Low temperature etch chuck: Modeling and experimental results of heat transfer and wafer temperature

Abstract

Backside-gas wafer cooling has been studied in order to better understand the control of wafer temperature in a low temperature etch tool. Thermal models were developed to predict heat transfer coefficients for helium and nitrogen backside gases. Model results were confirmed experimentally by measuring wafer cooldown times using helium and nitrogen backside gas on a commercial 150 mm wafer chuck. Additional modeling predicted the influence of gap variations on the spatial nonuniformity of wafer temperature. Further calculations detailed the effect of the choice of thermal insulating material on the total heat load to the low-temperature chuck. Additional experiments were performed with etching plasmas, using direct in situ measurement of both wafer and chuck temperatures. These results not only confirm the heat transfer calculations, they also offer an estimate of what portion of the total etch (radio frequency generator) power appears as heat in the wafer for oxide and polysilicon etch plasmas.