A method for producing a german law on pharmaceuticals - eprom, with a fast access time

摘要

A fast access EPROM array formed in a silicon substrate of P- type conductivity comprises a layer of gate oxide formed on the silicon substrate. A first layer of polysilicon is formed on the gate oxide. A layer of oxide/nitride/oxide composite is formed on the first polysilicon layer. The ONO and underlying Poly1 define a plurality of parallel strips. N-type dopant introduced into the silicon substrate between the ONO/Poly1 strips define buried N+ bit lines. Alternate buried N+ bit lines to define drain lines that alternate with buried N+ source lines. Each of the drain lines is contacted only once for a plurality of EPROM cells sharing that drain line such that the EPROM array is subdivided into a plurality of segments. The source lines are uncontacted. A plurality of Poly2 wordlines are formed perpendicular to the ONO/Poly1 strips such that an intersection of the Poly2 word lines and the Poly1 floating gate define the location of a cross-point EPROm cell of the array. Each segment of the array include first and second Poly2 select lines the intersection of which with the Poly1 defines first and second select transistors such that each buried N+ source line is electrically connectable to one of its adjacent drain lines via the first select transistor and to the other adjacent drain line via the second select transistor. Finally, each segment also includes a segment select line that defines the gate of a segment select transistor associated with each drain line.