AVS 45th International Symposium
    Plasma Science and Technology Division Thursday Sessions
       Session PS-ThA

Paper PS-ThA7
Diagnostics in a Novel Capacitively Shielded, Inductively Coupled Plasma Source

Thursday, November 5, 1998, 4:00 pm, Room 318/319/320

Session: Diagnostics II
Presenter: V.A. Shamamian, Naval Research Laboratory
Authors: V.A. Shamamian, Naval Research Laboratory
J.E. Butler, Naval Research Laboratory
D. Leonhardt, Naval Research Laboratory
J.L. Giuliani, Naval Research Laboratory
Correspondent: Click to Email
An electrostatic shield in the form of a slotted metal cylinder is often placed between the exciting coil and the dielectric discharge tube of an inductively coupled plasma system in order to screen the electric field generated by the coil. Such fields can, under some circumstances, have a deleterious effect on the process for which the plasma is being used. For very high power systems, the dielectric discharge tube can be replaced by a thick-walled, water-cooled, slotted metal cylinder (i.e., a cold crucible). It is not generally realized that the electrostatic shield can also lead to a significant reduction of the r.f. magnetic fields inside the tube as well as altering its axial distribution. This effect needs to be considered in detailed modeling of inductively coupled plasma systems and is of practical importance in determining the impedance the plasma presents to the r.f. generator. In this combined experimental and theoretical work, we have employed induction probes to study the effect by measuring the r.f. magnetic field inside hydrogen discharges. We interrogated the level to which the plasma screens the field as a function of pressure and coupled power. In addition, we have employed optical emission imaging techniques and a radiation transport model to extract the axial and radial dependence of the electron and neutral temperatures, and plasma spatial extent in the axial direction. We have found that the electron temperature is constant in the axial direction but strongly dependent in the radial dimension, and the plasma extent is self-similar with respect to the value of power divided by pressure. Finally, we have developed electromagnetic models that give good agreement with the plasma induction probe observations. We are currently developing a global 2D model which incorporates electromagnetics, gas phase chemistry and transport, and surface recombination. Work supported by IST/BMDO, DARPA, and ONR.