Patent ID: 6375860
Filing Date: 2002-04-23
Classification: C23C,H01J

Abstract:
A method of controlling a plasma to prevent negative ions and negatively-charged particulates from becoming trapped within the plasma comprising the steps of:forming a plasma from a specified gas within a plasma formation chamber, the chamber having control electrodes at each end of the chamber that are aligned with a longitudinal axis of the chamber, and reference electrodes along opposing sides of the chamber that are aligned with a lateral axis of the chamber, at least one of the reference electrodes having a surface on which a workpiece may be supported and with which it is in electrical contact, the lateral axis being substantially orthogonal relative to the longitudinal axis; biasing the control electrodes with a first bias voltage that includes a negative dc component to control the plasma potential so that the plasma potential is positive with respect to the control electrodes; restricting electron flow in the plasma to a longitudinal flow that substantially parallels the longitudinal axis, while at the same time allowing a lateral negative ion flow or a lateral negative particulate flow in the plasma, wherein said step of restricting the flow of electrons in the plasma comprises applying a magnetic field of a specified magnitude to the plasma formation chamber that has magnetic field lines that substantially parallel the longitudinal axis, the specified magnitude of the magnetic field restricting the movement of electrons to a direction that substantially parallels the magnetic field lines, while at the same time allowing negative ions and negatively-charged particulates to laterally cross the magnetic field lines; and biasing the reference electrodes with a second bias voltage that is more positive than the plasma, whereby the plasma potential becomes negative relative to the reference electrodes; whereby negative ions and negatively-charged particulates in the plasma are laterally drawn out of the plasma across the magnetic field lines to the more positively charged reference electrodes and are not allowed to become trapped within the plasma.