Patent ID: 8440051
Filing Date: 2013-05-14
Classification: H01J,H01L

Abstract:
1. Apparatus for protecting a central die area of a wafer from charged particles in a process chamber, the apparatus comprising: a bottom electrode configured to mount the wafer in the process chamber with the central area within a circular wafer border centered on a wafer axis and with a wafer edge exclusion area extending radially relative to the axis and outside the border, the bottom electrode having a support surface and a step down surface with a first ring mount section; a top electrode having a surface that opposes the support surface of the bottom electrode and a step up surface with a second ring mount section; a bottom grounded electrode disposed around the bottom electrode at a level of the step down surface; a top grounded electrode disposed around the top electrode at a level of the step up surface; and a ring-shaped permanent magnet arrangement configured with a first permanent magnet section mounted in the first ring mount section and a second permanent magnet section mounted in the second ring mount section, the first and second mounted permanent magnet sections being configured to establish a magnetic field that extends axially between the first and second mounted permanent magnet sections and in an annular path centered on the axis, the first and second mounted permanent magnet sections being further configured to establish the magnetic field configured with a magnetic field strength that is uniform around the wafer axis and that has a field strength gradient that varies with respect to radial distance relative to the axis and away from the border, the gradient variation being from a peak value located adjacent to the border and inversely proportional to increased radial distance away from the axis, the gradient and the peak value of the field strength being configured to repel the charged particles from moving radially past the border toward the axis, wherein the first and second ring mount sections are further configured to adjustably mount the respective first and second permanent magnet sections for movement relative to each other in a direction parallel to the axis.