Electrically programmable memory cell configuration

Abstract

The memory cell configuration comprises vertical transistors which are connected in a NOR architecture. The vertical transistors are disposed on flanks of trenches. Each vertical transistor includes an electrically insulated floating gate electrode, whose charge can be varied by Fowler-Nordheim tunneling due to a voltage drop between a control gate electrode and a source/drain region. The length of a coupling area in a direction parallel to a channel width, between the control gate electrode and the floating gate electrode is less than the channel width, in order to reduce the operating voltage. This is achieved by thermal oxidation of parts of the flanks of the trenches. Transistors which are adjacent in a direction transverse to the trenches share bit lines. Each bit line has a lightly doped first part and a highly doped second part. The coupling area can be enlarged even further by using a strip-shaped mask, which is extended by spacers.