Particle Deposition on Semiconductor Wafers

The deposition of aerosol particles on semiconductor wafers in the typical manufacturing environment of the clean room has been calculated using the equations of convective diffusion and sedimentation. The result shows that the deposition velocity decreases with increasing particle size in the diffusion regime and increases with increasing particle size in the sedimentation regime, with a minimum deposition velocity occurring in the vicinity of 0.2 μm. The minimum deposition velocity varies from approximately 0.2 × 10^?3 to 0.7 × 10^?3 cm/s, depending on the size of the wafer, the airflow velocity, and whether the wafer is freestanding or placed on top of a workbench.     

Experimental Measurement and Numerical Study of Particle Deposition in Highly Idealized Mouth-Throat Models

Particle deposition in the human mouth-throat is an important factor in evaluating efficiency of drug delivered by inhalation devices, such as pMDIs or DPIs. Current USP standard impactor induction ports (which serve as an in vitro representative of the adult mouth-throat) underpredict in vivo mouth-throat deposition. However, preliminary experimental data in the prototype geometry of a highly idealized mouth-throat has indicated that it is a promising replacement for the USP mouth-throat (Zhang et al. 2004 Zhang, Y., Finlay, W. H. and Matida, E. A. 2004. Particle Deposition Measurements and Numerical Simulation in a Highly Idealized Mouth-Throat. J. Aerosol Sci., 35: 789–803. [CROSSREF][CSA][Crossref] , [Google Scholar]).

In this study, partial optimization design of the highly idealized mouth-throat was performed using computational fluid dynamics (CFD) simulations. The performance of six candidate highly idealized mouth-throat geometries, each with a straight tube inlet of inner diameter 17.3 mm, was evaluated experimentally by measuring monodisperse particle deposition efficiency. Gravimetry was used to determine particle deposition in these geometries. Monodisperse particles of di-2-ethylhexyl-sebecate (DEHS) oil with mass median diameters of 2.1–7.5 μm (GSD < 1.1) were used at two steady inhalation flow rates of 30 and 90 l/min. The results showed that, at the higher flow rate of 90 l/min, a mouth-throat with a bend region 8.5 mm in diameter and a curvature radius of 50 mm follows the in vivo average summarized by Stahlhofen et al. (1989) Stahlhofen, W., Rudolf, G. and James, A. C. 1989. Intercomparison of Experimental Regional Aerosol Deposition Data. J. Aerosol Med., 2(3): 285–308. [CSA][Crossref] , [Google Scholar] most closely. In contrast, at the lower flow rate of 30 l/min, the mouth-throat with a bend region 7.5 mm in diameter mimics the above in vivo curve but the in vivo-in vitro match is worse than for 90 l/min case. Enhanced particle deposition caused by a Reynolds number effect was observed in all geometries studied. Overall, an adequately designed highly idealized mouth-throat can largely reproduce in vivo mouth-throat deposition. For different flow rates, different key dimensions are required with the present highly idealized mouth-throats in order to adequately reproduce the in vivo average curve.     

环道法对蜡沉积规律实验研究

环道法能够测量原油温度、原油与沉积面之间的温差、冷却速率、时间、剪切速率、流量等因素对含蜡原油管道蜡沉积规律的影响,测量的因素较全面;且环道法比其他蜡沉积实验装置更接近实际含蜡原油管道。在一定的工况下,研究了使用环道法实验装置的蜡沉积实验。通过对油温、壁温和流量这3个影响蜡沉积的主要因素的控制,得出了不同工况下管道的蜡沉积规律。     

大气有害颗粒物室内自然沉降实验研究

大气有害颗粒物(PM)对人体有极大的危害,紧闭门窗可使颗粒物自沉降,从而实现空气洁净。为研究室内有害颗粒物自然沉降的净化效果,该研究采用激光离散式颗粒物传感器与数据采集系统,对自然条件下室内大气有害颗粒物自然沉降进行实验研究。通过实验发现:室内大气有害颗粒物在重度污染(粒径小于2.5μm的PM150μg/m~3)浓度下,有较明显的自然沉降速率,PM粒径2.5μm～10μm、1.0μm～2.5μm、0.3μm～1.0μm自然沉降速率分别为:1.76μg/(m~3·min)、0.67μg/(m~3·min)和0.51μg/(m~3·min),当颗粒物为中度与轻度污染浓度时(150μg/m~3),自然沉降速率随浓度降低逐渐放缓;当密闭室内存在人员时,会加快室内大气有害颗粒物下降速率;此外,不同粒径的大气有害颗粒在空气中的分布均匀状态不同,粒径越大在空气中分布越不均匀,粒径越小越均匀,其在空气中自然沉降的速率越低。     

Effect of Particle Deposition on Granular Aerosol Filtration: A Comparative Study of Methods in Evaluating and Interpreting Experimental Data

Three methods which can be applied to extract quantitative information on the effect of deposition on filter performance from effluent concentration and pressure drop data were developed. It was found that all three methods are capable of describing the deposition effect in terms of the amount of deposited particles. Furthermore, the method of extrapolation was found to give the most consistent, if not the most accurate, interpretation of experimental data.     

Computational Fluid Dynamic Predictions and Experimental Results for Particle Deposition in an Airway Model

An area identified as having a high priority by the National Research Council (NRC 1998) relating to health effects of exposure to urban particulate matter is the investigation of particle deposition patterns in potentially-susceptible subpopulations. A key task for risk assessment is development and refinement of mathematical models that predict local deposition patterns of inhaled particles in airways. Recently, computational fluid dynamic modeling (CFD) has provided the ability to predict local airflows and particle deposition patterns in various structures of the human respiratory tract. Although CFD results generally agree with available data from human studies, there is a need for experimental particle deposition investigations that provide more detailed comparisons with computed local patterns of particle deposition. Idealized 3-generation hollow tracheo-bronchial models based on the Weibel symmetric morphometry for airway lengths and diameters (generations 3-5) were constructed with physiologically-realistic bifurcations. Monodisperse fluorescent polystyrene latex particles (1 and 10 mu m aerodynamic diameter) were deposited in these models at a steady inspiratory flow of 7.5 L /min (equivalent to heavy exertion with a tracheal flow of 60 L /min). The models were opened and the locations of deposited particles were mapped using fluorescence microscopy. The particle deposition predictions using CFD for 10 mu m particles correlated well with those found experimentally. CFD predictions were not available for the 1 mu m diameter case, but the experimental results for such particles are presented.     

Particle Removal Efficiency and Damage Analysis on Silicon Wafers after Megasonic Cleaning in Solvents

The increasing complexity of semiconductor devices imposes challenging requirements on particle contamination and surface damage. To meet these requirements novel surface-cleaning processes are evaluated, which combine physical energy with organic solvents. In this work, the performance of megasonic cleaning with deionized water (DIW) and N-methylpyrrolidone (NMP) was evaluated in terms of particle removal efficiency (PRE) and damage analysis. The goal was to define an optimum process window where the PRE was maximum and the damage was minimum. Particle removal and damage analysis were performed on unpatterned silicon wafers and with patterned polysilicon lines, respectively, under identical sonic power and process parameters. A comparison between these two solvents reveals that at low sonic power the particle-cleaning performances in DIW and NMP are similar. At high sonic power, in both solvents a detailed analysis of the PRE and damage indicates a non-homogeneous trend over the surface of the wafer. More particularly, in DIW higher PRE and damage are noticed towards the edge of the wafer. In NMP, the opposite trend was observed. However, an equivalent performance was obtained at a lower sonic power in case of NMP compared to DIW. Further understanding of megasonic cleaning in solvents, and an optimization of the process parameters are the key to improve the performance of megasonic cleaning in organic solvents like NMP.     

Modeling Particle Deposition in Extrathoracic Airways

The extrathoracic (ET) airways filter, warm, and humidify the inspired air and provide olfactory function. These multiple functions are reflected in its complex anatomy and physiology. The ET airways form the first line of defense against inhaled pollutants, both gaseous as well as particulate. To accurately assess the risk posed by inhaled particulate matter to the lung, it is essential to understand the filtering efficiency of the ET airways. In this paper computational fluid dynamics is used to simulate the airflow patterns and the thermodynamics of the ET airways. We detail the procedure to develop a computer reconstruction of the ET airways and the computer model to simulate the flow variable. Using this information we compute the particle trajectories, for both hygroscopic and nonhygroscopic aerosols, and use this data to evaluate the particle deposition pattern in the ET airways. The model predicts high relative humidity conditions in the ET airways. The model also shows that the high relative humidity conditions are conducive for rapid growth of hygroscopic particles and dramatically alter the deposition characteristics of ambient (hygroscopic) aerosol.     

A Numerical Study of Spray Particle Deposition in a Human Nasal Cavity

Particle depositional studies from nasal sprays are important for efficient drug delivery. The main influences on deposition involve the nasal cavity geometry and the nasal spray device of which its parameters are controlled by the product design. It is known that larger particle sizes (? 10 μm) at a flow rate of 333 ml/s impact in the anterior portion of the nose, leaving a significant portion of the nasal cavity unexposed to the drugs. Studies have found correlations for the spray cone angles and particle sizes with deposition efficiencies. This study extends these ideas to incorporate other parameters such as the insertion angle of the nasal spray and the injected particle velocity to observe its effect on deposition. A numerical method utilizing a particle tracking procedure found that the most important parameter was the particle's Stokes number which affected all other parameters on the deposition efficiency.     

Selective Particle Deposition in Crossflow Filtration

Abstract

To study the mechanism of particle deposition in crossflow filtration, hydrodynamic forces exerted on a spherical particle touching the surface of filter medium are analyzed to derive the critical selective cut-diameter of the deposited particles under various crossflow velocities and filtration rates in a crossflow filtration system. Experimental data of turbulent crossflow filtration of dilute light calcium carbonate suspension agree with the prediction of this theory within 30% error under the crossflow velocity of from 0.57 to 1.14 m/s. Equations to estimate the characteristics of crossflow filtration, such as steady-state filtration rate and average specific resistance of cake, are also presented.     

Simulation of Three-Dimensional Particle Deposition Patterns in Human Lungs and Comparison with Experimental SPECT Data

To further validate a stochastic particle deposition model, three-dimensional deposition patterns predicted by that model were compared with corresponding spatial particle deposition data obtained from SPECT measurements. In the in vivo inhalation experiments, two different polydisperse aerosols with mass median aerodynamic diameters of 1.6 μ m and 6.8 μ m were inhaled by 12 test subjects, using different nebulizers. Predicted and measured deposition data were compared on three different levels: (1) total lung deposition, (2) deposition per hemispherical shell, and (3) deposition per airway generation. First, experimental and theoretical total lung deposition data showed good agreement for both the fine (65 ± 9% vs. 55 ± 21%) and the coarse aerosols (55 ± 8% vs. 46 ± 4%). Second, predicted deposition per hemispherical shell also corresponded well with the experimental data, both exhibiting small deposition fractions in the inner shells and a roughly quadratic increase in the outer shells. Third, fair agreement was observed for the deposition fractions per airway generation, both experimental data and modelling predictions exhibiting relatively small deposition fractions in central bronchial airway generations, followed by a steep increase in the peripheral respiratory airways. While the overall agreement between measured SPECT data and computed deposition fractions demonstrates that SPECT data can indeed be used for model validation, the current spatial resolution of the SPECT method allows only a limited validation of model predictions at the single airway generation level.     

模拟环道的蜡沉积实验研究

实验研究分析是一项十分重要且合理的科学研究方式,结蜡实验装置主要是模拟油品温度、管壁温度、油品流量等参数对蜡沉积的影响。着重介绍了一组以压差法为依据的室内环道仿真模拟装置,并以苏嵯原油为例来研究管道结蜡情况,通过得出的实验数据来分析其结蜡规律。     

Experimental Study of Particle Collection by Small Cyclones

A new set of experimental data on the particle collection characteristics of small cyclones is reported. The collection efficiency for particles ranging from 2 to 10 μm in diameter was measured systematically for nine cyclones at flow rates ranging from 8.8 to 18.4 L/min. Special emphasis was given to the effects of the exit tube size and of the cyclone body size on the particle collection efficiency. The size ratio of the exit tube to the cyclone body was varied from 0.24 to 0.80. The experimental results show that the stiffness of the particle collection cutoff with size does not change noticeably with a change in the cyclone body size while operation of a cyclone at a low flow rate can cause the particle collection characteristics to become less stiff. It was also found that the exit tube diameter influences the particle collection efficiency substantially, with results showing that as the exit tube size is decreased, the collection efficiency increases. A large cyclone body size increases the efficiency. However, when the cyclone body is increased excessively, the collection efficiency appears to decrease somewhat. The experimental data were compared with existing cyclone theories and Barth's (1956) theory was found to be in good agreement. Finally, the exit tube was found to affect substantially the pressure drop of cyclones. As the exit tube size increased, the pressure drop decreased. However, when the exit tube size was further increased until it approached the body size, the pressure drop increased again.     

Wind Tunnel Modeling of Small Particle Deposition

An inexpensive microsphere dispersion, deposition, and sampling system is described. This system was used to examine the transport and deposition of small particles (? 1 μm diameter) across the aerodynamic boundary layer which developed over a prototype deposition surface (smooth, flat, acrylic plate). Unit density, polystyrene latex microspheres (0.8 and 1.1 μm diameter) were deposited onto both oil-coated and dry, upper and lower surfaces. Observed deposition velocities were significantly larger than those reported in the literature, possibly because low relative humidities increased electrostatic charge on the experimental plate. The experimental results were greater than those predicted by a turbulent flow particle deposition model.     

Particle Deposition on Spheres by Inertial and Electrostatic Forces

The theoretical collision efficiency of a sphere is examined considering the simultaneous effects of inertial impaction and electrostatic attraction. The competition between these two mechanisms is discussed. Electrostatic attraction is found to be much more effective in terms of energy consumption than inertial impaction. Also the effects of the use of a more accurate non-Stokesian drag and interception are examined under typical industrial conditions. A well-defined experimental system was designed and constructed to investigate the combined effects of inertial impaction and electrostatic attraction on particle collection by spheres. The experimental results were compared with theoretical predictions with and without the non-Stokesian drag correction. Good agreement between experiment and the model with the non-Stokesian drag correction was obtained.     

光学玻璃上HFCVD法沉积金刚石膜的实验研究

采用热丝化学气相沉积(HFCVD)技术在石英玻璃上成功制备出高质量金刚石膜.采用表面三维轮廓仪和傅立叶红外光谱仪测试了不同工艺条件下金刚石薄膜的表面粗糙度和红外透射率,并分析了测试结果.结果表明所制备的金刚石膜表面平整,红外透射性能良好.     

Experimental Study on Time Features of Particle Motion in Rotating Drums

Rotating drums are widely used in pharmaceutical industry to coat tablets. The motion of the tablet particle is one of the most important factors affecting coating uniformity. The purpose of the research is to experimentally investigate two important time variables for the coating process, residence time and turnover time, and their dependence on operating parameters (rotation speed and filling degree of the drum). The average residence time was found to decrease with increasing rotation speed and filling degree. The average turnover time was observed to increase approximately linearly with the inverse of the drum speed, but was found to be independent of the filling degree. A dimensionless time variable, the fractional residence time, i.e., the residence time divided by the turnover time, was introduced. Analysis showed that the fractional residence time could be a good indicator of coating uniformity. Results of the present work provide useful information for theoretical modeling which may ultimately serve as a tool for coating optimization.     

Deposition and Sintering of Particle Films on a Rigid Substrate

Experimental techniques for the deposition and sintering of ceramic particle films on a rigid substrate have been investigated. Three representative systems (SiO₂, ZnO-Bi₂O₃, and Al₂O₃) were chosen to determine the validity of the conceptual processing model. Crack-free, sintered films 1 to 50 μm thick were produced using single or multiple deposition/sintering cycles.     

Numerical Study of Particle Deposition in Bends of a Circular Cross-Section-Laminar Flow Regime

Particle deposition in a 90° bend has been studied numerically using a realistic three-dimensional developing flow field. In addition to the Stokes number as the impaction parameter, both the curvature ratio and the Dean number have been found to have considerable effects on the deposition efficiency. At a fixed Stokes number, the deposition efficiency increases with an increasing Dean number and a decreasing curvature ratio. The inlet velocity profile also influences the deposition efficiency. In the case of a parabolic velocity profile, the deposition efficiency is always higher than that of a uniform profile. These increases in deposition efficiency are due to the increase of secondary flow strength and the increased skewness of the axial velocity profile toward the outside of the bend.     

Particle Deposition in Cyclic Bifurcating Tube Flow

Deposition efficiency (DE) of aerosol particles in a bifurcating tube was determined experimentally with cyclic flow conditions at a frequency of 16, 30, and 50 cycles/min. Two bifurcation tube models with identical dimensions but different branching angles (θ = 30° and 45°) were used. Monodispersed oleic acid droplets (3, 5, and 7 μm in diameter) tagged with uranine were used as test aerosols and sampled through the model tube at a mean Reynolds number (Re) of 679–5548. Stokes number (Stk) ranged between 0.028 and 0.25. The model tube was washed section by section with deionized water and the fluorescence content in the washed solution was used to determine deposition efficiency. DE increased monotonically with increasing Stk at Re < ～ 2000. However, at higher values of Re, Stk failed to unify DE. There was no significant difference in DE between θ = 30° and 45° and among different cyclic frequencies used. However, DE with cyclic flows was 80–200% higher than those obtained with constant flows. The implications of the results were also discussed.