Temperature calibration substrate

An apparatus for measuring the temperature of an object within a process chamber is described. The process chamber includes a platform for receiving the object and an energy source for transferring energy to the object. The apparatus includes a shield, and a first and second energy sensor. The shield is positioned in the chamber adjacent the object to create an isothermal cavity in the space between the object and the shield. The shield is designed to receive from the energy source an amount of energy approximating that received by the object. The first energy sensor is positioned between the shield and the platform to measure the temperature of the object. The second energy sensor measures the temperature of the shield. A method for establishing an isothermal condition within the process chamber includes the steps of varying the shield temperature in inverse relationship to the difference between the shield temperature and a target temperature. Then the temperature of the object is valued in inverse relationship to the difference between the temperature of a cavity sensor and the target temperature. When the readings are within a predetermined range of the target temperature an isothermal condition is indicated. A method for monitoring the temperature of an object within the process chamber is also described. The method includes the steps of obtaining the coupling ratio for a cavity temperature sensor; obtaining the response time of the cavity temperature sensor and determining the temperature of the object Tw on the basis of a formula which correlates the coupling ratio, the response time, and temperature readings of the shield and cavity.