The dependence of chemical mechanical planarization (CMP) performance on both composite polymer core and colloidal silica shell particle sizes is examined. The highest removal rate is observed for the largest diameter cores combined with the smallest silica particles. The model used to explain the results takes into account both the total number of active silica particles still bonded to the polymer core but at the same time pressed against the wafer surface and the indentation depth of each single particle. A contact-area-based mechanism is dominant at the large core (600 nm)-small shell (15 nm) particle sizes, and an indentation mechanism takes over as the shell particle size increases (90 nm). Larger cores elastically deform and gently transfer the applied downforce to a higher number of silica particles with respect to smaller cores. (C) 2008 The Electrochemical Society.

Chemical mechanical planarization (CMP) of silicon dioxide films was performed using mixed abrasive slurries (MASs) achieved by mixing in situ polymer and inorganic particles. The results were discussed in terms of material removal rate (MRR) and defectivity. We compared 30 nm silica colloids and 14 nm primary size ceria particles. Our experiments shed some light on the importance of the bond between polymer core and inorganic particles in the shell and on the differences between silica-based and ceria-based MASs. Although for the silica-based MAS the MRR passes through a maximum (17 nm/min for 2:3 ratio polymer: silica), for the ceria-based MAS it increases with the ceria solid content. The polymer:silica ratios used in the experiments spanned in the range from 1:15 to 10:1.

Self-assembled monolayers (SAMs) are investigated as potential Cu diffusion barriers for application in back-end-of-line (BEOL) interconnections. A screening of SAMs derived from molecules with different head group (SiCl3, Si(OCH3)3, Si(OCH3)Cl2) bonding to the dielectric substrate, chain lengths (n=3–21) and terminal group (CH3, Br, CN, NH2, C5H4N and SH) bonding to the Cu overlayer are compared in terms of inhibition of interfacial Cu diffusion and promotion of Cu–SiO2 adhesion. SAM barrier properties against Cu silicide formation are examined upon annealing from 200 to 400°C by visual inspection, sheet resistance measurements (Rs) and X-ray Diffraction Spectroscopy (XRD). Cu/SAM/SiO2 adhesion is evaluated by tape test and four-point probe measurements. Results indicate that NH2-SAM derived from 3-aminopropyltrimethoxysilane is the most promising for Cu diffusion barrier application. Silicide formation is inhibited to at least 400°C, essential stability for BEOL integration. However, the 2.9Gc (J/m2) adhesion of the layer compared with 3.1Gc (J/m2) on SiO2 does need improvement.

We use oxide chemical mechanical planarization (CMP) as a convenient test vehicle for comparing the material removal rate and defectivity induced by different silica abrasives. The effect of particle shape is investigated by comparing fumed and colloidal silica. In particular, the effect of a polymer core on the behavior of a composite abrasive is explored. Overall, fewer and shallower scratches are detected for the composites with a colloidal silica shell as compared with colloidal silica, as well as composites with a fumed silica shell. It is difficult to control the shape and dimension of the fumed silica and fumed silica-based composite agglomerates. Both the length and depth of microscratches increase with particle size and irregularity. Under the same pH conditions, fumed silica and fumed silica-coated abrasives lead to a comparable scratch depth. Fumed silica exhibits agglomerates of greater hardness but higher overall particle stability with respect to its composites, which show lower hardness and lower overall particle stability.

Multi-wall carbon nanotubes (MWCNTs) were exposed to a CF4 rf-plasma. X-ray photoelectron spectroscopy analysis shows that the treatment effectively grafts fluorine atoms onto the MWCNTs. The fluorine atomic concentration and the nature of the C–F bond (semi-ionic or covalent) can be tuned by varying the exposure time. Ultraviolet photoelectron spectroscopy analysis confirms that the valence electronic states are altered by the grafting of fluorine atoms. Characterization with high-resolution transmission electron microscopy reveals that while the plasma treatment does not induce significant etching impact on the CNT-surface, it does increase the number of active sites for gold cluster formation.

2008 International Conference on Solid State Devices and Materials,Materials Engineering for Future Interconnects: "Catalyst-free" Electroless Cu Deposition on Self-assembly Monolayer Alternative Barriers

This paper investigates a selective self-assembly process for formation of a self-assembled monolayers (SAM) barrier to Cu diffusion in dual damascene integration. In selecting a barrier, trichlorosilanes are promising due to their high thermal stability (above 550degC) and dense molecular packing. Overall, this study demonstrates that the tuneable structure and chemistry of SAMs provides a molecular level engineering approach for future device structures.

The effects of polishing time and abrasive solid content on the chemical mechanical polishing (CMP) process of blanket oxide films were investigated. Four different abrasive systems were tested in the CMP process and their performances thoroughly evaluated combining different characterization techniques. Composite abrasives achieved by either creating chemical bonds (composite A) or electrostatic attractive interactions between core and shell (composite B), were compared with conventional colloidal silica in terms of removal rate, roughness, and defectivity. In addition, the behavior of the poly(methyl methacrylate) based terpolymer cores as abrasives in the slurry composition was investigated. While 1 min oxide CMP with 5 wt % composites results in shallower defects compared with conventional colloidal silica, the number of defects increases with polishing time, especially for composite B, and with an increase in solid content up to 10 wt % for all the abrasives. (c) 2007 The Electrochemical Society.

The growth of tungsten nitride carbide, WNxCy, films obtained by atomic layer deposition (ALD), using tri-ethylboron, tungsten hexafluoride and ammonia precursors is determined by the density and type of substrate reactive sites. During an initial period, referred to as transient regime, the SiC oxidation state and the tri-ethylboron pulse time determine the amount of metal deposited. WNxCy growth on SiC is similar to that on PECVD SiO2 explained by decomposition of the tri-ethylboron precursor, giving rise to a carbon rich WNxCy-oxide interface.

The growth of tungsten nitride carbide (WNxCy) films obtained by atomic layer deposition using triethylboron, tungsten hexafluoride, and ammonia precursors is determined by the density and type of reactive sites. The film properties change as a function of thickness. On silicon dioxide and silicon carbide, growth is initially nonlinear such that the transient regimes are characterized by island formation, as evidenced by a parabolic tungsten growth curve extending to film thicknesses of up to 5 nm. Such films have low densities of similar to 4-6 g cm(-3) corresponding to only similar to 30%-45% of the bulk density of similar to 13.1 g cm(-3) determined for a WN0.45C0.55 composition. X-ray reflectivity, thermal desorption, and elastic recoil detection spectroscopies reveal surface roughening and compositional and density differences close to the substrate surface. The offset from linear growth in the case of WNxCy films deposited on silicon dioxide is induced by the initial reaction of silanol and siloxane groups with triethylborane resulting in passivating ethylsilyl groups on the surface. A transient regime is not observed for WNxCy growth on hydrogen-terminated silicon with the initial growth being dominated by the reduction of tungsten hexafluoride to tungsten. On silicon nitride a short transient regime is observed relative to the carbide and oxide surfaces attributed to the enhanced binding of the triethylboron precursor. (c) 2006 American Institute of Physics.

The ongoing transition to lower dimension devices requires the replacement of SiO2 by a lower-k dielectric insulator. Such materials are porous, introducing the need for sealing against penetration of gaseous and/or liquid species during subsequent processing. In this work, we investigate the effect of different plasma treatments on a porous low-k polymer film. Ion bombardment induces the formation of a dense surface layer capable of sealing the polymer. A competing etching reaction by the plasma gases determines the extent of the densified layer. Structural and chemical changes induced by the plasma treatments can extend into the bulk of the film and irreversibly change its properties. Exposing the plasma treated films to chemical precursors during an atomic layer deposition process is used to test sealing. The sealing behavior is discussed in view of the reactivity of the plasma and the post sealing temperature treatment.

We investigated the mechanism of chemical and galvanic corrosion of tungsten nitride carbide (WNXCY) barrier during Cu chemical mechanical planarization (CMP). Our results demonstrate that chemical corrosion is caused by the oxidation of tungsten (W) in the WNXCY film by H2O2 followed by the dissolution of a tungsten oxide complex, which leads to WNXCY loss. WNXCY loss is enhanced during CMP due to galvanic corrosion driven by the Cu/WNXCY couple. A high loss rate occurs due to the strong potential difference between Cu and WNXCY in H2O2-containing slurries. A model representing WNXCY loss in Cu damascene lines during the CMP process is proposed. It supports WNXCY loss in the top part of the trench sidewall at the interface with Cu. We demonstrate that the use of HNO3 instead of H2O2 as the oxidizer, in the formulation of the corrosion-inhibiting model slurries reduces chemical and galvanic corrosion of WNXCY. Addition of monosaccharides or organic acids prevents excessive Cu loss. Wafer-level tests done with in-house corrosion-inhibiting model slurries show promising Cu and WNXCY compatibility without significant WNXCY loss. (c) 2005 The Electrochemical Society.

Formation and stability of thiol-derived self-assembled monolayers (SAMs) on Cu surfaces have been investigated using a multitechnique characterization approach, including contact angle measurements, X-ray photoelectron spectroscopy, ellipsometry, and electrochemistry. High-quality SAMs were formed on Cu surfaces under various conditions of substrate preparation, thiol molecular structure, adsorption from the gas and liquid phases, concentration, solvent effects, and self-assembly time. Stability studies exploring SAM resistance to aging, processing chemicals, temperature, and electrochemically induced oxidation-reduction reactions demonstrate promising corrosion inhibition properties. The feasibility of exploiting SAMs in microelectronics applications was demonstrated by the enhancement of Cu wire bonding onto thiol-passivated Cu bond pads. (C) 2004 The Electrochemical Society.

The effect of CF4/O-2 plasma treatment on two types of porous low dielectric constant (low-k) materials was investigated. For a microporous film, the surface appears to be sealed, most likely by the formation of a silicon oxide-like layer within 5 sec of treatment. For both microporous and mesoporous materials, fluorine incorporation at the surface was found to be low after 15 sec exposure to the plasma (similar to 3-6 atomic %). Processing using CF4/O-2 plasma appears not to induce any damage to the porous low-k materials as evidenced by similar chemical compositions and mechanical properties measured using Auger spectroscopy and nanoindentaion, respectively. These results point to a mechanism that involves a competition between surface modification/oxidation and material removal under the action of fluorine-containing species in the plasma.

Ultraviolet-ozone (UV-O3) treatment of polyarylene, a semiconductor dielectric polymer, has been characterized using contact angle measurements, x-ray photoelectron spectroscopy, spectroscopic ellipsometry (SE), and ellipsometric porosimetry. Significant modification of the film surface composition is already observed after a short exposure time (30s). Longer treatment time leads to further increase in oxygen concentration and formation of an oxidized surface layer and densification of the film as evidenced by solvent adsorption data. Results obtained from SE indicate few changes in optical parameters, thickness, and refractive index (RI) of the film, up to 5min of UV-O3 treatment. Increasing the exposure time further leads to a substantial change in film thickness and an increase in RI. The same trend was observed for porous polyarylene but to a stronger extent. A dense layer at the porous polymer surface is only formed after 20min of treatment. Under these conditions, the optical properties of the material are strongly modified, with a substantial thickness shrinkage and increase in RI.