Narrow-pitch contact array patterning technique for Gb DRAM using multi-phase-shifting mask

Application of a multi-phase-shifting mask to hole arrays for giga-bit DRAM has been studied. Self-aligned contact plugs for a cell pitch of 0.38 micrometer under the bit-line contacts and the storage-node contacts have been formed at the same time by using a multi-phase-shifting mask with two different phase-shifters. Sufficient depth of focus (DOF) of 0.8 micrometer has been obtained. Furthermore, hole-shape distortion caused by focus offset can be suppressed under the off-axis illumination condition with a quadrupole aperture