L. P. Li

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.

Parametric investigation of laser nanoimprinting of hemispherical cavity arrays

A monolayer of self-assembled silica particles can be imprinted into a silicon substrate by laser irradiation (KrF excimer laser, λ=248nm). Periodical hemispherical cavities can be therefore created on the substrate surface. The influences of various particle sizes and laser fluence were investigated. In addition, preheating of the substrate significantly improves the performance. One-dimensional thermal calculation was employed to understand the thermal effect in this process. Three-dimensional optical simulation provided an accurate insight into the light intensity enhancement. Raman spectroscopy was used to examine the stress induced by the laser imprinting process resided in the cavity structures.

Laser-assisted nanopatterning of aluminium using particle-induced near-field optical enhancement and nanoimprinting

Laser-assisted nanopatterning of aluminium (Al) thin films using particle-induced near-field optical enhancement and nanoimprinting has been investigated experimentally and theoretically. It is found that nano pit arrays can be created on Al surfaces by laser irradiation (KrF excimer laser, ? = 248?nm) on an Al surface on which a monolayer of silica particles has been self-assembled. The influence of particle size and laser fluence on the structuring of Al surfaces has been examined. Particles with various diameters of 0.97, 2.34 and 5.06??m were used in the experiment. Near-field optical enhancement and nanoimprinting were identified to explain the mechanisms for the formation of different structures on Al?surfaces under different laser fluences. A high frequency structure simulator?(HFSS) was used to simulate the optical field distribution in the particles attached on Al surfaces.

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.

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.

Laser-assisted nanoimprinting of self-assembled single size and binary-size nanoparticles on silicon and aluminum substrates

A monolayer of self-assembled silica particles can be imprinted into a silicon (Si) substrate by laser irradiation (KrF excimer laser, λ=248 nm). Periodical hemispherical cavities can be therefore created on the substrate surface. The influences of various particle sizes and laser fluence were investigated. In addition, preheating of the substrate significantly improves the performance. One-dimensional thermal calculation was employed to understand the thermal effects in this process. Three-dimensional optical simulation provided an accurate insight into the light intensity enhancement. Raman spectroscopy was used to examine the stress induced by the laser imprinting process resided in the cavity structures. Self-assembly of binary-size nanoparticles was achieved and its application on the fabrication of binary-size nanocavity arrays by laser-assisted nanoimprinting was investigated.A monolayer of self-assembled silica particles can be imprinted into a silicon (Si) substrate by laser irradiation (KrF excimer laser, λ=248 nm). Periodical hemispherical cavities can be therefore created on the substrate surface. The influences of various particle sizes and laser fluence were investigated. In addition, preheating of the substrate significantly improves the performance. One-dimensional thermal calculation was employed to understand the thermal effects in this process. Three-dimensional optical simulation provided an accurate insight into the light intensity enhancement. Raman spectroscopy was used to examine the stress induced by the laser imprinting process resided in the cavity structures. Self-assembly of binary-size nanoparticles was achieved and its application on the fabrication of binary-size nanocavity arrays by laser-assisted nanoimprinting was investigated.

Fabrication of hemispherical cavity arrays on silicon substrates using laser-assisted nanoimprinting

We have developed a new method of laser-assisted nanoimprinting to fabricate hemispherical-cavity arrays on silicon (Si) and germanium (Ge) substrates. A monolayer of silica particles, with different diameters ranging from 0.30 to 5 µm, was deposited on a Si or Ge substrate by self-assembly technique. A quartz plate was tightly placed on the sample surface to form a quartz/nanoparticle/substrate structure. The silica particles were imprinted into Si or Ge substrates after laser irradiation (KrF excimer laser, λ=248 nm) on the structure with a single pulse. Ultrasonic cleaning and hydrofluoric-acid (HF) solution were used to remove the silica particles on the substrate surface. Hemispherical cavities were formed on the substrate surface. The influences of different particle size and laser fluence on the structuring of the surface have been investigated. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were performed to observe the dimensions of the cavities. One-dimensional thermal calculation was employed to understand the thermal effects in this process.We have developed a new method of laser-assisted nanoimprinting to fabricate hemispherical-cavity arrays on silicon (Si) and germanium (Ge) substrates. A monolayer of silica particles, with different diameters ranging from 0.30 to 5 µm, was deposited on a Si or Ge substrate by self-assembly technique. A quartz plate was tightly placed on the sample surface to form a quartz/nanoparticle/substrate structure. The silica particles were imprinted into Si or Ge substrates after laser irradiation (KrF excimer laser, λ=248 nm) on the structure with a single pulse. Ultrasonic cleaning and hydrofluoric-acid (HF) solution were used to remove the silica particles on the substrate surface. Hemispherical cavities were formed on the substrate surface. The influences of different particle size and laser fluence on the structuring of the surface have been investigated. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were performed to observe the dimensions of the cavities. One-dimensional thermal calc...

Nanostructuring using laser-assisted scanning probe microscope

Nanostructures were fabricated using laser irradiating at the conductive tip of an atomic force microscope (AFM). The conductive tip behaves like an antenna, which receives electromagnetic energy from the laser beam and then emits electromagnetic wave in nanometer range. In this study, a commercial atomic force microscope, combined with a 514.5 nm argon ion laser and a vertically-polarized 532 nm Nd:YAG pulsed laser, was utilized for modification on the gold and 1813 photo-resist films. AFM imaging and nanostructure modification were conducted at the contact-constant-height mode. AFM images were obtained right after the laser irradiations to monitor the modification process. The effect of the laser intensity, the optical field enhancement, and the thermal expansion of the tip under laser irradiation are investigated.Nanostructures were fabricated using laser irradiating at the conductive tip of an atomic force microscope (AFM). The conductive tip behaves like an antenna, which receives electromagnetic energy from the laser beam and then emits electromagnetic wave in nanometer range. In this study, a commercial atomic force microscope, combined with a 514.5 nm argon ion laser and a vertically-polarized 532 nm Nd:YAG pulsed laser, was utilized for modification on the gold and 1813 photo-resist films. AFM imaging and nanostructure modification were conducted at the contact-constant-height mode. AFM images were obtained right after the laser irradiations to monitor the modification process. The effect of the laser intensity, the optical field enhancement, and the thermal expansion of the tip under laser irradiation are investigated.