In a chemical vapor deposition apparatus for coating semiconductor wafers, the wafer is held face down in the reaction chamber. A radiant heat source above the wafer and outside the reaction chamber. The wafer is held on a ring chuck by means of a retractable clamp heats the wafer from its backside to a temperature in excess of 1000.degree. C. rapidly. The radiant heat source includes cylindrical lamps placed in a radial pattern to improve heating uniformity. In the selective tungsten process the temperature of the wafer is raised from ambient to about 600.degree. C. while flowing process gases. At the upper temperature range the heating source can be rapidly cycled on and off to improve the uniformity of coating.