Abstract: A substrate processing chamber of the type adapted for processing a substrate having edges and a surface at a reduced pressure and elevated temperature relative to ambient. Typically, a combination of the elevated temperature and the reduced pressure tends to produce spallation of the substrate near the edges, which spallation produces chips that are redeposited across the surface of the substrate. Such chips inhibit proper operation of subsequent processing of the substrate. The improvement is a shield disposed in proximity to the surface of the substrate, but not touching the substrate. The shield forms a perimeter barrier at a circumference of the substrate that is interior to the edges of the substrate where the spallation occurs, and the shield prohibits the chips from redepositing across portions of the surface of the substrate that are interior to the perimeter barrier.