the importance of ultraclean processing in establishing advanced process technologies for deep submicron ulsi fabrication is discussed. the most essential requirement for the process technologies is the simultaneous fulfilment of the three principles of ultraclean technology' ultraclean wafer surface, ultraclean processing environment, and perfect process-parameter control. the growth of high-crystallinity silicon epitaxial layers at temperatures as low as 250 degrees c with accompanying in situ impurity doping as a result of optimizing pertinent process parameters in a low-kinetic-energy particle process is described advanced copper metallization for large-current driving interconnect formation is discussed. ultraclean oxidation, which is characterized by native-oxide-free and surface-microroughness-free oxidation, is confirmed to form high-quality very thin oxide films ranging from 5 to 10 nm with complete uniformity. a low-temperature annealing ion implantation that makes practical a metal gate self-aligned mos lsi, which is crucial for high-speed cmos having high current driving capability, is described