Abstract: An etching gas having a good chemical property for silicon etch back is made by mixing a SF6 gas with a Cl2 gas. With addition of an inert gas, good chamber conditions are maintained during silicon etch back, and the etching selectivity for silicon to an etching stop layer is improved.

Abstract: A plasma erosion resistive clamping ring is provided for clamping a wafer in a plasma treatment chamber. The plasma erosion resistive clamping ring comprises a ring and one or more tips secured to, and mutually spaced apart about, a circumference of the ring. Each of the tips projects away from the ring, in a radial direction, towards an interior of the ring. Each tip has plural side surfaces that taper to, and meet, a single, continuous surface of rotation. The surface of rotation is located in the interior of the ring at a location of the tip which is radially most distant from the ring. The meeting of the tapered sides at the single continuous surface of rotation has a cross-section, taken in a plane of the ring, as follows. The cross-section comprises first and second line segments, on lines that intersect at an acute angle, and an arc of a convex ellipse, that begins at an end of the first line segment most distant from the ring, and ends at an end of the second line segment most distant from the ring.