Hisanori Matsuo

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.

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.

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.

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.

Role of Frictional Force on the Polishing Rate of Cu Chemical Mechanical Polishing

In the chemical mechanical polishing (CMP) of low-dielectric-constant (low-k) materials and Cu for ultralarge-scale integrated circuits, one of the major issues is the adhesion failure of the film caused by frictional force. An in situ quantitative measurement technique for frictional force during CMP has been developed. We have examined frictional force with respect to process parameters and slurries. A low frictional force and a high polishing rate (PR), which are desirable for a low-k/Cu CMP process, have been achieved simultaneously by optimizing slurry flow rate. The groove structures of the polishing pad did not affect frictional force at a low relative velocity. Frictional force and polishing rate increased with increasing glycine and H2O2 concentration in the slurry, and saturated at concentrations above 0.3 M and 3 vol%, respectively. A modified Prestons equation describing polishing rate as a function of frictional force instead of polishing pressure was proposed.

Influence of Slurry Chemistry on Frictional Force in Copper Chemical Mechanical Polishing

In situ frictional force measurement technique was developed for chemical mechanical polishing (CMP) process, and the influence of slurry chemistry of glycine/quinaldic acid/H 2 O 2 on the frictional force was investigated. The results indicate that the CMP polishing rate increases nonlinearly with frictional force, and the coefficient of friction changes at the transitional friction force which is controlled by the concentration of the chelating agents.

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.

Plasma-enhanced co-polymerization of organo-siloxane and hydrocarbon for low-k/Cu interconnects

A plasma-enhanced co-polymerization technique was developed for low-k/Cu damascene integration on 300 mm wafers. This technique enables us to control dielectric film properties by introducing organo-siloxane and hydrocarbon into a He-plasma. The growth rate of the low-k film derived from divinyl siloxane–benzocyclobutene (DVS–BCB) as a matrix monomer is increased by adding C2H2 as a deposition acceleration monomer and the Youngs modulus was enhanced by adding diisopropenylbenzene (DIPB) or divinylbenzene (DVB) as a reinforcement monomer. Cu damascene interconnects with plasma polymerized low-k films were successfully fabricated on 300 mm wafers.

A Cu Electroplating Solution for Porous Low-k ∕ Cu Damascene Interconnects

A Cu electroplating solution applicable to porous silica ultralow-k films (k = 2.1) without pore sealing was investigated. A suppressor which causes permeation of Cu electroplating solution was replaced by polyethylene glycol (PEG) with specific molecular weight (Mw). Transmission electron microscopy observation revealed that permeation by the Cu solution into the porous silica layer can be suppressed by decreasing the molecular weight of the PEG suppressor in the electroplating solution. A Cu electroplating solution using PEG with Mw = 600 was examined for the low-k porous silica/Cu single-damascene integration process of 300 mm wafer. The filling characteristics in trenches and the uniformity of Cu film thickness were investigated. Interline leakage current on low-k/Cu damascene interconnects was successfully reduced by six orders of magnitude using this Cu plating solution compared with the conventional solution.

Study on evaluation method for polishing pad surface topography based on optical fourier transform

An optical technique based on the optical Fourier transform has been developed to evaluate the characteristics of polishing pad surface topography. The power spectrum from the optical Fourier transform, which correlates with the diffracted light intensity distribution from the diffused reflection laser light of the polishing pad surface, is observed by an area sensor camera. Then, the correlation between the spatial frequency characteristic of the polishing pad topographies and the material removal rate are investigated.