0.228 μm2 trench cell technologies with bottle-shapedcapacitor for 1 Gbit DRAMs

摘要

In order to realize 1 Gbit DRAMs, we have developed a 0.228 μm2 trench type cell. Two methods are employed to shrink thememory cell size. One is a “bottle shaped” capacitor, whichhas a larger diameter than the opening for the storage node. For thiscapacitor structure, we have verified 30% capacitance increase keepingthe trench opening, sufficiently high breakdown field of capacitordielectric, and less than 1/1000 of a soft-error rate compared with theconventional one. The other is a 6F2 cell layout suitable foran open-folded-bit-line architecture, which reduces to 75% for theconventional 8F2 cell layout with the same feature size, F.We have also confirmed that a P+ poly gate transistor has asufficient overlap tolerance (more than 0.1 μm) between the transfergate and the trench edge by using three-dimensional device simulator.These results strongly support feasibility of our novel cell