Robert Donovan

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.

Ultrafine Aerosol Particles in Semiconductor Cleanrooms

Revue de divers instruments de mesure pour les particules ultrafines et resultats obtenus dans des salles propres pour semiconducteurs, ayant differents degres de proprete

Measurement of ultrafine aerosol particle size distributions at low concentrations by parallel arrays of a diffusion battery and a condensation nucleus counter in series

Abstract This paper describes an instrument configuration capable of measuring size distributions over the 0.014–0.2 μm size range at particle concentrations typical of state-of-the-art clean rooms (10 −3 particles/cc or less). The configuration consists of a parallel array of diffusion batteries each with its own condensation nucleus counter and each drawing an independent air sample for analysis at one size cut. The combined outputs of all CNC/DB pairs yield the desired size distribution as illustrated for several clean room operating conditions.

Comparison of baghouse test results with the GCA/EPA design model

The GCA/EPA fabric filter design model Is evaluated for its ability to predict pressure drop, penetration, and dynamics of full-scale baghouses. Model predictions are compared with data measured at the Kramer station of the Nebraska Public Power District. Two different values of specific resistance coefficient (K2) and effective residual drag (SE) are used in the modeling of the Kramer baghouse. The field-measured value of K2 combined with the laboratory-measured value of SE produces the best predictions of pressure-drop performance, but the field data exhibit fluctuations that cannot be accounted for by the model. The model overpredicts penetration just after a compartment has been cleaned; but, as the dust cake on the filter grows, the discrepancy between predicted and measured values diminishes.

Electric-Field-Enhanced Fabric Filtration of Electrically Charged Flyash

This paper summarizes measurements in which both external electric field, applied by electrodes at the fabric surface, and flyash electrical charge, controlled by an upstream corona precharger, are independent variables in a factorial performance experiment carried out in a laboratory pulse-jet baghouse. In agreement with previous publications, increasing either the electric field strength or the magnitude of the flyash charge/mass reduced the rate at which the pressure drop across the bags built up. And although increasing both field and dust charge together produced still further reduction in the pressure drop buildup rate, bag weighings showed that adding charge to the flyash reduced the quantity of flyash deposited on the bag during one filtration cycle, whereas increasing the electric field had no detectable effect on this quantity. These observations suggest that the mechanism by which the external field enhances the performance of the fabric filter is increasing the permeability of the collected fl...

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...

Particle Deposition Velocity Studies in Silicon Technology

Mechanisms of particle deposition on silicon wafers are briefly reviewed by reference to and citation of results from several recent theoretical and experimental papers. Two mechanisms--one originating from electrical forces and a second from thermal forces--are shown to strongly affect particle deposition velocity based on measurements carried out primarily in a specially designed particle deposition chamber but also on supplementing measurements of particle deposition made in the semiconductor clean room at the Microelectronics Center of North Carolina.