Heru Setyawan

Visualization and numerical simulation of fine particle transport in a low-pressure parallel plate chemical vapor deposition reactor

Abstract The behavior of fine particles in a low-pressure parallel plate chemical vapor deposition reactor was investigated by constructing a system that permits particle motion in the reactor to be visualized. The test spherical silica aerosol particles, which were 1.0 μm in diameter and dispersed in argon gas, were fed into the reactor from the outside and particle motion was detected by a laser light scattering method. The effect of operating conditions, such as pressure and temperature, on particle transport in the reactor was investigated. The pressure was varied from 2.0 to 4.0 Torr and the wafer-substrate plate temperature was varied over the range of 25°C to 300°C. A three-dimensional numerical simulation was performed using the commercially available computational fluid dynamics code Fluent. A detailed configuration of the reactor, including the showerhead structure was considered when investigating this mechanism. It is found, both experimentally and by numerical simulation that, when the wafer-substrate plate is not heated, the effect of pressure on particle trajectory in the space between plates cannot be observed. However, at elevated temperature, i.e. when the wafer-substrate plate is heated, the particle trajectory is apparently influenced by pressure. In addition, the effect of thermophoresis, as the result of a temperature gradient by heating of the wafer-substrate plate is very pronounced for gas pressures of both 2.0 and 4.0 Torr . The experimentally observed phenomena were satisfactorily reproduced by simulation.

Effect of Particle Size on Simulation of Three-Dimensional Solid Dispersion in Stirred Tank

This work concerns the effect of particle size on three-dimensional solid dispersion in a baffled tank stirred with a disc turbine. The system studied consists of a cylindrical flat bottom four-baffled tank, 30 cm in diameter, with a six-blade disc turbine impeller, 10 cm in diameter, filled with water. Baffle width is 0.1-tank diameter and impeller clearance from tank bottom is 0.3-tank diameter. The height of liquid level in the tank is equal to tank diameter. The density of solid particle used is 2360 kg m −3 and the diameters are 87 μm, 50 μm and l0μm. Average solid concentration in the tank is 5% and 20% by volume. The impeller rotation speed is 13.3rps. In this work the three-dimensional solid concentration distribution was predicted using the Algebraic Slip Mixture model (ASM model) under FLUENT 1 5.1 facility. Standard k-ɛ turbulent model is used to model fluid flow field in the tank, and swirling radial jet model (SRJ model) approximates the velocity profile at the impeller tip. The simulation results are presented as concentration contour on r-z plane and r-θ plane in several positions in the tank for different average solid concentration and particle sizes. The solid concentration contour for 87 μm diameter solid and 5% average concentration shows that there is still a rather high solid concentration in the centre of the tank bottom, while in the liquid surface around the shaft the solid concentration is very low. This indicates the accumulation of solid particles in the centre of the tank bottom. For the other particle sizes the pattern of solid concentration distribution is similar. Below the impeller region the solid concentration near to the shaft is higher than the concentration far from the shaft. However, in the above impeller region the solid concentration near to the shaft is lower than the concentration far from the shaft. The distribution of the smaller particles is more uniform than the larger particles. Under the same rotation speed of 13.3 rps the distribution of l0 μ mon particles is almost uniform. The simulation result was verified using experimental data 2 . The simulation result agreed very well with experimental data up to average solid concentration, 20% by volume.

An experimental and theoretical investigation of rarefied gas flow through circular tube of finite length

Abstract The conductance of nitrogen gas through circular tube of finite length was measured in the continuum and transition regimes for length to diameter ratios L / D ranging from 0.045 to 33.4 and pressure ratios across the tubes P 1 / P 2 from 1.1 to 23. A numerical analysis was carried out to estimate the conductance using the continuum approach in the continuum regime and transition regime at low Knudsen number, and using direct simulation Monte Carlo (DSMC) method in the transition regime at high Knudsen number. The observed conductances were compared with the simulation and an empirical equation derived by Hanks–Weissberg. Both the experimental and simulation results show that the conductances at a constant gas flow rate increases linearly with increasing arithmetic mean pressure across the tube P av =( P 1 + P 2 )/2, irrespective of the P 1 / P 2 ratio. The observed conductances were smaller than those predicted by the Hanks–Weissbergs equation. The deviation increases with increasing gas flow rate, and with decreasing L / D ratio. It was confirmed that the deviation occurs due to the increase in the effects of inertia and expansion in the flowing gas with increasing flow rate and decreasing L / D . A semi-empirical equation was derived by substituting the Poiseuille term in the Bernoulli formula with Hank–Weissbergs equation under the condition of isothermal expansion. The proposed equation was found to be valid in the range of the continuum regime to the transition regime at low Knudsen number.

Characterization of particle contamination in process steps during plasma-enhanced chemical vapor deposition operation

Abstract The occurrence time and the contribution level of particle contamination on the wafer in individual steps during plasma-enhanced chemical vapor deposition (PECVD) operation were investigated. A method was proposed to determine the occurrence time of particle contamination by making use of the capability of thermophoresis to shield the wafer from particle deposition. The level of particle contamination on the wafer was determined by a scanning electron microscopy (SEM) and the particle behavior in the reactor was observed using a laser light scattering (LLS) technique. The particles were continuously injected into the plasma reactor from the outside. Using this technique, the effect of particle size on the particle behavior can be studied with high certainty. It was found that the particle contamination occurred during the postplasma when the injected particles were trapped in the sheath region below the powered electrode. On the other hand, when the injected particles were not trapped due to a strong inertial effect of particle, the contamination occurred during plasma operation. There is a regime of operation condition in which the lowest level of contamination occurs. Most particles retained their negative charge in the postplasma as shown by their movement and deposition on the wafer in the presence of either a negative or positive dc field. The charge on these particles was determined from particle motion with high certainty using the current experimental technique.

Characterization of fine particle trapping in a plasma-enhanced chemical vapor deposition reactor

The distribution and transport of fine particles trapped in a radio-frequency (rf) plasma-enhanced chemical vapor deposition reactor was investigated using a laser light scattering technique. Structured clouds of particles were observed at localized regions between the holes below the showerhead. Typically, at a high rate of gas flow, particles emerging from the showerhead holes overshoot the equilibrium position of the particle trap, and the particle clouds in the trap were small and thin (winding mode). At a low rate of gas flow, the particles are directly attracted to the trap locations, and large particle clouds (lumping mode) were observed. The particle number concentration of trapped particles tends to increase with increasing rf power and decrease with increasing particle size. When the gas flow rate is increased, a sharp decrease occurs at a certain flow rate.

Modeling of and experiments on dust particle levitation in the sheath of a radio frequency plasma reactor

The equilibrium and trapping of dust particles in a plasma sheath are investigated, both experimentally and theoretically. A self-consistent sheath model including input power as one of the model parameters is proposed, to predict the equilibrium position of particle trap. The electron temperature and density are estimated from the observed current and power (I-P) characteristics using the sheath model developed. Direct comparisons are made between the measured equilibrium position and the predicted equilibrium position. The equilibrium position moves closer to the electrode with increasing rf power and particle size. The position is apparently related to the sheath thickness, which decreases with increasing rf power. The model can correctly predict the experimentally observed trend in the equilibrium position of particle trap. It is found that the particle charge becomes positive when the particle gets closer to the electrode, due to the dominant influence of ion currents to the particle surface.

Particle Formation and Trapping Behavior in a TEOS/O2 Plasma and Their Effects on Contamination of a Si Wafer

Particle formation and growth in a TEOS/O2 radiofrequency (rf) plasma were studied by an in situ laser light scattering (LLS) technique and ex situ scanning electron microscopy (SEM). The particles, after being generated, were located around the sheath near the electrodes. Visualization using a high-resolution video camera shows that the particles are trapped around the sheath near the powered electrode (showerhead) and are ultimately located in localized regions between the showerhead holes. Particle-free regions are present immediately below the holes and their surroundings within a certain radius. The particles form a lump cloud when a low gas flow rate is used, change to a line shape when the flow rate is increased, and finally the LLS technique can no longer detect them when high flow rates are used. The particle trapping behavior described above clearly has an influence on particle contamination on the wafer. The particles appear to grow through coagulation as shown by the SEM images of particles taken from the trap regions. A high gas flow rate and high substrate temperature tend to suppress particle formation and growth. On the other hand, particle formation and growth are enhanced with increasing rf power.

Observation of Heat-Induced Particle Resuspension and Transport in a Plasma Chemical Vapor Deposition Chamber

The influences of gas viscous force, thermal stress, and plasma electrostatic force on heat-induced particle resuspension and transport in a plasma chemical vapor deposition (CVD) chamber were studied experimentally. Using an in situ particle measurement system in a plasma CVD chamber based on a laser light scattering method, it was observed that silica particles with a diameter of 600 nm dispersed on a wafer were resuspended when the wafer was heated. At a wafer temperature of 573 K, when the pressure in the chamber was being changed, the removal ratio of particles from the wafer exhibited a weak dependence on pressure in the range from 13.3 Pa (0.1 Torr) to 1.33 kPa (10 Torr). A theoretical calculation based on thermophoresis that considers a temperature jump could explain the trend of the experimental results. Since the removal ratio of particles from the wafer is greater with larger difference in the linear coefficients of thermal expansion between the wafer and the particles, it is considered that the particles are separated from the wafer due to thermal stress and are scattered towards the upper electrode by the force of thermophoresis. It has also been revealed that, when plasma discharge is applied, the removal ratio of particles is reduced due to the electrostatic force of charged particles.

Incorporation of Dust Particles into a Growing Film During Silicon Dioxide Deposition from a TEOS/O2 Plasma

The effects of gas flow rate on particle formation and film deposition during the preparation of silica thin film using a TEOS/O2 plasma were investigated. Particle formation and growth are suppressed with increasing gas flow rates. The film deposition rate increases with increasing gas flow rate, reaches a maximum value, and eventually decreases again. However, the uniformity of the film tends to degrade at high gas flow rates. At a high gas flow rate, some particles trapped in the sheath near the grounded electrode pass through the sheath to reach the substrate and are then embedded in the growing film. A self-consistent sheath model combined with particle force balance based on charge fluctuation was developed to explain these experimental findings qualitatively. The model reveals that charge fluctuation is a key factor for the particle to overcome the potential barrier of the negatively charged particles to pass through the sheath, eventually reaching the substrate. The model further shows that the probability of a particle being deposited on the substrate is higher for increased gas flow rates, which correctly predicts the experimentally observed trend.

Particle formation of hydroxyapatite precursor containing two components in a spray pyrolysis process

The particle formation mechanism of hydroxyapatite precursor containing two components, Ca(OOCCH3)2 and (NH4)2HPO4 with a ratio of Ca/P = 1.67, in a spray pyrolysis process has been studied by computational fluid dynamics (CFD) simulation on the transfer of heat and mass from droplets to the surrounding media. The focus included the evaporation of the solvent in the droplets, a second evaporation due to crust formation, the decomposition reaction of each component of the precursor, and a solid-state reaction that included the kinetic parameters of the precursor regarding its two components that formed the hydroxyapatite product. The rate of evaporation and the reacted fraction of the precursor both increased with temperature. The predicted average size of the hydroxyapatite particles agreed well with the experimental results. Therefore, the selected models were also suitable for predicting the average size of particles that contain two components in the precursor solution.