Recent prominent progresses in synthesizing and manipulating single-walled carbon nanotubes (SWNTs) stimulated
extensive interests in developing SWNT-based devices for nanoelectronics and nanoelectromechanical systems (NEMS).
Thermal chemical vapor deposition (CVD) is one of the most widely accepted technique for growing SWNTs by heating
the whole chamber and substrate to required reaction temperatures. In this study, we demonstrated a process for position-controllable
synthesis of SWNT-FET by bridging the SWNT across pre-defined electrodes using the laser chemical
vapor deposition (LCVD) technique. The SWNT-FET was back-gate modulated, showing p-type semiconducting
characteristics. The process is very fast and can be conducted using both far-infrared CO2 laser (10.6 &mgr;m) and near-infrared
Nd:YAG laser (1064 nm). We have also demonstrated localized synthesis of SWNTs by a focused laser beam.
Due to the unique advantages of LCVD process, such as fast and local heating, as well as its potential to select chiralities
during the growing process, it may provide new features and versatilities in the device fabrication.
With recent advances in the aligned growth of carbon nanotubes (CNTs), there are great interests in CNT-based field-emission and electronic applications. In conventional thermal chemical vapor deposition, substrates as well as chambers need to be globally heated to a sufficiently-high reaction temperature. In this paper, we report a method for direct synthesis of CNTs on pre-defined electrodes using laser-assisted chemical vapor deposition. A CW CO2 laser (wavelength 10.6 μm, beam diameter 2 mm) was used to irradiate the pre-defined structures for CNT growth. The temperature of the substrate was measured by a pyrometer, ranging from 850-1000 °C. By varying catalysts and laser parameters, carbon nanostructures including carbon nanofiber, multi-walled and single-walled CNTs can be controllably synthesized.
Diamond-like carbon (DLC) coated tips have been successfully applied in field emitter arrays, and scanning probe microscope (SPM) based nanofabrications. DLC deposition on tips is conventionally realized by thermal and plasma-enhanced chemical vapor deposition processes. In this study, we use laser-assisted method employing strongly enhanced near field around the tip apex for DLC deposition. DLC films were deposited on tungsten (W) tips under KrF excimer laser irradiation in a benzene solution and in a laser chemical vapor deposition (LCVD) chamber. Simulation results showed a highly localized optical field enhancement at the tip apex. There was also an optical-field gradient from apex to tip body. Experiment results showed that a locally confined DLC film was deposited based on energy dispersive X-ray (EDX) analysis. Raman spectra showed that at positions close to apexes, films tend to be more diamond-like. This implies that quality of DLC film varies according to local optical intensity along the tip. Hence, the deposition process was confirmed to be induced by the local near field generated by laser and nanotip interaction.
Steam laser cleaning of alumina and titanium carbide nanoparticles from silicon substrates is presented. A KrF excimer laser with a wavelength of 248 nm was used to irradiate the substrates in laser cleaning. A water layer of micrometer thickness was deposited on silicon substrates to improve the cleaning process. Cleaning efficiency was measured for different laser fluences ranging from 50 to 250 mJ/cm2 and pulse numbers from 1 to 100. Research work was carried out to address the factors governing steam laser cleaning, during which thickness of water thin film and lift-off velocities of water films from Si substrate surfaces were monitored. In addition, one-dimensional simulations were employed to estimate the temperature increase on the material surfaces upon laser irradiation. Water layer thickness was measured using Fourier Transform Infrared Spectroscopy. Monitoring of both lift-off velocities and water thin film removal time were carried out by optical probing approaches using He-Ne laser of 632.8 nm wavelength.
Laser processing has large potential in the packaging of integrated circuits (IC). It can be used in many applications such as laser cleaning of IC mold tools, laser deflash to remove mold flash from heat sinks and lead wires of IC packages, laser singulation of BGA (ball grid array) and CSP (chip scale packages), laser reflow of solder ball on GBA, laser peeling for CSP, laser marking on packages and on Si wafers. Laser nanoimprinting of self-assembled nanoparticles has been recently developed to fabricate hemispherical cavity arrays on semiconductor surfaces. This process has the potential applications in fabrication and packaging of photonic devices such as waveguides and optical interconnections. During the implementation of all these applications, laser parameters, material issues, throughput, yield, reliability and monitoring techniques have to be taken into account. Monitoring of laser-induced plasma and laser induced acoustic wave has been used to understand and to control the processes involved in these applications. Numerical simulations can provide useful information on process analysis and optimization.