Nanoparticle Removal Using Laser-Induced Plasma Shock Waves

Removal of sub-100 nm particles from substrates such as wafers and photo masks is an essential requirement in semiconductor, microelectronics, and nanotechnology applications. The proposed laser-induced plasma (LIP) based approach is an effective technique for removal of sub-100 nm particles, as the minimum tolerable particle on the substrates shrinks to sub-100 nm levels with each technological node. In the current study, our progress in sub-100 nm particle removal is reviewed, and the results of the kinetic theory simulations conducted to understand the dynamics of the gas molecule-nanoparticle interactions excited by the shock front are discussed. It is shown from the simulations and experiments that particles as small as sub-100 nm can be successfully detached. To explain possible mechanisms for the nanoparticle detachment in nanoscale, the concepts of rolling resistance moment and rocking motion are utilized as novel detachment mechanisms. The pressure experiments illustrate that the peak pressure levels achieved with the LIP shock wave fields are below damage thresholds of most substrate materials. The potential of the proposed approach as a practical noncontact, dry, fast, and damage-free method for removal of sub-100 nm particles is discussed.     

SCALING LAWS FOR PARTICLE BREAKUP IN NOZZLE GENERATED SHOCKS

Conditions for the onset of particle breakup in normal shock waves have been investigated. A normalized particle drag behind the shock has been determined in terms of gas stagnation conditions and particle diameter for a range of gas Mach numbers 1 ≤ M₁ ≤ 5 by introducing appropriately defined particle Knudsen and Reynolds numbers into analytical expressions for the drag coefficient. Numerical computations of the particle drag, normalized with gas stagnation pressure and particle area, indicate a peak at a gas Mach number M₁ ≳ 2.2, The magnitude of the peak was found to decrease with increasing particle diameter and reservoir gas density.

Criteria for the onset of agglomerate breakup were defined in terms of a modified Weber number for the adhesion mechanisms due to Van der Waals forces, electrostatic attraction and adsorbed surface films. These results indicate that larger more closely packed agglomerates made up of smaller constituent particles have a greater tendency to resist breakup for a given set of stagnation conditions and shock Mach number.     

Numerical Study of Air Compressibility During Horizontal Pneumatic Transport

Using numerical simulations, the effect of the compressibility of air on the flow pattern of particles and pressure drop in the presence of particles during horizontal pneumatic transport operating under negative pressure was examined. The length and inside diameter of the pipeline were 30 m and 40 mm, respectively, and the chosen particles (4 mm in diameter) had densities of ρ_p = 1000 and 2000 kg/m³. The mean air velocities at pipe the inlet were U_inlet = 19, 22, and 28 m/s, and the range of the mass flow rate ratios of particle to air, μ, was varied up to 2.0. For a given inlet air velocity, the difference in the flow pattern between compressible and incompressible flow calculation is generally small. For ρ_p = 1000 kg/m³ particles the additional pressure drop in compressible flow increases when μ is above 0.5 and U_inlet is 28 m/s, μ is above 1.3 and U_inlet is 22 m/s, and μ is above 1.5 and U_inlet is 19 m/s. In these cases, the particle flow pattern is homogeneous. For ρ_p = 2000 kg/m³ particles, the pressure drop increases only when μ is above 1.5 and U_inlet is 28 m/s. The difference is not noticeable when the particle flow pattern is heterogeneous. Also, the difference in the additional pressure drop is much larger during homogeneous flow than heterogeneous flow.     

Electrically Conductive Composite Powders and Compounds Produced with Solid State Synthesis

Electrically conductive composite powders and compounds were produced using a mechanical alloying method. As starting materials, copper powder and a mixture of butadiene-acrylonitrile-copolymer and polyvinylchloride were used. After alloying, the powderlike material consisted of a mixture of fine copper powder embedded in the polymer matrix. Milling resulted in a copper powder of particle size 300 nm to 2 μm. The alloyed powders were compacted at a pressure of 0.37 GPa at 90°C with a holding time of 1 minute. The resistivity of the compound was measured to be 8.6 × 10^-4 ohm-cm. The unusual reduction in particle size to the nanometer level and formation of spherically formed copper polymer composite particles is explained by the reactions of the copper atoms with cyano and other functional groups of the polar polymers. The structurally modified polymer forms a tight encapsulation coating on the surface of the copper, and the flat-formed metal particles are recovered in spherical form due to strong interfacial forces, resulting in increased electrical conductivity.     

PARTICLE CONCENTRATION MEASUREMENTS BY LASER IMAGING FOR A TURBULENT DISPERSION

A laser imaging system has been developed which can be used for investigating the particle concentration variation in explosive test apparatus such as the Ciba-Geigi and Hartmann Bomb during turbulent dispersions of air-particle mixtures. The pulsed UV (337 nm) laser imaging system using a 500X optical and electronic magnification system has a measurement volume of 900 µm by 675 µm and an in-focus depth of field of 780 µm for a 32 µm diameter particle. Particles in the measurement control volume are imaged every 33 ms during the dispersion process and viewed in real time but stored for later analysis on a video tape system.

This paper presents the results of investigating the lycopodium particle concentration variations during the dispersion process of 0.200 grams of lycopodium particles in the Hartmann Bomb explosive test apparatus. Data were taken at the center line and at a radius ratio of 0.5 at a height of 0.102 m (4 inches) above the base of the Hartmann lucite tube. Twenty-five separate dispersions were made at each radius ratio and were based on a reservoir pressure of 103 kPa (15 psig) and 0.200 g of lycopodium powder. The average number of lycopodium particles based upon 25 dispersions at 33 ms intervals in the 473.9 × 10⁶ m³ control volume are reported for a total elapsed time of 15 seconds. The maximum average particle concentration observed was 6.4 particles at 133 ms for r/R = 0.0 and 6.5 particles in 333 ms for r/R = 0.5. Based upon uniform dispersion model for 0.200 g of lycopodium powder, 6.8 particles per control volume, would be expected. The time averaged data followed a Poisson Distribution for each time increment after 0.73 s for both radius ratios of r/R = 0.0 and 0.5 (based upon 95% confidence interval and Kolmogorov-Smirnov test). Data from 0 to 0.73 seconds could not be assigned confidence levels as the data did not follow a Poisson Distribution or any other known statistical distribution. No significant particle agglomeration was observed for the dispersion of lycopodium particles. In any one dispersion the number of lycopodium particles in the control volume was observed to vary widely during each 033 second measurement cycle.

To further investigate the particle dispersion, the flow pattern characteristics in the Hartmann dispersion apparatus were studied using flow visualization techniques based upon a matched Reynolds number (3.13 × 10⁶) dispersion of fluorescent dye by turbulent water injection. The matched Reynolds number flow visualization work further indicated the Hartmann Bomb dispersion method produces local pockets of nonuniformly-mixed mixtures during initial stages of the dispersion process, and this work further points out the shortcomings of integrating optical probes.     

Alkoxide route to La0.5Sr0.5CoO3 epitaxial thin films on SrTiO3

An all alkoxide based sol–gel route was investigated for preparation of epitaxial La_0.5Sr_0.5CoO₃ (LSCO) films on 100 SrTiO₃ (STO) substrates. Films with 20–30 to 80–100 nm thickness were prepared by spin-coating 0.2–0.6 M (metal) solutions on the STO substrates and heat treatment to 800 °C at 2 °C min^− 1, 30 min, in air. The films were epitaxial with a cube-on-cube alignment and the LSCO cell was strained to match the STO substrate of 3.905 Å closely; a and b = 3.894 Å and 3.897 Å for the 20–30 and 80–100 nm films, respectively. The c-axis was compressed to 3.789 Å and 3.782 Å for the 20–30 and 80–100 nm films, respectively, which resulted in an almost unchanged cell volume as compared to polycrystalline film and nano-phase powders prepared in the same way. The SEM study showed mainly very smooth, featureless surfaces, but also some defects. A film prepared in the same way on an -Al₂O₃ substrate was dense and polycrystalline with crystallite sizes in the range 10–50 nm and gave cubic cell dimensions of a_c = 3.825 Å. The conductivity of the ca 30–40 nm thick polycrystalline film was 1.7 mΩcm, while the epitaxial 80–100 nm film had a conductivity of around 1.9 mΩcm.     

Cubic TaN diffusion barrier for Cu interconnects using an ultra-thin TiN seed layer

Epitaxial metastable cubic TaN (B1-NaCl) thin films were grown on Si (001) substrates using an ultra-thin TiN (B1-NaCl) seed layer, as thin as ~ 1 nm. The TiN/TaN stacks were deposited by pulsed laser deposition and kept below 25 nm, with the TiN thickness systematically reduced from 15 nm to ~ 1 nm. Detailed microstructural studies including X-ray diffraction, transmission electron microscopy (TEM) and high-resolution TEM, and, preliminary Cu diffusion experiments all suggest that, the TiN seed layer thickness (~ 1 nm–15 nm) has little or no obvious effects on the overall microstructure and the diffusion barrier properties of the TaN/TiN stacks.     

High resolution material ablation and deposition with femtosecond lasers and applications to photomask repair

Abstract

We describe experiments using 100 femtosecond pulses of 266 nm light to ablate Cr defects from photomasks with resolution below 100 nm. In addition to the ablative removal of Cr, experiments were carried out to deposit Cr metal onto fused silica substrates using 100 fs, 400 nm light at atmospheric pressure. Multiphoton dissociation of Cr(CO)₆ adsorbed on fused silica substrates initiates Cr deposition. The mechanisms for deposition on both transparent (fused silica) and absorbing (Cr metal) substrates are discussed. Finally we describe initial experiments to ablate Cr metal at wavelengths below 200 nm using light generated by frequency mixing of ultrashort, 30 fs pulses in an Ar filled capillary.     

Observation Evaluation of Nozzle Clogging in a Micro-orifice Impactor Used for Atmospheric Aerosol Sampling

A micro-orifice impactor uses micro-orifice nozzles to extend the cut sizes of the lower stages to as small as 0.18 μm in diameter without resorting to low pressures or creating excessive pressure drops across the impactor stages. In this work, the phenomenon of nozzle clogging caused by particle deposition was investigated experimentally for a commercial micro-orifice uniform deposit impactor (MOUDI, MSP model 100). Using an optical microscope, we observed that the micro-orifice nozzles of the lower three stages were partially clogged due to particle deposition during the atmospheric aerosol sampling. To examine the effect of nozzle clogging on the performance of the impactor, the pressure drop and the particle collection efficiency were evaluated for the lower three stages. The pressure drops across the clogged nozzles were higher than the nominal values given by the manufacturer. The particle collection efficiency of each stage was evaluated by using an electrical method for fine particles with diameters in the range of 0.1-0.6 μm. Monodisperse liquid dioctyl sebacate (DOS) particles were used as test aerosols. A Faraday cage was employed to measure the low-level current of the charged particles upstream and downstream of each stage. The collection efficiency curves shifted to correspondence to smaller orifice sizes, and the 50% cutoff sizes were much smaller than those given by the manufacturer for the three stages with nozzles less than 400 μm in diameter.     

Dynamic Effects in Microparticle Pull-Off Using an AFM

We report a series of measurements aimed at understanding the dynamics of microparticle detachment from surfaces. Microparticles were adhered to AFM cantilever tips and load/displacement curves were obtained while the particles were repeatedly attached and detached from the surface with frequencies ranging from 1 to 30 Hz. Particles ranging in size from 1 to 30 micrometers and composed of alumina and polystyrene were studied. For each particle studied, a decrease in the pull-off force was consistently observed with increasing measurement frequency, indicating a dynamic effect that is not accounted for by equilibrium adhesion models. We present a lumped mass model of the canitilever/particle/surface system to definitively rule out the possibility that bulk inertial effects within the particle or cantilever may be responsible at these time scales. Furthermore, we ensured dry conditions for each experiment making it unlikely that humidity effects, such as water bridge formation, could have been responsible. Although we have not pinpointed the physical nature of the dynamics, we offer the possibility that energy dissipation mechanisms at the particle/surface interface may cause dynamic effects during microparticle attachment or detachment on time scales similar to those of the present experiments.     

CONTRIBUTIONS OF ROAD DUST RESUSPENSION TO THE AIRBORNE PARTICLE CONCENTRATIONS IN TAIPEI

The high concentrations of airborne particles have been one of the main air pollution problems in Taipei, Taiwan. In this study, the possible sources of airborne particles were investigated using concentration profile and chemical composition. The vertical concentration profile of TSP was measured at 1.5 m, 11 m, and 38 m above ground. The concentrations of TSP at 1.5 m above ground are always greater than 300 µg/m³; and even up to 1230 µg/m³, while those at 11 m above ground are only half of these values. The concentrations at 38 m above ground are only about half of those at 11 m above ground. Similar concentration profiles are found for Mg, Ca, Pb, Fe, and Zn measured and the enrichment factors with respect to the composition of road dust are generally less than 3. Therefore, there is a not upward flux of airborne particles from ground. The net upward fluxes are estimated to be about 100 ton/yr/km¹ from the vertical concentrations profiles and particle size distributions. The particle resuspension rates due to wind flow from a Teflon filter were also determined at the same time. The resuspension rates of particles by wind were found to be on the order of 10^-6 to 10^-5sec^-1. These particle resuspension fluxes are much smaller than those calculated by concentration profile. Other mechanisms, e.g. traffic-induced resuspension, are needed to be included in further study.     

Study of the Comminution Characteristics of Coal by Single Particle Breakage Test Device

Single-particle breakage tests of South Blackwater and Ensham coal from the Bowen Basin area in Queensland were conducted by a computer-monitored twin-pendulum device to measure the energy utilization pattern of the breakage particles. Three particle sizes (-16.0 + 13.2 mm, -13.2 + 11.2 mm, -11.2 + 9.5 mm) of each coal were tested by a pendulum device at five input energy levels to measure the specific comminution energy. When particles were tested at constant input energy, the variation of comminution energy between the same size broken particles of Ensham coal was minimal, because Ensham coal is a softer and higher friability coal, which absorbs more input energy than harder coal during breakage tests. For different particle sizes, the specific comminution energy increases linearly with the input energy and the fineness of the breakage products increases with the specific comminution energy.The size distribution graphs are curved but approach linearity in the finer region. At a constant input energy, the twin pendulum breakage product results show that the fineness of the products increases with decrease in particle size and South Blackwater coal produced finer products than the Ensham coal. The t-curves are the family of size distribution curves, which can describe the product size distribution of the breakage particles during single-particle breakage tests.     

PARTICLE SIZE ANALYSIS FOR OFLOXACIN, PREDNISOLONE ACETATE, AND AN OPHTHALMIC SUSPENSION CONTAINING THE OFLOXACIN/STEROID DRUG COMBINATION

Image analysis (LA), Photon Correlation Spectroscopy (PCS), and Single Particle Optical Sizing (SPOS) have been applied to the analysis of particle size for ofloxacin, prednisolone acetate and an ofloxacin/prednisolone acetate ophthalmic suspension. LA shows that ofloxacin particles suspended in mineral oil are on the order of 10 µor less. LA of prednisolone acetate in H₂O shows that the steroid particles are agglomerated and range in size from 20 to 50 µ. SPOS is used to verify LA results for prednisolone acetate. LA of the ofloxacin/steroid balled milled suspension yields a particle size of ∼ 1 µ with a few particles on the order of 5 µ, PCS analysis of three batches of ball-milled ofloxacin/steroid suspension shows that increased ball-milling time increases the reproducibility of the mean diameter value as determined by PCS. It is also observed by PCS that the mean diameter of the steroid achieves a constant value with ball-milling from 11 to 14 days (1386.4 to 1383.4 nm). Extended ball-milling past the 14 day time point (18 days) appears to reduce sample inhomogeneity, thereby eliminating larger particulates with a subsequent reduction in the mean diameter to 1097.4 nm, Results for PCS analysis of the ball-milled ofloxacin/steroid suspension are verified by SPOS.     

Synthesis and Optical Characterization of CdS Nanowires by Chemical Route

Cadmium sulphide (CdS) nanostructured materials were synthesized by a wet chemical route without using any capping agent. X-ray diffraction pattern showed the typical interplanar spacings corresponding to the cubic phase of CdS. The peaks were identified to originate from (100), (220), and (311) planes of CdS, respectively. Transmission electron microscopy studies showed the nanowire formation with an average length 1-5 μm and the average diameter was in the range 25-30 nm. UV-visible transmission spectrum of the films deposited on glass substrates was recorded in the region 300-800 nm at room temperature. Transmission spectrum showed 75%-90% transmittance in the visible region. The values of direct band gap were obtained as 3.07 eV and 3.00, 2.89, 2.86 eV for unannealed and annealed at 100°C, 150°C, 200°C films, respectively. It showed the blue shift with respect to the bulk value. Room temperature photoluminescence was also measured, which showed a broad band lying in the range 510-625 nm.     

Study of the moderate-temperature growth process of optical quality synthetic diamond films on quartz substrates

Growth of undoped and boron-doped diamond films on quartz substrates at moderate temperature of 500 °C by microwave plasma chemical vapor deposition method was studied in terms of growth rate, surface roughness and optical transmittance. Similar density of diamond seed particles on quartz surfaces seeded mechanically before the deposition process and diamond grains within diamond films grown on those substrates is observed. The growth rate is found similar to that reported for diamond deposited on silicon substrates in the same plasma deposition system, although with substantially higher activation energy. Furthermore, increased level of dopant concentration in the gas mixture resulted in a decrease of the growth rate, while a gradual reduction of the surface roughness occurred at high dopant levels. Overall, the highest measured regular optical transmittance of the undoped diamond film on quartz was 45% at 1100 nm (including quartz absorption), whereas that of boron-doped diamond peaked 5% at 700 nm (tail absorption of boron centers).     

Effect of Erodent Particle Hardness on Velocity Exponent in Erosion of Steels and Cast Irons

This article reports the effect of hardness of erodent particles on velocity exponent of some weld deposited alloys. Three steels and two alloy cast irons were selected for the present investigation. The bulk hardness of the alloys was in the range of 300 to 800 HV, whereas erodnet particles were having hardness in the range of 400 to 1875 HV. Erosion tests were conducted with 125-150 µm cement clinker, 125-150 µm blast furnace sinter, 100-150 µm silica sand, and 125-150 µm alumina particles and at impingement angles of 30° and 90° and with impingement velocities in the range of 25 to 120 m sec^-1. The erosion rate showed power-law dependence on impingement velocity, E = kVⁿ, where kis a constant and nis the velocity exponent. The velocity exponents obtained in the present work were in the range of 1.91 to 2.52. The velocity exponent showed an increasing trend with increasing hardness of the alloys irrespective of the hardness of the erodent particles and the impingement angle. The velocity exponent increased with increasing hardness of erodent particles, irrespective of the impingement angle and hardness of the alloys. The velocity exponents obtained in the present work were rationalized with respect to erodent particle properties, material properties and erosion mechanisms.     

A NUMERICAL SIMULATION OF SWIRLING FLOW PNEUMATIC CONVEYING IN A HORIZONTAL PIPELINE

A numerical simulation for swirling and axial flow pneumatic conveying in a horizontal pipe was carried out with a Eulerian approach for the gas phase and a stochastic Lagrangian approach for particle phase, where particle-particle and particle-wall collisions were taken into consideration. The k-ε turbulence model is used to characterize the time and length scales of the gas-phase turbulence. Models are proposed for predicting the particle source and additional pressure loss. The numerical results are presented for polyethylene pellets of 3.1 mm diameter conveyed through a pipeline of 13 m in length with an inner diameter of 80 mm, solid mass flow rate was 0.084 kg/s, and gas velocity was varied from 10 m/s to 18 m/s. The particle flow patterns, the particle concentration and the particle velocity, and additional pressure loss were obtained. It is found that the particle velocity and concentration has almost same value along flow direction in swirling flow pneumatic conveying. The profile of particle concentration for swirling flow pneumatic conveying exhibits symmetric distribution towards the centerline and the higher particle concentration appears in neighbor of wall in the acceleration region. At downstream, the uniform profile of particle concentration is observed. The particle velocity profile, on the other hand, is uniform for both swirling and axial flow pneumatic conveying. A comparison of the calculations with the measured data shows a good agreement within an average error of less than 15 percent.     

PREDICTION OF PRESSURE DROP IN PNEUMATIC TRANSPORT SYSTEMS AT VARIOUS PIPE ORIENTATIONS USING AN EMPIRICAL CORRELATION FOR THE PARTICLE VELOCITY

A new empirical correlation for the particle velocity which incorporates the angle of inclination is proposed here. This correlation coupled with the expression for the solids friction factor obtained from the force balance on the particle was used to predict the pressure drops in the 0.0266 m and 0.0504 m systems held at various angles of inclination. Particles used in these systems included glass particles of 67, 450, and 900 µm weight mean diameter. The existence of minimum points in the predicted pressure drop curves as a function of gas velocity was corroborated by these two expressions.     

Recent Innovative Methods for Characterization of Small Particles

Characterization of submicrometer and subnanometer size particles is essential to understanding their interactions and to developing micro- and nanostructures. Because of this importance, many advances and new developments have been made in characterization techniques for particles in this size range. Examples include neutron holography, in situ wet transmission electron microscopy, ultrafast microscopy, magnetic resonance force microscopy for imaging a single electron spin, and high-resolution X-ray crystallography of noncrystalline structures. It is now possible to completely characterize very small particles from 0.1 nm to 100 nm size. Selected recent developments are discussed.     

Motion of Large Particles in a Horizontal Pneumatic Pipe

The horizontal pneumatic transport of large particles with particle to pipe diameter ratio of 0.6 and particle densities of 928 kg/m³ and 2193 kg/m³ was examined experimentally and numerically. The pipe diameter and length were 10 mm and 8.8 m, respectively. The mean air velocity was between 14.2 m/s and 23.0 m/s and the number feed rate of particle was almost constant at seven per second. In this study, the method of characteristics was used for the simulation of gas flow, which considered not only the particle-particle collisions but also the particle-wall collisions. It is found that particle transport is possible even when the mean air velocity is smaller than the terminal settling velocity of particle's and that the arrival time intervals at the downstream section are not always uniform although the particles are fed uniformly. Furthermore, the velocity difference between different density particles becomes small as the mean air velocity decreases, because the particle velocities become uniform due to particle-particle collisions, and the ratio of particle velocity to the mean air velocity is almost independent of air velocity. In addition, it is shown that the particle-wall collision at the pipe joint due to pipeline misalignment can be one of the sources of bouncing motion of particles as shown by simulation results.