Semiconductor memory device and its method of manufacture

摘要

A semiconductor memory device comprises a semiconductor substrate having a memory cell region and a periphery circuit region. The memory cell region includes first and second conductivity type wells and an array of memory cell formed on the first and second conductivity type wells. The periphery circuit region comprises a guard ring that is formed at a location next to a second conductivity type well and to surround a side portion of the array of memory cells. The guard ring is formed with a depth different from that of the second conductivity type well.