S. L. Cheng

Synthesis of taperlike Si nanowires with strong field emission

Taperlike Si nanowires (SiNWs) have been synthesized by annealing of high-density FeSi2 nanodots on (001)Si at 1200°C in a N2 ambient. The tip regions of SiNWs are about 5–10nm in diameter. The average length of the SiNWs is about 6μm with aspect ratios as high as 150–170. A growth model based on oxide-assisted growth is proposed. The taperlike morphology may be caused by the passivation of the SiO2 coating layer, which results in the different levels of absorption of SiO along the length of the nanowires. The SiNWs exhibit a turn-on field of 6.3–7.3V∕μm and a threshold field of 9–10V∕μm. The excellent field emission characteristics are attributed to the taperlike geometry of the crystalline Si nanowires.

Effects of nitrogen ion implantation on the formation of nickel silicide contacts on shallow junctions

Abstract The effects of nitrogen ion implantation on the formation of nickel silicide contacts on shallow junctions have been investigated. The phase formation of nickel silicides on nitrogen implanted (001)Si was suppressed and shifted to a higher temperature compared to samples not implanted with nitrogen. The sheet resistance was found to be nearly constant in a wide range of temperature in nitrogen ion implanted samples. It indicates that low-resistivity NiSi is the dominant phase for the 1×1015 N+/cm2 implanted samples annealed at 400–750°C and for the 2×1015 N2+/cm2 implanted samples annealed at 400–800°C. The diffusion of nickel atoms is thought to be retarded by the presence of nitrogen atoms. The presence of nitrogen ion can also improve the thermal stability of nickel disilicide. The effects of nitrogen on nickel silicide formation become more pronounced with an increase in the nitrogen dose up to a certain value.

Self-assembled hexagonal Au particle networks on silicon from Au nanoparticle solution

Self-assembled hexagonal Au particle networks, 2–12 μm in cell size, on silicon have been achieved by a simple method. Honeycomb structure of Au nanoparticles on silicon was drop cast from the Au nanoparticle solution under appropriate concentration, evaporation rate, substrate temperature, and humidity. Hexagonal networks with discrete Au particles were generated in samples annealed in N2 ambient. Two-step annealing, i.e., annealing at 400 °C followed by annealing at 1000 °C for 1 h each was found to be effective to improve the regularity of the Au particle network. As the cell size can be adjusted by the tuning of the deposition conditions, the scheme promises to be an effective patterning method without complex lithography.

Synthesis and characterization of metallic TaSi2 nanowires

TaSi2 nanowires have been synthesized by annealing FeSi2 thin film and nanodots grown on a Si substrate in an ambient containing Ta vapor. The TaSi2 nanowires are formed in three steps; segregation of Si atoms from the FeSi2 underlayer to form Si base, growth of TaSi2 nanodots on Si base, and elongation of TaSi2 nanowire along the growth direction. Strong field-emission properties promise future electronics and optoelectronics applications.

EFFECTS OF STRESS ON THE GROWTH OF TISI2 THIN FILMS ON (001)SI

Tensile stress induced by backside CoSi2 films on a silicon substrate has been found to enhance the growth of C54–TiSi2 on (001)Si. In contrast, compressive stress induced by backside oxide films on the silicon substrate was found to retard significantly the growth of C54–TiSi2 on (001)Si. For Ti on stressed (001)Si after rapid thermal annealing at 800 °C for 30 s, the thickness of the C54– TiSi2 films was found to increase and decrease with the tensile and compressive stress levels, respectively. The retarded growth is attributed to the hindrance of the migration of Si through the Ti/Si interface by the compressive stress. On the other hand, the presence of tensile stress promotes the Si diffusion to facilitate the formation of Ti silicide thin films.

Structural and Electrical Characteristics of Low-Dielectric Constant Porous Hydrogen Silsesquioxane for Cu Metallization

The structural and electrical properties of porous hydrogen silsesquioxane (XLK) have been characterized using a combination of Fourier transform infrared spectroscopy, transmission electron microscope, Auger electron spectroscopy, current-voltage analyzer, and capacitance-voltage analyzer. The pores, about 2 nm in size and of spherical shape, were distributed randomly and uniformly in the XLK film. The dielectric constant of XLK film was as low as 2.1 owing to the high porosity and uniformity of the film. A smooth amorphous-like layer including Cu-O-Si was found to form between Cu and the XLK film after annealing at 500°C for 30 min. The mixed layer led to the higher leakage current of the XLK film. Cu was found to diffuse into XLK film after annealing at 600°C for 30 min.

Enhanced growth of low-resistivity NiSi on epitaxial Si0.7Ge0.3 on (001)Si with a sacrificial amorphous Si interlayer

Enhanced growth of low-resistivity NiSi on epitaxial Si0.7Ge0.3 with a sacrificial amorphous Si (a-Si) interlayer has been achieved. The a-Si layer with appropriate thickness was found to prevent Ge segregation, decrease the growth temperature, as well as maintain the interface flatness and morphological stability in forming low-resistivity NiSi on Si0.7Ge0.3 grown by molecular beam eptiaxy. The process promises to be applicable to the fabrication of high-speed Si–Ge devices.

Enhanced growth of CoSi2 on epitaxial Si0.7Ge0.3 with a sacrificial amorphous Si interlayer

Enhanced growth of CoSi2 on epitaxial Si0.7Ge0.3 has been achieved with an interposing amorphous-Si (a-Si) layer. The a-Si layer was used as a sacrificial layer to prevent Ge segregation, decrease the growth temperature, as well as maintain the interface flatness and morphological stability in forming CoSi2 on Si0.7Ge0.3 grown by molecular beam eptiaxy. The process promises to be applicable to the fabrication of high-speed Si–Ge devices.

Roles of Additives in Damascene Copper Electropolishing

cBASF Electronic Materials, Taiwan This study explores how the dissolution of damascene Cu depends on accelerators of organic acids in alcohol-containing H3PO4 electropolishing electrolytes. Four two-additive electrolytes that contain different accelerators, acetic, citric, citrazinic, and benzoic acids, are evaluated. At the bottom of damascene features, an esterification reaction between alcohols and organic acids efficiently forms a highly resistive layer and reduces the acidity of the solution. Accordingly, outside the damascene features, the rate of removal of Cu is dominated by the acidity of electrolytes but, inside the features, it is also determined by the resistance of the viscous layer. For a weak acidic additive, acetic acid, an extremely high additive concentration is introduced to sustain the moderate acidity of the solution to initiate intense esterification. Therefore, acetic-acid-based two-additive electrolytes exhibit excellent Cu planarization capability.

Growth of light-emitting silicate nanowires on individual Au particles in self-assembled hexagonal Au particle networks

Hierarchical growth of silicate nanowires on individual Au particles in self-organized hexagonal Au particle networks has been achieved by appropriate control of annealing conditions in N2 ambient. Cathodoluminescence data showed that the silicate nanowires emit light with a wavelength of 415nm. The scheme to form the regular Au particle network offers an effective and economical means to produce a universal template to grow functional structures without complex lithography.