Syozo Takada

Theoretical Analysis of Elastic Modulus and Dielectric Constant for Low-k Two-Dimensional Periodic Porous Silica Films

To lower the dielectric constant k of interlayer-dielectric films with two-dimensional pore structures while maintaining their mechanical strength, the influences of pore arrangement on the elastic modulus E and k of the films were investigated. It was found that periodicity in pore structure enhances E with constant k. Periodic porous silica films having a hexagonal arrangement of circular cylindrical pores with k 3 GPa were demonstrated to be feasible at a porosity of 0.614 using a bulk material with a k of 4.0 and E>21 GPa.

Quantum-confinement effects on the optical and dielectric properties for mesocrystals of BaTiO3 and SrBi2Ta2O9

We present optical and dielectric quantum-confinement effects for mesocrystals smaller than 30 A of BaTiO3 and SrBi2Ta2O9 in uniform mesopores of the MCM-41 molecular sieve. For BaTiO3 mesocrystals we observed a blueshift in optical absorption edge from 3.02 to 3.35 eV, and a decrease in dielectric constant maximum temperature from 130 to 55 °C. For SrBi2Ta2O9 mesocrystals we also observed an increase in the optical absorption edge from 2.70 to 4.18 eV, and a decrease in the dielectric constant maximum temperature from 320 to 180 °C. The observed optical and dielectric quantum-confinement effects generally agree with the recognized consequence of reduced size.

Theoretical Investigation of Dielectric Constant and Elastic Modulus of Two-Dimensional Periodic Porous Silica Films with Elliptical Cylindrical Pores

The effects of film shrinkage during the thermal curing of two-dimensional periodic porous silica films on the relative dielectric constant k with respect to the vacuum value and the relative elastic modulus E with respect to the skeletal (pore-wall) value Ew were investigated by theoretical calculations. Two extreme models of the film thickness shrinkage were assumed in the calculation: the constant porosity model and the constant wall volume model. It was found that E/Ew decreased more markedly upon film thickness shrinkage in the constant porosity model than it did in the constant wall volume model. The calculated results were confirmed by the experimental data together with the elliptical cylindrical pore shape. It is shown that the film shrinkage of ultralow-k porous silica films must be suppressed for achieving the higher elastic modulus while keeping the k value constant.

Skeletal silica characterization in porous-silica low-dielectric-constant films by infrared spectroscopic ellipsometry

Porous-silica low-dielectric-constant (low-k) films were prepared using a sol-gel method based on the self-assembly of surfactant templates. No change in the refractive index at 633 nm nor in the infrared-absorption intensities of C–H and O–H stretching vibrations at around 2900 and 3400cm−1 of porous-silica low-k films were observed after annealing at each temperature from 523 to 723 K. On the other hand, the Young’s elastic modulus and hardness increased with the increase of annealing temperature. The structure in the complex dielectric function of porous-silica low-k films observed in between 1000 and 1400cm−1 is assigned as the asymmetric stretching vibration mode of the Si–O–Si bond. By applying the effective-medium theory by Bruggeman to the experimental results from infrared spectroscopic ellipsometry, we analyzed the skeletal silica structures. The peak positions of transverse (ωTO) and longitudinal (ωLO) vibration modes for Si–O–Si network in the silica skeleton of porous-silica films changed fro...

Mechanical Property and Network Structure of Porous Silica Films

We investigated the relationship between Youngs elastic modulus of a series of spin-on sol-gel silica films and the shift of the longitudinal-optical component of the asymmetric stretching vibration mode of Si–O–Si (LO4), by nanoindentation measurements and Fourier transform infrared reflection spectroscopy. With the increase of the annealing temperature from 673–1073 K in air, the position of the LO4 mode reflection peak shifted from 1203 to 1253 cm-1, in parallel with the increase of Youngs elastic modulus. The correlation between the LO4 peak position and Youngs elastic modulus was also confirmed among a set of silica films in which the preparation conditions and/or the postpreparation treatment conditions were varied. It was concluded that the shift of the LO4 mode peak position is a good measure of the skeletal silica mechanical property of porous silica films.

Effects of Surfactants on the Properties of Ordered Periodic Porous Silica Films

We report the effects of surfactants on the properties of ordered periodic porous silica films. Silica films with a periodically ordered structure were synthesized on crystalline silicon substrates by spin-coating an alkoxysilane solution mixed with a self-assembling template and a cationic alkyltrimethylammonium chloride (ATMACl, CH3(CH2)n-1N(CH3)3 Cl) surfactant, where n was 12, 14, or 16. The effects of surfactants on the properties of porous silica films with a periodic pore structure were investigated. Both dielectric constant and refractive index decreased with the length of alkylchain in the template molecule ATMACl. The pore structure was successfully controlled by the alkylchain length of the template molecule when the tetraethyl-orthosilicate (TEOS) vapor treatment was applied.

Dependences of Young’s modulus of porous silica low dielectric constant films on skeletal structure and porosity

Porous silica films were prepared by spin coating the mixtures of acidic silica sol and nonionic surfactant template. The (a) porosity and (b) skeletal structure of the films were varied by adjusting the (a) template concentration and the (b) annealing temperature, respectively. Fourier transform infrared spectroscopic ellipsometry was employed to evaluate the skeletal silica structure of the films. The analysis was focused on the midinfrared (1000–1300cm−1) spectral structure which is assigned as the asymmetric stretching vibration mode of Si–O–Si bonds [Kamitsos et al., Phys. Rev. B 48, 12499 (1993)]. The spectral structure depended on both porosity and chemical bonding structure. Bruggemann’s effective medium theory was employed to obtain the spectrum of “skeletal” silica from that of “porous” silica. The skeletal silica structure was then discussed in terms of the peak positions of the transverse optical (ωTO) and longitudinal optical (ωLO) vibration modes of Si–O–Si network. It was shown that the You...

A Novel Organosiloxane Vapor Annealing Process for Improving Elastic Modulus of Porous Low-k Films

A novel organosiloxane-vapor-annealing method has been developed for improving the mechanical strength of porous silica films with a low dielectric constant. Treatment of a porous silica film with 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS) under atmospheric nitrogen above 350 °C significantly enhanced the mechanical strength (i.e., elastic modulus and hardness) of the film. Results of Fourier transform infrared spectroscopy (FT-IR) and thermal desorption spectroscopy (TDS) suggested the formation of cross-linked poly(TMCTS) network on the porous silica internal wall surfaces by the TMCTS treatment. Such TMCTS cross-linked network is thought to enhance the mechanical strength of the low-k film.

Novel self-assembled ultra-low-k porous silica films with high mechanical strength for 45 nm BEOL technology

Novel ultra-low-k porous silica films were developed by use of a self-assembly technology. The mechanical properties of the porous silica films could be reinforced independently of the dielectric constant by introducing a tetramethyl-cyclo-tetra-siloxane (TMCTS) treatment. High modulus porous silica films, with an elastic modulus of 8 GPa and dielectric constant of 2, can be achieved simultaneously. Ultra-low-k/Cu damascene with sufficient mechanical strength was demonstrated for 45 nm BEOL (back-end-of-line) technology.

Determination of Mechanical Properties of Porous Silica Low-k Films on Si Substrates Using Orientation Dependence of Surface Acoustic Wave

The measurement accuracy of Youngs modulus E and Poissons ratio σ of thin low-dielectric-constant (low-k) films is improved by the simultaneous analysis of the laser-pulse-generated surface-acoustic wave (SAW) propagating along two different crystalline Si orientations. Frequency ( f)-dependent phase velocities v110( f) and v100( f) of SAW propagating along [110] and [100] directions of the Si substrate were obtained by analyzing the SAW waveforms measured using a piezoelectric transducer. The mass density ρ and the thickness d of low-k films were determined by X-ray reflectance and spectroscopic ellipsometry, and were then used to determine the values of E and σ that fit the dispersion curves v110( f) and v100( f) best. Different dependencies of v110( f) and v100( f) on E and σ were the key for the accurate determination of the values. This method was employed to study a series of porous organosilica films in which methyl content was varied. The results showed that E and σ decrease with methyl content from 9.5 to 4.3 GPa and from 0.36 to 0.25, respectively, in the studied range of methyl content. It is concluded that the reported method is an accurate nondestructive technique for the simultaneous determination of E and σ of low-k films on Si.