Characterizing contamination inspection capabilities using programmed defect test reticles

Physical vapor deposition (PVD) aluminum films present unique challenges when detecting particulate defects with a Surface Scanning Inspection System (SSIS). Aluminum (Al) films 4500Å thick were deposited on 300mm particle grade bare Si wafers at two temperatures using a Novellus Systems INOVA® NExT,.. Film surface roughness and morphology measurements were performed using a Veeco Vx310® atomic force microscope (AFM). AFM characterization found the high deposition temperature (TD) Al roughness (Root Mean Square 16.5 nm) to be five-times rougher than the low-TD Al roughness (rms 3.7 nm). High-TD Al had grooves at the grain boundaries that were measured to be 20 to 80 nm deep. Scanning electron microscopy (SEM) examination, with a Hitachi RS6000 defect review SEM, confirmed the presence of pronounced grain grooves. SEM images established that the low-TD filmed wafers have fine grains (0.1 to 0.3 um diameter) and the high-TD film wafers have fifty-times larger equiaxed plateletshape grains (5 to 15 um diameter). Calibrated Poly-Styrene Latex (PSL) spheres ranging in size from 90 nm to 1 μm were deposited in circular patterns on the wafers using an aerosol deposition chamber. PSL sphere depositions at each spot were controlled to yield 2000 to 5000 counts. A Hitachi LS9100® dark field full wafer SSIS was used to experimentally determine the relationship of the PSL sphere scattered light intensity with S-polarized light, a measure of scattering cross-section, with respect to the calibrated PSL sphere diameter. Comparison of the SSIS scattered light versus PSL spot size calibration curves shows two distinct differences. Scattering cross-section (intensity) of the PSL spheres increased on the low-TD Al film with smooth surface roughness and the low-TD Al film defect detection sensitivity was 126 nm compared to 200 nm for the rougher high- TD Al film. This can be explained by the higher signal to noise attributed to the smooth low-TD Al. Dark field defect detection on surface scanning inspection systems is used to rapidly measure defectivity data. The user generates a calibration curve on the SSIS to plot the intensity of the light scattering derived at each National Institute of Standards and Technology (NIST) certified PSL deposition spot that was deposited. It is not uncommon for the end user to embark upon the time consuming process of attempting to "push" the maximal SSIS film specific sensitivity curve beyond the optical performance capability of the SSIS. Bidirectional reflectance distribution function (BRDF) light scattering modeling was utilized as a means of determining the most appropriate polarity prior to the SSIS recipe creation process. The modeling utilized the Al refractive index (n) and extinction coefficient (k) and the SSIS detector angles and laser wavelength. The modeling results allowed predetermination of the maximal sensitivity for each different Al thickness and eliminate unnecessary recipe modification trial-and-error in search of the SSIS maximal sensitivity. The modeling accurately forecasted the optimal polarization and maximal sensitivity of the SSIS recipe, which, by avoiding a trial and error approach, can result in a substantial savings in time and resources.

We report results of a systematic experimental study of interactions between charged polystyrene (PS) latex spheres at a water-air interface. Optical observations of stable bonded particle clusters and formation of circular chainlike structures at the interface demonstrate that the interaction potential is of dipole origin. Atomic force microscopy (AFM) is used to examine the distribution of charge groups on the colloidal surface. AFM phase images show patchy domains of size approximately 100 nm on the particle surface, indicating that the surface charge distribution of the PS spheres is not uniform, as is commonly believed. Such patchy charges can introduce fluctuating in-plane dipoles, leading to an attraction at short interparticle separations. A theoretical analysis is given to explain the mechanism for attractions between like-charged particles at the interface.

In order to investigate the effect of surface morphology on the sensing performance in detecting sulfur dioxide, two different types polystyrene, polystyrene latex spheres (PLS) and polystyrene film (PSF), are synthesized by using an emulsion polymerization, which are coated on quartz crystal microbalance (QCM) surfaces. It is found that the sensing performance is strongly dependent on the morphology of polymer materials. The adsorption capacity of the synthesized PLS is higher than that of the PSF. In addition, the response of the PLS coated QCM to SO2 is approximately 6 times faster than that of the PSF coated one. The adsorption characteristics of SO2 on the PLS coated QCM are also evaluated in terms of temperature and concentration. These results show that the PLS can be used as SO2 sensor materials due to their high sensitivity and quick response.

Distinguishing false counts caused by surface microroughness and haze when measuring particles below 0.1 μm has become a significant concern for ultralarge scale integrated (ULSI) product yield. Initial results are presented from an industry‐wide, cross‐functional, SEMATECH task force exploring this issue by investigating both measurement capability and alternative detector strategies for laser surface scanners. Polystyrene latex (PSL) spheres and real‐world particles deposited under controlled conditions on 150 mm polished silicon wafers are used. Particle counting measurements taken at several facilities using the same model of laser surface scanner and the same instrument parameter settings are compared. Silicon particles are consistently sized incorrectly when the laser surface scanner is calibrated using standardized procedures utilizing PSL spheres. Measurements from similarly prepared samples using angle‐resolved scattering (ARS) to obtain scattering cross section as a function of angle are favorably compared to a numerical light scattering model. Modeling allows the comparison of data from instruments which measure ARS from individual particles as well as those which measure ARS from multiple identical particles. The improved signal‐to‐noise ratio of the multiple particle technique allows study of particle scattering at sizes below typical commercial equipment detection limits. A novel haze surface is described which can be used to verify the modeling of both research and commercial light scattering instruments.

The Wide-range Particle Spectrometer (WPS™) is a recently introduced commercial instrument with the unique capability to measure size distributions of aerosols from 0.01 to 10 µm in diameter. The instrument includes a Scanning Mobility Spectrometer (SMS) comprised of a Differential Mobility Analyzer (DMA) and a Condensation Particle Counter (CPC) for particle measurement from 0.01 to 0.5 µm and a Laser Particle Spectrometer (LPS) for measurement in the ~0.4 to 10 µm range. These components are small enough to fit into a small portable cabinet (~26 kg) with all accompanying control hardware and electronics. No external pumps are required and power consumption is only about 150 W. The DMA is calibrated with Standard Reference Materials (SRM) from the U.S. National Institute of Standards and Technology (NIST), including SRM 1691 and SRM 1963a. These are uniform size polystyrene latex (PSL) spheres available from NIST with mean diameters of 0.269 µm and 0.1018 µm respectively. The CPC has a dual reservoir design to prevent the working fluid from being contaminated by water due to moisture condensation in the condenser. The LPS is calibrated with four NIST-traceable PSL sphere sizes. Calibration curves are generated not only for PSL (real refractive index of 1.585), but also for discrete values real refractive index ranging from 1.30 to 1.60. This procedure allows the user to select the most appropriate curve for determination of the light-scattering-equivalent sphere size that takes into account the effect due to refractive index of real aerosols. The LPS has a wide-angle collection optics design to produce a monotonic response curve for routine measurement in the field.

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Actin plays a major role in the structural integrity and motility of cells as well as in the intracellular dynamics of other macromolecules. Photon Correlation Spectroscopy (PCS) has been used to monitor the diffusion of polystyrene latex spheres (PLS) of different sizes within in vitro polymerized actin solutions under a variety of conditions. Specific actin-binding proteins were added to regulate the actin filament lengths as well as to cross-link filaments together. PCS measurements give information on the mobility of PLS over probing distances equal to the inverse scattering vector magnitude which range from 40 to 420 nm for the data. Results allow estimation of the mean pore sizes within the actin networks as a function of both actin concentration (0.4 - 5 mg/ml) and the presence of actin-binding proteins. Probe diffusion coefficients were measured for PLS samples in length-regulated actin networks at a fixed actin concentration, c (0.65 mg/ml) as c*, the semi-dilute overlap concentration, was varied. There was a change in the dependence on c/c* near the value 1 at which the filaments just overlap. Quasi-static low-angle diffraction patterns from actin solutions have been detected and quantified using a CCD video camera/frame grabber system to study the spatial and slow temporal variations in the intensity patterns.

The diffusion of monodisperse polystyrene latex spheres (PLS) in column-purified 0.65 mg/mL actin solutions, polymerized with 100 mM KCl in the absence and presence of a cross-linker, actin binding protein (ABP), has been studied using dynamic light scattering. Measurements over a wide range of scattering angles from 90 degrees to 8 degrees, corresponding to inverse scattering vector probing distances of about 40-400 nm, respectively, give a measure of both the fraction of PLS mobile over the probing distance (from the normalized time autocorrelation function amplitude) and the average diffusion coefficient of the mobile PLS. Both 100- and 500-nm diameter PLS are fully mobile in polymerized actin solutions over distances of less than 100 nm, as reported previously (Newman, J., Schick, K. S. & Gukelberger, G. Biophys. J. 53, 573a, and Newman, J., Mroczka, N. & Schick, K. L. Biopolymers, 28, 655-666). At increasing probing distances, or when ABP is added at molar ratios of 1:750 or 1:150, greater fractions of the PLS are immobilized, up to almost 99% at the conditions of a 400-nm probing distance with 500-nm probes and at a ratio of 1:150 added ABP to actin. The degree of immobilization correlated well with the amount of added ABP, the size of the PLS, and the probing distance. At increasing probe distances, as the degree of immobilization increases, the remaining mobile fraction of PLS has an increasing average diffusion coefficient. These results suggest a range of pore sizes in the actin gels with a mean size of a few hundred nanometers.

Alternating nanoparticle/polymer composite multilayers have been assembled on submicrometer-sized polystyrene (PS) latex spheres by the sequential adsorption of silica nanoparticles (SiO2) and poly(diallyldimethylammonium chloride) (PDADMAC) from aqueous solutions. Growth of the composite multilayers on the PS latices was followed by electrophoretic mobility (EPM), single-particle light scattering (SPLS), scanning (SEM) and transmission (TEM) electron microscopy, and atomic force microscopy (AFM). EPM measurements revealed a reversal in ζ-potential with deposition of each SiO2 or PDADMAC layer; negative and positive values were observed for SiO2 and PDADMAC depositions, respectively. SPLS experiments showed a linear increase in SiO2/PDADMAC multilayer film thickness with deposition layer number; approximately one monolayer of nanoparticles was deposited with each SiO2 adsorption step. Both SEM and TEM provided direct evidence of stepwise multilayer growth, and AFM revealed a uniform covering of the PS col...

We conducted a detailed evaluation of a method for measuring the mass concentrations and size distributions of black carbon (BC) particles in rainwater and snow. The method uses an ultrasonic nebulizer (USN) and a single particle soot photometer (SP2). The USN disperses sample water into micron-size droplets at a constant rate and then dries them to release BC particles into the air. The masses of individual BC particles are measured by the SP2, using the laser-induced incandescence technique. The loss of BC particles during the extraction from liquid water to air depends on their sizes. We determined the size-dependent extraction efficiency using polystyrene latex (PSL) spheres with 12 different diameters between 107 and 1025 nm. The PSL concentrations in water were measured by the light extinction at 532 nm. The extraction efficiency of the USN showed a broad maximum of about 10% in the diameter range 200–500 nm and decreased substantially at larger sizes. The accuracy and reproducibility of the measure...

We compared the performance of a low-cost (∼$500), compact optical particle counter (OPC, OPC-N2, Alphasense) to another OPC (PAS-1.108, Grimm Technologies) and reference instruments. We measured the detection efficiency of the OPCs by size from 0.5 to 5 μm for monodispersed, polystyrene latex (PSL) spheres. We then compared number and mass concentrations measured with the OPCs to those measured with reference instruments for three aerosols: salt, welding fume and Arizona road dust. The OPC-N2 detection efficiency for monodispersed was similar to the PAS-1.108 for particles larger than 0.8 μm (minimum of 79% at 1 μm and maximum of 101% at 3 μm). For 0.5-μm particles, the detection efficiency of OPCN2 was underestimated at 78%, whereas PAS-1.108 overestimated concentrations by 183%. The mass concentrations from the OPCs were linear (r ≥ 0.97) with those from the reference instruments for all aerosols, although the slope and intercept were different. The mass concentrations were overestimated for dust (OPC-N2, slope = 1.6; PAS-1.108, slope = 2.7) and underestimated for welding fume (OPC-N2, slope = 0.05; PAS-1.108, slope = 0.4). The coefficient of variation (CV, precision) for OPC-N2 for all experiments was between 4.2% and 16%. These findings suggest that, given site-specific calibrations, the OPC-N2 can provide number and mass concentrations similar to the PAS-1.108 for particles larger than 1 μm.

Preparation of Three-Dimensionally Ordered Macroporous Composite Bi<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> and Its Photocatalytic Degradation of Crystal Violet under Multiple Modes

The aerodynamic behavior of aggregates consisting of uniform polystyrene latex (PSL) spheres and unaggregated cuboidal Natrojarosite particles in a TSI aerodynamic particle sizer (Model APS33B) has been studied. In initial tests, monodisperse PSL micro-spheres ranging from 0.3 to 7 μm in geometric diameter were generated from aqueous suspensions using a Lovelace nebulizer. APS33B responses for these uniform-sized particles showed multiple peaks. The major (primary) peak, which resulted from the smallest particle, corresponded to the unaggregated single spheres (singlets); the second, third, and fourth peaks were identified as doublets, triangular triplets, and tetrahedral quadruplets, respectively. Both doublets and triplets moved with their long axes in perpendicular (maximum drag) orientation to the flow direction in the APS33B. In contrast, the tetrahedral particles were isometric and had the same dynamic shape factor (drag resistance) for all three primary orientations. The particle Reynolds numbers (Re p) for these particles were calculated and ranged from 0.2 to 30 in the sensing volume of the APS33B detector (i.e., ultra-Stokesian conditions). Ultra-Stokesian drag forces for all three types of aggregates were, therefore, estimated and expressed as a function of an empirical factor (1 + aRe b p) to the Stokesian drag force. The ultra-Stokesian drag of a Natrojarosite particle was measured in the range 20 Re p < 50 and could be described with a similar expression. This approach facilitates the study of the dynamic behavior of nonspherical particles and yields new information about the characteristics of drag forces in the ultra-Stokesian regime

This work provides examples of some of the imaging capabilities of environmental scanning electron microscopy applied to easily charged samples relevant to particle analysis. Environmental SEM (also referred to as high pressure or low vacuum SEM) can address uncoated samples that are known to be difficult to image. Most of these specimens are difficult to image by conventional SEM even when coated with a conductive layer. Another area where environmental SEM is particularly applicable is for specimens not compatible with high vacuum, such as volatile specimens. Samples from which images were obtained that otherwise may not have been possible by conventional methods included fly ash particles on an oiled plastic membrane impactor substrate, a one micrometer diameter fiber mounted on the end of a wire, uranium oxide particles embedded in oil-bearing cellulose nitrate, teflon and polycarbonate filter materials with collected air particulate matter, polystyrene latex spheres on cellulosic filter paper, polystyrene latex spheres "loosely" sitting on a glass slide, and subsurface tracks in an etched nuclear track-etch detector. Surface charging problems experienced in high vacuum SEMs are virtually eliminated in the low vacuum SEM, extending imaging capabilities to samples previously difficult to use or incompatible with conventional methods.

Shifts in polystyrene particle surface charge upon adsorption of the Pluronic F108 surfactant