Zeolite-inspired low-k dielectrics overcoming limitations of zeolite films.

Spin-on zeolite films deposited from Silicalite-1 nanocrystal suspensions prepared by hydrothermal treatment of clear solutions have the required properties for insulating media in microelectronics. However, on the scale of the feature sizes in on-chip interconnects of a few tens of nanometers, their homogeneity is still insufficient. We discovered a way to overcome this problem by combining the advantages of the clear solution approach of Silicalite-1 synthesis with a sol-gel approach. A combination of tetraethyl orthosilicate and methyltrimethoxysilane silica sources was hydrolyzed and cocondensed in the presence of an aqueous tetraalkylammonium hydroxide template. The resulting suspension of nanoparticles of a few nanometers in size together with residual oligomeric silica species were spun onto support. The final zeolite-inspired low-k films (ZLK) with respect to pore size and homogeneity satisfied all requirements and presented excellent hydrophobicity, stiffness, and dielectric constant. The size and content of initially formed nanoparticles and the spatial hindrance promoted by occluded tetraalkylammonium molecules were found to be crucial elements in the definition of the final pore network.

Reaction of trimethylchlorosilane in spin-on Silicalite-1 zeolite film.

We present a study on the hydrophobization of spin-on Silicalite-1 zeolite films through silylation with trimethylchlorosilane. Microporous and micro-mesoporous Silicalite-1 films were synthesized by spin coating of suspensions of Silicalite-1 nanozeolite crystallized for different times. Ellipsometric porosimetry with toluene and water adsorbates reveals that silylation decreases the porosity and makes the films hydrophobic. The decrease in porosity depends on the exposed surface area in the pores. Water contact angle measurements confirm the hydrophobicity. Fourier transform infrared spectroscopy reveals that the trimethylsilyl groups are chemisorbed selectively on isolated silanols and less on geminal and vicinal silanols due to steric limitations. Time-of-flight secondary-ion mass spectroscopy and in situ ellipsometry analysis of the reaction kinetics show that the silylation is a bulk process occurring in the absence of diffusion limitation. Electrical current leakage on films decreases upon silylation. Silylation with trimethylchlorosilane is shown to be an effective hydrophobization method for spin-on Silicalite-1 zeolite films.

Patterning of metallic nanoparticles for the growth of carbon nanotubes.

We report a straightforward method of patterning large ordered arrays of metallic nanoparticles using existing semiconductor processing technology. The topographies of contact holes created on full 200 mm wafers serve as templates to pattern Ni or Co nanoparticles. Over a large range of synthesis conditions, these patterned nanoparticles are demonstrated to successfully catalyse the growth of carbon nanotubes (CNTs) selectively in the patterned areas of the wafer. This approach to catalyst deposition is scalable and fully compatible with existing semiconductor processing technology. Thus, it can be exploited for a variety of applications where confinement of materials in nanometric domains is necessary. These results represent a further step towards the integration of CNTs into conventional Si-based technology.

Characterization of a molecular sieve coating using ellipsometric porosimetry.

Ellipsometric porosimetry was used to determine the adsorption isotherms of toluene, methanol, and water on b-oriented Silicalite-1 coatings with a thickness of less than ca. 250 nm and to obtain adsorption kinetics. The adsorption isotherms are of sufficient quality to reveal several aspects of the pore structure such as the adsorbate capacity and the adsorbate/framework affinity. The use of a combination of different molecular probes in ellipsometric porosimetry to elucidate the molecular accessibility of Silicalite-1 pores is demonstrated. It is shown that ellipsometric porosimetry is an appropriate technique for probing the influence of aging of the Silicalite-1 coating and of planarization polishing on the porosity, pore accessibility, and adsorbate/framework affinity.

Nanoscale indentation of polymer and composite polymer-silica core-shell submicrometer particles by atomic force microscopy.

Atomic force microscopy was employed to probe the mechanical properties of surface-charged polymethylmethacrylate (PMMA)-based terpolymer and composite terpolymer core-silica shell particles in air and water media. The composite particles were achieved with two different approaches: using a silane coupling agent (composite A) or attractive electrostatic interactions (composite B) between the core and the shell. Young's moduli (E) of 4.3+/-0.7, 11.1+/-1.7, and 8.4+/-1.7 GPa were measured in air for the PMMA-based terpolymer, composite A, and composite B, respectively. In water, E decreases to 1.6+/-0.2 GPa for the terpolymer; it shows a slight decrease to 8.0+/-1.2 GPa for composite A, while it decreases to 2.9+/-0.6 GPa for composite B. This trend is explained by considering a 50% swelling of the polymer in water confirmed by dynamic light scattering. Close agreement is found between the absolute values of elastic moduli determined by nanoindentation and known values for the corresponding bulk materials. The thickness of the silica coating affects the mechanical properties of composite A. In the case of composite B, because the silica shell consists of separate particles free to move in the longitudinal direction that do not individually deform when the entire composite deforms, the elastic properties of the composites are determined exclusively by the properties of the polymer core. These results provide a basis for tailoring the mechanical properties of polymer and composite particles in air and in solution, essential in the design of next-generation abrasive schemes for several technological applications.

Porous low dielectric constant materials for microelectronics.

Materials with a low dielectric constant are required as interlayer dielectrics for the on-chip interconnection of ultra-large-scale integration devices to provide high speed, low dynamic power dissipation and low cross-talk noise. The selection of chemical compounds with low polarizability and the introduction of porosity result in a reduced dielectric constant. Integration of such materials into microelectronic circuits, however, poses a number of challenges, as the materials must meet strict requirements in terms of properties and reliability. These issues are the subject of the present paper.