a rotatable substrate supporting mechanism for use in a chemical vapor deposition reaction chamber of the type used in producing semi - conductor devices is provided with a susceptor for supporting a single substrate , or wafer , for rotation about an axis normal to the center of the wafer . the mechanism is provided with a temperature sensing system for producing signals indicative of sensed temperatures taken at the center of the susceptor and at various points about the periphery thereof . a gas purging system is provided for inhibiting the flow of reactant gas in unwanted areas of the reaction chamber and in the supporting system itself . rotational driving of the mechanism is accomplished by a variable speed motor under control of a circuit which stops and starts the rotation at controlled speeds and stops the rotation at a home position for enhancing the handling of the wafers .