Abstract
This thesis presents methods for improving thermal uniformity of stainless steel (SST) 316L pedestal heater. With low thermal conductivity, SST cannot satisfy the thermal uniformity requirement of 2% at 400oC for pedestal heaters. Thus, a different material is used as a heat spreader to improve the overall thermal conductivity. Copper and thermal pyrolytic graphite (TPG) are being considered due to their high thermal conductivity and stable performance at high temperature. In order to utilize heat spreader material, three different configurations of the design are proposed: 1. Using copper as a heat spreader through dry bond and eGraf foil as a thermal interface layer 2. Using thermal pyrolytic graphite (TPG) as a heat spreader through brazing 3. Using coated TPG as a heat spreader through dry bonding Thermal simulations from Autodesk Computation Fluid Dynamics (CFD) software show that all proposed designs can achieve the thermal uniformity requirement. However, thermal simulation does not consider the effect of thermal interface because ideal conditions are assumed. Each design has a different type of thermal interface between the heater spreader, and each type of interface is discussed and evaluated by different authors. Lastly, common problems with pedestal heaters i.e. cracked TPG, thermocouples drift, copper contamination, and brazing voids, are discussed in detail. Based on thermal simulations and multiple literature sources discussed in chapter III, a thermal uniformity of 2% at 400oC and a stable performance can be achieved from the new designs.