In our previous studies, thin Ti-rich diffusion barrier layers were found to be formed at the interface between Cu(Ti) films and SiO 2 /Si substrates after annealing at elevated temperatures. This technique was called self-formation of the diffusion barrier, and is attractive for fabrication of ultralarge-scale integrated (ULSI) interconnects. In the present study, we investigated the applicability of this technique to Cu(Ti) alloy films which were deposited on low dielectric constant (low-k) materials (SiO x C y ), SiCO, and SiCN dielectric layers, which are potential dielectric layers for future ULSI Si devices. The microstructures were analyzed by transmission electron microscopy (TEM) and secondary-ion mass spectrometry (SIMS), and correlated with the electrical properties of the Cu(Ti) films. It was concluded that the Ti-rich interface layers were formed in all the Cu(Ti)/dielectric-layer samples. The primary factor to control the composition of the self-formed Ti-rich interface layers was the C concentration in the dielectric layers rather than the enthalpy of formation of the Ti compounds (TiC, TiSi, and TiN). Crystalline TiC was formed on the dielectric layers with a C concentration higher than 17 at.%.
A new fabrication technique to prepare ultrathin barrier layers for nanoscale Cu wires was proposed in our previous studies. Ti-rich layers formed at Cu(Ti)/ dielectric layer interfaces consisted of crystalline TiC or TiSi and amorphous Ti oxides. The primary control factor for the Ti-rich interface layer composition was C concentration in the dielectric layers rather than the formation enthalpy of the Ti compounds. To investigate Ti-rich interface layer growth in Cu(Ti)/ dielectric layer samples annealed in ultrahigh vacuum, Rutherford backscattering spectrometry (RBS) was employed in the present study. Ti peaks were obtained only at the interfaces for all samples. Molar amounts of Ti atoms segregated to the interfaces (n) were estimated from Ti peak areas. Log n values were proportional to log t values. Slopes were similar for all samples, suggesting similar growth mechanisms. The activation energy (E) for Ti atoms reacting with the dielectric layers containing carbon (except SiO 2 ) tended to decrease with decreasing C concentration (decreasing k), while those for the SiO 2 layers were much higher. Reaction rate coefficients [Z AE exp(ÀE/RT)] were insensitive to C concentration in the dielectric layers. These factors lead to the conclusion that growth of the Ti-rich interface layers is controlled by chemical reactions, represented by the Z and E values, of the Ti atoms with the dielectric layers, although there are a few diffusion processes possible.
Articles you may be interested inStructural characterization of He ion microscope platinum deposition and sub-surface silicon damage Analysis of subsurface beam spread and its impact on the image resolution of the helium ion microscope J. Vac. Sci. Technol. B 28, C6F6 (2010); 10.1116/1.3497012Direct-write patterning of microstructured porous silicon arrays by focused-ion-beam Pt deposition and metalassisted electroless etching Thermal stability and hydrogen atom induced etching of nanometer-thick a-Si:H films grown by ion-beam deposition on Si(100) surfaces J.The authors use a helium ion microscope (HIM) equipped with a tungsten hexacarbonyl gas injection system (GIS) to form tungsten-based pillars on carbon and silicon substrates by helium ion beaminduced deposition. Tungsten-based pillars with a width of $40 nm and height of $2 lm (aspect ratio of $50) are successfully fabricated using the HIM-GIS method. The pillars consist of face-centered cubic WC 1Àx and/or W 2 (C, O) grains. Columnar voids with a width of 1-15 nm form in the center of the pillars, suggesting that the pillars are continuously sputter-etched by the incident helium ion beam during deposition. In addition, the authors observe beam irradiation damage in the form of blistering of the Si substrate at the interface between the pillar and Si substrate. The columnar void width and Si blister height decreases as the volumetric growth rate of the pillars increases regardless of the deposition parameters. The authors consider that at least three phenomena compete during pillar formation, namely pillar deposition, sputter-etching, and Si blistering. Although there are numerous parameters involved in HIM-GIS deposition, it appears that the volumetric growth rate determines both the microstructure of the tungsten-based pillars and the degree of substrate damage.
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