Improvement of VRT immunity using low 10-boron word line in recent DRAM

This paper investigated the variable retention time (VRT) problems in DRAM owing to 10-Boron (10B) in dynamic random access memory (DRAM). Recently, since the random telegraph noise (RTN) increased due to the shrink of DRAM, it is very difficult to secure the robust VRT properties. The main types of VRT problems are single-bit (SB) failures which are caused by 10B in DRAM cell, so it is important to develop a proper technology to reduce 10B. In particular, a large amount of 10B flows into DRAM cell from Diborane (B2H6) used as a precursor for the word line (WL) formation in sub-20 nm DRAMs. In this paper, we present and discuss the effect of 10B on the cell transistors (Cell Tr) from a process perspective. In addition, we propose the appropriate reduction of 10B in WL with improved VRT properties.