▪ Abstract The transition to copper-based interconnects for sub-quarter-micron device technologies has generated significant challenges in the identification and development of the robust material and process technologies required to form reliable multilevel metallization interconnects. In particular, a critical need exists for the identification and development of diffusion barrier/adhesion promoter liner materials that provide excellent performance in preventing the diffusion and intermixing of copper with the adjacent dielectric and semiconductor regions of the computer chip. This review summarizes key technology trends in interconnect metallization, with emphasis on ultrathin liner materials, predominant diffusion mechanisms in liner materials, and most promising candidate liners for copper metallization. Key results are presented from the development of physical vapor deposition and chemical vapor deposition processes for binary refractory metal nitrides, such as tantalum nitride and tungsten nitride, and amorphous ternary liners, including the titanium-silicon-nitrogen, tantalum-silicon-nitrogen, and tungsten-silicon-nitrogen systems. The applicability of these materials as diffusion barriers in copper-based interconnects is reviewed and assessed, particularly in terms of driving failure mechanisms and performance metrics.
A de novo, genetically engineered 687 residue polypeptide expressed in E. coli has been found to form highly rectilinear, beta-sheet containing fibrillar structures. Tapping-mode atomic force microscopy, deep-UV Raman spectroscopy, and transmission electron microscopy definitively established the tendency of the fibrils to predominantly display an apparently planar bilayer or ribbon assemblage. The ordered self-assembly of designed, extremely repetitive, high molecular weight peptides is a harbinger of the utility of similar materials in nanoscience and engineering applications.
Findings are presented from a systematic study of the effects of postdeposition thermal treatment on the optical characteristics of hydrogenated amorphous silicon-oxycarbide (a-SiCxOyHz) materials. Three different classes of a-SiCxOyHz films: SiC-like (SiC1.08O0.07H0.21), Si-C-O (SiC0.50O1.20H0.22), and SiO2-like (SiC0.20O1.70H0.24), were deposited by thermal chemical vapor deposition. The effects of thermal annealing on the compositional and optical properties of the resulting films were characterized using Fourier-transform infrared spectroscopy, x-ray photoelectron spectroscopy, nuclear reaction analysis, and spectroscopic ultraviolet-visible ellipsometry. As the Si-C-O system evolved from a SiC-like to SiO2-like matrix, its refractive index and optical absorption strength decreased, while its optical band gap increased. Thermal annealing between 500 and 1100 °C resulted in hydrogen desorption from and densification of the a-SiCxOyHz films. Concurrently, thermally induced changes were also observed for the optical properties of the films, as evidenced by an increase in film refractive index and an accompanying decrease in optical gap. These changes are analyzed in the context of the underlying physical processes, particularly modifications in the electronic configuration (bonding) and hydrogen desorption mechanisms. Furthermore, based on the observed structural and optical properties of the thermally treated a-SiCxOyHz films, the Si-C-O matrix was employed in the successful development of an Er-doped Si-C-O system with efficient Er excitation and strong room-temperature photoluminescence emission around 1540 nm within a broad (460–600 nm) excitation band. As such, a-Si-C-O represents a material system that provides considerably efficient energy transfer mechanisms at the same Er concentration level than previously investigated Si-based materials.
The composition, structure, morphology, and optical characteristics of hydrogenated amorphous silicon-oxycarbide (a-SiCxOyHz) materials were investigated as a function of experimental processing conditions and post-deposition thermal treatment. Thermal chemical vapor deposition (TCVD) was applied to the growth of three different types of a-SiCxOyHz films, namely, SiC-like (SiC1.08O0.07H0.21), Si-C-O (SiC0.50O1.20H0.22), and SiO2-like (SiC0.20O1.70H0.24). The resulting films were subsequently annealed at temperatures ranging from 500 °C to 1100 °C for 1 h in an argon atmosphere. The composition, structure, and morphology of as-deposited and post-annealed films were characterized by Fourier transform infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectroscopy (RBS), nuclear-reaction analysis (NRA), and scanning electron microscopy. Corresponding optical properties were assessed by spectroscopic ultraviolet-visible ellipsometry (UV-VIS-SE). These studies led to the identification of an optimized process window for the growth of Er doped silicon oxycarbide (SiC0.5O1.0:Er) thin film with strong room-temperature photoluminescence emission measured around 1540 nm within a broad (460 nm to 600 nm) wavelength band. Associated modeling studies showed that the effective cross section for Er excitation in the SiC0.5O1.0:Er matrix was approximately four orders of magnitude larger than its analog for direct optical excitation of Er ions.
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