Pattern shift reduction in dual side heated RTP systems with hot shielding technology

Pattern induced thermal nonuniformities play an important role in modem rapid thermal processing (RTP). Implementation of hot shielding technology has been reported in the literature to reduce slip line generation and pattern induced thermal nonuniformities on test structures. The hot shielding consists of a thermally stable, light absorbing plate that is positioned. in a small distance above the wafer in Mattson RTP tools. This plate causes a shift of the radiative energy flux to longer wavelengths and partially converts the radiative energy to a convective mode. In this work the process improvements obtained with hot shielding technology in a 200 mm BiCMOS process are described. RTP processes were run on split lots with conventional wafer tray setup and with a hot shielding wafer tray setup. Identical temperature distribution profiles for both setups were obtained by adjusting PID parameter settings and lamp correction tables. Comparison of the overlay residuum in contact lithography following the RTP step revealed a significant improvement of up to a factor of 5 for the wafer groups processed with the hot shielding option. These benefits and first promising results measured on process control monitor structures of product wafers show the high potential of hot shielding technology in reducing pattern related effects in RTP processing.