Improvement in ultrathin rapid thermal oxide uniformity by the control of gas flow

A methodology to improve the temperature uniformity for the wafer in a rapid thermal processing (RTP) system is presented. The work aims at the temperature compensation at the wafer surface by thermal convection. From simulation results of the flow field, it is seen that the cold gas, while flowing from the periphery of the wafer toward the wafer center, causes a lower pressure at and around the center. This lower pressure is due to the flow away of gas by buoyancy and it aggregates thermal nonuniformity. A technique is suggested that consists of suppressing the upward gas flow using a transparent quartz cap above the monitored wafer. Simulation and experimental results show that by implementing this technique, the temperature uniformity of the wafer is improved.