Porous SiCOH Films Research Articles

High-performance ultra-low-k fluorine-doped nanoporous organosilica films for inter-layer dielectric

Development of low-k materials is critical for further improving the performance of integrated circuits. In this work, a novel type of fluorine-doped ultra-low-k porous SiCOH films has been produced. The chemical composition and bond configurations of the nanometer-scale porous films were determined using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. A low dielectric constant of 2.15 was achieved with an elastic modulus of 4.84 GPa which is significantly larger than the minimum requirement of 4 GPa for ultra-large-scale integrated circuit inter-layer dielectric applications. The cage/net Si–O–Si ratio method has been proposed to elucidate the influence of molecular structure on the mechanical properties of the film. The breaking and remaking of certain bonds under UV irradiation results in the formation of increased amounts of the net Si–O–Si molecular configuration which plays a major role in increasing the elastic modulus of the film. Furthermore, it was found that increase in elastic modulus is proportional to the duration of irradiation and an increase of 20% can be achieved after 4 h of UV irradiation. The methodology and approach described in this paper can be further followed to study the mechanical properties of ultra-low k materials under various annealing and porosity conditions, and to use fluorine-doping and UV irradiation processes for optimum ultra-low k materials in application.

Nonthermal combined ultraviolet and vacuum-ultraviolet curing process for organosilicate dielectrics

Porous SiCOH films are of great interest in semiconductor fabrication due to their low-dielectric constant properties. Post-deposition treatments using ultraviolet (UV) light on organosilicate thin films are required to decompose labile pore generators (porogens) and to ensure optimum network formation to improve the electrical and mechanical properties of low-k dielectrics. The goal of this work is to choose the best vacuum-ultraviolet photon energy in conjunction with vacuum ultraviolet (VUV) photons without the need for heating the dielectric to identify those wavelengths that will have the most beneficial effect on improving the dielectric properties and minimizing damage. VUV irradiation between 8.3 and 8.9 eV was found to increase the hardness and elastic modulus of low-k dielectrics at room temperature. Combined with UV exposures of 6.2 eV, it was found that this “UV/VUV curing” process is improved compared with current UV curing. We show that UV/VUV curing can overcome drawbacks of UV curing and improve the properties of dielectrics more efficiently without the need for high-temperature heating of the dielectric.

Plasma Treatment Effects on Molecular Structures at Dense and Porous Low-k SiCOH Film Surfaces and Buried Interfaces

The effects of oxygen plasma treatment on molecular structures at low-k organosilicate (SiCOH) film surfaces and buried interfaces were investigated using sum frequency generation (SFG) vibrational spectroscopy and Raman spectroscopy. SFG and Raman spectra were acquired from pristine and plasma-treated low-k SiCOH films to characterize the interfacial and bulk molecular structures of the films before and after plasma treatment. Two SiCOH films with similar molecular structures but different porosities were investigated to correlate the effects of plasma treatment to the porosity of low-k films. SFG spectra indicated that the surface molecular structure of dense SiCOH films was more resistant to plasma damage than the surface molecular structure of porous SiCOH films. Furthermore, the ratio of SFG peak intensities before and after plasma treatment enabled quantification of methyl depletion at the surface of SiCOH films after plasma treatment. The molecular structure at buried Si/SiCOH interfaces was charac...

Effect of thermal annealing on the structure and properties of plasma enhanced chemical vapor deposited SiCOH film

The development of high-performance integrated circuit chips and the shrinkage of feature sizes according to Moore’s law bring forward continuously the requirements for low dielectric constant (low-k) materials with various excellent properties in the back-end-of-the-line (BEOL) interconnect. Porous SiCOH films prepared by plasma enhanced chemical vapor deposition (PECVD) through a porogen approach are widely applied to industry and extensively studied. Thermal annealing is an important process for fabricating the porous low-k films, which has a great influence on film structure as well as properties. SiCOH films are deposited by PECVD using tetraethoxysilane and limonene as precursors, and annealed at 450 ℃ for 1.5 h under nitrogen atmosphere. The evolutions of film structure and properties during thermal annealing are revealed, and the reaction mechanism for structure change is also proposed. Fourier transform inferred spectroscopy and solid state nuclear magnetic resonance results show that the as-deposited film is an organic-inorganic hybrid film composed of various kinds of Si-O-Si, -CHx, Si-O-CH2CH3, etc. The organic component is removed almost completely during thermal annealing, making a porous film with a Si-O-Si inorganic skeleton. The skeleton is also rearranged at the same time. Deconvolution of the Si-O-Si absorption band of the FTIR spectrum reveals that the cage-like Si-O-Si occupies the major part for both as-deposited and annealed films, while the amount of silicon suboxide Si-O-Si decreases and that of network Si-O-Si increases during thermal annealing, making the film more robust. More C=C and Si-C are formed through chemical reactions between Si-H, -CHx and Si-O-CH2-CH3, and crosslinking is further enhanced. Nitrogen adsorption/desorption isothermal measurement reveals that a large number of micropores with diameter less than 2-3 nm are created during thermal annealing, which is consistent with the removal of organic groups and the existence of cage-like Si-O-Si. As a result, both the refractive index and dielectric constant decrease significantly from 1.476 (λ =630 nm) and 3.45 to 1.365 and 2.60, respectively. Because of the increase of C=C after annealing, extinction coefficient and leakage current density increase. Although there is a shrinkage of 14.7% in film thickness and a reduction of mechanical properties after annealing, the Young’s modulus is still larger than 4 GPa. Considering all kinds of properties, the obtained film appears to be a competitive candidate as inter layer dielectrics in the BEOL interconnect of integrated circuits.

Effect of low-frequency radio frequency on plasma-enhanced chemical vapor deposited ultra low-κ dielectric films for very large-scale integrated interconnects

The addition of a low frequency RF (LFRF) component during plasma-enhanced chemical vapor deposition of porous SiCOH ultra low-κ films allowed for the incorporation of higher carbon content without lowering the Young's modulus or increasing the dielectric constant. The porous SiCOH films typically contain carbon bonded into the silica matrix primarily as Si(CH3)x species. The low frequency RF increased the total carbon content by adding CH2 and –CH = CH- species with some reduction of Si(CH3)x species. It also altered the SiOx bonding structure by increasing network SiOx bonding at the expense of the suboxide, indicating an increase in SiOx crosslink density. Although higher carbon content usually lowers the modulus of porous SiCOH films, the modulus of the higher carbon films generated by LFRF did not decrease because of their increased network SiOx bonding.

Correlation between Plasma Damage and Dielectric Reliability for Ultra-Porous Low-k Materials

The effects of plasma damage on dielectric reliability were studied using voltage ramp stress experiments. Altering ramp rates allowed us to identify the main mechanisms for failure, namely intrinsic and metal catalyzed failure. Failure mechanisms are identified using ∂ln (tBD)/∂ln (R) trends for pristine and plasma damaged SiCOH films. Failure dynamics are discussed for 7% and 25% porous SiCOH films. O2 plasma treatment was found to lower the breakdown strength of 7% SiCOH from 79.5 V to 67.1 V at low ramp rates (0.01 V/s), and from 135.7 V to 109.3 V at fast ramp rates (20 V/s). The breakdown strength of 25% SiCOH films was enhanced from 41.0 V to 55.4 V after plasma treatment at slow ramp rates. However, at fast ramp rates, the plasma treatment lowered the breakdown voltage from 112.0 V to 99.7 V. The enhancement in breakdown strength for highly porous samples under slow ramp rates is attributed to film densification upon plasma treatment, while the deterioration at fast ramp rates is associated with the generation of defects catalyzing dielectric failure.

Preparation and Characterization of Ultralow-Dielectric-Constant Porous SiCOH Thin Films Using 1,2-Bis(triethoxysilyl)ethane, Triethoxymethylsilane, and a Copolymer Template

Ultralow-dielectric-constant (k) porous SiCOH films have been prepared using 1,2-bis(triethoxysilyl)ethane, triethoxymethylsilane, and a poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock copolymer template by means of spin-coating. The resulting films were characterized by cross-section scanning electron microscopy, small-angle x-ray diffraction, atomic force microscopy, Fourier-transform infrared spectroscopy, nanomechanical testing, and electrical measurements. Thermal treatment at 350°C for 2 h resulted in the formation of ultralow-k films with k of ∼2.0, leakage current density of 3 × 10−8 A/cm2 at 1 MV/cm, reduced modulus (Er) of ∼4.05 GPa, and hardness (H) of ∼0.32 GPa. After annealing between 400°C and 500°C for 30 min, the resulting films showed fluctuant k values of 1.85 to 2.22 and leakage current densities of 3.7 × 10−7 A/cm2 to 3 × 10−8 A/cm2 at 0.8 MV/cm, likely due to the change of the film microstructure. Compared with 350°C annealing, higher-temperature annealing can improve the mechanical strength of the ultralow-k film, i.e., Er ≈ 5 GPa and H ≈ 0.56 GPa after 500°C annealing.

Property modifications of nanoporous pSiCOH dielectrics to enhance resistance to plasma-induced damage

The resistance to plasma-induced damage of various nanoporous, ultra low-κ porous SiCOH films used as interconnect dielectric materials in integrated circuits was studied. These films are susceptible to damage by plasma processes used during nanofabrication. The dielectric constants and chemical compositions of four dielectric films were correlated with measured amounts of plasma damage. Films deposited with higher carbon content in the form of Si–CH3 and Si(CH3)2 bonding exhibited less plasma damage than similar films with lower carbon content.

The Effect of Plasma Chemistry on the Damage Induced to Porous SiCOH Dielectrics

The scope of this study was to compare the plasma damage produced on porous dielectrics by different chemistries under identical plasma conditions and evaluate different techniques for characterization of the damage. We have investigated the effects of , , and plasmas on the properties of three porous SiCOH dielectrics. All plasma treatments have been performed in the same plasma tool under identical conditions. The plasma treatment caused modifications to the bonding structure of the films, loss of film thickness, and increase in refractive index and dielectric constant that varied with plasma and among the films. Fourier transform infrared spectroscopy indicated the type of structural modification caused by a certain plasma treatment but could not be used to predict the damage to the dielectric constant. No correlation was observed between the shrinkage of the film and the corresponding increase of its dielectric constant. The increases of the dielectric constant correlated only to the increases of refractive index after the plasma treatments. The largest damages to the dielectric constants were caused by plasma treatments at room temperature. The most damaging to the porous SiCOH films was the plasma, while the overall lowest damage was produced by the plasma at .