Zhiquan Luo

Comparison study of catalyst nanoparticle formation and carbon nanotube growth: Support effect

A comparison study has been conducted on the formation of catalyst nanoparticles on a high surface tension metal and low surface tension oxide for carbon nanotube (CNT) growth via catalytic chemical vapor deposition (CCVD). Silicon dioxide (SiO2) and tantalum have been deposited as supporting layers before deposition of a thin layer of iron catalyst. Iron nanoparticles were formed after thermal annealing. It was found that densities, size distributions, and morphologies of iron nanoparticles were distinctly different on the two supporting layers. In particular, iron nanoparticles revealed a Volmer-Weber growth mode on SiO2 and a Stranski-Krastanov mode on tantalum. CCVD growth of CNTs was conducted on iron∕tantalum and iron∕SiO2. CNT growth on SiO2 exhibited a tip growth mode with a slow growth rate of less than 100nm∕min. In contrast, the growth on tantalum followed a base growth mode with a fast growth rate exceeding 1μm∕min. For comparison, plasma enhanced CVD was also employed for CNT growth on SiO2 a...

Controlled formation and resistivity scaling of nickel silicide nanolines

We demonstrate a top-down method for fabricating nickel mono-silicide (NiSi) nanolines (also referred to as nanowires) with smooth sidewalls and line widths down to 15 nm. Four-probe electrical measurements reveal that the room temperature electrical resistivity of the NiSi nanolines remains constant as the line widths are reduced to 23 nm. The resistivity at cryogenic temperatures is found to increase with decreasing line width. This finding can be attributed to electron scattering at the sidewalls and is used to deduce an electron mean free path of 6.3 nm for NiSi at room temperature. The results suggest that NiSi nanolines with smooth sidewalls are able to meet the requirements for implementation at the 22 nm technology node without degradation of device performance.

Moisture Transport and its Effects on Fracture Strength and Dielectric Constant of Underfill Materials

With continuing demands on increasing die size and device density, underfills are widely used in flip-chip and ball-grid array packages for improvement of reliability. Fracture of the underfill/die interfaces is often observed, particularly at the die corners under a humid environment, raising serious reliability concerns. Moisture uptake can also increase the dielectric constant of underfill materials to degrade the electrical performance of the packages. In this paper, we investigated the diffusion kinetics of moisture and its effects on the fracture energy and effective dielectric constant for two underfill materials. The moisture transport kinetics was studied by a TGA weight loss method and a capacitance measurement method. Based on these results together with diffusion modeling, Arrhenius type relations for moisture diffusion constant and moisture concentration ratio were determined. The interfacial fracture energy of underfills sandwiched by SiN-deposited Si-substrate was measured under various humidity conditions using a double cantilever beam (DCB) method. The crack driving force was systematically reduced by more than 40% as the moisture content increased to saturation in the samples. The locus of failure was cohesive inside underfill materials. Sample preparation technique comprising narrower underfill layer than Si-substrate reduced the incidents of premature failure during testing. Finally, the moisture effect on the increase of dielectric constant was determined using capacitance measurement methods. The dielectric relaxation factor per unit moisture content is reported for the two underfills.

Environmental Effects on Dielectric Films in Plastic Encapsulated Silicon Devices

Mechanical integrity of interlayer and intralayer dielectric films and its impact on interconnect reliability has become more important as critical dimensions in ultralarge-scale integrated circuits are continuously reduced and Cu interconnect, low-k dielectrics (Cu/low-k) are widely adopted for the new technology nodes. Mechanical integrity of the dielectric films and reliability of interconnect can be affected by the film deposition process, stresses from chip-packaging interaction (CPI) and environmental factors such as moisture and temperature exposure. In this study attention has been focused on understanding the moisture and temperature effects on reliability of dielectric films in plastic encapsulated silicon devices. Sensitivities to moisture and temperature induced damage in the dielectric films of the silicon devices were first evaluated using accelerated temperature and humidity stress conditions. Multiple stress conditions were used so the testing results could be applied to validate a physical acceleration model for the combined temperature and humidity stresses. Moisture diffusion in the silicon devices and their packages was then modeled using commercial finite element analysis (FEA) software. Moisture sorption and diffusion properties of the packaging materials were also characterized to support the moisture diffusion modeling. Moisture distribution in the plastic package was analyzed for both the accelerated stress conditions and the product use or storage environmental conditions. The effectiveness of the peripheral seal ring on the silicon device as a moisture barrier was also investigated. Finally, reliability of the silicon devices under typical and extreme product use or storage environment conditions was assessed using the moisture distribution results and the validated acceleration model.

Nanoindentation of Si Nanostructures: Buckling and Friction at Nanoscales

A nanoindentation system was employed to characterize mechanical properties of silicon nanolines (SiNLs), which were fabricated by an anisotropic wet etching (AWE) process. The SiNLs had the linewidth ranging from 24 nm to 90 nm, having smooth and vertical sidewalls and the aspect ratio (height/linewidth) from 7 to 18. During indentation, a buckling instability was observed at a critical load, followed by a displacement burst without a load increase, men a full recovery of displacement upon unloading. This phenomenon was explained by two bucking modes. It was also found that the difference in friction at the contact between the indenter and SiNLs directly affected buckling response of these nanolines. The friction coefficient was estimated to be in a range of 0.02 to 0.05. For experiments with large indentation displacements, irrecoverable indentation displacements were observed due to fracture of Si nanolines, with the strain to failure estimated to be from 3.8% to 9.7%. These observations indicated that...

Indentation of single-crystal silicon nanolines: Buckling and contact friction at nanoscalesa)

High-quality single-crystal silicon nanolines (SiNLs) with a 24 nm linewidth and a height/width aspect ratio of 15 were fabricated. The mechanical properties of the SiNLs were characterized by nanoindentation tests with an atomic force microscope. The indentation load-displacement curves showed an instability with large displacement bursts at a critical load ranging from 9 to 30 μN. This phenomenon was attributed to a transition of the buckling mode of the SiNLs under indentation, which occurred preceding the final fracture of the nanolines. The mechanics of SiNLs under indentation was analyzed by finite element simulations, which revealed two different buckling modes depending on the contact friction at the nanoscale.

Nano-Grating Force Sensor for Measurement of Neuron Membrane Characteristics Under Growth and Cellular Differentiation

We fabricated single-layer pitch-variable diffractive nanogratings on silicon nitride probe using e-beam lithography and subsequent pattern transfer techniques. The nanogratings consist of flexure folding beams suspended between two parallel cantilevers of known stiffness. The probe displacement, therefore the force, can be measured through grating transmission spectrum. We measured the mechanical membrane characteristics of PC 12 cells using the force sensors with displacement range of 10 mum and force sensitivity 8 muN/mum. Youngs moduli of 425plusmn30 Pa are measured with membrane deflection of 1% for PC 12 cells cultured on polydimethylsiloxane(PDMS) substrate coated with collagen or laminin in Hams F-12 K medium. We have also observed stimulation of directed neurite contraction up to 6 mum on extended probing for a time period of 30 minutes.

Mechanical Characterization of High Aspect Ratio Silicon Nanolines

In this study, we performed nanoindentation experiments on two sets of silicon nanolines (SiNLs) of widths 24 nm and 90 nm, respectively, to investigate the mechanical behavior of silicon structures at tens of nanometer scale. The high height-to-width aspect ratio (∼15) SiNLs were fabricated by an anisotropic wet etching (AWE) method, having straight and nearly atomically flat sidewalls. In the test, buckling instability was observed at a critical load, which was fully recoverable upon unloading. It was found that friction at the contact between the indenter and SiNLs played an important role in the buckling response. Based on a finite element model (FEM), the friction coefficient was estimated to be in a range of 0.02 to 0.05. The strain to failure was estimated to range from 3.8% for 90 nm lines to 7.5% for 24 nm lines.

Nanoindentation Study of the Mechanical Behavior of Silicon Nano-springs

This paper presents results of nanoindentation performed on a set of silicon nano‐spring samples formed with glancing angle deposition (GLAD) technique. The load versus displacement curves were recorded to investigate the mechanical behavior of the nano‐spring structures with various column sizes and column spacings. With the combination of atomic force microscope (AFM) and nanoindentation capabilities, in‐situ observation can be carried out to determine local deformation at the nanometer scale on the sample surface. The mechanical response was found to depend on the relative dimensions of the tip with respect to the size of the silicon nano‐column. The study indicates that the mechanical behavior of the silicon nano‐column can be significantly modified by the optimization of the overall configuration and dimensions of the silicon springs.