Anthony Clint Clayton

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.

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.

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.