K. K. Mendu

Laser-assisted nanoscale deposition of diamond-like carbon films on tungsten tips

Diamond-like carbon (DLC) films were deposited on tungsten tips under KrF excimer laser irradiation in benzene solution. The deposition process was found to be highly dependent on tip sharpness. Tips with larger curvature radii and smaller aspect ratios could not be coated with DLC films under the same condition as that for sharp tips. Raman spectra showed that more sp3 tetrahedral structures were present in the DLC films on a tip with a smaller curvature radius. Simulation results showed that the tip sharpness dependent local optical enhancement played an important role in the DLC deposition process. An optical field gradient from apex to tip body was also found in the simulation. We suggest that there are two modes in the process of DLC deposition on nanotips under different laser fluences, i.e., local apex DLC deposition under low laser fluences and phase-graded DLC deposition under high laser fluences.

Phase-graded deposition of diamond-like carbon on nanotips by near-field induced chemical vapor deposition

Diamond-like carbon (DLC) films were deposited on tungsten (W) tips under the KrF excimer laser in a laser chemical vapor deposition (LCVD) chamber. Raman spectroscopy showed that the deposited DLC films were phase-graded along the tips from the apexes. The DLC films were more diamondlike at or near the tip apexes. From numerical simulation, there is a strongly confined and enhanced optical field at the tip apexes. The simulation also indicates that there is an optical-field gradient from tip apexes to tip bodies. Therefore, the variations in the phases of deposited DLC films were attributed to the corresponding variations in local optical intensities along the tips. Hence, optical local near field was confirmed to be responsible to the DLC deposition.

Near-field enhanced laser-assisted deposition

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.

Fabrication of multi-layered inverse opals using laser-assisted imprinting

Multi-layered inverse opals were fabricated by laser-assisted imprinting of self-assembled silica particles into silicon substrates. A single pulse (pulse duration 23 ns) of a KrF excimer laser instantaneously melts the silicon substrate, which infiltrates and solidifies over the assembled silica particles on the substrate. By removing silica particles embedded in the silicon surface using hydrofluoric acid, inverse-opal photonic crystals were fabricated. This technique is potentially capable of controlling the photonic crystal properties by flexibly varying the silica particle size and the substrate material.

Laser applications in integrated circuits and photonics packaging

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.

Laser-assisted imprinting of self-assembled nanostructures

Nanoscale structuring is a promising area in which the easiest and effective processing methods are being developed. Based on the advantage of lasers, associated with improved self-assembly technique, it is very effective to fabricate nanoscale structures, such as 3-D photonic bandgap structures, using laser-assisted imprinting method, even on the materials with high hardness and high melting point, such as silicon. This new approach to fabricate 3-D photonic bandgap structures on silicon will be presented. Self-assembly technique was used to deposit multi-layer of silica microparticles with a size of 0.81 µm. A pulsed KrF excimer laser (23ns, 248 nm) was applied as the imprinting energy source.Nanoscale structuring is a promising area in which the easiest and effective processing methods are being developed. Based on the advantage of lasers, associated with improved self-assembly technique, it is very effective to fabricate nanoscale structures, such as 3-D photonic bandgap structures, using laser-assisted imprinting method, even on the materials with high hardness and high melting point, such as silicon. This new approach to fabricate 3-D photonic bandgap structures on silicon will be presented. Self-assembly technique was used to deposit multi-layer of silica microparticles with a size of 0.81 µm. A pulsed KrF excimer laser (23ns, 248 nm) was applied as the imprinting energy source.

Fabrication of 3-D photonic bandgap structures on silicon using laser assisted-nanoimprinting

A new approach to fabricate 3-D photonic bandgap structures on silicon substrates using colloidal crystals and laser-assisted nanoimprinting is presented. Self assembly was used to deposit two layers of silica micro particles with a diameter of 0.97 µm. A KrF excimer laser beam with a wavelength of 248 nm was vertically irradiated on the quartz plate placed on the silicon substrate containing two layers of silica particles. The silica particles were imprinted into silicon substrate by the quartz plate during the laser pulse irradiation. Ultrasonic cleaning and hydrofluoric-acid (HF) solution were then used to remove the silica particles. 3-D hemispherical cavities were formed on the silicon substrate surface.A new approach to fabricate 3-D photonic bandgap structures on silicon substrates using colloidal crystals and laser-assisted nanoimprinting is presented. Self assembly was used to deposit two layers of silica micro particles with a diameter of 0.97 µm. A KrF excimer laser beam with a wavelength of 248 nm was vertically irradiated on the quartz plate placed on the silicon substrate containing two layers of silica particles. The silica particles were imprinted into silicon substrate by the quartz plate during the laser pulse irradiation. Ultrasonic cleaning and hydrofluoric-acid (HF) solution were then used to remove the silica particles. 3-D hemispherical cavities were formed on the silicon substrate surface.