Wafer holder and clamping ring therefor for use in a deposition chamber

Abstract

Warping of a clamping ring, by which a series of semiconductor wafers is held to a wafer holder for vapor deposition of coatings onto the wafers, is retarded by providing a clamping ring formed of the material having a coefficient of thermal expansion that is approximately the same as or close to that of the coating material being deposited onto the wafers. Preferably also, the material of which the ring is formed has a high modulus of elasticity, high thermal conductivity and a high yield strength. For the deposition of tantalum and gold, which is useful for providing backside thermal conductivity on semiconductor wafers, a clamping ring of molybdenum is preferred. The onset of excessive warping is delayed by replacing clamping rings with clamping rings formed of a material having a thermal expansion coefficient closer to that of the material to be deposited, and preferably having the other preferred properties. Preferably, the clamping ring is one having a generally circular opening that is slightly smaller than the wafers to be clamped and that has a flat edge on the inner edge of the ring corresponding to the orientation flat found on the outer edge of an industry standard wafer, so that the ring engages the wafer during clamping around the entire outer rim of the wafer. A ring having a small number of discrete mounting points for spring attachment to the holder, and having a set of latches connected thereto, is preferred.