In the current study, vinyl ester matrix/glass hollow particle syntactic foams are analyzed to understand the effect of hollow particle wall thickness and volume fraction on the dielectric constant of syntactic foams. The dielectric constant is found to decrease with increase in the hollow particle volume fraction and decrease in the wall thickness. Theoretical estimates are obtained for the dielectric constant of syntactic foams. Parametric studies are conducted using the theoretical model. It is found that a wide range of syntactic foam compositions can be tailored to have the same dielectric constant, which provides possibility of independently tailoring density and other properties based on the requirement of the application.

Plasma etching: Yesterday, today, and tomorrow

The field of plasma etching is reviewed. Plasma etching, a revolutionary extension of the technique of physical sputtering, was introduced to integrated circuit manufacturing as early as the mid 1960s and more widely in the early 1970s, in an effort to reduce liquid waste disposal in manufacturing and achieve selectivities that were difficult to obtain with wet chemistry. Quickly,the ability to anisotropically etch silicon, aluminum, and silicon dioxide in plasmas became the breakthrough that allowed the features in integrated circuits to continue to shrink over the next 40 years. Some of this early history is reviewed, and a discussion of the evolution in plasma reactor design is included. Some basic principles related to plasma etching such as evaporation rates and Langmuir–Hinshelwood adsorption are introduced. Etching mechanisms of selected materials, silicon,silicon dioxide, and low dielectric-constant materials are discussed in detail. A detailed treatment is presented of applications in current silicon integrated circuit fabrication. Finally, some predictions are offered for future needs and advances in plasma etching for silicon and nonsilicon-based devices.

Detection of defect states in low-k dielectrics using reflection electron energy loss spectroscopy

Reflection electron energy loss spectroscopy (REELS) has been utilized to measure the band gap (Eg) and energy position of sub-gap defect states for both non-porous and porous low dielectric constant (low-k) materials. We find the surface band gap for non-porous k = 2.8–3.3 a-SiOC:H dielectrics to be ≅ 8.2 eV and consistent with that measured for a-SiO2 (Eg = 8.8 eV). Ar+ sputtering of the non-porous low-k materials was found to create sub-gap defect states at ≈ 5.0 and 7.2 eV within the band gap. Based on comparisons to observations of similar defect states in crystalline and amorphous SiO2, we attribute these sub-gap defect states to surface oxygen vacancy centers. REELS measurements on a porous low-k a-SiOC:H dielectric with k = 2.3 showed a slightly smaller band gap (Eg = 7.8 eV) and a broad distribution of defects states ranging from 2 to 6 eV. These defect states are attributed to a combination of both oxygen vacancy defects created by the UV curing process and carbon residues left in the film by incomplete removal of the sacrificial porogen. Plasma etching and ashing of the porous low-k dielectric were observed to remove the broad defect states attributed to carbon residues, but the oxygen vacancy defects remained.

Plasma processing of low-k dielectrics

This paper presents an in-depth overview of the present status and novel developments in the field of plasma processing of low dielectric constant (low-k) materials developed for advanced interconnects in ULSI technology. The paper summarizes the major achievements accomplished during the last 10 years. It includes analysis of advanced experimental techniques that have been used, which are most appropriate for low-k patterning and resist strip, selection of chemistries, patterning strategies, masking materials, analytical techniques, and challenges appearing during the integration. Detailed discussions are devoted to the etch mechanisms of low-k materials and their degradation during the plasma processing. The problem of k-value degradation (plasma damage) is a key issue for the integration, and it is becoming more difficult and challenging as the dielectric constant of low-k materials scales down. Results obtained with new experimental methods, like the small gap technique and multi-beams systems with separated sources of ions, vacuum ultraviolet light, and radicals, are discussed in detail. The methods allowing reduction of plasma damage and restoration of dielectric properties of damaged low-k materials are also discussed.

Ultra low dielectric, self-cleansing and highly oleophobic POSS-PFCP aryl ether polymer composites

Ultra low dielectric constant (k = 1.53) materials with self-cleansing properties were synthesized via incorporation of fluorodecyl-polyhedral oligomeric silsesquioxane (FD-POSS) into recently synthesized perfluorocyclopentenyl (PFCP) aryl ether polymers. Incorporation of fluorine rich, high free volume, and low surface energy POSS into a semifluorinated PFCP polymer matrix at various weight percentages resulted in a dramatic drop in dielectric constant, as well as a significant increase in hydrophobicity and oleophobicity of the system. These ultra-low dielectric self-cleansing materials (θtilt = 38°) were fabricated into electrospun mats from a solvent blend of fluorinated FD-POSS with PFCP polymers.

Design of Rectangular Dielectric Resonant Antenna for ku-band Applications

in this paper, a novel broadband, low-profile dielectric resonator antenna using relatively low dielectric constant substrate material .The rectangular DRA is fed with a modified stepped micro strip feed to ensure efficient coupling between the feeder and the RDR. By introducing the RDR with two narrow conducting metallic strips of suitable width the performance of the proposed antenna has been significantly improved, the result leads to a wider operating bandwidth. Parametric investigations for different geometrical variables have been presented. The return loss and radiation performance of the proposed antenna and the related prototypes are successfully optimized with numerical experimentation techniques using Ansoft HFSS software.