it is demonstrated that ultraclean technology is a crucial factor in developing high-quality processing technology for future ulsi fabrication. simultaneous establishment of three principles, i.e. ultraclean processing environment, ultraclean wafer surface, and perfect process-parameter control, makes it possible to realize high-quality processing. such high-quality processing technologies are recognized to be necessary for deep submicron ulsi and advanced power device manufacturing. in accordance with the development of advanced microfabrications based on the ultraclean technology, key processing temperatures are lowered by less than 500 degrees c, so that buried metal structures can be practically introduced in power devices in order to improve the speed performance due to the decrease of the electrode resistance. it is concluded that native oxide and adsorbed impurity molecule free processing can realize high-quality processes such as low-temperature thin-film formation and excellent metal-to-silicon contact without accompanying thermal treatment in conjunction with perfect process parameter control technology