Shapes of agglomerates in plasma etching reactors
Dust particle contamination of wafers in reactive ion etching (RIE) plasma tools is a continuing concern in the microelectronics industry. It is common to find that particles collected on surfaces or downstream of the etch chamber are agglomerates of smaller monodisperse spherical particles. The shapes of the agglomerates vary from compact, high fractal dimension structures to filamentary, low fractal dimension structures. These shapes are important with respect to the transport of particles in RIE tools under the influence electrostatic and ion drag forces, and the possible generation of polarization forces. A molecular dynamics simulation has been developed to investigate the shapes of agglomerates in plasma etching reactors. We find that filamentary, low fractal dimension structures are generally produced by smaller (<100s nm) particles in low powered plasmas where the kinetic energy of primary particles is insufficient to overcome the larger Coulomb repulsion of a compact agglomerate. This is analogou...
Contamination particle traps due to a cone, cube and disk
This paper studies asymmetric particle clouds confined within electrostatic particle traps in the presence of a molecular drag force. The drag force, due to flow of neutral Ar gas around a particle, is proportional to the gas flow, which can be controlled by a mass flow controller. Our system has a component of the drag force parallel to the wafer electrode surface. The particle clouds associated with a cube and a disc are seen to be highly asymmetric in the direction of the drag force, as would be expected. The asymmetry increases as gas flow increases. In order to visualize the clouds quantitatively, we have introduced a technique called spot scanning in which we move the laser beam slowly with a serpentine path through the particle cloud. The forward scattered light is recorded by a charge-coupled device camera onto videotape. The image of the scattered light on a frame of the videotape is a nearly circular red spot. Using commercially available computer software, the red spots can be used to determine the boundary of the cloud as well as to find contours of constant power density scattered from the cloud.
DESIGN CONSIDERATION TO PPM KLYSTRONS FOR INDUSTRIAL LINAC
Toshiba has been developing the C-band and X-band Periodic Permanent Magnet (PPM) focused klystron in collaboration with KEK and manufactured prototypes for the JLC project. [1] The PPM klystron has an advantage to enhance the total efficiency as a result of eliminating the electric power for the focusing magnet. From experience on the development the PPM focused klystrons for the JLC project, we plan to apply the PPM focused klystron to the medical and industrial linac. The periodic magnet focusing scheme has some technical difficulties such as stop band voltage. To design the PPM klystron for the medical and industrial linac, it is necessary to give heed to electron beam instability; so that the tube parameters of the PPM focused klystrons have some constraints. The size of the accelerator system is substantially reduced if a PPM focused klystron is used. The majority of medical and industrial linacs use frequencies of S-band range. We discuss the availability of the S-band PPM focused klystron in this paper.