Preparation and properties of polyimide/LTNO composite films with high dielectric constant

To develop the polymer-based materials with high dielectric constant and thermal stability, Li and Ti doped NiO (LTNO) particles with super high dielectric constant (ε) were dispersed into pyromellitic dianhydride (PMDA) and 4, 4′-oxydianiline (ODA)-based polyimide. Through mixing LTNO particles with the poly(amic acid) precursor solution, casting film and following thermal curing, the polyimide/LTNO composite films were obtained. The thermal stability and structure of the composites were studied by TGA and X-ray diffraction, respectively. Dielectric and conductive measurements were adopted to investigate the properties of the samples. The results revealed that the obtained composites had good morphology stability, but their thermal resistances become a little lower in comparison with pure polyimide. With increasing the content of LTNO particles, ε and conductivity of the composite films increased greatly. For the sample with the LTNO content at 0.4 in volume fraction, ε was as high as 570 at the frequency of 100 Hz. It showed that doping LTNO particles into polyimide would be an efficient route to high ε composites.     

Effect of filler content on the dielectric properties of anisotropic conductive adhesives materials for high-frequency flip–chip interconnection

The dielectric property of anisotropic conductive film (ACF) as an interconnect materials in the flip–chip joints is becoming important concern for device packaging solution at high-frequency due to low parasitic effect on the signal transfer. The effects of non-conductive, dielectric filler content on dielectric properties of ACA materials, like dielectric constant, loss factor and loss tangent, and conductivity at high-frequency were investigated. Frequency is dominating factor in determining dielectric constant, loss factor, and conductivity. However, the filler content is dominant only on dielectric constant, not on the loss factor, and conductivity at low-frequency range. The effect of low dielectric constant (low-k) filler addition on high-frequency behavior of ACF interconnection in flip–chip assembly was also investigated. Impedance parameters of low-k ACF with Ni filler and low-k SiO₂ filler extracted from measurement were compared with that of conventional ACF with only Ni filler. The resonant frequency of conventional ACF flip–chip interconnect was 13 GHz, while the resonant frequency of low-k ACF including low-k SiO₂ filler was found at 15 GHz. This difference is originated from capacitance decrease of polymer matrix between bump and substrate pad due to change in dielectric constant of polymer matrix, which was verified by measurement-based modeling. The high-frequency property of the conductive adhesive flip–chip joint, such as resonant frequency can be enhanced by low-k polymer matrix.     

Effect of the dispersibility of BaTiO3 nanoparticles in BaTiO3/polyimide composites on the dielectric properties

We have investigated the effect of coupling agents with different organic moiety on the dielectric properties of polyimide/BaTiO₃ (70 nm) composite films. INAAT (isopropyl tris(N-amino-ethyl aminoethyl)titanate, KR 44) and APTS (3-amino-propyl-triethoxysilane) were used as coupling agents, respectively, for homogeneous dispersion of BaTiO₃ particles into a polyimide matrix. The composite films were prepared by pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA)-based polyimide. Enhanced dispersion of BaTiO₃ particles was obtained by the use of INAAT with more organic moiety compared to that afforded by APTS. The polyimide composite with BaTiO₃ particles (BaTiO₃ content at 50 vol.%) treated by INAAT showed an increased dielectric constant of 19.03 while retaining an appropriate dielectric loss of 0.0109, as compared to the dielectric constant (14.64) of polyimide/APTS-treated BaTiO₃ composite. The results of this work demonstrate the potential use of an INAAT coupling agent with more organo functional groups for obtaining enhanced dielectric properties in a polyimide/BaTiO₃ composite for application in an embedded capacitor.     

Preparation of ultra-low dielectric constant silica/polyimide nanofiber membranes by electrospinning

Ultra-low dielectric constant silica/polyimide (SiO₂/PI) composite nanofiber membranes are prepared by the combined sol–gel and electrospinning techniques. The emulsion composed of partially hydrolyzed tetraethoxysilane (TEOS) and polyamic acid (PAA) is spun to yield the precursor of the SiO₂/PI fibers with a core–shell structure due to phase separation. The dielectric constant (k) of the composite membranes varies from 1.78 to 1.32 with increasing content of SiO₂. The fibers accumulate and form the film with a large amount of pores leading the lower k. In addition, the interfacial reaction between SiO₂ and the PI matrix reduces the value of k as the SiO₂ concentration is increased. The thermal stability of PI increase after mixing with SiO₂ and the SiO₂/PI composite fibers have large commercial potential in the electronics industry.     

Effect of oxygen plasma treatment on low dielectric constant carbon-doped silicon oxide thin films

Low dielectric constant (low k) carbon-doped silicon oxide (CDO) films are obtained by plasma-enhanced chemical vapor deposition. The k value of the as-deposited CDO film is less than 2.9. However, the k value may be changed during the integration process. In integration process, photoresist removal is commonly implemented with oxygen plasma ashing or by wet chemical stripping. In this work, the impact of oxygen plasma treatment has been investigated on the quality of the low-k CDO films. Different plasma treatment conditions, including variable pressure, r.f. power, and treatment time were employed. A variety of techniques, including X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, time-of-flight secondary ion mass spectrometry (TOF-SIMS), atomic force microscopy (AFM), and scanning electron microscope (SEM) were used to analyze the effect of the oxygen plasma post-treatment on the low-k CDO films. The result indicates that oxygen plasma will damage the CDO film by removing the entire carbon content in the upper part of the film with increasing treatment time, which results in an increase in the k value and film thickness loss. Our result also confirms that with low r.f. power and low pressure, the damage will be less.     

Application of the low dielectric methyl-silsesquiazane (MSZ) as a passivation layer on TFT-LCD

In this study a low-k material, methyl-silsesquiazane (MSZ) has been investigated as a passivation dielectric layer for thin-film transistor (TFT) arrays. Compared with the conventional nitride film (k ∼ 7), the MSZ passivation layer exhibits a low residual stress and low dielectric constant (k ∼ 2.6) which lowers the RC delay in a device. The high transmittance and good planarization characteristics of a low-k MSZ film enhance the brightness and aperture ratio of thin-film transistors liquid crystal displays (TFT-LCDs).     

Characteristics of organic-inorganic hybrid plasma polymer thin films for low-κ ILD applications

This study investigated the effects of plasma power and tetraethylorthosilane (TEOS) to cyclohexene ratios on low-κ organic-inorganic hybrid plasma polymer thin films deposited on silicon (100) substrates. These films were deposited using a plasma enhanced chemical vapor deposition (PECVD) method, in addition to the electrical and mechanical properties of the resulting composites. Cyclohexene and TEOS were used as organic and inorganic precursors, respectively, with hydrogen and argon as precursor bubbler gases. Furthermore, additional argon was used as a carrier gas. The as-grown polymerized thin films were analyzed using ellipsometry, Fourier-transform infrared (FT-IR) spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The ellipsometry results showed the thickness of the hybrid thin film, and the FT-IR spectra showed that the hybrid polymer thin films were completely fragmented and polymerized between cyclohexene and TEOS. AFM results showed that polymer films with a smooth surface could be grown under various deposition conditions, while TEM and XRD showed that the hybrid thin film was an amorphous plasma polymer thin film without porosity. In addition, current-voltage (C-V) curves were prepared to calculate the dielectric constants. Post-annealing was applied to investigate the thermal stability of hybrid plasma polymer thin films in the hardness, Young's modulus, thermal shrinkage, and the dielectric constant at 400 °C.     

Extraction of effective dielectric constants and the effect of process damage of low-k dielectrics for advanced interconnects

In this paper, the line-to-line parasitic capacitance of an advanced interconnects with a low-k dielectric (k < 3.0) was extracted by electrical measurement on comb-serpentine structures with various spacing. The empirical values are higher than the prediction from the filed solver, especially in the small geometries. A model was derived based on the damage of low-k dielectric during processing, which causes the increase of the dielectric constant. Then, the effective dielectric constant was evaluated by both simulation and theoretical models. The k value of damage zone was determined from blanket wafer by mercury probe after oxygen plasma treatment. Good agreement was obtained after we modified the simulation structure to include the damage zone. Especially, the concept of low-k damage due to plasma treatment was characterized for the first time. Thus, it is possible to use this model in the future study, such as the porous low-k in 65 nm or even 45 nm generations.     

The structures of low dielectric constant SiOC thin films prepared by direct and remote plasma enhanced chemical vapor deposition

Two structures of low dielectric constant (low-k) SiOC films were elucidated in this work. Low-k thin film by remote plasma mode was mainly composed of inorganic Si-O-Si backbone bonds and some oxygen atoms are partially substituted by CH₃, which lowers k value. The host matrix of low-k thin films deposited by direct plasma mode, however, was mainly composed of organic C-C bonds and “M” and “D” moieties of organosilicate building blocks, and thus the low dipole and ionic polarizabilities were the important factors on lowering k value.     

Increasing mechanical strength of mesoporous silica thin films by addition of tetrapropylammonium hydroxide and refluxing processes

The incorporation of mesopores into silica films is an effective way to reduce the dielectric constant. However, the pores reduce the film mechanical strength. This study investigates two steps for preparing coating solution. One was the reflux of the silica colloid at 70 °C. The other was the addition of TPAOH (tetrapropylammonium hydroxide) into the colloid. The reflux step can increase the mechanical strength, reduce the flat band voltage and reduce the leakage current of the films. Nevertheless, the low-k value (k represents dielectric constant) increases as the porosity of the film falls. Adding a slight amount of TPAOH before the reflux process can recover both the porosity and the low k value, while maintaining the high mechanical strength and the low flat band voltage. Results of this study demonstrate that two more steps (the addition of TPAOH and the reflux) in the preparation of the coating solution can increase the film hardness and elastic modulus from 0.8 to 1.4 GPa and from 5.8 to 9.9 GPa respectively, while maintaining the low-k value close to 2.05.     

Influences of atomic hydrogen on porous low-k dielectric for 45-nm node

Atomic hydrogen generated by a heated tungsten catalyzer has been investigated in terms of the damage-less ash and restoration of damaged low-k dielectric. No difference of damaged thickness of low-k dielectric between before and after the ash by HF dip using patterned porous methyl silsesquioxane (MSQ) film was found. Moreover atomic hydrogen exposure slightly reduced capacitance of the micro-structured capacitor with the Cu wire and the CVD porous low-k dielectric.     

Fluorinated polyimide–silica films with low permittivity and low dielectric loss

A sol–gel process was used to prepare polyimide–silica hybrid films from the fluorinated polyimide precursors (6FDA-ODA) and tetraethylorthosilicate (TEOS) in N,N-dimethyl acetamide. The hybrid film was then treated with hydrofluoric acid to remove the dispersed silica particles, leaving inside the film pores with diameters ranged from 80 nm to 1 μm, which depended on the size of the silica particles. The chemical structures and morphology of the hybrid and porous films were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. The synthesized porous fluorinated polyimide films show low relative dielectric permittivity of 1.9, rendering them promising for microelectronic packaging materials.     

Effect of etching on dielectric constant and surface composition of SiCOH low-k films in inductively coupled fluorocarbon plasmas

SiCOH low-k (k = 2.8) film etched in fluorocarbon (CF₄ and CHF₃) inductively coupled plasmas was characterized in this work. The surface composition and molecular structures of the low-k films after etching in the CF₄, CHF₃, CF₄/Ar, and CHF₃/Ar plasmas were characterized. A higher etch rate was observed with the CF₄ plasmas than with the CHF₃ plasmas. The etch rate of the low-k film in the CF₄ plasmas was decreased and the etch rate in the CHF₃ plasmas was increased by the Ar addition. After etching the low-k films, a decrease in the dielectric constant of up to 0.19 was observed. The thickness of the fluorocarbon (CF_x) layer and CF_x (x = 1, 2, 3)-to-carbon ratio obtained from the XPS C 1s peak increased with decreasing etch rate. The k-value was correlated with amount of Si-CH₃ and Si-O related groups determined from the Fourier transform infrared (FT-IR) spectrum. The Si-O related peaks were markedly decreased after etching in the CF₄ and CF₄/Ar plasmas. The lower k-value was attributed to the increase of the Si-CH₃/Si-O ratio after etching low-k film.     

Maintaining Cu metal integrity on low-k IMDs with a nanometer thick a-SiC:H film obtained by HWCVD

Hydrogenated amorphous silicon carbon (a-SiC:H) ultra thin films obtained by Hot wire chemical vapor deposition (HWCVD) have been shown to act as efficient diffusion barriers for copper on inter metal dielectric (IMD) layers which are of great significance for ultra-large scale integration (ULSI) circuits. In this work, we have studied the influence of the a-SiC:H barrier layer obtained by HWCVD which has implications towards issues related to the resistance to electromigration of Cu in the low dielectric (low-k) hydrogen silsesquioxane (HSQ) film. The presence of the ultra thin a-SiC:H film maintains the integrity of the Cu metal not only by suppressing Cu diffusion but also by increasing its crystallinity, which would have implications with respect to the mean time to failure (MTF) arising from metal electromigration. Though, we demonstrate this aspect on the low-k (HSQ)/Cu system, this should yield similar benefits for other low-k dielectric materials too.     

Synthesis and structure characterization of low dielectric constant MSQ films by using octamethyl cyclotetrasiloxane (D4) as a porosity promotion agent

Low dielectric methylsilsesquioxane (MSQ) film can be synthesized by spin-coating on P–Si (100) wafer. Octamethyl cyclotetrasiloxane (D4) was used as a porosity promotion agent to MSQ film. Seven samples with different treatment were prepared. The dielectric constants of these MSQ films significantly lowered from 3.0 to 2.1. Fourier transform infrared spectroscopy was used to identify the Si–O–Si network structure, Si–O–Si cage structure and other bonds. The change of structure resulted in significant lowering of the dielectric constant (k). The capacitance–voltage (C–V) characteristic by HP4294A was used to determine the dielectric constant. Current–voltage (I–V) measurement by Keithley6517A was used to determine the breakdown electric field.     

聚酰亚胺/LTNO复合膜介电性能及其影响因素

采用溶胶-凝胶法合成出Li和Ti改性的氧化镍(LTNO)粒子,并通过前体溶液共混法首先制备聚酰胺酸/LTNO前体膜,再经亚胺化得到高介电常数聚酰亚胺/LTNO复合膜。研究发现,复合膜的介电性能可以通过调节LTNO的含量以及Li和Ti在LTNO中的比例来进行调控。选用按Li、Ni和Ti的摩尔百分比为0.30∶0.68∶0.02制备的LTNO粒子做填料,当其体积分数为0.4时,复合膜在100 Hz电场中的介电常数可以达到570。     

Resisting oxygen plasma damage in low-k hydrogen silsesquioxane films by hydrogen plasma treatment

Low-density materials, such as the commercially available hydrogen silsesquioxane (HSQ) offer a low dielectric constant. Thus, HSQ with a low value of k (∼ 2.85) can be spin-coated if the density of Si–H bonding is maintained at a high level and the formation of –OH bonds and absorption of water in the film is minimized. O₂ plasma exposure on HSQ film increases leakage current. Also the dielectric constant shows a significant increase after O₂ plasma exposure. Another consequence of the O₂ plasma exposure is the significant decrease in the contact angle of the HSQ surface, which is not desirable. In this paper, we demonstrate that the surface passivation by hydrogen followed by oxygen plasma treatment of HSQ film for 30 min each leads to a regain of leakage current density and dielectric constant. These results show that the H₂ plasma treatment is a promising technique to prevent the damage in the commercially available and highly applicable low-k materials and it also increases the visibility of its use at the 0.1-μm technology. The more hydrophilic nature of the HSQ surface after O₂ plasma exposure leads to an increased moisture absorption with a subsequent increase in the dielectric constant.     

Mechanical characterization of zeolite low dielectric constant thin films by nanoindentation

With semiconductor technologies continuously pushing the miniaturization limits, there is a growing interest in developing novel low dielectric constant materials to replace the traditional dense SiO₂ insulators. In order to survive the multi-level integration process and provide reliable material and structure for the desired integrated circuits (IC) functions, the new low-k materials have to be mechanically strong and stable. Therefore the material selection and mechanical characterization are vital for the successful development of next generation low-k dielectrics. A new class of low-k materials, nanoporous pure-silica zeolite, is prepared in thin films using IC compatible spin coating process and characterized using depth sensing nanoindentation technique. The elastic modulus of the zeolite thin films is found to be significantly higher than that of other low-k materials with similar porosity and dielectric constants. Correlations between the mechanical, microstructural and electrical properties of the thin films are discussed in detail.     

Characterization and integration of new porous low-k dielectric (k < 2.3) for 65 nm technology and beyond

In this paper, new porous spin-on dielectric (HL02™, trademark of the LG Ltd.) was studied. The characterizations, such as thermal stability, chemical structure, dielectric constant (k) and mechanical properties (hardness and modulus), of methylsilsesquioxane (MSQ)-based dielectrics were evaluated. An optimized material (k = 2.25), characterized by a hardness and a modulus of 1.0 GPa and 6.5 GPa each in association with a porosity of 30% and a mean pore radius of 2.2 nm, was successfully integrated in damascene process with 10 levels of Cu/low-k film for 65 nm technology and beyond. Good electrical results were obtained in metal line resistance and leakage current.     

Effects of porous carbon additives and induced fluorine on low dielectric constant polyimide synthesized with an e-beam

We report the synthesis of a polyimide matrix with a low dielectric constant for application as an intercalation material between metal interconnections in electronic devices. Porous activated carbon was embedded in the polyimide to reduce the dielectric constant, and a thin film of the complex was obtained using the spin-coating and e-beam irradiation methods. The surface of the thin film was modified with fluorine functional groups to impart water resistance and reduce the dielectric constant further. The water resistance was significantly improved by the modification with hydrophobic fluorine groups. The dielectric constant was effectively decreased by porous activated carbon. The fluorine modification also resulted in a low dielectric constant on the polyimide surface by reducing the polar surface free energy. The dielectric constant of polyimide film decreased from 2.98 to 1.9 by effects of porous activated carbon additive and fluorine surface modification.