Rows of memory cells are electrically isolated from one another by trenches
formed in the substrate between the rows that are filled with a dielectric, commonly
called "shallow trench isolation" or "STI." Discontinuous source and drain regions
of the cells are connected together by column oriented bit lines, preferably made
of doped polysilicon, that extend in the column direction on top of the substrate.
This structure is implemented in a flash memory array of cells having either one
floating gate per cell or at least two floating gates per cell. A process of making
a dual-floating gate memory cell array includes etching the word lines twice along
their lengths, once to form openings through which source and drain implants are
made and in which the conductive bit lines are formed, and second to form individual
floating gates with a select transistor gate positioned between them that also
serves to erase charge from the adjacent floating gates.