Nonvolatile semiconductor memory device and its writing method

Abstract

A nonvolatile semiconductor memory device and its writing method for reducing a writing rate variation without changing a voltage condition applied for each memory cell in writing operation is provided. The device comprises a memory cell array configuration where each drain of the memory cells on the same column is connected to a first bit line via a second bit line and a bit line contact, and the shortest distance from each drain of the memory cells to the bit line contact varies according to a location of the memory cell in the column direction. The method includes a writing operation carried out sequentially from the nearest memory cell to the bit line contact, upon writing continuously so that the memory cell current becomes small for all or some of the memory cells on the same column between the two adjacent bit line contacts in the column direction.