Ravindran Periasamy

Mechanisms of Particle Transport in Process Equipment

Mechanisms affecting particle transport in wafer processing environments include: sedimentation, convective diffusion, thermophoresis, electrophoresis, and photophoresis. The first two mechanisms are universal; they exist everywhere and at all times. The latter three mechanisms, however, depend on conditions that can be introduced and used to minimize particle deposition on product wafers. This paper reviews theoretical models of all five mechanisms and describes procedures and hardware configurations that use one or more of the three controllable mechanisms to protect wafers from particulate contamination

Generation of Uniformly Sized, Charged-Particles in A Vacuum

An experimental technique that uses a modified vibrating orifice aerosol generator has been developed for the continuous generation of monodisperse, charged particles in subatmospheric pressure. The technique achieves well-defined control of charge of either polarity by induction charging of the uniformly sized particles produced by the aerosol generator. Particle charge was measured by the collection of particles in a Faraday cup connected to a microammeter. The size and morphology of the particles generated by this device were investigated by using optical and scanning electron microscopy. The performance of the vibrating orifice aerosol generator with and without the use of the conventional syringe pump was investigated for vacuum operation. The technique is found to be a useful method to generate charged aerosol particles for the study of aerosol behavior in vacuum conditions.

Particle Transport at Subatmospheric Pressures: Models and Verification

This paper reports on a program comparing calculated and experimental values of particle deposition velocity at pressures down to 100 pascals (1 millibar). The calculated values were obtained by incorporating the pressure dependence of gas density and the Cunningham slip correction factor into previously published particle deposition models. While the deposition mechanisms modeled included sedimentation, diffusion, thermophoresis, electrophoresis, and photophoresis, experimental measurements have been made so far to verify only the sedimentation model. The experimental results presented confirm the predicted increased importance of gravitational settling at subatmospheric pressures

Theoretical and experimental study of particle transport in vacuum chambers

Abstract Particle deposition models applicable to low pressure were developed by incorporating known pressure dependencies into well established atmospheric deposition models. Contributions by various particle deposition mechanisms such as sedimentation, diffusion, and other external forces are accounted for in the particle deposition model. Particle deposition experiments were conducted at both the University of Duisburg (UD) and the Research Triangle Institute (RTI). Each organization used its own customized vacuum chamber and differing methods of particle generation and detection. Results from both experimental setups are compared with the deposition models to assess the capability of the models in describing particle deposition in semiconductor vacuum processing equipments.

Flow cell for real time observation of single particle adhesion and detachment

A flow cell was built for observing particle removal from test surfaces in real time. The removal force is the hydrodynamic force exerted on the particle by liquid flowing parallel to the test surface. Particle removal was detected visually either through a microscope or on a video monitor. All experimental results reported here are based on the removal of deposited 10 μm polystyrene (PSL) spheres from one of 3 surfaces: polished aluminum; polished bare silicon wafers (native oxide only); or thertnally oxidized silicon wafers. One of 3 cleaning liquids was used: dilute SC-1, dilute SC-2, or de-ionized water containing 0.01% Micro®. The hydrodynamic removal force was controlled primarily by controlling the liquid flow rate. In all experiments, as the flow rate increased, single polystyrene latex (PSL) spheres detached first, then doublets, then triplets and finally larger agglomerates; that is, the adhesion force increased more rapidly with agglomeration than the hydrodynamic removal force. By applying the...

THE MEASUREMENT OF OXYGEN TRANSPORT PARAMETERS FOR ASPHALT/AGGREGATE AND ASPHALT/GLASS SYSTEMS USING AN ELECTRODYNAMIC BALANCE

ABSTRACT A gravimetric method using an eledrodynamic balance was developed for the measurement of transport properties such as the diffusion coefficient, D, solubility, S, and permeability, P, for oxygen into thin layers of asphalt materials deposited on aggregate and glass particles. Glass spheres and aggregate particles in the 14 to 50 μm size range coated with asphalt materials (AAB1, AAG1, and AAK1) were suspended contactless in the balance to measure D, S, and P in the temperature range 21 to 61° C. Transport parameters were determined from the changes in the particle mass due to the uptake of oxygen by the asphalt coating on glass spheres and nonspherical aggregate particles.

Effect of wafer orientation on the particle deposition in subatmospheric pressures

Abstract The significance of gravity, electrostatic force, and turbulence on particle deposition on wafers in subatmospheric pressure chambers was investigated by conducting experiments with wafers placed in various orientations in an e-beam evaporator chamber used in the fab line at the Microelectronics Center of North Carolina (MCNC). These experiments carried out with naturally occurring particles generated by the operation of the equipment indicated that gravity usually dominanted deposition. However, particle contamination on wafers in the vertical and upside down orientations suggested that electrostatic forces and turbulence within the chamber during venting and pumpdown also contributed to wafer contamination. In order to study particle deposition characteristics with known particles at subatmospheric pressures, a new particle generating method using a modified vibrating orifice aerosol generator (VOAG) was developed for the production of monodisperse particles at low pressures with controllable charge and concentration.

GAS PERMEABILITY MEASUREMENTS ON ASPHALT USIHO THE ELECTRODTNAMIC BALANCE

A novel experimental method developed for the measurement of the transport properties such as the diffusion coefficient, D, solubility, S, and permeability, P, for oxygen into asphalt materials using an electrodynamic balance is described. Both unaged and aged rolling thin-film oven test (RTFOT) asphalt particle samples in the 12 to 62 micrometer size range were suspended contactless and weighted in the balance to measure D, S, and P in the temperature range 17 degrees Celsius to 66 degrees Celsius. Volatilization rate data were obtained from the particle mass measurements made prior to the start of the sorption experiments. Sorption curves obtained in this study for unweathered asphalt samples showed a non-Fickian, two-stage type sorption behavior indicating the possibility of an additional mechanism other than diffusion. Analogous behavior in sorption was observed for weathered samples.ABSTRACT A novel experimental method developed for the measurement of the transport properties such as the diffusion coefficient, D, solubility, S, and permeability, P, for oxygen Into asphalt materials using an electrodynamic balance Is described. Both imaged and aged rolling thin-film oven test (RTFOT) asphalt particle samples In the 12 to 62 pm size range were suspended contactless and weighed In the balance to measure D, S, and P In the temperature range 17°C to 66°C. Volatilization rate data were obtained from the particle mass measurements made prior to the start of the sorption experiments. Sorption curves obtained in this study for unweathered asphalt samples showed a non-Pickian, two-stage type sorption behavior indicating the possibility of an additional mechanism other than diffusion. Analogous behavior in sorption was observed for weathered samples

Particles in High-Pressure Cylinder Gases

An improved test protocol is presented for the measurement of particle concentrations in high-pressure cylinder gases. With the screening method, particles entrained in a cylinder gas can be collected and chemically analyzed for the isolation of particle sources. Results are presented for argon, helium, and nitrogen cylinder gases. Many fine particles are formed from the trace organic vapors present in the cylinder gas by gas-to-particle conversion occurring downstream of such pressure-reducing devices as an orifice plate. It is demonstrated that these fine particles in the cylinder gas can be significantly reduced by as much as three orders of magnitude by the insertion of an appropriate purifying stage before the pressure-reducing devices.