Examples described herein generally relate to apparatus and methods for rapid thermal processing (RTP) of a substrate. In one or more embodiments, a process chamber includes chamber body, a window disposed on a first portion of the chamber body, a chamber bottom, and a shield disposed on a second portion of the chamber body. The shield has a flat surface facing the window to reduce reflected radiant energy to a back side of a substrate disposed in the process chamber during operation. The process chamber further includes an edge support for supporting the substrate and a cooling member disposed on the chamber bottom. The cooling member is disposed in proximity of the edge support to cool the edge support during low temperature operation in order to improve the temperature uniformity of the substrate.