Nobutoshi Fujii

Influence of CMP Chemicals on the Properties of Porous Silica Low-k Films

This paper describes the influence of the chemical mechanical polishing (CMP) process on the degradation in the leakage currents and dielectric constants of porous silica low-k films. It is found that the leakage current and dielectric constant increased by post-CMP cleaning solution due to the increase of CH x and OH bonds according to Fourier transform infrared (FTIR) absorption. This is because the surfactant in the post-CMP cleaning solution permeated into the porous silica. The permeated surfactant in the porous silica can be removed by rinsing with 2-propanol or ethanol after the CMP process. Degradations of the leakage current density and dielectric constant can be recovered by ethanol rinse and subsequent 1,3,5,7-tetramethyl-cyclo-tetrasiloxane vapor treatment, which makes the pore wall surfaces hydrophobic.

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...

Theoretical Investigation of Dielectric Constant and Elastic Modulus of Three-Dimensional Isotropic Porous Silica Films with Cubic and Disordered Pore Arrangements

The dielectric constant (k) and elastic modulus (E) of self-assembled three-dimensional porous silica films were investigated by analytical and numerical calculations to reveal the relationship between k and E. It was found that cubic pore arrangements have E values higher than those of random pore arrangements and two-dimensional periodic hexagonal pore arrangements for the same k. It was also found that disordered isotropic porous silica films having cylindrical pores with well-controlled pore size distributions exhibit an E vs k relationship similar to that of two-dimensional hexagonal periodic porous silica films. The elastic modulus of the skeletal silica was determined to be 40 GPa from the combination of the calculated results and experimental data on ultralow-k disordered porous silica film with a k value of 2.0 and a modulus of 8 GPa.

Comparative Studies of Ultra Low-κ Porous Silica Films with 2-D Hexagonal and Disordered Pore Structures

Periodic 2-dimensional (2-D) hexagonal and the disordered pore structure silica films have been developed using nonionic surfactants as the templates. The pore structure was controlled by the static electrical interaction between the micelle of the surfactant and the silica oligomer. No X-ray diffraction peaks were observed for the disordered mesoporous silica films, while the pore diameters of 2.0-4.0 nm could be measured by small angle X-ray scattering spectroscopy. By comparing the properties of the 2-D hexagonal and the disordered porous silica films which have the same porosity, it is found that the disordered porous silica film has advantages in terms of the dielectric constant and Youngs modulus as well as the hardness. The disordered porous silica film is more suitable for the interlayer dielectrics for ULSI.

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...

Carbon loss induced by plasma beam irradiation in porous silica films

Plasma-induced damages of porous silica films during plasma processes were investigated by using a plasma beam irradiation apparatus. We used the porous silica films incorporated with methyl groups to achieve high hydrophobicity. The carbon (methyl group) reductions in the film as an index of the level of damages induced by Ar, He, O2, H2, and N2 plasma irradiations were examined by x-ray photoelectron spectroscopy and secondary ion mass spectroscopy. The damage due to Ar and He plasma bombardment increased with an increase in the ion dosage, although it was not strongly affected by the ion energy in the range higher than 130eV. Furthermore, it was found that the damage near the film surface was influenced more by metastable He atoms than by metastable Ar atoms. Both O ions and O atoms caused severe damage. N atoms did not affect the decrease of carbon content but reacted with carbon to form CN bonds. H atoms decreased carbon content slightly, but the amount of decrease was saturated by the further irradi...

Recovery from Plasma-Process-Induced Damage in Porous Silica Low-k Films by Organosiloxane Vapor Annealing

It was demonstrated that recovery from dry etching and ashing damage in porous silica low-k films occurred by 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS) vapor annealing. The increase in k-value after Ar/C5F8/O2 plasma etching was reduced from 35 to 6.5% of the initial value (k=2.25) by TMCTS vapor annealing. Leakage current also returned to the initial level. Hydrofluoric acid wet etching revealed the sidewall damaged region in a porous silica trench due to plasma processes. The TMCTS vapor annealing was found to be effective for recovery from the sidewall damage. Fourier transformed infrared absorption spectroscopy indicated that the replacement of Si–CH3 bonds in low-k films by Si–O and Si–OH bonds occurred during plasma processes. The recovery mechanism involves hydrophobic bond (–CH3) reintroduction into the film followed by stable cross-linked poly(TMCTS) network formation on pore wall surfaces by TMCTS vapor annealing.

Plasma Etch Rates of Porous Silica Low-k Films with Different Dielectric Constants

The reactive ion etch rates of porous silica films with different dielectric constants (k-values) or film densities were measured by varying wafer bias and gas ratio for Ar/C5F8/O2 plasma. Both the etch rates of porous silica films and the optical emission intensities from the etching products (SiF) increased with wafer bias power. Etch rate increased with decreasing k-value of porous silica, whereas SiF emission intensity was maintained constant regardless of k-value, indicating that the amount of etching products escaping from the porous silica surface to the gas phase remained unchanged. From this result it is concluded that mass etch rate, defined as the weight of a porous silica film etched from a unit area per unit time, is constant for Ar/C5F8/O2 plasma.

Recovery Processes of CMP-Induced Damages for Copper/Porous Silica Damascene Interconnects

This paper describes the effects of recovery processes for the degradation caused by chemical mechanical polishing (CMP) in the integration of Cu/porous silica low-k material interconnects (Cu/po-SiO), in which SiOC is used as CMP-Cap film (Cap-SiOC) for po-SiO film. The leakage current and capacitance between Cu damascene interconnects increased when Cap-SiOC was removed by CMP and the po-SiO was exposed, because the surfactant in CMP chemicals penetrated the po-SiO and the hydrophobicity of the po-SiO decreased, resulting in the increase of water absorption in the po-SiO. As a result of the recovery process after CMP, the leakage current has decreased by three orders of magnitude by applying an isopropyl alcohol rinse and 1,3,5,7-tetramethyl-cyclo-tetrasiloxane (TMCTS) gas treatment, and the capacitance has decreased by 15% by applying the TMCTS gas treatment.

Integration of Self-Assembled Porous Silica in Low-

Integration of a self-assembled porous silica film layered with a cap film was carried out for low-k/Cu damascene structures. The dielectric constant of the porous silica in the layered damascene structure was extracted, and the process-induced damage layer was characterized. Due to the integration process of low-k/Cu damascene, the hydrophobic methyl group was decomposed by plasma etching and subsequent barrier and seed sputtering as well as by Cu electroplating, resulting in the formation of hydrophilic silanol groups. The lateral dimension of the process-induced damaged layer and its effective dielectric constant were found to be 35 nm and 10, respectively.