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 < 2:0 and E > 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.

This paper describes the influence of the chemical mechanical polishing ͑CMP͒ 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 ͑FTIR͒ 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.The chemical mechanical polishing ͑CMP͒ process is necessary to form copper damascene interconnects in ultralarge-scale integrated circuits ͑ULSI͒. Recently, low-dielectric-constant ͑low-k͒ materials have been used for interlayer dielectrics to meet the demands for high-speed operation and low-power consumption in ULSI. For the 65 nm half-pitch technology node, low-k materials whose dielectric constants are 2.4 or less are required. 1 It was reported that degradation in low-k materials was caused during the Cu/low-k damascene process. Yoon et al. 2 and Kodera et al. 3 reported that the film peeling and the crack occurred during the CMP process because the adhesion between the low-k material and other films was weak. Baklanov et al. 4 reported that the low-k material with porous structure was degraded by etching gas and wet chemicals. In order to solve the problems, the low-pressure CMP process was developed to suppress the film peeling and the crack in the CMP process. In addition, the cap film was layered in damascene structure to protect the low-k film from the CMP chemicals ͑CMP slurries and post-CMP cleaning solutions͒.It is necessary to lower the effective dielectric constant ͑k eff ͒ to achieve higher-speed operation and lower power consumption. Figure 1 shows a typical structure of Cu/low-k damascene for 32 nm half-pitch technology node. Table I shows properties of cap layer and stopper layer for two cases considered in the present work: A and B. Figure 2 shows the calculated effective dielectric constant as a function of thickness of cap layers for the two cases. As seen, it is necessary to lower the dielectric constant and the thickness of the cap layer. As an extreme case, the damascene structure without the cap layer is worth considering. To achieve this cap-layer-less structure, it is necessary to clarify the degradation of low-k materials due to the CMP chemicals to establish the recovery process of degradation and the CMP chemicals free from degradation. Kondo et al. 5 investigated the deterioration of low-k material due to the post-CMP cleaning solution and reported on a post-CMP cleaning solution by which the deterioration of dielectric constant was not caused. However, neither the c...

Excellent results on copper (Cu) diffusion barrier characteristics of a self-assembled monolayer (SAM) of 2-(diphenylphosphino)ethyltriethoxy-silane are reported. The thickness and roughness of the SAM were determined by grazing incidence x-ray reflectometry as 1.7 and 0.3 nm, respectively. To evaluate Cu diffusion barrier performance of the SAM, Cu/SiO2/Si and Cu/SAM/SiO2/Si metal-oxide-semiconductor capacitors were prepared to measure their lifetimes under the 2 MV/cm electric bias at 498–548 K. The mean times to failure obtained from the Weibull plots of time to failures were 33.6, 9.24, 4.57, and 2.03 h at 498, 523, 533 and 548 K, respectively. These values show that the barrier characteristic of the SAM of 1.7 nm in thickness is comparable to that of physical-vapor-deposited Ta film of 20 nm in thickness. The estimated lifetime of the SAM barrier at the device operation temperature of 392 K is longer than 10 yr.

The uncertainties inherent in the normalization of subgap photoconductivity spectra to the optical absorption spectra α(hv) in a-Si:H based films have been addressed. An analysis is presented which is based on optical transitions of constant dipole matrix element between parabolic distributions of extended states and exponential distributions of localized tail states. This analysis has been used to normalize the two sets of results accurately, as verified by photothermal deflection spectroscopy measurements, and is shown to be useful in the commonly encountered cases, in which the two spectra do not overlap over an extended region. Improved quantitative fits of α(hv), for photon energy from ∼1.5 to 2.4 eV, obtained on different a-Si:H based films indicate that the localized exponential band tail regions extend ∼60–70 meV above the optical gap.

The influence of humidity on the dielectric constant and leakage current of self-assembled porous silica films which have two-dimensional hexagonal periodic porous structures was investigated quantitatively by proposing a new water adsorption model. The amount of H 2 O adsorption was calculated by the modified Rayleigh model, where H 2 O molecules are assumed to be adsorbed on the inner surface of cylindrical porous silica structures and form a dispersal concentric double-layer dielectric cylinder system. The amount of H 2 O calculated by the proposed model was consistent with the measured dielectric constant and thermogravimetry data. It suggests that inner-surface coverage of the cylindrical porous silica wall with a hydrophobic group is the most effective way to suppress water adsorption. Hexamethyldisilazane as a surface coverage molecule was introduced to the periodic cylindrical porous silica film and the leakage current was suppressed by a factor of 1/100 even below 0.5% relative humidity, resulting in the improvement of time-dependent dielectric breakdown lifetime by a factor of 30.Scaling of interconnects in ultralarge-scale integrated circuits ͑ULSI͒ has caused the increase of signal delay time due to the increase of interconnect resistance ͑R͒ and its parasitic capacitance ͑C͒, 1 while the transistor scaling is still effective to reduce the gate delay time. 2 For a 1-mm-long interconnect line fabricated on a Si chip, the RC delay time becomes a few hundred picoseconds, which is approximately 10 times larger than that of a metal oxide semiconductor field effect transistor ͑MOSFET͒. The RC delay time increases with decreasing the thickness and width of the metal interconnect as well as the spacing. In order to overcome this problem, copper and low-k interlayer dielectrics have been introduced. The interlayer dielectric films with the dielectric constants k ഛ 2.0 are required for future ULSI beyond 45 nm technology node. From the material point of view, various porous films have been developed to lower the dielectric constants. 3 However, the porous low-k films absorb moisture, resulting in the degradation of the film properties. To avoid this problem, a hexamethyldisilazane ͑HMDS͒ treatment has been commonly used to make the film hydrophobic.In this study, the influence of water adsorption on the dielectric constant and leakage current in the porous silica films 4 are investigated quantitatively, and the effect of HMDS treatment is discussed.Experimental p-Type Si substrates were cleaned in an RCA solution ͑NH 4 OH:H 2 O 2 :H 2 O = 36:720:1680͒ and dipped into a 0.5% HF solution. They were oxidized in O 2 ambient at 900°C to form 5 nm thick SiO 2 .A precursor solution for porous silica films was prepared by adding a surfactant, which was a PEO ͑polyethylene oxide͒-PPO ͑poly-propylene oxide͒-PEO triblock copolymer and an acidic silica sol derived from tetraethyl orthosilicate ͑TEOS͒ in ethanol diluted with water. The precursor solution was spin-coated on a Si substrate to form a homogeneous thin layer. Af...