Emissivity-Independent Rapid Thermal Processing using Radiation Shields

Abstract

Simple rapid thermal processing (RTP) system configurations, in which the wafer temperature is controlled by a pyrometer viewing the wafer’s backside, are vulnerable to changes in the spectral emissivity of this surface. One method for emissivity-independent temperature control is to use an opaque plate beneath the wafer as a radiation shield, which masks the wafer’s backside from the heating lamps and provides a target whose temperature can be monitored easily by a pyrometer or a thermocouple. Experimental studies of the dynamic temperature responses of the wafer and the shield are in good agreement with predictions from a theoretical model based on a simple analysis of radiation heat transfer in the system. For the set of wafers studied here, pyrometer control of the shield temperature gave a spread of wafer temperatures of 4°C, as compared to a range of 160°C when the shield was not used. The radiation shield was also shown to give RTP process results which are immune to changes in wafer backside coatings.