DEPOSITION OF SUBMICRON AEROSOL PARTICLES DURING INTEGRATED CIRCUIT MANUFACTURING: THEORY

ABSTRACT

Submicron (≤1μm) particle contamination can produce unacceptably low yields in the manufacture of integrated circuits. Calculations were made to predict deposition velocities of 0·01-lOμm particles, incorporating gravitational, dlffusional, and electrostatic effects. The results were summarized in equations that correlate non-dimensional deposition (Sherwood number) with convective-diffusion (Peclet number) and with electrostatics (Boltzmann and Fuchs charge distributions). These equations were used In conjunction with particle size distributions to predict particle deposition. In a companion paper |25| the predictions were shown to compare well with limited experimental data. To reduce deposition product surfaces should not be electrically charged and, where possible, these surfaces should be at higher temperatures than the ambient gas. For quality control purposes, the deposition flux predictions could serve to link the specifications of gas cleanliness with the specifications of surface cleanliness.     

Relationship Between Particle Size and Dissolution Rate of Bulk Powders and Sieving Characterized Fractions of two Qualities of Orthoboric Acid

We have carried out a study of the particle size distribution and aqueous dissolution rate of two commercially available qualities of orthoboric acid, labeled “crystal” (ABC) and “powder” (ABP). In a previous work, we have shown that the two commercial qualities of orthoboric acid chosen as model compound (“powder” and “crystal”) are related to the same crystal network in spite of their dvferent names. However, these two qualities have very different size particle distributions, as previously determined by sieving and confirmed by the present laser light scattering study. Dissolution testing is performed under sink conditions and show that the bulk ABC quality dissolves far more rapidly that the bulk ABP quality, For each quality, dissolution rates of four sieved particle size fractions (0-90 μm; 90-125 μm; 125-180 μm; 180-250 μm) were compared. Concerning the ABC quality, comparisons were also done with three other particles size fractions: 250-355 μm, 355-500 μm, and 500-710 μm. This study used the dQ/dt versus t profile. Dissolution profiles of the fractions enclosing particles with a size superior to 125 μm are very close. On the other hand, fractions enclosing particles with a size smaller than 90 μm present a different profile and a slower rate of dissolution.     

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.     

Micromeritic Properties of Nitrofurantoin Microcapsules

In our previous study, we have prepared nitrofurantoin microcapsules using carboxymethylcellulose (CMC) and aluminium sulphate by a coacervation technique. In the present study, the micromeritics of these microcapsules were investigated in terms of standardization of the crude materials employed, the microcapsules product and the dosage forms prepared from these microcapsules. The microcapsules were prepared with a 1:1 core: wall ratio and sieved into three particle sizes. Both the micromeritic properties of the pure drug and the polymer were studied by determining their bulk volume and weight, tapping volume and weight, fluidity, angle of repose, weight deviation, particle size distribution, density and porosity, The particle size range went from approximately 250μm to 3000μm with a peak between 900μm and 1350μm. The results indicate that the flowability and the particle size of the resultant microcapsules were much increased compared with the raw materials. As the microcapsule size increases the porosity also increases but the density decreases.

The weight deviation of the microcapsules first sieved then filled into hard gelatin capsules was carried on according to the USP XXII. Hard gelatin capsule size was found by Lindenwald-Tawashi nomogram as number 3. The geometric mean diameters and the geometric standard deviation of microcapsules were calculated as 750 pm for number distribution and 1275μm for weight distribution and 1.52 for number and weight distribution respectively.

In addition to evaluate whether some kind of glidant will be needed during tableting of microcapsules and filling of them into hard gelatines, “Hausner ratio and consolidation indexes” were calculated.

The results obtained suggest that sustained release dosage forms of nitrofirantoin can be prepared from the obtained microcapsules as far as the micromeritic properties is concerned and the microencapsulation changed the micromeritic properties of the crude materials significantly.     

Size Distribution Characteristics of Particulates from Glass and Plastic Lvp's

An automated microscopic system was used to detect particulates from four different large-volume parenteral solutions in glass and plastic containers. Solutions from glass containers were found to contain a significantly greater number of particles; however, the mean diameter of particles from plastic containers was greater. Characteristics of the size distribution of particles from glass and plastic containers were also different. An overall (particle size 5-50μ) cleanliness factor was calculated. Cleanliness factors for glass containers were larger by 55.5% to 264.1% than those for plastic.     

Transmission electron microscopy characterisation of metalorganic chemical vapour deposition grown GaN layers

GaN layers grown onto sapphire substrates by metalorganic chemical vapour deposition were characterised by optical microscopy, transmission electron microscopy and atomic force microscopy measurements. Mirror like surfaces were obtained at certain growth conditions despite the hexagonal based pyramids found on the growth surface. The typical pyramids have a base diameter of 20–30 μm and height of about 1.5–3 μm. The GaN layers are of the wurtzite type and epitaxially oriented to the sapphire substrate. Beside the threading dislocations, hexagonal rods of GaN surrounded by inversion domain boundaries are observed. An AlN layer has been formed at the interface region during the nitridation process of sapphire.     

Effect of Particle Size on Deformation and Compaction Characteristics of Ascorbic acid and Potassium Chloride: Neat and Granulated Drug

Deformation and compaction characteristics of two soluble drugs, ascorbic acid and potassium chloride, were investigated. Five different particle size fractions of ascorbic acid with mean particle size (d₅₀) ranging from 30-300μm and four different particle size fractions of potassium chloride with d₅₀ ranging from 20-400 μm were selected in the study. The compaction behavior of the drug substances as neat drugs or as granulated drugs were evaluated on both a Carver press and an instrumented single-punch tablet press. The results clearly show that mean particle size of the drug substances plays an important role in their compactibility. Intrinsic compactibility of both drug substances was slightly improved with increased particle size. Granulations of the drugs with polyvinyl pyrrolidone significantly improved their compactibility. However, this effect was more pronounced in the drug substance with finer particle size. The Heckel plots indicate that deformation characteristics of both granulated drugs were related to their original mean particle sizes. The granulations prepared from the coarser particle size (d₅₀ 250 μm to 400 μm) underwent two stages of deformation, so-called “brittle fracture” and “plastic deformation”. While the granulations prepared from the finer particle size predoninantly underwent “plastic deformation”. The results indicated that the plastic deformation of both granulated drugs was progressively enhanced whilst fragmentation of particles was correspondingly reduced as the particle size of the drugs was decreased. Scanning electron photomicrographs indicated that the granulation process changed the surface morphology of the drug particles imparting more “microirregularities” or “defects”, thereby providing greater “interparticulate bonding” as compared with the neat drugs. Optimum particle size range of ascorbic acid and potassium chloride for satisfactory compactibility was found to be 30-40 μm and 20-40 μm, respectively. The present study demonstrates the importance of selecting the appropriate particle size of drug for the development of tablet dosage forms.     

Computational simulation of thermally sprayed WC–Co powder

WC–Co cemented carbides are a class of hard composite materials of great technological importance. They are widely used as tool materials in a large variety of applications that have high demands on hardness and toughness, including mining, turning, cutting and milling. The HVOF (high velocity oxygen fuel) technology has been very successful in spraying wear resistant WC–Co coatings with higher density, superior bond strengths and less decarburization than many other thermal spray processes, attributed mainly to its high particle impact velocities and relatively low peak particle temperatures. The degree of decomposition and bond strength is directly related to relevant particle parameters such as velocity, temperature and state of melting or solidification. These are consecutively related to process parameters such as powder particle size distribution, carrier gas flow rate, and fuel type employed. To obtain detailed particle data important for thermal spraying, mathematical models are developed in the present paper to predict the particle dynamic behavior in a liquid fuelled HVOF thermal spray gun. The particle transport equations are coupled with the three-dimensional, chemically reacting, turbulent gas flow, and solved in a Lagrangian manner. The melting and solidification within the particles as a result of heat exchange with the surrounding gas flow is solved numerically. The in-flight characteristics of WC–Co particles are studied and the effects of carrier gas parameters on particle behavior are examined. The results demonstrate that WC–Co particles smaller than 5 μm in diameter undergo melting and solidification prior to impact while most particles never reach liquid state during the HVOF thermal spraying. The flow rate of carrier gas has considerable influence on particle dynamics as well as deposition on substrate. At higher flow rate the powder particles are redirected further away from the substrate center, while smaller flow rate results in better heating, higher impact velocity and deposition closer to the substrate center.     

The Quantitative Evaluation of a Granulation Milling Process III. Prediction of Output Particle Size

Regression analysis was performed using comminution data from the previously presented Comil®G/aspirin granulation characterization study. Polynomial models were constructed using mill speed, output screen size and impeller shape as independent variables. The models were used to predict the mean particle size (µ_d) and geometric standard deviation (σ_d) of particle size distributions resulting from the comminution of aspirin using the Comil®G. The predictions were found to compare well with observed values.     

Development of a New Tablet Formulation of Theophylline: In Vitro and in Vivo Studies

The preparation of a new scored 250 mg theophylline tablet is described, for which effects of particle size of the active principle, aspects of granulation and changes in tabletting settings were investigated.

In vitro studies showed the dissolution rate from tablets prepared from theophylline of commercial quality (50 μm) or of selected particle size (30 μm) to be faster than that from tablets prepared from micronized theophylline (10 μm). In vivo studies in dog showed that only the tablet from theophylline of selected particle size has the same bioavailability as an aqueous solution.

The scale up study showed that the characteristics of the tablets, including dissolution rate, are independent of the formulation factors.     

Protecting aluminum alloy from particle-impact ignition with an Al2O3 film

Bare aluminum alloy is compared to soft-anodized aluminum alloy (oxide film thickness 5 μm, 10 μm, 20 μm, or 50 μm) for susceptibility to ignition by supersonic particle impact in pure oxygen. The particle diameter ranged from 1600 μm to 2000 μm, temperature ranged from 220 K to 672 K and oxygen pressure was 27.6 MPa. The event of ignition was recorded on video tape. The results of ignition frequency are reported as a Logistic Regression Model over the variable space. In addition, the impact process was simulated using the computer code ZEUS to identify ignition temperatures and ignition sites as well as to qualitatively describe the mechanism of protection offered by the soft-anodized oxide film. Significant improvement against particle-impact ignition was achieved through the use of the anodized oxide film.     

Preparation, Characterization and In-Vitro Release Kinetics of Salbutamol Sulphate Loaded Albumin Microspheres

Salbutamol sulphate loaded Bovine serum albumin microspheres were prepared by heat denaturation method. The effects of such preparation conditions as denaturation temperature, denaturation time, protein concentration and phase volume ratio on the extent of drug loading, size and size distribution and drug release were studied. An increase in protein concentration from 5% w/v to 15% w/v increased the mean particle size from 8.5 μm to 16.6 μm and decreased the drug loading from 46% w/w to 18% w/w. A decrease in the phase volume ratio substantially lowered mean particle size and size distribution. An increase in the severity of denaturaion conditions lowered both the drug incorporated and drug released. The kinetics of drug release from microspheres were compared to the theoretical models of Higuchi diffusional release and first order release. Both the models gave an adequate fit to the data. Scanning electron microscopy revealed that the dummy microspheres are spherical with smooth surfaces. As the drug-protein ratio increased, the microspheres exhibited rough surfaces showing the presence of drug crystals.     

THE PSEUDOHOMOGENEOUS FLOW APPROXIMATION FOR DISPERSED TWO-PHASE SYSTEMS

The unsuitabllity of a continuum model for turbulent flow of solid-liquid mixtures has been demonstrated by a number of experimental studies which employed industrial slurries and a wide range of pipe diameters. However effective particle sizes and slurry viscosities are difficult to define for such mixtures. Using spherical glass particles of median diameter 125 μm and 240 μm, vertical flow experiments have been conducted in a test pipeline 26.17 mm in diameter. These experiments confirm earlier sand flow measurements by showing that wall friction decreases as particle size increases, in the absence of Bagnold stress or Coulombic friction effects.

Using a turbulent flow simulation, and assuming a linear increase of solids concentration in a thin layer near the pipe wall, dimensionless excess wall frictional resistances have been calculated. These predictions are likely to be valid for fine particles which do not display Bagnold stress or Coulombic friction effects.

The turbulent flow simulations confirm the effects observed in the experiments. They show that the pseudohomogeneous flow assumption is not useful for pressure drop prediction with slurries of fine particles.     

Effects of constituent particle clusters on fatigue behavior of 2024-T3 aluminum alloy

Fatigue tests of 2024-T3 aluminum sheet were run to determine the effects of constituent particles and particle clusters on fatigue life for all three metallurgical planes. In addition, a model to account for crack coalescence within particle clusters was developed to determine if particle clusters can be more damaging than single particles as crack nucleation sites. On the LS and ST planes, cracks formed primarily at single particles or holes, indicating that coalescence was not an issue. On the LT plane, coalescence was observed when the particle clusters were aligned with the crack growth direction, and the life was reduced about 30%. The crack coalescence and growth model showed that varying the initial separation between two particles (potential cracks) causes at most about a 15–20% change in fatigue life over a separation range of 5 μm to 1200 μm for a pair of 50 μm² particles.     

Investigation of hypromellose particle size effects on drug release from sustained release hydrophilic matrix tablets

Selected combinations of six model drugs and four hypromellose (USP 2208) viscosity grades were studied utilizing direct compression and in vitro dissolution testing. Experimental HPMC samples with differing particle size distributions (coarse, fine, narrow, bimodal) were generated by sieving. For some formulations, the impact of HPMC particle size changes was characterized by faster drug release and an apparent shift in drug release mechanism when less than 50% of the HPMC passed through a 230 mesh (63 μm) screen. Within the ranges studied, drug release from other formulations appeared to be unaffected by HPMC particle size changes.     

Hypervelocity impact testing of micrometeorite capture cells in conjunction with a PVDF thin-film velocity/trajectory sensor and a simple plasma velocity detector

Five different small particle capture cell designs were evaluated for their ability to capture fragments and residue from 10–200 μm diameter glass projectiles and oblong olivine crystals impacting at 1–15 km/s in sufficient quantity for chemical and isotopic analyses. Aluminum multi-foils (0.1–100 μm thick with ≈10, 000 and 1800 μm spacing), foil covered germanium crystals, and 0.50 and 0.120 g/cm³ Aerogels, were positioned behind either multi-film (1.4–6.0 μm thick) polyvinylidene fluoride (PVDF) velocity/trajectory sensor devices of a simple wire-grid plasma velocity detector. All capture cells collected significant amounts of impactor debris behind the PVDF sensors from nominal 100 μm diameter glass projectiles and olivine crystals which struck the sensor at velocities up to 6.4 km/s. At velocities >8 km/s little or no debris penetrated the second PVDF film. Results were incolsive for velocities between 6.5 and 8 km/s. Plasma detector results showed identifiable impactor residue on Al foils for velocities up to 8.7 km/s and impact tracks with apparent debris imbedded in the Aerogels for velocities up to 12.7 km/s. Maximum foil penetration of glass spheres and olivine crystals were the same, but more particulate debris was associated with olivine crystal ipacts versus glass impacts. Foil spacing beyond one particle diameter had no effect on total penetration. Aerogels are identified as a capture cell media that warrants further investigation. The Al multi-foil capture cell with 100 μm net spacers is identified as the most effective of the other designs and offers the advantages of compact structure, low secondary ejecta from impacts, and easy recovery of impactor debris for analysis.     

Dynamic crack growth in particulate bimaterials having discrete and diffuse interfaces: Role of microstructure

Role of microstructure on interfacial crack growth in particulate bimaterials made of glass particle reinforced epoxy is examined experimentally. Two types of bimaterials, one with a discrete jump in mean filler particle size across the interface and the other with two intermixed particle sizes in the interfacial region, are studied. The choice of particle sizes used in bimaterials is based on a set of experiments in which particle size effects on fracture behavior of monolithic specimens with single particle size are established using optical interferometry and high-speed photography. A non-monotonic steady state stress intensity factor (K_Iss) variation with mean particle size is observed in the size range of 7–203 μm for 10% volume fraction. Among the selected particles sizes, 35 μm mean diameter is found to produce the highest K_Iss. Increasing or decreasing particle size results in measurable reduction in K_Iss of the composite. Based on this result, discrete and diffuse bimaterials made of 35 μm and 203 μm diameter filler particles are studied. The K_Iss of the diffuse interface with intermixed particle sizes is bounded by the ones for monolithic configurations with single size particles. Further, K_Iss appears to vary linearly with the volume fraction of particle size having lower K_Iss in monolithic configurations. On the contrary, in case of a microstructurally discrete interface, the measured K_Iss is same as the one for the weaker half of the bimaterial.     

Preparation of (Ti1−xAlx)N films from mixed alkoxide solutions by plasma CVD

(Ti_1−xAl_x)N films were prepared on a Si wafer at 700°C from toluene solution of alkoxides (titanium tetraetoxide and aluminum tri-butoxide) in an Ar/N₂/H₂ plasma by the thermal plasma chemical vapor deposition (CVD) method. The films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, electrical resistivity, and Vickers micro-hardness. Single phase TiN formed at an Al atomic fraction of 0–0.2, with a mixed TiN and AlN phase occurring up to 0.6 and single phase AlN forming above 0.8. The films had relatively sooth surfaces, 0.4 μm thick at an Al atomic fraction of 0.2, and thickened with increasing Al fraction. The atomic concentration of Ti, Al, N, O, and C determined from their respective XPS areas showed that the Ti and Al contents of the films changes with the solution composition in a complementary way. The impurities were about 10 at.% oxygen and carbon. The electrical resistivity was almost unchanged from the value of 10³ μΩ cm at 0–0.6 Al but then suddenly increased to 10⁴ μΩ cm at higher Al contents. The hardness showed a synergic maximum of about 20 GPa at an Al fraction of 0.6–0.8.     

Residual stress development in Pb(Zr,Ti)O3/ZrO2/SiO2 stacks for piezoelectric microactuators

The residual stress of multilayers in piezoelectric microelectromechanical systems structures influences their electromechanical properties and performance. This paper describes the development of residual stress in 1.6 μm Pb(Zr_0.52,Ti_0.48)O₃ (PZT)/0.3 μm ZrO₂/0.5 μm SiO₂ stacks for microactuator applications. The residual stresses were characterized by wafer curvature or load-deflection measurements. PZT and zirconia films were deposited on 4-in. (100) silicon wafers with 0.5 μm thick thermally grown SiO₂ by sol–gel processes. After the final film deposition, the obtained residual stress of PZT, ZrO₂, and SiO₂ were 100–150, 230–270, and − 147 MPa, respectively. The average stress in the stack was  80 MPa. These residual stresses are explained in terms of the thermal expansion mismatch between the layers and the substrate. Load-deflection measurements were conducted to evaluate localized residual stresses using released circular diaphragms. The load-deflection results were consistent with the average stress value from the wafer curvature measurements. It was found that more reasonable estimates of the stack stresses could be obtained when mid-point vertical deflection data below 6 μm were used, for diaphragms 0.8–1.375 mm in diameter.     

Nanostructure in a Ti alloy processed using a cryomilling technique

A nanocrystalline Ti alloy with a uniform distribution of grains was synthesized using cryogenic mechanical milling. The effects of cryomilling parameters, such as milling time and ball to powder ratio (BPR), on the particle size, grain size, chemistry, and structure of cryomilled Ti powders were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The experimental results show that nanocrystalline Ti powders with a grain size of about 20 nm can be prepared using the cryomilling technique. Compared to SPEX milling at room temperature, cryomilling led to lower contamination levels of oxygen, nitrogen, and iron in the cryomilled Ti powder. The average particle size initially increased from the original 55 μm to a maximum value of 125 μm after 2 h of milling, and then decreased to 44 μm after 8 h of milling. Both the average particle size and the grain size decreased as the BPR increased.